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rfc:rfc3530

Network Working Group S. Shepler Request for Comments: 3530 B. Callaghan Obsoletes: 3010 D. Robinson Category: Standards Track R. Thurlow

                                                Sun Microsystems, Inc.
                                                              C. Beame
                                                      Hummingbird Ltd.
                                                             M. Eisler
                                                             D. Noveck
                                               Network Appliance, Inc.
                                                            April 2003
            Network File System (NFS) version 4 Protocol

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

 The Network File System (NFS) version 4 is a distributed filesystem
 protocol which owes heritage to NFS protocol version 2, RFC 1094, and
 version 3, RFC 1813.  Unlike earlier versions, the NFS version 4
 protocol supports traditional file access while integrating support
 for file locking and the mount protocol.  In addition, support for
 strong security (and its negotiation), compound operations, client
 caching, and internationalization have been added.  Of course,
 attention has been applied to making NFS version 4 operate well in an
 Internet environment.
 This document replaces RFC 3010 as the definition of the NFS version
 4 protocol.

Key Words

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].

Shepler, et al. Standards Track [Page 1] RFC 3530 NFS version 4 Protocol April 2003

Table of Contents

 1.   Introduction . . . . . . . . . . . . . . . . . . . . . . .    8
      1.1.  Changes since RFC 3010 . . . . . . . . . . . . . . .    8
      1.2.  NFS version 4 Goals. . . . . . . . . . . . . . . . .    9
      1.3.  Inconsistencies of this Document with Section 18 . .    9
      1.4.  Overview of NFS version 4 Features . . . . . . . . .   10
            1.4.1.  RPC and Security . . . . . . . . . . . . . .   10
            1.4.2.  Procedure and Operation Structure. . . . . .   10
            1.4.3.  Filesystem Mode. . . . . . . . . . . . . . .   11
                    1.4.3.1.  Filehandle Types . . . . . . . . .   11
                    1.4.3.2.  Attribute Types. . . . . . . . . .   12
                    1.4.3.3.  Filesystem Replication and
                              Migration. . . . . . . . . . . . .   13
            1.4.4.  OPEN and CLOSE . . . . . . . . . . . . . . .   13
            1.4.5.  File locking . . . . . . . . . . . . . . . .   13
            1.4.6.  Client Caching and Delegation. . . . . . . .   13
      1.5.  General Definitions. . . . . . . . . . . . . . . . .   14
 2.   Protocol Data Types. . . . . . . . . . . . . . . . . . . .   16
      2.1.  Basic Data Types . . . . . . . . . . . . . . . . . .   16
      2.2.  Structured Data Types. . . . . . . . . . . . . . . .   18
 3.   RPC and Security Flavor. . . . . . . . . . . . . . . . . .   23
      3.1.  Ports and Transports . . . . . . . . . . . . . . . .   23
            3.1.1.  Client Retransmission Behavior . . . . . . .   24
      3.2.  Security Flavors . . . . . . . . . . . . . . . . . .   25
            3.2.1.  Security mechanisms for NFS version 4. . . .   25
                    3.2.1.1.  Kerberos V5 as a security triple .   25
                    3.2.1.2.  LIPKEY as a security triple. . . .   26
                    3.2.1.3.  SPKM-3 as a security triple. . . .   27
      3.3.  Security Negotiation . . . . . . . . . . . . . . . .   27
            3.3.1.  SECINFO. . . . . . . . . . . . . . . . . . .   28
            3.3.2.  Security Error . . . . . . . . . . . . . . .   28
      3.4.  Callback RPC Authentication. . . . . . . . . . . . .   28
 4.  Filehandles . . . . . . . . . . . . . . . . . . . . . . . .   30
      4.1.  Obtaining the First Filehandle . . . . . . . . . . .   30
            4.1.1.  Root Filehandle. . . . . . . . . . . . . . .   31
            4.1.2.  Public Filehandle. . . . . . . . . . . . . .   31
      4.2.  Filehandle Types . . . . . . . . . . . . . . . . . .   31
            4.2.1.  General Properties of a Filehandle . . . . .   32
            4.2.2.  Persistent Filehandle. . . . . . . . . . . .   32
            4.2.3.  Volatile Filehandle. . . . . . . . . . . . .   33
            4.2.4.  One Method of Constructing a
                    Volatile Filehandle. . . . . . . . . . . . .   34
      4.3.  Client Recovery from Filehandle Expiration . . . . .   35
 5.   File Attributes. . . . . . . . . . . . . . . . . . . . . .   35
      5.1.  Mandatory Attributes . . . . . . . . . . . . . . . .   37
      5.2.  Recommended Attributes . . . . . . . . . . . . . . .   37
      5.3.  Named Attributes . . . . . . . . . . . . . . . . . .   37

Shepler, et al. Standards Track [Page 2] RFC 3530 NFS version 4 Protocol April 2003

      5.4.  Classification of Attributes . . . . . . . . . . . .   38
      5.5.  Mandatory Attributes - Definitions . . . . . . . . .   39
      5.6.  Recommended Attributes - Definitions . . . . . . . .   41
      5.7.  Time Access. . . . . . . . . . . . . . . . . . . . .   46
      5.8.  Interpreting owner and owner_group . . . . . . . . .   47
      5.9.  Character Case Attributes. . . . . . . . . . . . . .   49
      5.10. Quota Attributes . . . . . . . . . . . . . . . . . .   49
      5.11. Access Control Lists . . . . . . . . . . . . . . . .   50
             5.11.1.  ACE type . . . . . . . . . . . . . . . . .   51
             5.11.2.  ACE Access Mask. . . . . . . . . . . . . .   52
             5.11.3.  ACE flag . . . . . . . . . . . . . . . . .   54
             5.11.4.  ACE who  . . . . . . . . . . . . . . . . .   55
             5.11.5.  Mode Attribute . . . . . . . . . . . . . .   56
             5.11.6.  Mode and ACL Attribute . . . . . . . . . .   57
             5.11.7.  mounted_on_fileid. . . . . . . . . . . . .   57
 6.  Filesystem Migration and Replication  . . . . . . . . . . .   58
      6.1.  Replication. . . . . . . . . . . . . . . . . . . . .   58
      6.2.  Migration. . . . . . . . . . . . . . . . . . . . . .   59
      6.3.  Interpretation of the fs_locations Attribute . . . .   60
      6.4.  Filehandle Recovery for Migration or Replication . .   61
 7.  NFS Server Name Space . . . . . . . . . . . . . . . . . . .   61
      7.1.  Server Exports . . . . . . . . . . . . . . . . . . .   61
      7.2.  Browsing Exports . . . . . . . . . . . . . . . . . .   62
      7.3.  Server Pseudo Filesystem . . . . . . . . . . . . . .   62
      7.4.  Multiple Roots . . . . . . . . . . . . . . . . . . .   63
      7.5.  Filehandle Volatility. . . . . . . . . . . . . . . .   63
      7.6.  Exported Root. . . . . . . . . . . . . . . . . . . .   63
      7.7.  Mount Point Crossing . . . . . . . . . . . . . . . .   63
      7.8.  Security Policy and Name Space Presentation. . . . .   64
 8.   File Locking and Share Reservations. . . . . . . . . . . .   65
      8.1.  Locking. . . . . . . . . . . . . . . . . . . . . . .   65
            8.1.1.    Client ID. . . . . . . . . . . . . . . . .   66
            8.1.2.    Server Release of Clientid . . . . . . . .   69
            8.1.3.    lock_owner and stateid Definition. . . . .   69
            8.1.4.    Use of the stateid and Locking . . . . . .   71
            8.1.5.    Sequencing of Lock Requests. . . . . . . .   73
            8.1.6.    Recovery from Replayed Requests. . . . . .   74
            8.1.7.    Releasing lock_owner State . . . . . . . .   74
            8.1.8.    Use of Open Confirmation . . . . . . . . .   75
      8.2.  Lock Ranges. . . . . . . . . . . . . . . . . . . . .   76
      8.3.  Upgrading and Downgrading Locks. . . . . . . . . . .   76
      8.4.  Blocking Locks . . . . . . . . . . . . . . . . . . .   77
      8.5.  Lease Renewal. . . . . . . . . . . . . . . . . . . .   77
      8.6.  Crash Recovery . . . . . . . . . . . . . . . . . . .   78
             8.6.1.   Client Failure and Recovery. . . . . . . .   79
             8.6.2.   Server Failure and Recovery. . . . . . . .   79
             8.6.3.   Network Partitions and Recovery. . . . . .   81
      8.7.   Recovery from a Lock Request Timeout or Abort . . .   85

Shepler, et al. Standards Track [Page 3] RFC 3530 NFS version 4 Protocol April 2003

      8.8.   Server Revocation of Locks. . . . . . . . . . . . .   85
      8.9.   Share Reservations. . . . . . . . . . . . . . . . .   86
      8.10.  OPEN/CLOSE Operations . . . . . . . . . . . . . . .   87
             8.10.1.  Close and Retention of State
                      Information. . . . . . . . . . . . . . . .   88
      8.11.  Open Upgrade and Downgrade. . . . . . . . . . . . .   88
      8.12.  Short and Long Leases . . . . . . . . . . . . . . .   89
      8.13.  Clocks, Propagation Delay, and Calculating Lease
             Expiration. . . . . . . . . . . . . . . . . . . . .   89
      8.14.  Migration, Replication and State. . . . . . . . . .   90
             8.14.1.  Migration and State. . . . . . . . . . . .   90
             8.14.2.  Replication and State. . . . . . . . . . .   91
             8.14.3.  Notification of Migrated Lease . . . . . .   92
             8.14.4.  Migration and the Lease_time Attribute . .   92
 9.  Client-Side Caching . . . . . . . . . . . . . . . . . . . .   93
      9.1.   Performance Challenges for Client-Side Caching. . .   93
      9.2.   Delegation and Callbacks. . . . . . . . . . . . . .   94
             9.2.1.  Delegation Recovery . . . . . . . . . . . .   96
      9.3.   Data Caching. . . . . . . . . . . . . . . . . . . .   98
             9.3.1.   Data Caching and OPENs . . . . . . . . . .   98
             9.3.2.   Data Caching and File Locking. . . . . . .   99
             9.3.3.   Data Caching and Mandatory File Locking. .  101
             9.3.4.   Data Caching and File Identity . . . . . .  101
      9.4.   Open Delegation . . . . . . . . . . . . . . . . . .  102
             9.4.1.   Open Delegation and Data Caching . . . . .  104
             9.4.2.   Open Delegation and File Locks . . . . . .  106
             9.4.3.   Handling of CB_GETATTR . . . . . . . . . .  106
             9.4.4.   Recall of Open Delegation. . . . . . . . .  109
             9.4.5.   Clients that Fail to Honor
                      Delegation Recalls . . . . . . . . . . . .  111
             9.4.6.   Delegation Revocation. . . . . . . . . . .  112
      9.5.   Data Caching and Revocation . . . . . . . . . . . .  112
             9.5.1.   Revocation Recovery for Write Open
                      Delegation . . . . . . . . . . . . . . . .  113
      9.6.   Attribute Caching . . . . . . . . . . . . . . . . .  113
      9.7.   Data and Metadata Caching and Memory Mapped Files .  115
      9.8.   Name Caching  . . . . . . . . . . . . . . . . . . .  118
      9.9.   Directory Caching . . . . . . . . . . . . . . . . .  119
 10.  Minor Versioning . . . . . . . . . . . . . . . . . . . . .  120
 11.  Internationalization . . . . . . . . . . . . . . . . . . .  122
      11.1.  Stringprep profile for the utf8str_cs type. . . . .  123
             11.1.1.  Intended applicability of the
                      nfs4_cs_prep profile . . . . . . . . . . .  123
             11.1.2.  Character repertoire of nfs4_cs_prep . . .  124
             11.1.3.  Mapping used by nfs4_cs_prep . . . . . . .  124
             11.1.4.  Normalization used by nfs4_cs_prep . . . .  124
             11.1.5.  Prohibited output for nfs4_cs_prep . . . .  125
             11.1.6.  Bidirectional output for nfs4_cs_prep. . .  125

Shepler, et al. Standards Track [Page 4] RFC 3530 NFS version 4 Protocol April 2003

      11.2.  Stringprep profile for the utf8str_cis type . . . .  125
             11.2.1.  Intended applicability of the
                      nfs4_cis_prep profile. . . . . . . . . . .  125
             11.2.2.  Character repertoire of nfs4_cis_prep  . .  125
             11.2.3.  Mapping used by nfs4_cis_prep  . . . . . .  125
             11.2.4.  Normalization used by nfs4_cis_prep  . . .  125
             11.2.5.  Prohibited output for nfs4_cis_prep  . . .  126
             11.2.6.  Bidirectional output for nfs4_cis_prep . .  126
      11.3.  Stringprep profile for the utf8str_mixed type . . .  126
             11.3.1.  Intended applicability of the
                      nfs4_mixed_prep profile. . . . . . . . . .  126
             11.3.2.  Character repertoire of nfs4_mixed_prep  .  126
             11.3.3.  Mapping used by nfs4_cis_prep  . . . . . .  126
             11.3.4.  Normalization used by nfs4_mixed_prep  . .  127
             11.3.5.  Prohibited output for nfs4_mixed_prep  . .  127
             11.3.6.  Bidirectional output for nfs4_mixed_prep .  127
      11.4.  UTF-8 Related Errors. . . . . . . . . . . . . . . .  127
 12.  Error Definitions  . . . . . . . . . . . . . . . . . . . .  128
 13.  NFS version 4 Requests . . . . . . . . . . . . . . . . . .  134
      13.1.  Compound Procedure. . . . . . . . . . . . . . . . .  134
      13.2.  Evaluation of a Compound Request. . . . . . . . . .  135
      13.3.  Synchronous Modifying Operations. . . . . . . . . .  136
      13.4.  Operation Values. . . . . . . . . . . . . . . . . .  136
 14.  NFS version 4 Procedures . . . . . . . . . . . . . . . . .  136
      14.1.  Procedure 0: NULL - No Operation. . . . . . . . . .  136
      14.2.  Procedure 1: COMPOUND - Compound Operations . . . .  137
             14.2.1.   Operation 3: ACCESS - Check Access
                       Rights. . . . . . . . . . . . . . . . . .  140
             14.2.2.   Operation 4: CLOSE - Close File . . . . .  142
             14.2.3.   Operation 5: COMMIT - Commit
                       Cached Data . . . . . . . . . . . . . . .  144
             14.2.4.   Operation 6: CREATE - Create a
                       Non-Regular File Object . . . . . . . . .  147
             14.2.5.   Operation 7: DELEGPURGE -
                       Purge Delegations Awaiting Recovery . . .  150
             14.2.6.   Operation 8: DELEGRETURN - Return
                       Delegation. . . . . . . . . . . . . . . .  151
             14.2.7.   Operation 9: GETATTR - Get Attributes . .  152
             14.2.8.   Operation 10: GETFH - Get Current
                       Filehandle. . . . . . . . . . . . . . . .  153
             14.2.9.   Operation 11: LINK - Create Link to a
                       File. . . . . . . . . . . . . . . . . . .  154
             14.2.10.  Operation 12: LOCK - Create Lock  . . . .  156
             14.2.11.  Operation 13: LOCKT - Test For Lock . . .  160
             14.2.12.  Operation 14: LOCKU - Unlock File . . . .  162
             14.2.13.  Operation 15: LOOKUP - Lookup Filename. .  163
             14.2.14.  Operation 16: LOOKUPP - Lookup
                       Parent Directory. . . . . . . . . . . . .  165

Shepler, et al. Standards Track [Page 5] RFC 3530 NFS version 4 Protocol April 2003

             14.2.15.  Operation 17: NVERIFY - Verify
                       Difference in Attributes  . . . . . . . .  166
             14.2.16.  Operation 18: OPEN - Open a Regular
                       File. . . . . . . . . . . . . . . . . . .  168
             14.2.17.  Operation 19: OPENATTR - Open Named
                       Attribute Directory . . . . . . . . . . .  178
             14.2.18.  Operation 20: OPEN_CONFIRM -
                       Confirm Open . . . . . . . . . . . . . .   180
             14.2.19.  Operation 21: OPEN_DOWNGRADE -
                       Reduce Open File Access . . . . . . . . .  182
             14.2.20.  Operation 22: PUTFH - Set
                       Current Filehandle. . . . . . . . . . . .  184
             14.2.21.  Operation 23: PUTPUBFH -
                       Set Public Filehandle . . . . . . . . . .  185
             14.2.22.  Operation 24: PUTROOTFH -
                       Set Root Filehandle . . . . . . . . . . .  186
             14.2.23.  Operation 25: READ - Read from File . . .  187
             14.2.24.  Operation 26: READDIR -
                       Read Directory. . . . . . . . . . . . . .  190
             14.2.25.  Operation 27: READLINK -
                       Read Symbolic Link. . . . . . . . . . . .  193
             14.2.26.  Operation 28: REMOVE -
                       Remove Filesystem Object. . . . . . . . .  195
             14.2.27.  Operation 29: RENAME -
                       Rename Directory Entry. . . . . . . . . .  197
             14.2.28.  Operation 30: RENEW - Renew a Lease . . .  200
             14.2.29.  Operation 31: RESTOREFH -
                       Restore Saved Filehandle. . . . . . . . .  201
             14.2.30.  Operation 32: SAVEFH - Save
                       Current Filehandle. . . . . . . . . . . .  202
             14.2.31.  Operation 33: SECINFO - Obtain
                       Available Security. . . . . . . . . . . .  203
             14.2.32.  Operation 34: SETATTR - Set Attributes. .  206
             14.2.33.  Operation 35: SETCLIENTID -
                       Negotiate Clientid. . . . . . . . . . . .  209
             14.2.34.  Operation 36: SETCLIENTID_CONFIRM -
                       Confirm Clientid. . . . . . . . . . . . .  213
             14.2.35.  Operation 37: VERIFY -
                       Verify Same Attributes. . . . . . . . . .  217
             14.2.36.  Operation 38: WRITE - Write to File . . .  218
             14.2.37.  Operation 39: RELEASE_LOCKOWNER -
                       Release Lockowner State . . . . . . . . .  223
             14.2.38.  Operation 10044: ILLEGAL -
                       Illegal operation . . . . . . . . . . . .  224
 15.  NFS version 4 Callback Procedures  . . . . . . . . . . . .  225
      15.1.  Procedure 0: CB_NULL - No Operation . . . . . . . .  225
      15.2.  Procedure 1: CB_COMPOUND - Compound
             Operations. . . . . . . . . . . . . . . . . . . . .  226

Shepler, et al. Standards Track [Page 6] RFC 3530 NFS version 4 Protocol April 2003

             15.2.1.  Operation 3: CB_GETATTR - Get
                      Attributes . . . . . . . . . . . . . . . .  228
             15.2.2.  Operation 4: CB_RECALL -
                      Recall an Open Delegation. . . . . . . . .  229
             15.2.3.  Operation 10044: CB_ILLEGAL -
                      Illegal Callback Operation . . . . . . . .  230
 16.  Security Considerations  . . . . . . . . . . . . . . . . .  231
 17.  IANA Considerations  . . . . . . . . . . . . . . . . . . .  232
      17.1.  Named Attribute Definition. . . . . . . . . . . . .  232
      17.2.  ONC RPC Network Identifiers (netids). . . . . . . .  232
 18.  RPC definition file  . . . . . . . . . . . . . . . . . . .  234
 19.  Acknowledgements . . . . . . . . . . . . . . . . . . . . .  268
 20.  Normative References . . . . . . . . . . . . . . . . . . .  268
 21.  Informative References . . . . . . . . . . . . . . . . . .  270
 22.  Authors' Information . . . . . . . . . . . . . . . . . . .  273
      22.1.  Editor's Address. . . . . . . . . . . . . . . . . .  273
      22.2.  Authors' Addresses. . . . . . . . . . . . . . . . .  274
 23.  Full Copyright Statement . . . . . . . . . . . . . . . . .  275

Shepler, et al. Standards Track [Page 7] RFC 3530 NFS version 4 Protocol April 2003

1. Introduction

1.1. Changes since RFC 3010

 This definition of the NFS version 4 protocol replaces or obsoletes
 the definition present in [RFC3010].  While portions of the two
 documents have remained the same, there have been substantive changes
 in others.  The changes made between [RFC3010] and this document
 represent implementation experience and further review of the
 protocol.  While some modifications were made for ease of
 implementation or clarification, most updates represent errors or
 situations where the [RFC3010] definition were untenable.
 The following list is not all inclusive of all changes but presents
 some of the most notable changes or additions made:
 o  The state model has added an open_owner4 identifier.  This was
    done to accommodate Posix based clients and the model they use for
    file locking.  For Posix clients, an open_owner4 would correspond
    to a file descriptor potentially shared amongst a set of processes
    and the lock_owner4 identifier would correspond to a process that
    is locking a file.
 o  Clarifications and error conditions were added for the handling of
    the owner and group attributes.  Since these attributes are string
    based (as opposed to the numeric uid/gid of previous versions of
    NFS), translations may not be available and hence the changes
    made.
 o  Clarifications for the ACL and mode attributes to address
    evaluation and partial support.
 o  For identifiers that are defined as XDR opaque, limits were set on
    their size.
 o  Added the mounted_on_filed attribute to allow Posix clients to
    correctly construct local mounts.
 o  Modified the SETCLIENTID/SETCLIENTID_CONFIRM operations to deal
    correctly with confirmation details along with adding the ability
    to specify new client callback information.  Also added
    clarification of the callback information itself.
 o  Added a new operation LOCKOWNER_RELEASE to enable notifying the
    server that a lock_owner4 will no longer be used by the client.
 o  RENEW operation changes to identify the client correctly and allow
    for additional error returns.

Shepler, et al. Standards Track [Page 8] RFC 3530 NFS version 4 Protocol April 2003

 o  Verify error return possibilities for all operations.
 o  Remove use of the pathname4 data type from LOOKUP and OPEN in
    favor of having the client construct a sequence of LOOKUP
    operations to achieive the same effect.
 o  Clarification of the internationalization issues and adoption of
    the new stringprep profile framework.

1.2. NFS Version 4 Goals

 The NFS version 4 protocol is a further revision of the NFS protocol
 defined already by versions 2 [RFC1094] and 3 [RFC1813].  It retains
 the essential characteristics of previous versions: design for easy
 recovery, independent of transport protocols, operating systems and
 filesystems, simplicity, and good performance.  The NFS version 4
 revision has the following goals:
 o  Improved access and good performance on the Internet.
    The protocol is designed to transit firewalls easily, perform well
    where latency is high and bandwidth is low, and scale to very
    large numbers of clients per server.
 o  Strong security with negotiation built into the protocol.
    The protocol builds on the work of the ONCRPC working group in
    supporting the RPCSEC_GSS protocol.  Additionally, the NFS version
    4 protocol provides a mechanism to allow clients and servers the
    ability to negotiate security and require clients and servers to
    support a minimal set of security schemes.
 o  Good cross-platform interoperability.
    The protocol features a filesystem model that provides a useful,
    common set of features that does not unduly favor one filesystem
    or operating system over another.
 o  Designed for protocol extensions.
    The protocol is designed to accept standard extensions that do not
    compromise backward compatibility.

1.3. Inconsistencies of this Document with Section 18

 Section 18, RPC Definition File, contains the definitions in XDR
 description language of the constructs used by the protocol.  Prior
 to Section 18, several of the constructs are reproduced for purposes

Shepler, et al. Standards Track [Page 9] RFC 3530 NFS version 4 Protocol April 2003

 of explanation.  The reader is warned of the possibility of errors in
 the reproduced constructs outside of Section 18.  For any part of the
 document that is inconsistent with Section 18, Section 18 is to be
 considered authoritative.

1.4. Overview of NFS version 4 Features

 To provide a reasonable context for the reader, the major features of
 NFS version 4 protocol will be reviewed in brief.  This will be done
 to provide an appropriate context for both the reader who is familiar
 with the previous versions of the NFS protocol and the reader that is
 new to the NFS protocols.  For the reader new to the NFS protocols,
 there is still a fundamental knowledge that is expected.  The reader
 should be familiar with the XDR and RPC protocols as described in
 [RFC1831] and [RFC1832].  A basic knowledge of filesystems and
 distributed filesystems is expected as well.

1.4.1. RPC and Security

 As with previous versions of NFS, the External Data Representation
 (XDR) and Remote Procedure Call (RPC) mechanisms used for the NFS
 version 4 protocol are those defined in [RFC1831] and [RFC1832].  To
 meet end to end security requirements, the RPCSEC_GSS framework
 [RFC2203] will be used to extend the basic RPC security.  With the
 use of RPCSEC_GSS, various mechanisms can be provided to offer
 authentication, integrity, and privacy to the NFS version 4 protocol.
 Kerberos V5 will be used as described in [RFC1964] to provide one
 security framework.  The LIPKEY GSS-API mechanism described in
 [RFC2847] will be used to provide for the use of user password and
 server public key by the NFS version 4 protocol.  With the use of
 RPCSEC_GSS, other mechanisms may also be specified and used for NFS
 version 4 security.
 To enable in-band security negotiation, the NFS version 4 protocol
 has added a new operation which provides the client a method of
 querying the server about its policies regarding which security
 mechanisms must be used for access to the server's filesystem
 resources.  With this, the client can securely match the security
 mechanism that meets the policies specified at both the client and
 server.

1.4.2. Procedure and Operation Structure

 A significant departure from the previous versions of the NFS
 protocol is the introduction of the COMPOUND procedure.  For the NFS
 version 4 protocol, there are two RPC procedures, NULL and COMPOUND.
 The COMPOUND procedure is defined in terms of operations and these
 operations correspond more closely to the traditional NFS procedures.

Shepler, et al. Standards Track [Page 10] RFC 3530 NFS version 4 Protocol April 2003

 With the use of the COMPOUND procedure, the client is able to build
 simple or complex requests.  These COMPOUND requests allow for a
 reduction in the number of RPCs needed for logical filesystem
 operations.  For example, without previous contact with a server a
 client will be able to read data from a file in one request by
 combining LOOKUP, OPEN, and READ operations in a single COMPOUND RPC.
 With previous versions of the NFS protocol, this type of single
 request was not possible.
 The model used for COMPOUND is very simple.  There is no logical OR
 or ANDing of operations.  The operations combined within a COMPOUND
 request are evaluated in order by the server.  Once an operation
 returns a failing result, the evaluation ends and the results of all
 evaluated operations are returned to the client.
 The NFS version 4 protocol continues to have the client refer to a
 file or directory at the server by a "filehandle".  The COMPOUND
 procedure has a method of passing a filehandle from one operation to
 another within the sequence of operations.  There is a concept of a
 "current filehandle" and "saved filehandle".  Most operations use the
 "current filehandle" as the filesystem object to operate upon.  The
 "saved filehandle" is used as temporary filehandle storage within a
 COMPOUND procedure as well as an additional operand for certain
 operations.

1.4.3. Filesystem Model

 The general filesystem model used for the NFS version 4 protocol is
 the same as previous versions.  The server filesystem is hierarchical
 with the regular files contained within being treated as opaque byte
 streams.  In a slight departure, file and directory names are encoded
 with UTF-8 to deal with the basics of internationalization.
 The NFS version 4 protocol does not require a separate protocol to
 provide for the initial mapping between path name and filehandle.
 Instead of using the older MOUNT protocol for this mapping, the
 server provides a ROOT filehandle that represents the logical root or
 top of the filesystem tree provided by the server.  The server
 provides multiple filesystems by gluing them together with pseudo
 filesystems.  These pseudo filesystems provide for potential gaps in
 the path names between real filesystems.

1.4.3.1. Filehandle Types

 In previous versions of the NFS protocol, the filehandle provided by
 the server was guaranteed to be valid or persistent for the lifetime
 of the filesystem object to which it referred.  For some server
 implementations, this persistence requirement has been difficult to

Shepler, et al. Standards Track [Page 11] RFC 3530 NFS version 4 Protocol April 2003

 meet.  For the NFS version 4 protocol, this requirement has been
 relaxed by introducing another type of filehandle, volatile.  With
 persistent and volatile filehandle types, the server implementation
 can match the abilities of the filesystem at the server along with
 the operating environment.  The client will have knowledge of the
 type of filehandle being provided by the server and can be prepared
 to deal with the semantics of each.

1.4.3.2. Attribute Types

 The NFS version 4 protocol introduces three classes of filesystem or
 file attributes.  Like the additional filehandle type, the
 classification of file attributes has been done to ease server
 implementations along with extending the overall functionality of the
 NFS protocol.  This attribute model is structured to be extensible
 such that new attributes can be introduced in minor revisions of the
 protocol without requiring significant rework.
 The three classifications are: mandatory, recommended and named
 attributes.  This is a significant departure from the previous
 attribute model used in the NFS protocol.  Previously, the attributes
 for the filesystem and file objects were a fixed set of mainly UNIX
 attributes.  If the server or client did not support a particular
 attribute, it would have to simulate the attribute the best it could.
 Mandatory attributes are the minimal set of file or filesystem
 attributes that must be provided by the server and must be properly
 represented by the server.  Recommended attributes represent
 different filesystem types and operating environments.  The
 recommended attributes will allow for better interoperability and the
 inclusion of more operating environments.  The mandatory and
 recommended attribute sets are traditional file or filesystem
 attributes.  The third type of attribute is the named attribute.  A
 named attribute is an opaque byte stream that is associated with a
 directory or file and referred to by a string name.  Named attributes
 are meant to be used by client applications as a method to associate
 application specific data with a regular file or directory.
 One significant addition to the recommended set of file attributes is
 the Access Control List (ACL) attribute.  This attribute provides for
 directory and file access control beyond the model used in previous
 versions of the NFS protocol.  The ACL definition allows for
 specification of user and group level access control.

Shepler, et al. Standards Track [Page 12] RFC 3530 NFS version 4 Protocol April 2003

1.4.3.3. Filesystem Replication and Migration

 With the use of a special file attribute, the ability to migrate or
 replicate server filesystems is enabled within the protocol.  The
 filesystem locations attribute provides a method for the client to
 probe the server about the location of a filesystem.  In the event of
 a migration of a filesystem, the client will receive an error when
 operating on the filesystem and it can then query as to the new file
 system location.  Similar steps are used for replication, the client
 is able to query the server for the multiple available locations of a
 particular filesystem.  From this information, the client can use its
 own policies to access the appropriate filesystem location.

1.4.4. OPEN and CLOSE

 The NFS version 4 protocol introduces OPEN and CLOSE operations.  The
 OPEN operation provides a single point where file lookup, creation,
 and share semantics can be combined.  The CLOSE operation also
 provides for the release of state accumulated by OPEN.

1.4.5. File locking

 With the NFS version 4 protocol, the support for byte range file
 locking is part of the NFS protocol.  The file locking support is
 structured so that an RPC callback mechanism is not required.  This
 is a departure from the previous versions of the NFS file locking
 protocol, Network Lock Manager (NLM).  The state associated with file
 locks is maintained at the server under a lease-based model.  The
 server defines a single lease period for all state held by a NFS
 client.  If the client does not renew its lease within the defined
 period, all state associated with the client's lease may be released
 by the server.  The client may renew its lease with use of the RENEW
 operation or implicitly by use of other operations (primarily READ).

1.4.6. Client Caching and Delegation

 The file, attribute, and directory caching for the NFS version 4
 protocol is similar to previous versions.  Attributes and directory
 information are cached for a duration determined by the client.  At
 the end of a predefined timeout, the client will query the server to
 see if the related filesystem object has been updated.
 For file data, the client checks its cache validity when the file is
 opened.  A query is sent to the server to determine if the file has
 been changed.  Based on this information, the client determines if
 the data cache for the file should kept or released.  Also, when the
 file is closed, any modified data is written to the server.

Shepler, et al. Standards Track [Page 13] RFC 3530 NFS version 4 Protocol April 2003

 If an application wants to serialize access to file data, file
 locking of the file data ranges in question should be used.
 The major addition to NFS version 4 in the area of caching is the
 ability of the server to delegate certain responsibilities to the
 client.  When the server grants a delegation for a file to a client,
 the client is guaranteed certain semantics with respect to the
 sharing of that file with other clients.  At OPEN, the server may
 provide the client either a read or write delegation for the file.
 If the client is granted a read delegation, it is assured that no
 other client has the ability to write to the file for the duration of
 the delegation.  If the client is granted a write delegation, the
 client is assured that no other client has read or write access to
 the file.
 Delegations can be recalled by the server.  If another client
 requests access to the file in such a way that the access conflicts
 with the granted delegation, the server is able to notify the initial
 client and recall the delegation.  This requires that a callback path
 exist between the server and client.  If this callback path does not
 exist, then delegations can not be granted.  The essence of a
 delegation is that it allows the client to locally service operations
 such as OPEN, CLOSE, LOCK, LOCKU, READ, WRITE without immediate
 interaction with the server.

1.5. General Definitions

 The following definitions are provided for the purpose of providing
 an appropriate context for the reader.
 Client    The "client" is the entity that accesses the NFS server's
           resources.  The client may be an application which contains
           the logic to access the NFS server directly.  The client
           may also be the traditional operating system client remote
           filesystem services for a set of applications.
           In the case of file locking the client is the entity that
           maintains a set of locks on behalf of one or more
           applications.  This client is responsible for crash or
           failure recovery for those locks it manages.
           Note that multiple clients may share the same transport and
           multiple clients may exist on the same network node.
 Clientid  A 64-bit quantity used as a unique, short-hand reference to
           a client supplied Verifier and ID.  The server is
           responsible for supplying the Clientid.

Shepler, et al. Standards Track [Page 14] RFC 3530 NFS version 4 Protocol April 2003

 Lease     An interval of time defined by the server for which the
           client is irrevocably granted a lock.  At the end of a
           lease period the lock may be revoked if the lease has not
           been extended.  The lock must be revoked if a conflicting
           lock has been granted after the lease interval.
           All leases granted by a server have the same fixed
           interval.  Note that the fixed interval was chosen to
           alleviate the expense a server would have in maintaining
           state about variable length leases across server failures.
 Lock      The term "lock" is used to refer to both record (byte-
           range) locks as well as share reservations unless
           specifically stated otherwise.
 Server    The "Server" is the entity responsible for coordinating
           client access to a set of filesystems.
 Stable Storage
           NFS version 4 servers must be able to recover without data
           loss from multiple power failures (including cascading
           power failures, that is, several power failures in quick
           succession), operating system failures, and hardware
           failure of components other than the storage medium itself
           (for example, disk, nonvolatile RAM).
           Some examples of stable storage that are allowable for an
           NFS server include:
           1. Media commit of data, that is, the modified data has
              been successfully written to the disk media, for
              example, the disk platter.
           2. An immediate reply disk drive with battery-backed on-
              drive intermediate storage or uninterruptible power
              system (UPS).
           3. Server commit of data with battery-backed intermediate
              storage and recovery software.
           4. Cache commit with uninterruptible power system (UPS) and
              recovery software.
 Stateid   A 128-bit quantity returned by a server that uniquely
           defines the open and locking state provided by the server
           for a specific open or lock owner for a specific file.

Shepler, et al. Standards Track [Page 15] RFC 3530 NFS version 4 Protocol April 2003

           Stateids composed of all bits 0 or all bits 1 have special
           meaning and are reserved values.
 Verifier  A 64-bit quantity generated by the client that the server
           can use to determine if the client has restarted and lost
           all previous lock state.

2. Protocol Data Types

 The syntax and semantics to describe the data types of the NFS
 version 4 protocol are defined in the XDR [RFC1832] and RPC [RFC1831]
 documents.  The next sections build upon the XDR data types to define
 types and structures specific to this protocol.

2.1. Basic Data Types

 Data Type       Definition
 ____________________________________________________________________
 int32_t         typedef int             int32_t;
 uint32_t        typedef unsigned int    uint32_t;
 int64_t         typedef hyper           int64_t;
 uint64_t        typedef unsigned hyper  uint64_t;
 attrlist4       typedef opaque        attrlist4<>;
                 Used for file/directory attributes
 bitmap4         typedef uint32_t        bitmap4<>;
                 Used in attribute array encoding.
 changeid4       typedef       uint64_t        changeid4;
                 Used in definition of change_info
 clientid4       typedef uint64_t        clientid4;
                 Shorthand reference to client identification
 component4      typedef utf8str_cs      component4;
                 Represents path name components
 count4          typedef uint32_t        count4;
                 Various count parameters (READ, WRITE, COMMIT)
 length4         typedef uint64_t        length4;
                 Describes LOCK lengths

Shepler, et al. Standards Track [Page 16] RFC 3530 NFS version 4 Protocol April 2003

 linktext4       typedef utf8str_cs      linktext4;
                 Symbolic link contents
 mode4           typedef uint32_t        mode4;
                 Mode attribute data type
 nfs_cookie4     typedef uint64_t        nfs_cookie4;
                 Opaque cookie value for READDIR
 nfs_fh4         typedef opaque          nfs_fh4<NFS4_FHSIZE>;
                 Filehandle definition; NFS4_FHSIZE is defined as 128
 nfs_ftype4      enum nfs_ftype4;
                 Various defined file types
 nfsstat4        enum nfsstat4;
                 Return value for operations
 offset4         typedef uint64_t        offset4;
                 Various offset designations (READ, WRITE,
                 LOCK, COMMIT)
 pathname4       typedef component4      pathname4<>;
                 Represents path name for LOOKUP, OPEN and others
 qop4            typedef uint32_t        qop4;
                 Quality of protection designation in SECINFO
 sec_oid4        typedef opaque          sec_oid4<>;
                 Security Object Identifier
                 The sec_oid4 data type is not really opaque.
                 Instead contains an ASN.1 OBJECT IDENTIFIER as used
                 by GSS-API in the mech_type argument to
                 GSS_Init_sec_context.  See [RFC2743] for details.
 seqid4          typedef uint32_t        seqid4;
                 Sequence identifier used for file locking
 utf8string      typedef opaque          utf8string<>;
                 UTF-8 encoding for strings
 utf8str_cis     typedef opaque          utf8str_cis;
                 Case-insensitive UTF-8 string
 utf8str_cs      typedef opaque          utf8str_cs;
                 Case-sensitive UTF-8 string

Shepler, et al. Standards Track [Page 17] RFC 3530 NFS version 4 Protocol April 2003

 utf8str_mixed   typedef opaque          utf8str_mixed;
                 UTF-8 strings with a case sensitive prefix and
                 a case insensitive suffix.
 verifier4       typedef opaque        verifier4[NFS4_VERIFIER_SIZE];
                 Verifier used for various operations (COMMIT,
                 CREATE, OPEN, READDIR, SETCLIENTID,
                 SETCLIENTID_CONFIRM, WRITE) NFS4_VERIFIER_SIZE is
                 defined as 8.

2.2. Structured Data Types

 nfstime4
                struct nfstime4 {
                        int64_t seconds;
                        uint32_t nseconds;
                }
 The nfstime4 structure gives the number of seconds and nanoseconds
 since midnight or 0 hour January 1, 1970 Coordinated Universal Time
 (UTC).  Values greater than zero for the seconds field denote dates
 after the 0 hour January 1, 1970.  Values less than zero for the
 seconds field denote dates before the 0 hour January 1, 1970.  In
 both cases, the nseconds field is to be added to the seconds field
 for the final time representation.  For example, if the time to be
 represented is one-half second before 0 hour January 1, 1970, the
 seconds field would have a value of negative one (-1) and the
 nseconds fields would have a value of one-half second (500000000).
 Values greater than 999,999,999 for nseconds are considered invalid.
 This data type is used to pass time and date information.  A server
 converts to and from its local representation of time when processing
 time values, preserving as much accuracy as possible.  If the
 precision of timestamps stored for a filesystem object is less than
 defined, loss of precision can occur.  An adjunct time maintenance
 protocol is recommended to reduce client and server time skew.
 time_how4
                enum time_how4 {
                        SET_TO_SERVER_TIME4 = 0,
                        SET_TO_CLIENT_TIME4 = 1
                };

Shepler, et al. Standards Track [Page 18] RFC 3530 NFS version 4 Protocol April 2003

 settime4
                union settime4 switch (time_how4 set_it) {
                 case SET_TO_CLIENT_TIME4:
                         nfstime4       time;
                 default:
                         void;
                };
 The above definitions are used as the attribute definitions to set
 time values.  If set_it is SET_TO_SERVER_TIME4, then the server uses
 its local representation of time for the time value.
 specdata4
                struct specdata4 {
                        uint32_t specdata1; /* major device number */
                        uint32_t specdata2; /* minor device number */
                };
 This data type represents additional information for the device file
 types NF4CHR and NF4BLK.
 fsid4
                struct fsid4 {
                  uint64_t        major;
                  uint64_t        minor;
                };
 This type is the filesystem identifier that is used as a mandatory
 attribute.
 fs_location4
                struct fs_location4 {
                        utf8str_cis    server<>;
                        pathname4     rootpath;
                };
 fs_locations4
                struct fs_locations4 {
                        pathname4     fs_root;
                        fs_location4  locations<>;
                };

Shepler, et al. Standards Track [Page 19] RFC 3530 NFS version 4 Protocol April 2003

 The fs_location4 and fs_locations4 data types are used for the
 fs_locations recommended attribute which is used for migration and
 replication support.
 fattr4
                struct fattr4 {
                        bitmap4       attrmask;
                        attrlist4     attr_vals;
                };
 The fattr4 structure is used to represent file and directory
 attributes.
 The bitmap is a counted array of 32 bit integers used to contain bit
 values.  The position of the integer in the array that contains bit n
 can be computed from the expression (n / 32) and its bit within that
 integer is (n mod 32).
                         0            1
       +-----------+-----------+-----------+--
       |  count    | 31  ..  0 | 63  .. 32 |
       +-----------+-----------+-----------+--
 change_info4
                struct change_info4 {
                        bool          atomic;
                        changeid4     before;
                        changeid4     after;
                };
 This structure is used with the CREATE, LINK, REMOVE, RENAME
 operations to let the client know the value of the change attribute
 for the directory in which the target filesystem object resides.
 clientaddr4
                struct clientaddr4 {
                        /* see struct rpcb in RFC 1833 */
                        string r_netid<>;    /* network id */
                        string r_addr<>;     /* universal address */
                };
 The clientaddr4 structure is used as part of the SETCLIENTID
 operation to either specify the address of the client that is using a
 clientid or as part of the callback registration.  The

Shepler, et al. Standards Track [Page 20] RFC 3530 NFS version 4 Protocol April 2003

 r_netid and r_addr fields are specified in [RFC1833], but they are
 underspecified in [RFC1833] as far as what they should look like for
 specific protocols.
 For TCP over IPv4 and for UDP over IPv4, the format of r_addr is the
 US-ASCII string:
    h1.h2.h3.h4.p1.p2
 The prefix, "h1.h2.h3.h4", is the standard textual form for
 representing an IPv4 address, which is always four octets long.
 Assuming big-endian ordering, h1, h2, h3, and h4, are respectively,
 the first through fourth octets each converted to ASCII-decimal.
 Assuming big-endian ordering, p1 and p2 are, respectively, the first
 and second octets each converted to ASCII-decimal.  For example, if a
 host, in big-endian order, has an address of 0x0A010307 and there is
 a service listening on, in big endian order, port 0x020F (decimal
 527), then the complete universal address is "10.1.3.7.2.15".
 For TCP over IPv4 the value of r_netid is the string "tcp".  For UDP
 over IPv4 the value of r_netid is the string "udp".
 For TCP over IPv6 and for UDP over IPv6, the format of r_addr is the
 US-ASCII string:
       x1:x2:x3:x4:x5:x6:x7:x8.p1.p2
 The suffix "p1.p2" is the service port, and is computed the same way
 as with universal addresses for TCP and UDP over IPv4.  The prefix,
 "x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for
 representing an IPv6 address as defined in Section 2.2 of [RFC2373].
 Additionally, the two alternative forms specified in Section 2.2 of
 [RFC2373] are also acceptable.
 For TCP over IPv6 the value of r_netid is the string "tcp6".  For UDP
 over IPv6 the value of r_netid is the string "udp6".
 cb_client4
                struct cb_client4 {
                        unsigned int  cb_program;
                        clientaddr4   cb_location;
                };
 This structure is used by the client to inform the server of its call
 back address; includes the program number and client address.

Shepler, et al. Standards Track [Page 21] RFC 3530 NFS version 4 Protocol April 2003

 nfs_client_id4
                struct nfs_client_id4 {
                        verifier4     verifier;
                        opaque        id<NFS4_OPAQUE_LIMIT>;
                };
 This structure is part of the arguments to the SETCLIENTID operation.
 NFS4_OPAQUE_LIMIT is defined as 1024.
 open_owner4
                struct open_owner4 {
                        clientid4     clientid;
                        opaque        owner<NFS4_OPAQUE_LIMIT>;
                };
 This structure is used to identify the owner of open state.
 NFS4_OPAQUE_LIMIT is defined as 1024.
 lock_owner4
                struct lock_owner4 {
                        clientid4     clientid;
                        opaque        owner<NFS4_OPAQUE_LIMIT>;
                };
 This structure is used to identify the owner of file locking state.
 NFS4_OPAQUE_LIMIT is defined as 1024.
 open_to_lock_owner4
                struct open_to_lock_owner4 {
                        seqid4          open_seqid;
                        stateid4        open_stateid;
                        seqid4          lock_seqid;
                        lock_owner4     lock_owner;
                };
 This structure is used for the first LOCK operation done for an
 open_owner4.  It provides both the open_stateid and lock_owner such
 that the transition is made from a valid open_stateid sequence to
 that of the new lock_stateid sequence.  Using this mechanism avoids
 the confirmation of the lock_owner/lock_seqid pair since it is tied
 to established state in the form of the open_stateid/open_seqid.

Shepler, et al. Standards Track [Page 22] RFC 3530 NFS version 4 Protocol April 2003

 stateid4
                struct stateid4 {
                  uint32_t        seqid;
                  opaque          other[12];
                };
 This structure is used for the various state sharing mechanisms
 between the client and server.  For the client, this data structure
 is read-only.  The starting value of the seqid field is undefined.
 The server is required to increment the seqid field monotonically at
 each transition of the stateid.  This is important since the client
 will inspect the seqid in OPEN stateids to determine the order of
 OPEN processing done by the server.

3. RPC and Security Flavor

 The NFS version 4 protocol is a Remote Procedure Call (RPC)
 application that uses RPC version 2 and the corresponding eXternal
 Data Representation (XDR) as defined in [RFC1831] and [RFC1832].  The
 RPCSEC_GSS security flavor as defined in [RFC2203] MUST be used as
 the mechanism to deliver stronger security for the NFS version 4
 protocol.

3.1. Ports and Transports

 Historically, NFS version 2 and version 3 servers have resided on
 port 2049.  The registered port 2049 [RFC3232] for the NFS protocol
 should be the default configuration.  Using the registered port for
 NFS services means the NFS client will not need to use the RPC
 binding protocols as described in [RFC1833]; this will allow NFS to
 transit firewalls.
 Where an NFS version 4 implementation supports operation over the IP
 network protocol, the supported transports between NFS and IP MUST be
 among the IETF-approved congestion control transport protocols, which
 include TCP and SCTP.  To enhance the possibilities for
 interoperability, an NFS version 4 implementation MUST support
 operation over the TCP transport protocol, at least until such time
 as a standards track RFC revises this requirement to use a different
 IETF-approved congestion control transport protocol.
 If TCP is used as the transport, the client and server SHOULD use
 persistent connections.  This will prevent the weakening of TCP's
 congestion control via short lived connections and will improve
 performance for the WAN environment by eliminating the need for SYN
 handshakes.

Shepler, et al. Standards Track [Page 23] RFC 3530 NFS version 4 Protocol April 2003

 As noted in the Security Considerations section, the authentication
 model for NFS version 4 has moved from machine-based to principal-
 based.  However, this modification of the authentication model does
 not imply a technical requirement to move the TCP connection
 management model from whole machine-based to one based on a per user
 model.  In particular, NFS over TCP client implementations have
 traditionally multiplexed traffic for multiple users over a common
 TCP connection between an NFS client and server.  This has been true,
 regardless whether the NFS client is using AUTH_SYS, AUTH_DH,
 RPCSEC_GSS or any other flavor.  Similarly, NFS over TCP server
 implementations have assumed such a model and thus scale the
 implementation of TCP connection management in proportion to the
 number of expected client machines.  It is intended that NFS version
 4 will not modify this connection management model.  NFS version 4
 clients that violate this assumption can expect scaling issues on the
 server and hence reduced service.
 Note that for various timers, the client and server should avoid
 inadvertent synchronization of those timers.  For further discussion
 of the general issue refer to [Floyd].

3.1.1. Client Retransmission Behavior

 When processing a request received over a reliable transport such as
 TCP, the NFS version 4 server MUST NOT silently drop the request,
 except if the transport connection has been broken.  Given such a
 contract between NFS version 4 clients and servers, clients MUST NOT
 retry a request unless one or both of the following are true:
 o  The transport connection has been broken
 o  The procedure being retried is the NULL procedure
 Since reliable transports, such as TCP, do not always synchronously
 inform a peer when the other peer has broken the connection (for
 example, when an NFS server reboots), the NFS version 4 client may
 want to actively "probe" the connection to see if has been broken.
 Use of the NULL procedure is one recommended way to do so.  So, when
 a client experiences a remote procedure call timeout (of some
 arbitrary implementation specific amount), rather than retrying the
 remote procedure call, it could instead issue a NULL procedure call
 to the server.  If the server has died, the transport connection
 break will eventually be indicated to the NFS version 4 client.  The
 client can then reconnect, and then retry the original request.  If
 the NULL procedure call gets a response, the connection has not
 broken.  The client can decide to wait longer for the original
 request's response, or it can break the transport connection and
 reconnect before re-sending the original request.

Shepler, et al. Standards Track [Page 24] RFC 3530 NFS version 4 Protocol April 2003

 For callbacks from the server to the client, the same rules apply,
 but the server doing the callback becomes the client, and the client
 receiving the callback becomes the server.

3.2. Security Flavors

 Traditional RPC implementations have included AUTH_NONE, AUTH_SYS,
 AUTH_DH, and AUTH_KRB4 as security flavors.  With [RFC2203] an
 additional security flavor of RPCSEC_GSS has been introduced which
 uses the functionality of GSS-API [RFC2743].  This allows for the use
 of various security mechanisms by the RPC layer without the
 additional implementation overhead of adding RPC security flavors.
 For NFS version 4, the RPCSEC_GSS security flavor MUST be used to
 enable the mandatory security mechanism.  Other flavors, such as,
 AUTH_NONE, AUTH_SYS, and AUTH_DH MAY be implemented as well.

3.2.1. Security mechanisms for NFS version 4

 The use of RPCSEC_GSS requires selection of: mechanism, quality of
 protection, and service (authentication, integrity, privacy).  The
 remainder of this document will refer to these three parameters of
 the RPCSEC_GSS security as the security triple.

3.2.1.1. Kerberos V5 as a security triple

 The Kerberos V5 GSS-API mechanism as described in [RFC1964] MUST be
 implemented and provide the following security triples.
 column descriptions:
 1 == number of pseudo flavor
 2 == name of pseudo flavor
 3 == mechanism's OID
 4 == mechanism's algorithm(s)
 5 == RPCSEC_GSS service
 1      2     3                    4             5
 --------------------------------------------------------------------
 390003 krb5  1.2.840.113554.1.2.2 DES MAC MD5   rpc_gss_svc_none
 390004 krb5i 1.2.840.113554.1.2.2 DES MAC MD5   rpc_gss_svc_integrity
 390005 krb5p 1.2.840.113554.1.2.2 DES MAC MD5   rpc_gss_svc_privacy
                                   for integrity,
                                   and 56 bit DES
                                   for privacy.
 Note that the pseudo flavor is presented here as a mapping aid to the
 implementor.  Because this NFS protocol includes a method to
 negotiate security and it understands the GSS-API mechanism, the

Shepler, et al. Standards Track [Page 25] RFC 3530 NFS version 4 Protocol April 2003

 pseudo flavor is not needed.  The pseudo flavor is needed for NFS
 version 3 since the security negotiation is done via the MOUNT
 protocol.
 For a discussion of NFS' use of RPCSEC_GSS and Kerberos V5, please
 see [RFC2623].
 Users and implementors are warned that 56 bit DES is no longer
 considered state of the art in terms of resistance to brute force
 attacks.  Once a revision to [RFC1964] is available that adds support
 for AES, implementors are urged to incorporate AES into their NFSv4
 over Kerberos V5 protocol stacks, and users are similarly urged to
 migrate to the use of AES.

3.2.1.2. LIPKEY as a security triple

 The LIPKEY GSS-API mechanism as described in [RFC2847] MUST be
 implemented and provide the following security triples.  The
 definition of the columns matches the previous subsection "Kerberos
 V5 as security triple"
 1      2        3                   4              5
 --------------------------------------------------------------------
 390006 lipkey   1.3.6.1.5.5.9       negotiated  rpc_gss_svc_none
 390007 lipkey-i 1.3.6.1.5.5.9       negotiated  rpc_gss_svc_integrity
 390008 lipkey-p 1.3.6.1.5.5.9       negotiated  rpc_gss_svc_privacy
 The mechanism algorithm is listed as "negotiated".  This is because
 LIPKEY is layered on SPKM-3 and in SPKM-3 [RFC2847] the
 confidentiality and integrity algorithms are negotiated.  Since
 SPKM-3 specifies HMAC-MD5 for integrity as MANDATORY, 128 bit
 cast5CBC for confidentiality for privacy as MANDATORY, and further
 specifies that HMAC-MD5 and cast5CBC MUST be listed first before
 weaker algorithms, specifying "negotiated" in column 4 does not
 impair interoperability.  In the event an SPKM-3 peer does not
 support the mandatory algorithms, the other peer is free to accept or
 reject the GSS-API context creation.
 Because SPKM-3 negotiates the algorithms, subsequent calls to
 LIPKEY's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality
 of protection value of 0 (zero).  See section 5.2 of [RFC2025] for an
 explanation.
 LIPKEY uses SPKM-3 to create a secure channel in which to pass a user
 name and password from the client to the server.  Once the user name
 and password have been accepted by the server, calls to the LIPKEY
 context are redirected to the SPKM-3 context.  See [RFC2847] for more
 details.

Shepler, et al. Standards Track [Page 26] RFC 3530 NFS version 4 Protocol April 2003

3.2.1.3. SPKM-3 as a security triple

 The SPKM-3 GSS-API mechanism as described in [RFC2847] MUST be
 implemented and provide the following security triples.  The
 definition of the columns matches the previous subsection "Kerberos
 V5 as security triple".
 1      2        3                   4              5
 --------------------------------------------------------------------
 390009 spkm3    1.3.6.1.5.5.1.3     negotiated  rpc_gss_svc_none
 390010 spkm3i   1.3.6.1.5.5.1.3     negotiated  rpc_gss_svc_integrity
 390011 spkm3p   1.3.6.1.5.5.1.3     negotiated  rpc_gss_svc_privacy
 For a discussion as to why the mechanism algorithm is listed as
 "negotiated", see the previous section "LIPKEY as a security triple."
 Because SPKM-3 negotiates the algorithms, subsequent calls to SPKM-
 3's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality of
 protection value of 0 (zero).  See section 5.2 of [RFC2025] for an
 explanation.
 Even though LIPKEY is layered over SPKM-3, SPKM-3 is specified as a
 mandatory set of triples to handle the situations where the initiator
 (the client) is anonymous or where the initiator has its own
 certificate.  If the initiator is anonymous, there will not be a user
 name and password to send to the target (the server).  If the
 initiator has its own certificate, then using passwords is
 superfluous.

3.3. Security Negotiation

 With the NFS version 4 server potentially offering multiple security
 mechanisms, the client needs a method to determine or negotiate which
 mechanism is to be used for its communication with the server.  The
 NFS server may have multiple points within its filesystem name space
 that are available for use by NFS clients.  In turn the NFS server
 may be configured such that each of these entry points may have
 different or multiple security mechanisms in use.
 The security negotiation between client and server must be done with
 a secure channel to eliminate the possibility of a third party
 intercepting the negotiation sequence and forcing the client and
 server to choose a lower level of security than required or desired.
 See the section "Security Considerations" for further discussion.

Shepler, et al. Standards Track [Page 27] RFC 3530 NFS version 4 Protocol April 2003

3.3.1. SECINFO

 The new SECINFO operation will allow the client to determine, on a
 per filehandle basis, what security triple is to be used for server
 access.  In general, the client will not have to use the SECINFO
 operation except during initial communication with the server or when
 the client crosses policy boundaries at the server.  It is possible
 that the server's policies change during the client's interaction
 therefore forcing the client to negotiate a new security triple.

3.3.2. Security Error

 Based on the assumption that each NFS version 4 client and server
 must support a minimum set of security (i.e., LIPKEY, SPKM-3, and
 Kerberos-V5 all under RPCSEC_GSS), the NFS client will start its
 communication with the server with one of the minimal security
 triples.  During communication with the server, the client may
 receive an NFS error of NFS4ERR_WRONGSEC.  This error allows the
 server to notify the client that the security triple currently being
 used is not appropriate for access to the server's filesystem
 resources.  The client is then responsible for determining what
 security triples are available at the server and choose one which is
 appropriate for the client.  See the section for the "SECINFO"
 operation for further discussion of how the client will respond to
 the NFS4ERR_WRONGSEC error and use SECINFO.

3.4. Callback RPC Authentication

 Except as noted elsewhere in this section, the callback RPC
 (described later) MUST mutually authenticate the NFS server to the
 principal that acquired the clientid (also described later), using
 the security flavor the original SETCLIENTID operation used.
 For AUTH_NONE, there are no principals, so this is a non-issue.
 AUTH_SYS has no notions of mutual authentication or a server
 principal, so the callback from the server simply uses the AUTH_SYS
 credential that the user used when he set up the delegation.
 For AUTH_DH, one commonly used convention is that the server uses the
 credential corresponding to this AUTH_DH principal:
       unix.host@domain
 where host and domain are variables corresponding to the name of
 server host and directory services domain in which it lives such as a
 Network Information System domain or a DNS domain.

Shepler, et al. Standards Track [Page 28] RFC 3530 NFS version 4 Protocol April 2003

 Because LIPKEY is layered over SPKM-3, it is permissible for the
 server to use SPKM-3 and not LIPKEY for the callback even if the
 client used LIPKEY for SETCLIENTID.
 Regardless of what security mechanism under RPCSEC_GSS is being used,
 the NFS server, MUST identify itself in GSS-API via a
 GSS_C_NT_HOSTBASED_SERVICE name type.  GSS_C_NT_HOSTBASED_SERVICE
 names are of the form:
       service@hostname
 For NFS, the "service" element is
       nfs
 Implementations of security mechanisms will convert nfs@hostname to
 various different forms.  For Kerberos V5 and LIPKEY, the following
 form is RECOMMENDED:
       nfs/hostname
 For Kerberos V5, nfs/hostname would be a server principal in the
 Kerberos Key Distribution Center database.  This is the same
 principal the client acquired a GSS-API context for when it issued
 the SETCLIENTID operation, therefore, the realm name for the server
 principal must be the same for the callback as it was for the
 SETCLIENTID.
 For LIPKEY, this would be the username passed to the target (the NFS
 version 4 client that receives the callback).
 It should be noted that LIPKEY may not work for callbacks, since the
 LIPKEY client uses a user id/password.  If the NFS client receiving
 the callback can authenticate the NFS server's user name/password
 pair, and if the user that the NFS server is authenticating to has a
 public key certificate, then it works.
 In situations where the NFS client uses LIPKEY and uses a per-host
 principal for the SETCLIENTID operation, instead of using LIPKEY for
 SETCLIENTID, it is RECOMMENDED that SPKM-3 with mutual authentication
 be used.  This effectively means that the client will use a
 certificate to authenticate and identify the initiator to the target
 on the NFS server.  Using SPKM-3 and not LIPKEY has the following
 advantages:
 o  When the server does a callback, it must authenticate to the
    principal used in the SETCLIENTID.  Even if LIPKEY is used,
    because LIPKEY is layered over SPKM-3, the NFS client will need to

Shepler, et al. Standards Track [Page 29] RFC 3530 NFS version 4 Protocol April 2003

    have a certificate that corresponds to the principal used in the
    SETCLIENTID operation.  From an administrative perspective, having
    a user name, password, and certificate for both the client and
    server is redundant.
 o  LIPKEY was intended to minimize additional infrastructure
    requirements beyond a certificate for the target, and the
    expectation is that existing password infrastructure can be
    leveraged for the initiator.  In some environments, a per-host
    password does not exist yet.  If certificates are used for any
    per-host principals, then additional password infrastructure is
    not needed.
 o  In cases when a host is both an NFS client and server, it can
    share the same per-host certificate.

4. Filehandles

 The filehandle in the NFS protocol is a per server unique identifier
 for a filesystem object.  The contents of the filehandle are opaque
 to the client.  Therefore, the server is responsible for translating
 the filehandle to an internal representation of the filesystem
 object.

4.1. Obtaining the First Filehandle

 The operations of the NFS protocol are defined in terms of one or
 more filehandles.  Therefore, the client needs a filehandle to
 initiate communication with the server.  With the NFS version 2
 protocol [RFC1094] and the NFS version 3 protocol [RFC1813], there
 exists an ancillary protocol to obtain this first filehandle.  The
 MOUNT protocol, RPC program number 100005, provides the mechanism of
 translating a string based filesystem path name to a filehandle which
 can then be used by the NFS protocols.
 The MOUNT protocol has deficiencies in the area of security and use
 via firewalls.  This is one reason that the use of the public
 filehandle was introduced in [RFC2054] and [RFC2055].  With the use
 of the public filehandle in combination with the LOOKUP operation in
 the NFS version 2 and 3 protocols, it has been demonstrated that the
 MOUNT protocol is unnecessary for viable interaction between NFS
 client and server.
 Therefore, the NFS version 4 protocol will not use an ancillary
 protocol for translation from string based path names to a
 filehandle.  Two special filehandles will be used as starting points
 for the NFS client.

Shepler, et al. Standards Track [Page 30] RFC 3530 NFS version 4 Protocol April 2003

4.1.1. Root Filehandle

 The first of the special filehandles is the ROOT filehandle.  The
 ROOT filehandle is the "conceptual" root of the filesystem name space
 at the NFS server.  The client uses or starts with the ROOT
 filehandle by employing the PUTROOTFH operation.  The PUTROOTFH
 operation instructs the server to set the "current" filehandle to the
 ROOT of the server's file tree.  Once this PUTROOTFH operation is
 used, the client can then traverse the entirety of the server's file
 tree with the LOOKUP operation.  A complete discussion of the server
 name space is in the section "NFS Server Name Space".

4.1.2. Public Filehandle

 The second special filehandle is the PUBLIC filehandle.  Unlike the
 ROOT filehandle, the PUBLIC filehandle may be bound or represent an
 arbitrary filesystem object at the server.  The server is responsible
 for this binding.  It may be that the PUBLIC filehandle and the ROOT
 filehandle refer to the same filesystem object.  However, it is up to
 the administrative software at the server and the policies of the
 server administrator to define the binding of the PUBLIC filehandle
 and server filesystem object.  The client may not make any
 assumptions about this binding.  The client uses the PUBLIC
 filehandle via the PUTPUBFH operation.

4.2. Filehandle Types

 In the NFS version 2 and 3 protocols, there was one type of
 filehandle with a single set of semantics.  This type of filehandle
 is termed "persistent" in NFS Version 4.  The semantics of a
 persistent filehandle remain the same as before.  A new type of
 filehandle introduced in NFS Version 4 is the "volatile" filehandle,
 which attempts to accommodate certain server environments.
 The volatile filehandle type was introduced to address server
 functionality or implementation issues which make correct
 implementation of a persistent filehandle infeasible.  Some server
 environments do not provide a filesystem level invariant that can be
 used to construct a persistent filehandle.  The underlying server
 filesystem may not provide the invariant or the server's filesystem
 programming interfaces may not provide access to the needed
 invariant.  Volatile filehandles may ease the implementation of
 server functionality such as hierarchical storage management or
 filesystem reorganization or migration.  However, the volatile
 filehandle increases the implementation burden for the client.

Shepler, et al. Standards Track [Page 31] RFC 3530 NFS version 4 Protocol April 2003

 Since the client will need to handle persistent and volatile
 filehandles differently, a file attribute is defined which may be
 used by the client to determine the filehandle types being returned
 by the server.

4.2.1. General Properties of a Filehandle

 The filehandle contains all the information the server needs to
 distinguish an individual file.  To the client, the filehandle is
 opaque.  The client stores filehandles for use in a later request and
 can compare two filehandles from the same server for equality by
 doing a byte-by-byte comparison.  However, the client MUST NOT
 otherwise interpret the contents of filehandles.  If two filehandles
 from the same server are equal, they MUST refer to the same file.
 Servers SHOULD try to maintain a one-to-one correspondence between
 filehandles and files but this is not required.  Clients MUST use
 filehandle comparisons only to improve performance, not for correct
 behavior.  All clients need to be prepared for situations in which it
 cannot be determined whether two filehandles denote the same object
 and in such cases, avoid making invalid assumptions which might cause
 incorrect behavior.  Further discussion of filehandle and attribute
 comparison in the context of data caching is presented in the section
 "Data Caching and File Identity".
 As an example, in the case that two different path names when
 traversed at the server terminate at the same filesystem object, the
 server SHOULD return the same filehandle for each path.  This can
 occur if a hard link is used to create two file names which refer to
 the same underlying file object and associated data.  For example, if
 paths /a/b/c and /a/d/c refer to the same file, the server SHOULD
 return the same filehandle for both path names traversals.

4.2.2. Persistent Filehandle

 A persistent filehandle is defined as having a fixed value for the
 lifetime of the filesystem object to which it refers.  Once the
 server creates the filehandle for a filesystem object, the server
 MUST accept the same filehandle for the object for the lifetime of
 the object.  If the server restarts or reboots the NFS server must
 honor the same filehandle value as it did in the server's previous
 instantiation.  Similarly, if the filesystem is migrated, the new NFS
 server must honor the same filehandle as the old NFS server.
 The persistent filehandle will be become stale or invalid when the
 filesystem object is removed.  When the server is presented with a
 persistent filehandle that refers to a deleted object, it MUST return
 an error of NFS4ERR_STALE.  A filehandle may become stale when the
 filesystem containing the object is no longer available.  The file

Shepler, et al. Standards Track [Page 32] RFC 3530 NFS version 4 Protocol April 2003

 system may become unavailable if it exists on removable media and the
 media is no longer available at the server or the filesystem in whole
 has been destroyed or the filesystem has simply been removed from the
 server's name space (i.e., unmounted in a UNIX environment).

4.2.3. Volatile Filehandle

 A volatile filehandle does not share the same longevity
 characteristics of a persistent filehandle.  The server may determine
 that a volatile filehandle is no longer valid at many different
 points in time.  If the server can definitively determine that a
 volatile filehandle refers to an object that has been removed, the
 server should return NFS4ERR_STALE to the client (as is the case for
 persistent filehandles).  In all other cases where the server
 determines that a volatile filehandle can no longer be used, it
 should return an error of NFS4ERR_FHEXPIRED.
 The mandatory attribute "fh_expire_type" is used by the client to
 determine what type of filehandle the server is providing for a
 particular filesystem.  This attribute is a bitmask with the
 following values:
 FH4_PERSISTENT
           The value of FH4_PERSISTENT is used to indicate a
           persistent filehandle, which is valid until the object is
           removed from the filesystem.  The server will not return
           NFS4ERR_FHEXPIRED for this filehandle.  FH4_PERSISTENT is
           defined as a value in which none of the bits specified
           below are set.
 FH4_VOLATILE_ANY
           The filehandle may expire at any time, except as
           specifically excluded (i.e., FH4_NO_EXPIRE_WITH_OPEN).
 FH4_NOEXPIRE_WITH_OPEN
           May only be set when FH4_VOLATILE_ANY is set.  If this bit
           is set, then the meaning of FH4_VOLATILE_ANY is qualified
           to exclude any expiration of the filehandle when it is
           open.
 FH4_VOL_MIGRATION
           The filehandle will expire as a result of migration.  If
           FH4_VOL_ANY is set, FH4_VOL_MIGRATION is redundant.

Shepler, et al. Standards Track [Page 33] RFC 3530 NFS version 4 Protocol April 2003

 FH4_VOL_RENAME
           The filehandle will expire during rename.  This includes a
           rename by the requesting client or a rename by any other
           client.  If FH4_VOL_ANY is set, FH4_VOL_RENAME is
           redundant.
 Servers which provide volatile filehandles that may expire while open
 (i.e., if FH4_VOL_MIGRATION or FH4_VOL_RENAME is set or if
 FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set), should
 deny a RENAME or REMOVE that would affect an OPEN file of any of the
 components leading to the OPEN file.  In addition, the server should
 deny all RENAME or REMOVE requests during the grace period upon
 server restart.
 Note that the bits FH4_VOL_MIGRATION and FH4_VOL_RENAME allow the
 client to determine that expiration has occurred whenever a specific
 event occurs, without an explicit filehandle expiration error from
 the server.  FH4_VOL_ANY does not provide this form of information.
 In situations where the server will expire many, but not all
 filehandles upon migration (e.g., all but those that are open),
 FH4_VOLATILE_ANY (in this case with FH4_NOEXPIRE_WITH_OPEN) is a
 better choice since the client may not assume that all filehandles
 will expire when migration occurs, and it is likely that additional
 expirations will occur (as a result of file CLOSE) that are separated
 in time from the migration event itself.

4.2.4. One Method of Constructing a Volatile Filehandle

 A volatile filehandle, while opaque to the client could contain:
 [volatile bit = 1 | server boot time | slot | generation number]
 o  slot is an index in the server volatile filehandle table
 o  generation number is the generation number for the table
    entry/slot
 When the client presents a volatile filehandle, the server makes the
 following checks, which assume that the check for the volatile bit
 has passed.  If the server boot time is less than the current server
 boot time, return NFS4ERR_FHEXPIRED.  If slot is out of range, return
 NFS4ERR_BADHANDLE.  If the generation number does not match, return
 NFS4ERR_FHEXPIRED.
 When the server reboots, the table is gone (it is volatile).
 If volatile bit is 0, then it is a persistent filehandle with a
 different structure following it.

Shepler, et al. Standards Track [Page 34] RFC 3530 NFS version 4 Protocol April 2003

4.3. Client Recovery from Filehandle Expiration

 If possible, the client SHOULD recover from the receipt of an
 NFS4ERR_FHEXPIRED error.  The client must take on additional
 responsibility so that it may prepare itself to recover from the
 expiration of a volatile filehandle.  If the server returns
 persistent filehandles, the client does not need these additional
 steps.
 For volatile filehandles, most commonly the client will need to store
 the component names leading up to and including the filesystem object
 in question.  With these names, the client should be able to recover
 by finding a filehandle in the name space that is still available or
 by starting at the root of the server's filesystem name space.
 If the expired filehandle refers to an object that has been removed
 from the filesystem, obviously the client will not be able to recover
 from the expired filehandle.
 It is also possible that the expired filehandle refers to a file that
 has been renamed.  If the file was renamed by another client, again
 it is possible that the original client will not be able to recover.
 However, in the case that the client itself is renaming the file and
 the file is open, it is possible that the client may be able to
 recover.  The client can determine the new path name based on the
 processing of the rename request.  The client can then regenerate the
 new filehandle based on the new path name.  The client could also use
 the compound operation mechanism to construct a set of operations
 like:
         RENAME A B
         LOOKUP B
         GETFH
 Note that the COMPOUND procedure does not provide atomicity.  This
 example only reduces the overhead of recovering from an expired
 filehandle.

5. File Attributes

 To meet the requirements of extensibility and increased
 interoperability with non-UNIX platforms, attributes must be handled
 in a flexible manner.  The NFS version 3 fattr3 structure contains a
 fixed list of attributes that not all clients and servers are able to
 support or care about.  The fattr3 structure can not be extended as
 new needs arise and it provides no way to indicate non-support.  With
 the NFS version 4 protocol, the client is able query what attributes
 the server supports and construct requests with only those supported
 attributes (or a subset thereof).

Shepler, et al. Standards Track [Page 35] RFC 3530 NFS version 4 Protocol April 2003

 To this end, attributes are divided into three groups: mandatory,
 recommended, and named.  Both mandatory and recommended attributes
 are supported in the NFS version 4 protocol by a specific and well-
 defined encoding and are identified by number.  They are requested by
 setting a bit in the bit vector sent in the GETATTR request; the
 server response includes a bit vector to list what attributes were
 returned in the response.  New mandatory or recommended attributes
 may be added to the NFS protocol between major revisions by
 publishing a standards-track RFC which allocates a new attribute
 number value and defines the encoding for the attribute.  See the
 section "Minor Versioning" for further discussion.
 Named attributes are accessed by the new OPENATTR operation, which
 accesses a hidden directory of attributes associated with a file
 system object.  OPENATTR takes a filehandle for the object and
 returns the filehandle for the attribute hierarchy.  The filehandle
 for the named attributes is a directory object accessible by LOOKUP
 or READDIR and contains files whose names represent the named
 attributes and whose data bytes are the value of the attribute.  For
 example:
    LOOKUP     "foo"       ; look up file
    GETATTR    attrbits
    OPENATTR               ; access foo's named attributes
    LOOKUP     "x11icon"   ; look up specific attribute
    READ       0,4096      ; read stream of bytes
 Named attributes are intended for data needed by applications rather
 than by an NFS client implementation.  NFS implementors are strongly
 encouraged to define their new attributes as recommended attributes
 by bringing them to the IETF standards-track process.
 The set of attributes which are classified as mandatory is
 deliberately small since servers must do whatever it takes to support
 them.  A server should support as many of the recommended attributes
 as possible but by their definition, the server is not required to
 support all of them.  Attributes are deemed mandatory if the data is
 both needed by a large number of clients and is not otherwise
 reasonably computable by the client when support is not provided on
 the server.
 Note that the hidden directory returned by OPENATTR is a convenience
 for protocol processing.  The client should not make any assumptions
 about the server's implementation of named attributes and whether the
 underlying filesystem at the server has a named attribute directory
 or not.  Therefore, operations such as SETATTR and GETATTR on the
 named attribute directory are undefined.

Shepler, et al. Standards Track [Page 36] RFC 3530 NFS version 4 Protocol April 2003

5.1. Mandatory Attributes

 These MUST be supported by every NFS version 4 client and server in
 order to ensure a minimum level of interoperability.  The server must
 store and return these attributes and the client must be able to
 function with an attribute set limited to these attributes.  With
 just the mandatory attributes some client functionality may be
 impaired or limited in some ways.  A client may ask for any of these
 attributes to be returned by setting a bit in the GETATTR request and
 the server must return their value.

5.2. Recommended Attributes

 These attributes are understood well enough to warrant support in the
 NFS version 4 protocol.  However, they may not be supported on all
 clients and servers.  A client may ask for any of these attributes to
 be returned by setting a bit in the GETATTR request but must handle
 the case where the server does not return them.  A client may ask for
 the set of attributes the server supports and should not request
 attributes the server does not support.  A server should be tolerant
 of requests for unsupported attributes and simply not return them
 rather than considering the request an error.  It is expected that
 servers will support all attributes they comfortably can and only
 fail to support attributes which are difficult to support in their
 operating environments.  A server should provide attributes whenever
 they don't have to "tell lies" to the client.  For example, a file
 modification time should be either an accurate time or should not be
 supported by the server.  This will not always be comfortable to
 clients but the client is better positioned decide whether and how to
 fabricate or construct an attribute or whether to do without the
 attribute.

5.3. Named Attributes

 These attributes are not supported by direct encoding in the NFS
 Version 4 protocol but are accessed by string names rather than
 numbers and correspond to an uninterpreted stream of bytes which are
 stored with the filesystem object.  The name space for these
 attributes may be accessed by using the OPENATTR operation.  The
 OPENATTR operation returns a filehandle for a virtual "attribute
 directory" and further perusal of the name space may be done using
 READDIR and LOOKUP operations on this filehandle.  Named attributes
 may then be examined or changed by normal READ and WRITE and CREATE
 operations on the filehandles returned from READDIR and LOOKUP.
 Named attributes may have attributes.

Shepler, et al. Standards Track [Page 37] RFC 3530 NFS version 4 Protocol April 2003

 It is recommended that servers support arbitrary named attributes.  A
 client should not depend on the ability to store any named attributes
 in the server's filesystem.  If a server does support named
 attributes, a client which is also able to handle them should be able
 to copy a file's data and meta-data with complete transparency from
 one location to another; this would imply that names allowed for
 regular directory entries are valid for named attribute names as
 well.
 Names of attributes will not be controlled by this document or other
 IETF standards track documents.  See the section "IANA
 Considerations" for further discussion.

5.4. Classification of Attributes

 Each of the Mandatory and Recommended attributes can be classified in
 one of three categories: per server, per filesystem, or per
 filesystem object.  Note that it is possible that some per filesystem
 attributes may vary within the filesystem.  See the "homogeneous"
 attribute for its definition.  Note that the attributes
 time_access_set and time_modify_set are not listed in this section
 because they are write-only attributes corresponding to time_access
 and time_modify, and are used in a special instance of SETATTR.
 o  The per server attribute is:
       lease_time
 o  The per filesystem attributes are:
    supp_attr, fh_expire_type, link_support, symlink_support,
    unique_handles, aclsupport, cansettime, case_insensitive,
    case_preserving, chown_restricted, files_avail, files_free,
    files_total, fs_locations, homogeneous, maxfilesize, maxname,
    maxread, maxwrite, no_trunc, space_avail, space_free, space_total,
    time_delta
 o  The per filesystem object attributes are:
    type, change, size, named_attr, fsid, rdattr_error, filehandle,
    ACL, archive, fileid, hidden, maxlink, mimetype, mode, numlinks,
    owner, owner_group, rawdev, space_used, system, time_access,
    time_backup, time_create, time_metadata, time_modify,
    mounted_on_fileid
 For quota_avail_hard, quota_avail_soft, and quota_used see their
 definitions below for the appropriate classification.

Shepler, et al. Standards Track [Page 38] RFC 3530 NFS version 4 Protocol April 2003

5.5. Mandatory Attributes - Definitions

 Name              #    DataType     Access   Description
 ___________________________________________________________________
 supp_attr         0    bitmap       READ     The bit vector which
                                              would retrieve all
                                              mandatory and
                                              recommended attributes
                                              that are supported for
                                              this object.  The
                                              scope of this
                                              attribute applies to
                                              all objects with a
                                              matching fsid.
 type              1    nfs4_ftype   READ     The type of the object
                                              (file, directory,
                                              symlink, etc.)
 fh_expire_type    2    uint32       READ     Server uses this to
                                              specify filehandle
                                              expiration behavior to
                                              the client.  See the
                                              section "Filehandles"
                                              for additional
                                              description.
 change            3    uint64       READ     A value created by the
                                              server that the client
                                              can use to determine
                                              if file data,
                                              directory contents or
                                              attributes of the
                                              object have been
                                              modified.  The server
                                              may return the
                                              object's time_metadata
                                              attribute for this
                                              attribute's value but
                                              only if the filesystem
                                              object can not be
                                              updated more
                                              frequently than the
                                              resolution of
                                              time_metadata.
 size              4    uint64       R/W      The size of the object
                                              in bytes.

Shepler, et al. Standards Track [Page 39] RFC 3530 NFS version 4 Protocol April 2003

 link_support      5    bool         READ     True, if the object's
                                              filesystem supports
                                              hard links.
 symlink_support   6    bool         READ     True, if the object's
                                              filesystem supports
                                              symbolic links.
 named_attr        7    bool         READ     True, if this object
                                              has named attributes.
                                              In other words, object
                                              has a non-empty named
                                              attribute directory.
 fsid              8    fsid4        READ     Unique filesystem
                                              identifier for the
                                              filesystem holding
                                              this object.  fsid
                                              contains major and
                                              minor components each
                                              of which are uint64.
 unique_handles    9    bool         READ     True, if two distinct
                                              filehandles guaranteed
                                              to refer to two
                                              different filesystem
                                              objects.
 lease_time        10   nfs_lease4   READ     Duration of leases at
                                              server in seconds.
 rdattr_error      11   enum         READ     Error returned from
                                              getattr during
                                              readdir.
 filehandle        19   nfs_fh4      READ     The filehandle of this
                                              object (primarily for
                                              readdir requests).

Shepler, et al. Standards Track [Page 40] RFC 3530 NFS version 4 Protocol April 2003

5.6. Recommended Attributes - Definitions

 Name                #    Data Type      Access   Description
 _____________________________________________________________________
 ACL                 12   nfsace4<>      R/W      The access control
                                                  list for the object.
 aclsupport          13   uint32         READ     Indicates what types
                                                  of ACLs are
                                                  supported on the
                                                  current filesystem.
 archive             14   bool           R/W      True, if this file
                                                  has been archived
                                                  since the time of
                                                  last modification
                                                  (deprecated in favor
                                                  of time_backup).
 cansettime          15   bool           READ     True, if the server
                                                  is able to change
                                                  the times for a
                                                  filesystem object as
                                                  specified in a
                                                  SETATTR operation.
 case_insensitive    16   bool           READ     True, if filename
                                                  comparisons on this
                                                  filesystem are case
                                                  insensitive.
 case_preserving     17   bool           READ     True, if filename
                                                  case on this
                                                  filesystem are
                                                  preserved.
 chown_restricted    18   bool           READ     If TRUE, the server
                                                  will reject any
                                                  request to change
                                                  either the owner or
                                                  the group associated
                                                  with a file if the
                                                  caller is not a
                                                  privileged user (for
                                                  example, "root" in
                                                  UNIX operating
                                                  environments or in
                                                  Windows 2000 the

Shepler, et al. Standards Track [Page 41] RFC 3530 NFS version 4 Protocol April 2003

                                                  "Take Ownership"
                                                  privilege).
 fileid              20   uint64         READ     A number uniquely
                                                  identifying the file
                                                  within the
                                                  filesystem.
 files_avail         21   uint64         READ     File slots available
                                                  to this user on the
                                                  filesystem
                                                  containing this
                                                  object - this should
                                                  be the smallest
                                                  relevant limit.
 files_free          22   uint64         READ     Free file slots on
                                                  the filesystem
                                                  containing this
                                                  object - this should
                                                  be the smallest
                                                  relevant limit.
 files_total         23   uint64         READ     Total file slots on
                                                  the filesystem
                                                  containing this
                                                  object.
 fs_locations        24   fs_locations   READ     Locations where this
                                                  filesystem may be
                                                  found.  If the
                                                  server returns
                                                  NFS4ERR_MOVED
                                                  as an error, this
                                                  attribute MUST be
                                                  supported.
 hidden              25   bool           R/W      True, if the file is
                                                  considered hidden
                                                  with respect to the
                                                  Windows API.
 homogeneous         26   bool           READ     True, if this
                                                  object's filesystem
                                                  is homogeneous,
                                                  i.e., are per
                                                  filesystem
                                                  attributes the same

Shepler, et al. Standards Track [Page 42] RFC 3530 NFS version 4 Protocol April 2003

                                                  for all filesystem's
                                                  objects?
 maxfilesize         27   uint64         READ     Maximum supported
                                                  file size for the
                                                  filesystem of this
                                                  object.
 maxlink             28   uint32         READ     Maximum number of
                                                  links for this
                                                  object.
 maxname             29   uint32         READ     Maximum filename
                                                  size supported for
                                                  this object.
 maxread             30   uint64         READ     Maximum read size
                                                  supported for this
                                                  object.
 maxwrite            31   uint64         READ     Maximum write size
                                                  supported for this
                                                  object.  This
                                                  attribute SHOULD be
                                                  supported if the
                                                  file is writable.
                                                  Lack of this
                                                  attribute can
                                                  lead to the client
                                                  either wasting
                                                  bandwidth or not
                                                  receiving the best
                                                  performance.
 mimetype            32   utf8<>         R/W      MIME body
                                                  type/subtype of this
                                                  object.
 mode                33   mode4          R/W      UNIX-style mode and
                                                  permission bits for
                                                  this object.
 no_trunc            34   bool           READ     True, if a name
                                                  longer than name_max
                                                  is used, an error be
                                                  returned and name is
                                                  not truncated.

Shepler, et al. Standards Track [Page 43] RFC 3530 NFS version 4 Protocol April 2003

 numlinks            35   uint32         READ     Number of hard links
                                                  to this object.
 owner               36   utf8<>         R/W      The string name of
                                                  the owner of this
                                                  object.
 owner_group         37   utf8<>         R/W      The string name of
                                                  the group ownership
                                                  of this object.
 quota_avail_hard    38   uint64         READ     For definition see
                                                  "Quota Attributes"
                                                  section below.
 quota_avail_soft    39   uint64         READ     For definition see
                                                  "Quota Attributes"
                                                  section below.
 quota_used          40   uint64         READ     For definition see
                                                  "Quota Attributes"
                                                  section below.
 rawdev              41   specdata4      READ     Raw device
                                                  identifier.  UNIX
                                                  device major/minor
                                                  node information.
                                                  If the value of
                                                  type is not
                                                  NF4BLK or NF4CHR,
                                                  the value return
                                                  SHOULD NOT be
                                                  considered useful.
 space_avail         42   uint64         READ     Disk space in bytes
                                                  available to this
                                                  user on the
                                                  filesystem
                                                  containing this
                                                  object - this should
                                                  be the smallest
                                                  relevant limit.
 space_free          43   uint64         READ     Free disk space in
                                                  bytes on the
                                                  filesystem
                                                  containing this
                                                  object - this should

Shepler, et al. Standards Track [Page 44] RFC 3530 NFS version 4 Protocol April 2003

                                                  be the smallest
                                                  relevant limit.
 space_total         44   uint64         READ     Total disk space in
                                                  bytes on the
                                                  filesystem
                                                  containing this
                                                  object.
 space_used          45   uint64         READ     Number of filesystem
                                                  bytes allocated to
                                                  this object.
 system              46   bool           R/W      True, if this file
                                                  is a "system" file
                                                  with respect to the
                                                  Windows API.
 time_access         47   nfstime4       READ     The time of last
                                                  access to the object
                                                  by a read that was
                                                  satisfied by the
                                                  server.
 time_access_set     48   settime4       WRITE    Set the time of last
                                                  access to the
                                                  object.  SETATTR
                                                  use only.
 time_backup         49   nfstime4       R/W      The time of last
                                                  backup of the
                                                  object.
 time_create         50   nfstime4       R/W      The time of creation
                                                  of the object.  This
                                                  attribute does not
                                                  have any relation to
                                                  the traditional UNIX
                                                  file attribute
                                                  "ctime" or "change
                                                  time".
 time_delta          51   nfstime4       READ     Smallest useful
                                                  server time
                                                  granularity.

Shepler, et al. Standards Track [Page 45] RFC 3530 NFS version 4 Protocol April 2003

 time_metadata       52   nfstime4       READ     The time of last
                                                  meta-data
                                                  modification of the
                                                  object.
 time_modify         53   nfstime4       READ     The time of last
                                                  modification to the
                                                  object.
 time_modify_set     54   settime4       WRITE    Set the time of last
                                                  modification to the
                                                  object.  SETATTR use
                                                  only.
 mounted_on_fileid   55   uint64         READ     Like fileid, but if
                                                  the target
                                                  filehandle is the
                                                  root of a filesystem
                                                  return the fileid of
                                                  the underlying
                                                  directory.

5.7. Time Access

 As defined above, the time_access attribute represents the time of
 last access to the object by a read that was satisfied by the server.
 The notion of what is an "access" depends on server's operating
 environment and/or the server's filesystem semantics.  For example,
 for servers obeying POSIX semantics, time_access would be updated
 only by the READLINK, READ, and READDIR operations and not any of the
 operations that modify the content of the object.  Of course, setting
 the corresponding time_access_set attribute is another way to modify
 the time_access attribute.
 Whenever the file object resides on a writable filesystem, the server
 should make best efforts to record time_access into stable storage.
 However, to mitigate the performance effects of doing so, and most
 especially whenever the server is satisfying the read of the object's
 content from its cache, the server MAY cache access time updates and
 lazily write them to stable storage.  It is also acceptable to give
 administrators of the server the option to disable time_access
 updates.

Shepler, et al. Standards Track [Page 46] RFC 3530 NFS version 4 Protocol April 2003

5.8. Interpreting owner and owner_group

 The recommended attributes "owner" and "owner_group" (and also users
 and groups within the "acl" attribute) are represented in terms of a
 UTF-8 string.  To avoid a representation that is tied to a particular
 underlying implementation at the client or server, the use of the
 UTF-8 string has been chosen.  Note that section 6.1 of [RFC2624]
 provides additional rationale.  It is expected that the client and
 server will have their own local representation of owner and
 owner_group that is used for local storage or presentation to the end
 user.  Therefore, it is expected that when these attributes are
 transferred between the client and server that the local
 representation is translated to a syntax of the form
 "user@dns_domain".  This will allow for a client and server that do
 not use the same local representation the ability to translate to a
 common syntax that can be interpreted by both.
 Similarly, security principals may be represented in different ways
 by different security mechanisms.  Servers normally translate these
 representations into a common format, generally that used by local
 storage, to serve as a means of identifying the users corresponding
 to these security principals.  When these local identifiers are
 translated to the form of the owner attribute, associated with files
 created by such principals they identify, in a common format, the
 users associated with each corresponding set of security principals.
 The translation used to interpret owner and group strings is not
 specified as part of the protocol.  This allows various solutions to
 be employed.  For example, a local translation table may be consulted
 that maps between a numeric id to the user@dns_domain syntax.  A name
 service may also be used to accomplish the translation.  A server may
 provide a more general service, not limited by any particular
 translation (which would only translate a limited set of possible
 strings) by storing the owner and owner_group attributes in local
 storage without any translation or it may augment a translation
 method by storing the entire string for attributes for which no
 translation is available while using the local representation for
 those cases in which a translation is available.
 Servers that do not provide support for all possible values of the
 owner and owner_group attributes, should return an error
 (NFS4ERR_BADOWNER) when a string is presented that has no
 translation, as the value to be set for a SETATTR of the owner,
 owner_group, or acl attributes.  When a server does accept an owner
 or owner_group value as valid on a SETATTR (and similarly for the
 owner and group strings in an acl), it is promising to return that
 same string when a corresponding GETATTR is done.  Configuration
 changes and ill-constructed name translations (those that contain

Shepler, et al. Standards Track [Page 47] RFC 3530 NFS version 4 Protocol April 2003

 aliasing) may make that promise impossible to honor.  Servers should
 make appropriate efforts to avoid a situation in which these
 attributes have their values changed when no real change to ownership
 has occurred.
 The "dns_domain" portion of the owner string is meant to be a DNS
 domain name.  For example, user@ietf.org.  Servers should accept as
 valid a set of users for at least one domain.  A server may treat
 other domains as having no valid translations.  A more general
 service is provided when a server is capable of accepting users for
 multiple domains, or for all domains, subject to security
 constraints.
 In the case where there is no translation available to the client or
 server, the attribute value must be constructed without the "@".
 Therefore, the absence of the @ from the owner or owner_group
 attribute signifies that no translation was available at the sender
 and that the receiver of the attribute should not use that string as
 a basis for translation into its own internal format.  Even though
 the attribute value can not be translated, it may still be useful.
 In the case of a client, the attribute string may be used for local
 display of ownership.
 To provide a greater degree of compatibility with previous versions
 of NFS (i.e., v2 and v3), which identified users and groups by 32-bit
 unsigned uid's and gid's, owner and group strings that consist of
 decimal numeric values with no leading zeros can be given a special
 interpretation by clients and servers which choose to provide such
 support.  The receiver may treat such a user or group string as
 representing the same user as would be represented by a v2/v3 uid or
 gid having the corresponding numeric value.  A server is not
 obligated to accept such a string, but may return an NFS4ERR_BADOWNER
 instead.  To avoid this mechanism being used to subvert user and
 group translation, so that a client might pass all of the owners and
 groups in numeric form, a server SHOULD return an NFS4ERR_BADOWNER
 error when there is a valid translation for the user or owner
 designated in this way.  In that case, the client must use the
 appropriate name@domain string and not the special form for
 compatibility.
 The owner string "nobody" may be used to designate an anonymous user,
 which will be associated with a file created by a security principal
 that cannot be mapped through normal means to the owner attribute.

Shepler, et al. Standards Track [Page 48] RFC 3530 NFS version 4 Protocol April 2003

5.9. Character Case Attributes

 With respect to the case_insensitive and case_preserving attributes,
 each UCS-4 character (which UTF-8 encodes) has a "long descriptive
 name" [RFC1345] which may or may not included the word "CAPITAL" or
 "SMALL".  The presence of SMALL or CAPITAL allows an NFS server to
 implement unambiguous and efficient table driven mappings for case
 insensitive comparisons, and non-case-preserving storage.  For
 general character handling and internationalization issues, see the
 section "Internationalization".

5.10. Quota Attributes

 For the attributes related to filesystem quotas, the following
 definitions apply:
 quota_avail_soft
       The value in bytes which represents the amount of additional
       disk space that can be allocated to this file or directory
       before the user may reasonably be warned.  It is understood
       that this space may be consumed by allocations to other files
       or directories though there is a rule as to which other files
       or directories.
 quota_avail_hard
       The value in bytes which represent the amount of additional
       disk space beyond the current allocation that can be allocated
       to this file or directory before further allocations will be
       refused.  It is understood that this space may be consumed by
       allocations to other files or directories.
 quota_used
       The value in bytes which represent the amount of disc space
       used by this file or directory and possibly a number of other
       similar files or directories, where the set of "similar" meets
       at least the criterion that allocating space to any file or
       directory in the set will reduce the "quota_avail_hard" of
       every other file or directory in the set.
       Note that there may be a number of distinct but overlapping
       sets of files or directories for which a quota_used value is
       maintained (e.g., "all files with a given owner", "all files
       with a given group owner", etc.).
       The server is at liberty to choose any of those sets but should
       do so in a repeatable way.  The rule may be configured per-
       filesystem or may be "choose the set with the smallest quota".

Shepler, et al. Standards Track [Page 49] RFC 3530 NFS version 4 Protocol April 2003

5.11. Access Control Lists

 The NFS version 4 ACL attribute is an array of access control entries
 (ACE).  Although, the client can read and write the ACL attribute,
 the NFSv4 model is the server does all access control based on the
 server's interpretation of the ACL.  If at any point the client wants
 to check access without issuing an operation that modifies or reads
 data or metadata, the client can use the OPEN and ACCESS operations
 to do so.  There are various access control entry types, as defined
 in the Section "ACE type".  The server is able to communicate which
 ACE types are supported by returning the appropriate value within the
 aclsupport attribute.  Each ACE covers one or more operations on a
 file or directory as described in the Section "ACE Access Mask".  It
 may also contain one or more flags that modify the semantics of the
 ACE as defined in the Section "ACE flag".
 The NFS ACE attribute is defined as follows:
       typedef uint32_t        acetype4;
       typedef uint32_t        aceflag4;
       typedef uint32_t        acemask4;
       struct nfsace4 {
               acetype4        type;
               aceflag4        flag;
               acemask4        access_mask;
               utf8str_mixed   who;
       };
 To determine if a request succeeds, each nfsace4 entry is processed
 in order by the server.  Only ACEs which have a "who" that matches
 the requester are considered.  Each ACE is processed until all of the
 bits of the requester's access have been ALLOWED.  Once a bit (see
 below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it is no longer
 considered in the processing of later ACEs.  If an ACCESS_DENIED_ACE
 is encountered where the requester's access still has unALLOWED bits
 in common with the "access_mask" of the ACE, the request is denied.
 However, unlike the ALLOWED and DENIED ACE types, the ALARM and AUDIT
 ACE types do not affect a requester's access, and instead are for
 triggering events as a result of a requester's access attempt.
 Therefore, all AUDIT and ALARM ACEs are processed until end of the
 ACL.  When the ACL is fully processed, if there are bits in
 requester's mask that have not been considered whether the server
 allows or denies the access is undefined.  If there is a mode
 attribute on the file, then this cannot happen, since the mode's
 MODE4_*OTH bits will map to EVERYONE@ ACEs that unambiguously specify
 the requester's access.

Shepler, et al. Standards Track [Page 50] RFC 3530 NFS version 4 Protocol April 2003

 The NFS version 4 ACL model is quite rich.  Some server platforms may
 provide access control functionality that goes beyond the UNIX-style
 mode attribute, but which is not as rich as the NFS ACL model.  So
 that users can take advantage of this more limited functionality, the
 server may indicate that it supports ACLs as long as it follows the
 guidelines for mapping between its ACL model and the NFS version 4
 ACL model.
 The situation is complicated by the fact that a server may have
 multiple modules that enforce ACLs.  For example, the enforcement for
 NFS version 4 access may be different from the enforcement for local
 access, and both may be different from the enforcement for access
 through other protocols such as SMB.  So it may be useful for a
 server to accept an ACL even if not all of its modules are able to
 support it.
 The guiding principle in all cases is that the server must not accept
 ACLs that appear to make the file more secure than it really is.

5.11.1. ACE type

 Type         Description
 _____________________________________________________
 ALLOW        Explicitly grants the access defined in
              acemask4 to the file or directory.
 DENY         Explicitly denies the access defined in
              acemask4 to the file or directory.
 AUDIT        LOG (system dependent) any access
              attempt to a file or directory which
              uses any of the access methods specified
              in acemask4.
 ALARM        Generate a system ALARM (system
              dependent) when any access attempt is
              made to a file or directory for the
              access methods specified in acemask4.
 A server need not support all of the above ACE types.  The bitmask
 constants used to represent the above definitions within the
 aclsupport attribute are as follows:
    const ACL4_SUPPORT_ALLOW_ACL    = 0x00000001;
    const ACL4_SUPPORT_DENY_ACL     = 0x00000002;
    const ACL4_SUPPORT_AUDIT_ACL    = 0x00000004;
    const ACL4_SUPPORT_ALARM_ACL    = 0x00000008;

Shepler, et al. Standards Track [Page 51] RFC 3530 NFS version 4 Protocol April 2003

 The semantics of the "type" field follow the descriptions provided
 above.
 The constants used for the type field (acetype4) are as follows:
    const ACE4_ACCESS_ALLOWED_ACE_TYPE      = 0x00000000;
    const ACE4_ACCESS_DENIED_ACE_TYPE       = 0x00000001;
    const ACE4_SYSTEM_AUDIT_ACE_TYPE        = 0x00000002;
    const ACE4_SYSTEM_ALARM_ACE_TYPE        = 0x00000003;
 Clients should not attempt to set an ACE unless the server claims
 support for that ACE type.  If the server receives a request to set
 an ACE that it cannot store, it MUST reject the request with
 NFS4ERR_ATTRNOTSUPP.  If the server receives a request to set an ACE
 that it can store but cannot enforce, the server SHOULD reject the
 request with NFS4ERR_ATTRNOTSUPP.
 Example: suppose a server can enforce NFS ACLs for NFS access but
 cannot enforce ACLs for local access.  If arbitrary processes can run
 on the server, then the server SHOULD NOT indicate ACL support.  On
 the other hand, if only trusted administrative programs run locally,
 then the server may indicate ACL support.

5.11.2. ACE Access Mask

 The access_mask field contains values based on the following:
 Access                 Description
 _______________________________________________________________
 READ_DATA              Permission to read the data of the file
 LIST_DIRECTORY         Permission to list the contents of a
                        directory
 WRITE_DATA             Permission to modify the file's data
 ADD_FILE               Permission to add a new file to a
                        directory
 APPEND_DATA            Permission to append data to a file
 ADD_SUBDIRECTORY       Permission to create a subdirectory to a
                        directory
 READ_NAMED_ATTRS       Permission to read the named attributes
                        of a file
 WRITE_NAMED_ATTRS      Permission to write the named attributes
                        of a file
 EXECUTE                Permission to execute a file
 DELETE_CHILD           Permission to delete a file or directory
                        within a directory
 READ_ATTRIBUTES        The ability to read basic attributes
                        (non-acls) of a file
 WRITE_ATTRIBUTES       Permission to change basic attributes

Shepler, et al. Standards Track [Page 52] RFC 3530 NFS version 4 Protocol April 2003

                        (non-acls) of a file
 DELETE                 Permission to Delete the file
 READ_ACL               Permission to Read the ACL
 WRITE_ACL              Permission to Write the ACL
 WRITE_OWNER            Permission to change the owner
 SYNCHRONIZE            Permission to access file locally at the
                        server with synchronous reads and writes
 The bitmask constants used for the access mask field are as follows:
 const ACE4_READ_DATA            = 0x00000001;
 const ACE4_LIST_DIRECTORY       = 0x00000001;
 const ACE4_WRITE_DATA           = 0x00000002;
 const ACE4_ADD_FILE             = 0x00000002;
 const ACE4_APPEND_DATA          = 0x00000004;
 const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
 const ACE4_READ_NAMED_ATTRS     = 0x00000008;
 const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
 const ACE4_EXECUTE              = 0x00000020;
 const ACE4_DELETE_CHILD         = 0x00000040;
 const ACE4_READ_ATTRIBUTES      = 0x00000080;
 const ACE4_WRITE_ATTRIBUTES     = 0x00000100;
 const ACE4_DELETE               = 0x00010000;
 const ACE4_READ_ACL             = 0x00020000;
 const ACE4_WRITE_ACL            = 0x00040000;
 const ACE4_WRITE_OWNER          = 0x00080000;
 const ACE4_SYNCHRONIZE          = 0x00100000;
 Server implementations need not provide the granularity of control
 that is implied by this list of masks.  For example, POSIX-based
 systems might not distinguish APPEND_DATA (the ability to append to a
 file) from WRITE_DATA (the ability to modify existing contents); both
 masks would be tied to a single "write" permission.  When such a
 server returns attributes to the client, it would show both
 APPEND_DATA and WRITE_DATA if and only if the write permission is
 enabled.
 If a server receives a SETATTR request that it cannot accurately
 implement, it should error in the direction of more restricted
 access.  For example, suppose a server cannot distinguish overwriting
 data from appending new data, as described in the previous paragraph.
 If a client submits an ACE where APPEND_DATA is set but WRITE_DATA is
 not (or vice versa), the server should reject the request with
 NFS4ERR_ATTRNOTSUPP.  Nonetheless, if the ACE has type DENY, the
 server may silently turn on the other bit, so that both APPEND_DATA
 and WRITE_DATA are denied.

Shepler, et al. Standards Track [Page 53] RFC 3530 NFS version 4 Protocol April 2003

5.11.3. ACE flag

 The "flag" field contains values based on the following descriptions.
 ACE4_FILE_INHERIT_ACE
    Can be placed on a directory and indicates that this ACE should be
    added to each new non-directory file created.
 ACE4_DIRECTORY_INHERIT_ACE
    Can be placed on a directory and indicates that this ACE should be
    added to each new directory created.
 ACE4_INHERIT_ONLY_ACE
    Can be placed on a directory but does not apply to the directory,
    only to newly created files/directories as specified by the above
    two flags.
 ACE4_NO_PROPAGATE_INHERIT_ACE
    Can be placed on a directory.  Normally when a new directory is
    created and an ACE exists on the parent directory which is marked
    ACL4_DIRECTORY_INHERIT_ACE, two ACEs are placed on the new
    directory.  One for the directory itself and one which is an
    inheritable ACE for newly created directories.  This flag tells
    the server to not place an ACE on the newly created directory
    which is inheritable by subdirectories of the created directory.
 ACE4_SUCCESSFUL_ACCESS_ACE_FLAG
 ACL4_FAILED_ACCESS_ACE_FLAG
    The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and
    ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits relate only to
    ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and ACE4_SYSTEM_ALARM_ACE_TYPE
    (ALARM) ACE types.  If during the processing of the file's ACL,
    the server encounters an AUDIT or ALARM ACE that matches the
    principal attempting the OPEN, the server notes that fact, and the
    presence, if any, of the SUCCESS and FAILED flags encountered in
    the AUDIT or ALARM ACE.  Once the server completes the ACL
    processing, and the share reservation processing, and the OPEN
    call, it then notes if the OPEN succeeded or failed.  If the OPEN
    succeeded, and if the SUCCESS flag was set for a matching AUDIT or
    ALARM, then the appropriate AUDIT or ALARM event occurs.  If the
    OPEN failed, and if the FAILED flag was set for the matching AUDIT
    or ALARM, then the appropriate AUDIT or ALARM event occurs.
    Clearly either or both of the SUCCESS or FAILED can be set, but if
    neither is set, the AUDIT or ALARM ACE is not useful.

Shepler, et al. Standards Track [Page 54] RFC 3530 NFS version 4 Protocol April 2003

    The previously described processing applies to that of the ACCESS
    operation as well.  The difference being that "success" or
    "failure" does not mean whether ACCESS returns NFS4_OK or not.
    Success means whether ACCESS returns all requested and supported
    bits.  Failure means whether ACCESS failed to return a bit that
    was requested and supported.
 ACE4_IDENTIFIER_GROUP
    Indicates that the "who" refers to a GROUP as defined under UNIX.
 The bitmask constants used for the flag field are as follows:
 const ACE4_FILE_INHERIT_ACE             = 0x00000001;
 const ACE4_DIRECTORY_INHERIT_ACE        = 0x00000002;
 const ACE4_NO_PROPAGATE_INHERIT_ACE     = 0x00000004;
 const ACE4_INHERIT_ONLY_ACE             = 0x00000008;
 const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG   = 0x00000010;
 const ACE4_FAILED_ACCESS_ACE_FLAG       = 0x00000020;
 const ACE4_IDENTIFIER_GROUP             = 0x00000040;
 A server need not support any of these flags.  If the server supports
 flags that are similar to, but not exactly the same as, these flags,
 the implementation may define a mapping between the protocol-defined
 flags and the implementation-defined flags.  Again, the guiding
 principle is that the file not appear to be more secure than it
 really is.
 For example, suppose a client tries to set an ACE with
 ACE4_FILE_INHERIT_ACE set but not ACE4_DIRECTORY_INHERIT_ACE.  If the
 server does not support any form of ACL inheritance, the server
 should reject the request with NFS4ERR_ATTRNOTSUPP.  If the server
 supports a single "inherit ACE" flag that applies to both files and
 directories, the server may reject the request (i.e., requiring the
 client to set both the file and directory inheritance flags).  The
 server may also accept the request and silently turn on the
 ACE4_DIRECTORY_INHERIT_ACE flag.

5.11.4. ACE who

 There are several special identifiers ("who") which need to be
 understood universally, rather than in the context of a particular
 DNS domain.  Some of these identifiers cannot be understood when an
 NFS client accesses the server, but have meaning when a local process
 accesses the file.  The ability to display and modify these
 permissions is permitted over NFS, even if none of the access methods
 on the server understands the identifiers.

Shepler, et al. Standards Track [Page 55] RFC 3530 NFS version 4 Protocol April 2003

 Who                    Description
 _______________________________________________________________
 "OWNER"                The owner of the file.
 "GROUP"                The group associated with the file.
 "EVERYONE"             The world.
 "INTERACTIVE"          Accessed from an interactive terminal.
 "NETWORK"              Accessed via the network.
 "DIALUP"               Accessed as a dialup user to the server.
 "BATCH"                Accessed from a batch job.
 "ANONYMOUS"            Accessed without any authentication.
 "AUTHENTICATED"        Any authenticated user (opposite of
                        ANONYMOUS)
 "SERVICE"              Access from a system service.
 To avoid conflict, these special identifiers are distinguish by an
 appended "@" and should appear in the form "xxxx@" (note: no domain
 name after the "@").  For example: ANONYMOUS@.

5.11.5. Mode Attribute

 The NFS version 4 mode attribute is based on the UNIX mode bits.  The
 following bits are defined:
    const MODE4_SUID = 0x800;  /* set user id on execution */
    const MODE4_SGID = 0x400;  /* set group id on execution */
    const MODE4_SVTX = 0x200;  /* save text even after use */
    const MODE4_RUSR = 0x100;  /* read permission: owner */
    const MODE4_WUSR = 0x080;  /* write permission: owner */
    const MODE4_XUSR = 0x040;  /* execute permission: owner */
    const MODE4_RGRP = 0x020;  /* read permission: group */
    const MODE4_WGRP = 0x010;  /* write permission: group */
    const MODE4_XGRP = 0x008;  /* execute permission: group */
    const MODE4_ROTH = 0x004;  /* read permission: other */
    const MODE4_WOTH = 0x002;  /* write permission: other */
    const MODE4_XOTH = 0x001;  /* execute permission: other */
 Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the principal
 identified in the owner attribute.  Bits MODE4_RGRP, MODE4_WGRP, and
 MODE4_XGRP apply to the principals identified in the owner_group
 attribute.  Bits MODE4_ROTH, MODE4_WOTH, MODE4_XOTH apply to any
 principal that does not match that in the owner group, and does not
 have a group matching that of the owner_group attribute.
 The remaining bits are not defined by this protocol and MUST NOT be
 used.  The minor version mechanism must be used to define further bit
 usage.

Shepler, et al. Standards Track [Page 56] RFC 3530 NFS version 4 Protocol April 2003

 Note that in UNIX, if a file has the MODE4_SGID bit set and no
 MODE4_XGRP bit set, then READ and WRITE must use mandatory file
 locking.

5.11.6. Mode and ACL Attribute

 The server that supports both mode and ACL must take care to
 synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with the
 ACEs which have respective who fields of "OWNER@", "GROUP@", and
 "EVERYONE@" so that the client can see semantically equivalent access
 permissions exist whether the client asks for owner, owner_group and
 mode attributes, or for just the ACL.
 Because the mode attribute includes bits (e.g., MODE4_SVTX) that have
 nothing to do with ACL semantics, it is permitted for clients to
 specify both the ACL attribute and mode in the same SETATTR
 operation.  However, because there is no prescribed order for
 processing the attributes in a SETATTR, the client must ensure that
 ACL attribute, if specified without mode, would produce the desired
 mode bits, and conversely, the mode attribute if specified without
 ACL, would produce the desired "OWNER@", "GROUP@", and "EVERYONE@"
 ACEs.

5.11.7. mounted_on_fileid

 UNIX-based operating environments connect a filesystem into the
 namespace by connecting (mounting) the filesystem onto the existing
 file object (the mount point, usually a directory) of an existing
 filesystem.  When the mount point's parent directory is read via an
 API like readdir(), the return results are directory entries, each
 with a component name and a fileid.  The fileid of the mount point's
 directory entry will be different from the fileid that the stat()
 system call returns.  The stat() system call is returning the fileid
 of the root of the mounted filesystem, whereas readdir() is returning
 the fileid stat() would have returned before any filesystems were
 mounted on the mount point.
 Unlike NFS version 3, NFS version 4 allows a client's LOOKUP request
 to cross other filesystems.  The client detects the filesystem
 crossing whenever the filehandle argument of LOOKUP has an fsid
 attribute different from that of the filehandle returned by LOOKUP.
 A UNIX-based client will consider this a "mount point crossing".
 UNIX has a legacy scheme for allowing a process to determine its
 current working directory.  This relies on readdir() of a mount
 point's parent and stat() of the mount point returning fileids as
 previously described.  The mounted_on_fileid attribute corresponds to
 the fileid that readdir() would have returned as described
 previously.

Shepler, et al. Standards Track [Page 57] RFC 3530 NFS version 4 Protocol April 2003

 While the NFS version 4 client could simply fabricate a fileid
 corresponding to what mounted_on_fileid provides (and if the server
 does not support mounted_on_fileid, the client has no choice), there
 is a risk that the client will generate a fileid that conflicts with
 one that is already assigned to another object in the filesystem.
 Instead, if the server can provide the mounted_on_fileid, the
 potential for client operational problems in this area is eliminated.
 If the server detects that there is no mounted point at the target
 file object, then the value for mounted_on_fileid that it returns is
 the same as that of the fileid attribute.
 The mounted_on_fileid attribute is RECOMMENDED, so the server SHOULD
 provide it if possible, and for a UNIX-based server, this is
 straightforward.  Usually, mounted_on_fileid will be requested during
 a READDIR operation, in which case it is trivial (at least for UNIX-
 based servers) to return mounted_on_fileid since it is equal to the
 fileid of a directory entry returned by readdir().  If
 mounted_on_fileid is requested in a GETATTR operation, the server
 should obey an invariant that has it returning a value that is equal
 to the file object's entry in the object's parent directory, i.e.,
 what readdir() would have returned.  Some operating environments
 allow a series of two or more filesystems to be mounted onto a single
 mount point.  In this case, for the server to obey the aforementioned
 invariant, it will need to find the base mount point, and not the
 intermediate mount points.

6. Filesystem Migration and Replication

 With the use of the recommended attribute "fs_locations", the NFS
 version 4 server has a method of providing filesystem migration or
 replication services.  For the purposes of migration and replication,
 a filesystem will be defined as all files that share a given fsid
 (both major and minor values are the same).
 The fs_locations attribute provides a list of filesystem locations.
 These locations are specified by providing the server name (either
 DNS domain or IP address) and the path name representing the root of
 the filesystem.  Depending on the type of service being provided, the
 list will provide a new location or a set of alternate locations for
 the filesystem.  The client will use this information to redirect its
 requests to the new server.

6.1. Replication

 It is expected that filesystem replication will be used in the case
 of read-only data.  Typically, the filesystem will be replicated on
 two or more servers.  The fs_locations attribute will provide the

Shepler, et al. Standards Track [Page 58] RFC 3530 NFS version 4 Protocol April 2003

 list of these locations to the client.  On first access of the
 filesystem, the client should obtain the value of the fs_locations
 attribute.  If, in the future, the client finds the server
 unresponsive, the client may attempt to use another server specified
 by fs_locations.
 If applicable, the client must take the appropriate steps to recover
 valid filehandles from the new server.  This is described in more
 detail in the following sections.

6.2. Migration

 Filesystem migration is used to move a filesystem from one server to
 another.  Migration is typically used for a filesystem that is
 writable and has a single copy.  The expected use of migration is for
 load balancing or general resource reallocation.  The protocol does
 not specify how the filesystem will be moved between servers.  This
 server-to-server transfer mechanism is left to the server
 implementor.  However, the method used to communicate the migration
 event between client and server is specified here.
 Once the servers participating in the migration have completed the
 move of the filesystem, the error NFS4ERR_MOVED will be returned for
 subsequent requests received by the original server.  The
 NFS4ERR_MOVED error is returned for all operations except PUTFH and
 GETATTR.  Upon receiving the NFS4ERR_MOVED error, the client will
 obtain the value of the fs_locations attribute.  The client will then
 use the contents of the attribute to redirect its requests to the
 specified server.  To facilitate the use of GETATTR, operations such
 as PUTFH must also be accepted by the server for the migrated file
 system's filehandles.  Note that if the server returns NFS4ERR_MOVED,
 the server MUST support the fs_locations attribute.
 If the client requests more attributes than just fs_locations, the
 server may return fs_locations only.  This is to be expected since
 the server has migrated the filesystem and may not have a method of
 obtaining additional attribute data.
 The server implementor needs to be careful in developing a migration
 solution.  The server must consider all of the state information
 clients may have outstanding at the server.  This includes but is not
 limited to locking/share state, delegation state, and asynchronous
 file writes which are represented by WRITE and COMMIT verifiers.  The
 server should strive to minimize the impact on its clients during and
 after the migration process.

Shepler, et al. Standards Track [Page 59] RFC 3530 NFS version 4 Protocol April 2003

6.3. Interpretation of the fs_locations Attribute

 The fs_location attribute is structured in the following way:
 struct fs_location {
         utf8str_cis     server<>;
         pathname4       rootpath;
 };
 struct fs_locations {
         pathname4       fs_root;
         fs_location     locations<>;
 };
 The fs_location struct is used to represent the location of a
 filesystem by providing a server name and the path to the root of the
 filesystem.  For a multi-homed server or a set of servers that use
 the same rootpath, an array of server names may be provided.  An
 entry in the server array is an UTF8 string and represents one of a
 traditional DNS host name, IPv4 address, or IPv6 address.  It is not
 a requirement that all servers that share the same rootpath be listed
 in one fs_location struct.  The array of server names is provided for
 convenience.  Servers that share the same rootpath may also be listed
 in separate fs_location entries in the fs_locations attribute.
 The fs_locations struct and attribute then contains an array of
 locations.  Since the name space of each server may be constructed
 differently, the "fs_root" field is provided.  The path represented
 by fs_root represents the location of the filesystem in the server's
 name space.  Therefore, the fs_root path is only associated with the
 server from which the fs_locations attribute was obtained.  The
 fs_root path is meant to aid the client in locating the filesystem at
 the various servers listed.
 As an example, there is a replicated filesystem located at two
 servers (servA and servB).  At servA the filesystem is located at
 path "/a/b/c".  At servB the filesystem is located at path "/x/y/z".
 In this example the client accesses the filesystem first at servA
 with a multi-component lookup path of "/a/b/c/d".  Since the client
 used a multi-component lookup to obtain the filehandle at "/a/b/c/d",
 it is unaware that the filesystem's root is located in servA's name
 space at "/a/b/c".  When the client switches to servB, it will need
 to determine that the directory it first referenced at servA is now
 represented by the path "/x/y/z/d" on servB.  To facilitate this, the
 fs_locations attribute provided by servA would have a fs_root value
 of "/a/b/c" and two entries in fs_location.  One entry in fs_location
 will be for itself (servA) and the other will be for servB with a

Shepler, et al. Standards Track [Page 60] RFC 3530 NFS version 4 Protocol April 2003

 path of "/x/y/z".  With this information, the client is able to
 substitute "/x/y/z" for the "/a/b/c" at the beginning of its access
 path and construct "/x/y/z/d" to use for the new server.
 See the section "Security Considerations" for a discussion on the
 recommendations for the security flavor to be used by any GETATTR
 operation that requests the "fs_locations" attribute.

6.4. Filehandle Recovery for Migration or Replication

 Filehandles for filesystems that are replicated or migrated generally
 have the same semantics as for filesystems that are not replicated or
 migrated.  For example, if a filesystem has persistent filehandles
 and it is migrated to another server, the filehandle values for the
 filesystem will be valid at the new server.
 For volatile filehandles, the servers involved likely do not have a
 mechanism to transfer filehandle format and content between
 themselves.  Therefore, a server may have difficulty in determining
 if a volatile filehandle from an old server should return an error of
 NFS4ERR_FHEXPIRED.  Therefore, the client is informed, with the use
 of the fh_expire_type attribute, whether volatile filehandles will
 expire at the migration or replication event.  If the bit
 FH4_VOL_MIGRATION is set in the fh_expire_type attribute, the client
 must treat the volatile filehandle as if the server had returned the
 NFS4ERR_FHEXPIRED error.  At the migration or replication event in
 the presence of the FH4_VOL_MIGRATION bit, the client will not
 present the original or old volatile filehandle to the new server.
 The client will start its communication with the new server by
 recovering its filehandles using the saved file names.

7. NFS Server Name Space

7.1. Server Exports

 On a UNIX server the name space describes all the files reachable by
 pathnames under the root directory or "/".  On a Windows NT server
 the name space constitutes all the files on disks named by mapped
 disk letters.  NFS server administrators rarely make the entire
 server's filesystem name space available to NFS clients.  More often
 portions of the name space are made available via an "export"
 feature.  In previous versions of the NFS protocol, the root
 filehandle for each export is obtained through the MOUNT protocol;
 the client sends a string that identifies the export of name space
 and the server returns the root filehandle for it.  The MOUNT
 protocol supports an EXPORTS procedure that will enumerate the
 server's exports.

Shepler, et al. Standards Track [Page 61] RFC 3530 NFS version 4 Protocol April 2003

7.2. Browsing Exports

 The NFS version 4 protocol provides a root filehandle that clients
 can use to obtain filehandles for these exports via a multi-component
 LOOKUP.  A common user experience is to use a graphical user
 interface (perhaps a file "Open" dialog window) to find a file via
 progressive browsing through a directory tree.  The client must be
 able to move from one export to another export via single-component,
 progressive LOOKUP operations.
 This style of browsing is not well supported by the NFS version 2 and
 3 protocols.  The client expects all LOOKUP operations to remain
 within a single server filesystem.  For example, the device attribute
 will not change.  This prevents a client from taking name space paths
 that span exports.
 An automounter on the client can obtain a snapshot of the server's
 name space using the EXPORTS procedure of the MOUNT protocol.  If it
 understands the server's pathname syntax, it can create an image of
 the server's name space on the client.  The parts of the name space
 that are not exported by the server are filled in with a "pseudo
 filesystem" that allows the user to browse from one mounted
 filesystem to another.  There is a drawback to this representation of
 the server's name space on the client: it is static.  If the server
 administrator adds a new export the client will be unaware of it.

7.3. Server Pseudo Filesystem

 NFS version 4 servers avoid this name space inconsistency by
 presenting all the exports within the framework of a single server
 name space.  An NFS version 4 client uses LOOKUP and READDIR
 operations to browse seamlessly from one export to another.  Portions
 of the server name space that are not exported are bridged via a
 "pseudo filesystem" that provides a view of exported directories
 only.  A pseudo filesystem has a unique fsid and behaves like a
 normal, read only filesystem.
 Based on the construction of the server's name space, it is possible
 that multiple pseudo filesystems may exist.  For example,
 /a         pseudo filesystem
 /a/b       real filesystem
 /a/b/c     pseudo filesystem
 /a/b/c/d   real filesystem
 Each of the pseudo filesystems are considered separate entities and
 therefore will have a unique fsid.

Shepler, et al. Standards Track [Page 62] RFC 3530 NFS version 4 Protocol April 2003

7.4. Multiple Roots

 The DOS and Windows operating environments are sometimes described as
 having "multiple roots".  Filesystems are commonly represented as
 disk letters.  MacOS represents filesystems as top level names.  NFS
 version 4 servers for these platforms can construct a pseudo file
 system above these root names so that disk letters or volume names
 are simply directory names in the pseudo root.

7.5. Filehandle Volatility

 The nature of the server's pseudo filesystem is that it is a logical
 representation of filesystem(s) available from the server.
 Therefore, the pseudo filesystem is most likely constructed
 dynamically when the server is first instantiated.  It is expected
 that the pseudo filesystem may not have an on disk counterpart from
 which persistent filehandles could be constructed.  Even though it is
 preferable that the server provide persistent filehandles for the
 pseudo filesystem, the NFS client should expect that pseudo file
 system filehandles are volatile.  This can be confirmed by checking
 the associated "fh_expire_type" attribute for those filehandles in
 question.  If the filehandles are volatile, the NFS client must be
 prepared to recover a filehandle value (e.g., with a multi-component
 LOOKUP) when receiving an error of NFS4ERR_FHEXPIRED.

7.6. Exported Root

 If the server's root filesystem is exported, one might conclude that
 a pseudo-filesystem is not needed.  This would be wrong.  Assume the
 following filesystems on a server:
       /       disk1  (exported)
       /a      disk2  (not exported)
       /a/b    disk3  (exported)
 Because disk2 is not exported, disk3 cannot be reached with simple
 LOOKUPs.  The server must bridge the gap with a pseudo-filesystem.

7.7. Mount Point Crossing

 The server filesystem environment may be constructed in such a way
 that one filesystem contains a directory which is 'covered' or
 mounted upon by a second filesystem.  For example:
       /a/b            (filesystem 1)
       /a/b/c/d        (filesystem 2)

Shepler, et al. Standards Track [Page 63] RFC 3530 NFS version 4 Protocol April 2003

 The pseudo filesystem for this server may be constructed to look
 like:
       /               (place holder/not exported)
       /a/b            (filesystem 1)
       /a/b/c/d        (filesystem 2)
 It is the server's responsibility to present the pseudo filesystem
 that is complete to the client.  If the client sends a lookup request
 for the path "/a/b/c/d", the server's response is the filehandle of
 the filesystem "/a/b/c/d".  In previous versions of the NFS protocol,
 the server would respond with the filehandle of directory "/a/b/c/d"
 within the filesystem "/a/b".
 The NFS client will be able to determine if it crosses a server mount
 point by a change in the value of the "fsid" attribute.

7.8. Security Policy and Name Space Presentation

 The application of the server's security policy needs to be carefully
 considered by the implementor.  One may choose to limit the
 viewability of portions of the pseudo filesystem based on the
 server's perception of the client's ability to authenticate itself
 properly.  However, with the support of multiple security mechanisms
 and the ability to negotiate the appropriate use of these mechanisms,
 the server is unable to properly determine if a client will be able
 to authenticate itself.  If, based on its policies, the server
 chooses to limit the contents of the pseudo filesystem, the server
 may effectively hide filesystems from a client that may otherwise
 have legitimate access.
 As suggested practice, the server should apply the security policy of
 a shared resource in the server's namespace to the components of the
 resource's ancestors.  For example:
       /
       /a/b
       /a/b/c
 The /a/b/c directory is a real filesystem and is the shared resource.
 The security policy for /a/b/c is Kerberos with integrity.  The
 server should apply the same security policy to /, /a, and /a/b.
 This allows for the extension of the protection of the server's
 namespace to the ancestors of the real shared resource.

Shepler, et al. Standards Track [Page 64] RFC 3530 NFS version 4 Protocol April 2003

 For the case of the use of multiple, disjoint security mechanisms in
 the server's resources, the security for a particular object in the
 server's namespace should be the union of all security mechanisms of
 all direct descendants.

8. File Locking and Share Reservations

 Integrating locking into the NFS protocol necessarily causes it to be
 stateful.  With the inclusion of share reservations the protocol
 becomes substantially more dependent on state than the traditional
 combination of NFS and NLM [XNFS].  There are three components to
 making this state manageable:
 o  Clear division between client and server
 o  Ability to reliably detect inconsistency in state between client
    and server
 o  Simple and robust recovery mechanisms
 In this model, the server owns the state information.  The client
 communicates its view of this state to the server as needed.  The
 client is also able to detect inconsistent state before modifying a
 file.
 To support Win32 share reservations it is necessary to atomically
 OPEN or CREATE files.  Having a separate share/unshare operation
 would not allow correct implementation of the Win32 OpenFile API.  In
 order to correctly implement share semantics, the previous NFS
 protocol mechanisms used when a file is opened or created (LOOKUP,
 CREATE, ACCESS) need to be replaced.  The NFS version 4 protocol has
 an OPEN operation that subsumes the NFS version 3 methodology of
 LOOKUP, CREATE, and ACCESS.  However, because many operations require
 a filehandle, the traditional LOOKUP is preserved to map a file name
 to filehandle without establishing state on the server.  The policy
 of granting access or modifying files is managed by the server based
 on the client's state.  These mechanisms can implement policy ranging
 from advisory only locking to full mandatory locking.

8.1. Locking

 It is assumed that manipulating a lock is rare when compared to READ
 and WRITE operations.  It is also assumed that crashes and network
 partitions are relatively rare.  Therefore it is important that the
 READ and WRITE operations have a lightweight mechanism to indicate if
 they possess a held lock.  A lock request contains the heavyweight
 information required to establish a lock and uniquely define the lock
 owner.

Shepler, et al. Standards Track [Page 65] RFC 3530 NFS version 4 Protocol April 2003

 The following sections describe the transition from the heavy weight
 information to the eventual stateid used for most client and server
 locking and lease interactions.

8.1.1. Client ID

 For each LOCK request, the client must identify itself to the server.
 This is done in such a way as to allow for correct lock
 identification and crash recovery.  A sequence of a SETCLIENTID
 operation followed by a SETCLIENTID_CONFIRM operation is required to
 establish the identification onto the server.  Establishment of
 identification by a new incarnation of the client also has the effect
 of immediately breaking any leased state that a previous incarnation
 of the client might have had on the server, as opposed to forcing the
 new client incarnation to wait for the leases to expire.  Breaking
 the lease state amounts to the server removing all lock, share
 reservation, and, where the server is not supporting the
 CLAIM_DELEGATE_PREV claim type, all delegation state associated with
 same client with the same identity.  For discussion of delegation
 state recovery, see the section "Delegation Recovery".
 Client identification is encapsulated in the following structure:
       struct nfs_client_id4 {
               verifier4     verifier;
               opaque        id<NFS4_OPAQUE_LIMIT>;
       };
 The first field, verifier is a client incarnation verifier that is
 used to detect client reboots.  Only if the verifier is different
 from that which the server has previously recorded the client (as
 identified by the second field of the structure, id) does the server
 start the process of canceling the client's leased state.
 The second field, id is a variable length string that uniquely
 defines the client.
 There are several considerations for how the client generates the id
 string:
 o  The string should be unique so that multiple clients do not
    present the same string.  The consequences of two clients
    presenting the same string range from one client getting an error
    to one client having its leased state abruptly and unexpectedly
    canceled.

Shepler, et al. Standards Track [Page 66] RFC 3530 NFS version 4 Protocol April 2003

 o  The string should be selected so the subsequent incarnations
    (e.g., reboots) of the same client cause the client to present the
    same string.  The implementor is cautioned against an approach
    that requires the string to be recorded in a local file because
    this precludes the use of the implementation in an environment
    where there is no local disk and all file access is from an NFS
    version 4 server.
 o  The string should be different for each server network address
    that the client accesses, rather than common to all server network
    addresses.  The reason is that it may not be possible for the
    client to tell if the same server is listening on multiple network
    addresses.  If the client issues SETCLIENTID with the same id
    string to each network address of such a server, the server will
    think it is the same client, and each successive SETCLIENTID will
    cause the server to begin the process of removing the client's
    previous leased state.
 o  The algorithm for generating the string should not assume that the
    client's network address won't change.  This includes changes
    between client incarnations and even changes while the client is
    stilling running in its current incarnation.  This means that if
    the client includes just the client's and server's network address
    in the id string, there is a real risk, after the client gives up
    the network address, that another client, using a similar
    algorithm for generating the id string, will generate a
    conflicting id string.
 Given the above considerations, an example of a well generated id
 string is one that includes:
 o  The server's network address.
 o  The client's network address.
 o  For a user level NFS version 4 client, it should contain
    additional information to distinguish the client from other user
    level clients running on the same host, such as a process id or
    other unique sequence.
 o  Additional information that tends to be unique, such as one or
    more of:
  1. The client machine's serial number (for privacy reasons, it is

best to perform some one way function on the serial number).

  1. A MAC address.

Shepler, et al. Standards Track [Page 67] RFC 3530 NFS version 4 Protocol April 2003

  1. The timestamp of when the NFS version 4 software was first

installed on the client (though this is subject to the

       previously mentioned caution about using information that is
       stored in a file, because the file might only be accessible
       over NFS version 4).
  1. A true random number. However since this number ought to be

the same between client incarnations, this shares the same

       problem as that of the using the timestamp of the software
       installation.
 As a security measure, the server MUST NOT cancel a client's leased
 state if the principal established the state for a given id string is
 not the same as the principal issuing the SETCLIENTID.
 Note that SETCLIENTID and SETCLIENTID_CONFIRM has a secondary purpose
 of establishing the information the server needs to make callbacks to
 the client for purpose of supporting delegations.  It is permitted to
 change this information via SETCLIENTID and SETCLIENTID_CONFIRM
 within the same incarnation of the client without removing the
 client's leased state.
 Once a SETCLIENTID and SETCLIENTID_CONFIRM sequence has successfully
 completed, the client uses the shorthand client identifier, of type
 clientid4, instead of the longer and less compact nfs_client_id4
 structure.  This shorthand client identifier (a clientid) is assigned
 by the server and should be chosen so that it will not conflict with
 a clientid previously assigned by the server.  This applies across
 server restarts or reboots.  When a clientid is presented to a server
 and that clientid is not recognized, as would happen after a server
 reboot, the server will reject the request with the error
 NFS4ERR_STALE_CLIENTID.  When this happens, the client must obtain a
 new clientid by use of the SETCLIENTID operation and then proceed to
 any other necessary recovery for the server reboot case (See the
 section "Server Failure and Recovery").
 The client must also employ the SETCLIENTID operation when it
 receives a NFS4ERR_STALE_STATEID error using a stateid derived from
 its current clientid, since this also indicates a server reboot which
 has invalidated the existing clientid (see the next section
 "lock_owner and stateid Definition" for details).
 See the detailed descriptions of SETCLIENTID and SETCLIENTID_CONFIRM
 for a complete specification of the operations.

Shepler, et al. Standards Track [Page 68] RFC 3530 NFS version 4 Protocol April 2003

8.1.2. Server Release of Clientid

 If the server determines that the client holds no associated state
 for its clientid, the server may choose to release the clientid.  The
 server may make this choice for an inactive client so that resources
 are not consumed by those intermittently active clients.  If the
 client contacts the server after this release, the server must ensure
 the client receives the appropriate error so that it will use the
 SETCLIENTID/SETCLIENTID_CONFIRM sequence to establish a new identity.
 It should be clear that the server must be very hesitant to release a
 clientid since the resulting work on the client to recover from such
 an event will be the same burden as if the server had failed and
 restarted.  Typically a server would not release a clientid unless
 there had been no activity from that client for many minutes.
 Note that if the id string in a SETCLIENTID request is properly
 constructed, and if the client takes care to use the same principal
 for each successive use of SETCLIENTID, then, barring an active
 denial of service attack, NFS4ERR_CLID_INUSE should never be
 returned.
 However, client bugs, server bugs, or perhaps a deliberate change of
 the principal owner of the id string (such as the case of a client
 that changes security flavors, and under the new flavor, there is no
 mapping to the previous owner) will in rare cases result in
 NFS4ERR_CLID_INUSE.
 In that event, when the server gets a SETCLIENTID for a client id
 that currently has no state, or it has state, but the lease has
 expired, rather than returning NFS4ERR_CLID_INUSE, the server MUST
 allow the SETCLIENTID, and confirm the new clientid if followed by
 the appropriate SETCLIENTID_CONFIRM.

8.1.3. lock_owner and stateid Definition

 When requesting a lock, the client must present to the server the
 clientid and an identifier for the owner of the requested lock.
 These two fields are referred to as the lock_owner and the definition
 of those fields are:
 o  A clientid returned by the server as part of the client's use of
    the SETCLIENTID operation.
 o  A variable length opaque array used to uniquely define the owner
    of a lock managed by the client.
    This may be a thread id, process id, or other unique value.

Shepler, et al. Standards Track [Page 69] RFC 3530 NFS version 4 Protocol April 2003

 When the server grants the lock, it responds with a unique stateid.
 The stateid is used as a shorthand reference to the lock_owner, since
 the server will be maintaining the correspondence between them.
 The server is free to form the stateid in any manner that it chooses
 as long as it is able to recognize invalid and out-of-date stateids.
 This requirement includes those stateids generated by earlier
 instances of the server.  From this, the client can be properly
 notified of a server restart.  This notification will occur when the
 client presents a stateid to the server from a previous
 instantiation.
 The server must be able to distinguish the following situations and
 return the error as specified:
 o  The stateid was generated by an earlier server instance (i.e.,
    before a server reboot).  The error NFS4ERR_STALE_STATEID should
    be returned.
 o  The stateid was generated by the current server instance but the
    stateid no longer designates the current locking state for the
    lockowner-file pair in question (i.e., one or more locking
    operations has occurred).  The error NFS4ERR_OLD_STATEID should be
    returned.
    This error condition will only occur when the client issues a
    locking request which changes a stateid while an I/O request that
    uses that stateid is outstanding.
 o  The stateid was generated by the current server instance but the
    stateid does not designate a locking state for any active
    lockowner-file pair.  The error NFS4ERR_BAD_STATEID should be
    returned.
    This error condition will occur when there has been a logic error
    on the part of the client or server.  This should not happen.
 One mechanism that may be used to satisfy these requirements is for
 the server to,
 o  divide the "other" field of each stateid into two fields:
  1. A server verifier which uniquely designates a particular server

instantiation.

  1. An index into a table of locking-state structures.

Shepler, et al. Standards Track [Page 70] RFC 3530 NFS version 4 Protocol April 2003

 o  utilize the "seqid" field of each stateid, such that seqid is
    monotonically incremented for each stateid that is associated with
    the same index into the locking-state table.
 By matching the incoming stateid and its field values with the state
 held at the server, the server is able to easily determine if a
 stateid is valid for its current instantiation and state.  If the
 stateid is not valid, the appropriate error can be supplied to the
 client.

8.1.4. Use of the stateid and Locking

 All READ, WRITE and SETATTR operations contain a stateid.  For the
 purposes of this section, SETATTR operations which change the size
 attribute of a file are treated as if they are writing the area
 between the old and new size (i.e., the range truncated or added to
 the file by means of the SETATTR), even where SETATTR is not
 explicitly mentioned in the text.
 If the lock_owner performs a READ or WRITE in a situation in which it
 has established a lock or share reservation on the server (any OPEN
 constitutes a share reservation) the stateid (previously returned by
 the server) must be used to indicate what locks, including both
 record locks and share reservations, are held by the lockowner.  If
 no state is established by the client, either record lock or share
 reservation, a stateid of all bits 0 is used.  Regardless whether a
 stateid of all bits 0, or a stateid returned by the server is used,
 if there is a conflicting share reservation or mandatory record lock
 held on the file, the server MUST refuse to service the READ or WRITE
 operation.
 Share reservations are established by OPEN operations and by their
 nature are mandatory in that when the OPEN denies READ or WRITE
 operations, that denial results in such operations being rejected
 with error NFS4ERR_LOCKED.  Record locks may be implemented by the
 server as either mandatory or advisory, or the choice of mandatory or
 advisory behavior may be determined by the server on the basis of the
 file being accessed (for example, some UNIX-based servers support a
 "mandatory lock bit" on the mode attribute such that if set, record
 locks are required on the file before I/O is possible).  When record
 locks are advisory, they only prevent the granting of conflicting
 lock requests and have no effect on READs or WRITEs.  Mandatory
 record locks, however, prevent conflicting I/O operations.  When they
 are attempted, they are rejected with NFS4ERR_LOCKED.  When the
 client gets NFS4ERR_LOCKED on a file it knows it has the proper share
 reservation for, it will need to issue a LOCK request on the region

Shepler, et al. Standards Track [Page 71] RFC 3530 NFS version 4 Protocol April 2003

 of the file that includes the region the I/O was to be performed on,
 with an appropriate locktype (i.e., READ*_LT for a READ operation,
 WRITE*_LT for a WRITE operation).
 With NFS version 3, there was no notion of a stateid so there was no
 way to tell if the application process of the client sending the READ
 or WRITE operation had also acquired the appropriate record lock on
 the file.  Thus there was no way to implement mandatory locking.
 With the stateid construct, this barrier has been removed.
 Note that for UNIX environments that support mandatory file locking,
 the distinction between advisory and mandatory locking is subtle.  In
 fact, advisory and mandatory record locks are exactly the same in so
 far as the APIs and requirements on implementation.  If the mandatory
 lock attribute is set on the file, the server checks to see if the
 lockowner has an appropriate shared (read) or exclusive (write)
 record lock on the region it wishes to read or write to.  If there is
 no appropriate lock, the server checks if there is a conflicting lock
 (which can be done by attempting to acquire the conflicting lock on
 the behalf of the lockowner, and if successful, release the lock
 after the READ or WRITE is done), and if there is, the server returns
 NFS4ERR_LOCKED.
 For Windows environments, there are no advisory record locks, so the
 server always checks for record locks during I/O requests.
 Thus, the NFS version 4 LOCK operation does not need to distinguish
 between advisory and mandatory record locks.  It is the NFS version 4
 server's processing of the READ and WRITE operations that introduces
 the distinction.
 Every stateid other than the special stateid values noted in this
 section, whether returned by an OPEN-type operation (i.e., OPEN,
 OPEN_DOWNGRADE), or by a LOCK-type operation (i.e., LOCK or LOCKU),
 defines an access mode for the file (i.e., READ, WRITE, or READ-
 WRITE) as established by the original OPEN which began the stateid
 sequence, and as modified by subsequent OPENs and OPEN_DOWNGRADEs
 within that stateid sequence.  When a READ, WRITE, or SETATTR which
 specifies the size attribute, is done, the operation is subject to
 checking against the access mode to verify that the operation is
 appropriate given the OPEN with which the operation is associated.
 In the case of WRITE-type operations (i.e., WRITEs and SETATTRs which
 set size), the server must verify that the access mode allows writing
 and return an NFS4ERR_OPENMODE error if it does not.  In the case, of
 READ, the server may perform the corresponding check on the access
 mode, or it may choose to allow READ on opens for WRITE only, to
 accommodate clients whose write implementation may unavoidably do

Shepler, et al. Standards Track [Page 72] RFC 3530 NFS version 4 Protocol April 2003

 reads (e.g., due to buffer cache constraints).  However, even if
 READs are allowed in these circumstances, the server MUST still check
 for locks that conflict with the READ (e.g., another open specify
 denial of READs).  Note that a server which does enforce the access
 mode check on READs need not explicitly check for conflicting share
 reservations since the existence of OPEN for read access guarantees
 that no conflicting share reservation can exist.
 A stateid of all bits 1 (one) MAY allow READ operations to bypass
 locking checks at the server.  However, WRITE operations with a
 stateid with bits all 1 (one) MUST NOT bypass locking checks and are
 treated exactly the same as if a stateid of all bits 0 were used.
 A lock may not be granted while a READ or WRITE operation using one
 of the special stateids is being performed and the range of the lock
 request conflicts with the range of the READ or WRITE operation.  For
 the purposes of this paragraph, a conflict occurs when a shared lock
 is requested and a WRITE operation is being performed, or an
 exclusive lock is requested and either a READ or a WRITE operation is
 being performed.  A SETATTR that sets size is treated similarly to a
 WRITE as discussed above.

8.1.5. Sequencing of Lock Requests

 Locking is different than most NFS operations as it requires "at-
 most-one" semantics that are not provided by ONCRPC.  ONCRPC over a
 reliable transport is not sufficient because a sequence of locking
 requests may span multiple TCP connections.  In the face of
 retransmission or reordering, lock or unlock requests must have a
 well defined and consistent behavior.  To accomplish this, each lock
 request contains a sequence number that is a consecutively increasing
 integer.  Different lock_owners have different sequences.  The server
 maintains the last sequence number (L) received and the response that
 was returned.  The first request issued for any given lock_owner is
 issued with a sequence number of zero.
 Note that for requests that contain a sequence number, for each
 lock_owner, there should be no more than one outstanding request.
 If a request (r) with a previous sequence number (r < L) is received,
 it is rejected with the return of error NFS4ERR_BAD_SEQID.  Given a
 properly-functioning client, the response to (r) must have been
 received before the last request (L) was sent.  If a duplicate of
 last request (r == L) is received, the stored response is returned.
 If a request beyond the next sequence (r == L + 2) is received, it is
 rejected with the return of error NFS4ERR_BAD_SEQID.  Sequence
 history is reinitialized whenever the SETCLIENTID/SETCLIENTID_CONFIRM
 sequence changes the client verifier.

Shepler, et al. Standards Track [Page 73] RFC 3530 NFS version 4 Protocol April 2003

 Since the sequence number is represented with an unsigned 32-bit
 integer, the arithmetic involved with the sequence number is mod
 2^32.  For an example of modulo arithmetic involving sequence numbers
 see [RFC793].
 It is critical the server maintain the last response sent to the
 client to provide a more reliable cache of duplicate non-idempotent
 requests than that of the traditional cache described in [Juszczak].
 The traditional duplicate request cache uses a least recently used
 algorithm for removing unneeded requests.  However, the last lock
 request and response on a given lock_owner must be cached as long as
 the lock state exists on the server.
 The client MUST monotonically increment the sequence number for the
 CLOSE, LOCK, LOCKU, OPEN, OPEN_CONFIRM, and OPEN_DOWNGRADE
 operations.  This is true even in the event that the previous
 operation that used the sequence number received an error.  The only
 exception to this rule is if the previous operation received one of
 the following errors: NFS4ERR_STALE_CLIENTID, NFS4ERR_STALE_STATEID,
 NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID, NFS4ERR_BADXDR,
 NFS4ERR_RESOURCE, NFS4ERR_NOFILEHANDLE.

8.1.6. Recovery from Replayed Requests

 As described above, the sequence number is per lock_owner.  As long
 as the server maintains the last sequence number received and follows
 the methods described above, there are no risks of a Byzantine router
 re-sending old requests.  The server need only maintain the
 (lock_owner, sequence number) state as long as there are open files
 or closed files with locks outstanding.
 LOCK, LOCKU, OPEN, OPEN_DOWNGRADE, and CLOSE each contain a sequence
 number and therefore the risk of the replay of these operations
 resulting in undesired effects is non-existent while the server
 maintains the lock_owner state.

8.1.7. Releasing lock_owner State

 When a particular lock_owner no longer holds open or file locking
 state at the server, the server may choose to release the sequence
 number state associated with the lock_owner.  The server may make
 this choice based on lease expiration, for the reclamation of server
 memory, or other implementation specific details.  In any event, the
 server is able to do this safely only when the lock_owner no longer
 is being utilized by the client.  The server may choose to hold the
 lock_owner state in the event that retransmitted requests are
 received.  However, the period to hold this state is implementation
 specific.

Shepler, et al. Standards Track [Page 74] RFC 3530 NFS version 4 Protocol April 2003

 In the case that a LOCK, LOCKU, OPEN_DOWNGRADE, or CLOSE is
 retransmitted after the server has previously released the lock_owner
 state, the server will find that the lock_owner has no files open and
 an error will be returned to the client.  If the lock_owner does have
 a file open, the stateid will not match and again an error is
 returned to the client.

8.1.8. Use of Open Confirmation

 In the case that an OPEN is retransmitted and the lock_owner is being
 used for the first time or the lock_owner state has been previously
 released by the server, the use of the OPEN_CONFIRM operation will
 prevent incorrect behavior.  When the server observes the use of the
 lock_owner for the first time, it will direct the client to perform
 the OPEN_CONFIRM for the corresponding OPEN.  This sequence
 establishes the use of an lock_owner and associated sequence number.
 Since the OPEN_CONFIRM sequence connects a new open_owner on the
 server with an existing open_owner on a client, the sequence number
 may have any value.  The OPEN_CONFIRM step assures the server that
 the value received is the correct one.  See the section "OPEN_CONFIRM
 - Confirm Open" for further details.
 There are a number of situations in which the requirement to confirm
 an OPEN would pose difficulties for the client and server, in that
 they would be prevented from acting in a timely fashion on
 information received, because that information would be provisional,
 subject to deletion upon non-confirmation.  Fortunately, these are
 situations in which the server can avoid the need for confirmation
 when responding to open requests.  The two constraints are:
 o  The server must not bestow a delegation for any open which would
    require confirmation.
 o  The server MUST NOT require confirmation on a reclaim-type open
    (i.e., one specifying claim type CLAIM_PREVIOUS or
    CLAIM_DELEGATE_PREV).
 These constraints are related in that reclaim-type opens are the only
 ones in which the server may be required to send a delegation.  For
 CLAIM_NULL, sending the delegation is optional while for
 CLAIM_DELEGATE_CUR, no delegation is sent.
 Delegations being sent with an open requiring confirmation are
 troublesome because recovering from non-confirmation adds undue
 complexity to the protocol while requiring confirmation on reclaim-
 type opens poses difficulties in that the inability to resolve

Shepler, et al. Standards Track [Page 75] RFC 3530 NFS version 4 Protocol April 2003

 the status of the reclaim until lease expiration may make it
 difficult to have timely determination of the set of locks being
 reclaimed (since the grace period may expire).
 Requiring open confirmation on reclaim-type opens is avoidable
 because of the nature of the environments in which such opens are
 done.  For CLAIM_PREVIOUS opens, this is immediately after server
 reboot, so there should be no time for lockowners to be created,
 found to be unused, and recycled.  For CLAIM_DELEGATE_PREV opens, we
 are dealing with a client reboot situation.  A server which supports
 delegation can be sure that no lockowners for that client have been
 recycled since client initialization and thus can ensure that
 confirmation will not be required.

8.2. Lock Ranges

 The protocol allows a lock owner to request a lock with a byte range
 and then either upgrade or unlock a sub-range of the initial lock.
 It is expected that this will be an uncommon type of request.  In any
 case, servers or server filesystems may not be able to support sub-
 range lock semantics.  In the event that a server receives a locking
 request that represents a sub-range of current locking state for the
 lock owner, the server is allowed to return the error
 NFS4ERR_LOCK_RANGE to signify that it does not support sub-range lock
 operations.  Therefore, the client should be prepared to receive this
 error and, if appropriate, report the error to the requesting
 application.
 The client is discouraged from combining multiple independent locking
 ranges that happen to be adjacent into a single request since the
 server may not support sub-range requests and for reasons related to
 the recovery of file locking state in the event of server failure.
 As discussed in the section "Server Failure and Recovery" below, the
 server may employ certain optimizations during recovery that work
 effectively only when the client's behavior during lock recovery is
 similar to the client's locking behavior prior to server failure.

8.3. Upgrading and Downgrading Locks

 If a client has a write lock on a record, it can request an atomic
 downgrade of the lock to a read lock via the LOCK request, by setting
 the type to READ_LT.  If the server supports atomic downgrade, the
 request will succeed.  If not, it will return NFS4ERR_LOCK_NOTSUPP.
 The client should be prepared to receive this error, and if
 appropriate, report the error to the requesting application.

Shepler, et al. Standards Track [Page 76] RFC 3530 NFS version 4 Protocol April 2003

 If a client has a read lock on a record, it can request an atomic
 upgrade of the lock to a write lock via the LOCK request by setting
 the type to WRITE_LT or WRITEW_LT.  If the server does not support
 atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP.  If the upgrade
 can be achieved without an existing conflict, the request will
 succeed.  Otherwise, the server will return either NFS4ERR_DENIED or
 NFS4ERR_DEADLOCK.  The error NFS4ERR_DEADLOCK is returned if the
 client issued the LOCK request with the type set to WRITEW_LT and the
 server has detected a deadlock.  The client should be prepared to
 receive such errors and if appropriate, report the error to the
 requesting application.

8.4. Blocking Locks

 Some clients require the support of blocking locks.  The NFS version
 4 protocol must not rely on a callback mechanism and therefore is
 unable to notify a client when a previously denied lock has been
 granted.  Clients have no choice but to continually poll for the
 lock.  This presents a fairness problem.  Two new lock types are
 added, READW and WRITEW, and are used to indicate to the server that
 the client is requesting a blocking lock.  The server should maintain
 an ordered list of pending blocking locks.  When the conflicting lock
 is released, the server may wait the lease period for the first
 waiting client to re-request the lock.  After the lease period
 expires the next waiting client request is allowed the lock.  Clients
 are required to poll at an interval sufficiently small that it is
 likely to acquire the lock in a timely manner.  The server is not
 required to maintain a list of pending blocked locks as it is used to
 increase fairness and not correct operation.  Because of the
 unordered nature of crash recovery, storing of lock state to stable
 storage would be required to guarantee ordered granting of blocking
 locks.
 Servers may also note the lock types and delay returning denial of
 the request to allow extra time for a conflicting lock to be
 released, allowing a successful return.  In this way, clients can
 avoid the burden of needlessly frequent polling for blocking locks.
 The server should take care in the length of delay in the event the
 client retransmits the request.

8.5. Lease Renewal

 The purpose of a lease is to allow a server to remove stale locks
 that are held by a client that has crashed or is otherwise
 unreachable.  It is not a mechanism for cache consistency and lease
 renewals may not be denied if the lease interval has not expired.

Shepler, et al. Standards Track [Page 77] RFC 3530 NFS version 4 Protocol April 2003

 The following events cause implicit renewal of all of the leases for
 a given client (i.e., all those sharing a given clientid).  Each of
 these is a positive indication that the client is still active and
 that the associated state held at the server, for the client, is
 still valid.
 o  An OPEN with a valid clientid.
 o  Any operation made with a valid stateid (CLOSE, DELEGPURGE,
    DELEGRETURN, LOCK, LOCKU, OPEN, OPEN_CONFIRM, OPEN_DOWNGRADE,
    READ, RENEW, SETATTR, WRITE).  This does not include the special
    stateids of all bits 0 or all bits 1.
    Note that if the client had restarted or rebooted, the client
    would not be making these requests without issuing the
    SETCLIENTID/SETCLIENTID_CONFIRM sequence.  The use of the
    SETCLIENTID/SETCLIENTID_CONFIRM sequence (one that changes the
    client verifier) notifies the server to drop the locking state
    associated with the client.  SETCLIENTID/SETCLIENTID_CONFIRM never
    renews a lease.
    If the server has rebooted, the stateids (NFS4ERR_STALE_STATEID
    error) or the clientid (NFS4ERR_STALE_CLIENTID error) will not be
    valid hence preventing spurious renewals.
 This approach allows for low overhead lease renewal which scales
 well.  In the typical case no extra RPC calls are required for lease
 renewal and in the worst case one RPC is required every lease period
 (i.e., a RENEW operation).  The number of locks held by the client is
 not a factor since all state for the client is involved with the
 lease renewal action.
 Since all operations that create a new lease also renew existing
 leases, the server must maintain a common lease expiration time for
 all valid leases for a given client.  This lease time can then be
 easily updated upon implicit lease renewal actions.

8.6. Crash Recovery

 The important requirement in crash recovery is that both the client
 and the server know when the other has failed.  Additionally, it is
 required that a client sees a consistent view of data across server
 restarts or reboots.  All READ and WRITE operations that may have
 been queued within the client or network buffers must wait until the
 client has successfully recovered the locks protecting the READ and
 WRITE operations.

Shepler, et al. Standards Track [Page 78] RFC 3530 NFS version 4 Protocol April 2003

8.6.1. Client Failure and Recovery

 In the event that a client fails, the server may recover the client's
 locks when the associated leases have expired.  Conflicting locks
 from another client may only be granted after this lease expiration.
 If the client is able to restart or reinitialize within the lease
 period the client may be forced to wait the remainder of the lease
 period before obtaining new locks.
 To minimize client delay upon restart, lock requests are associated
 with an instance of the client by a client supplied verifier.  This
 verifier is part of the initial SETCLIENTID call made by the client.
 The server returns a clientid as a result of the SETCLIENTID
 operation.  The client then confirms the use of the clientid with
 SETCLIENTID_CONFIRM.  The clientid in combination with an opaque
 owner field is then used by the client to identify the lock owner for
 OPEN.  This chain of associations is then used to identify all locks
 for a particular client.
 Since the verifier will be changed by the client upon each
 initialization, the server can compare a new verifier to the verifier
 associated with currently held locks and determine that they do not
 match.  This signifies the client's new instantiation and subsequent
 loss of locking state.  As a result, the server is free to release
 all locks held which are associated with the old clientid which was
 derived from the old verifier.
 Note that the verifier must have the same uniqueness properties of
 the verifier for the COMMIT operation.

8.6.2. Server Failure and Recovery

 If the server loses locking state (usually as a result of a restart
 or reboot), it must allow clients time to discover this fact and re-
 establish the lost locking state.  The client must be able to re-
 establish the locking state without having the server deny valid
 requests because the server has granted conflicting access to another
 client.  Likewise, if there is the possibility that clients have not
 yet re-established their locking state for a file, the server must
 disallow READ and WRITE operations for that file.  The duration of
 this recovery period is equal to the duration of the lease period.
 A client can determine that server failure (and thus loss of locking
 state) has occurred, when it receives one of two errors.  The
 NFS4ERR_STALE_STATEID error indicates a stateid invalidated by a
 reboot or restart.  The NFS4ERR_STALE_CLIENTID error indicates a

Shepler, et al. Standards Track [Page 79] RFC 3530 NFS version 4 Protocol April 2003

 clientid invalidated by reboot or restart.  When either of these are
 received, the client must establish a new clientid (See the section
 "Client ID") and re-establish the locking state as discussed below.
 The period of special handling of locking and READs and WRITEs, equal
 in duration to the lease period, is referred to as the "grace
 period".  During the grace period, clients recover locks and the
 associated state by reclaim-type locking requests (i.e., LOCK
 requests with reclaim set to true and OPEN operations with a claim
 type of CLAIM_PREVIOUS).  During the grace period, the server must
 reject READ and WRITE operations and non-reclaim locking requests
 (i.e., other LOCK and OPEN operations) with an error of
 NFS4ERR_GRACE.
 If the server can reliably determine that granting a non-reclaim
 request will not conflict with reclamation of locks by other clients,
 the NFS4ERR_GRACE error does not have to be returned and the non-
 reclaim client request can be serviced.  For the server to be able to
 service READ and WRITE operations during the grace period, it must
 again be able to guarantee that no possible conflict could arise
 between an impending reclaim locking request and the READ or WRITE
 operation.  If the server is unable to offer that guarantee, the
 NFS4ERR_GRACE error must be returned to the client.
 For a server to provide simple, valid handling during the grace
 period, the easiest method is to simply reject all non-reclaim
 locking requests and READ and WRITE operations by returning the
 NFS4ERR_GRACE error.  However, a server may keep information about
 granted locks in stable storage.  With this information, the server
 could determine if a regular lock or READ or WRITE operation can be
 safely processed.
 For example, if a count of locks on a given file is available in
 stable storage, the server can track reclaimed locks for the file and
 when all reclaims have been processed, non-reclaim locking requests
 may be processed.  This way the server can ensure that non-reclaim
 locking requests will not conflict with potential reclaim requests.
 With respect to I/O requests, if the server is able to determine that
 there are no outstanding reclaim requests for a file by information
 from stable storage or another similar mechanism, the processing of
 I/O requests could proceed normally for the file.
 To reiterate, for a server that allows non-reclaim lock and I/O
 requests to be processed during the grace period, it MUST determine
 that no lock subsequently reclaimed will be rejected and that no lock
 subsequently reclaimed would have prevented any I/O operation
 processed during the grace period.

Shepler, et al. Standards Track [Page 80] RFC 3530 NFS version 4 Protocol April 2003

 Clients should be prepared for the return of NFS4ERR_GRACE errors for
 non-reclaim lock and I/O requests.  In this case the client should
 employ a retry mechanism for the request.  A delay (on the order of
 several seconds) between retries should be used to avoid overwhelming
 the server.  Further discussion of the general issue is included in
 [Floyd].  The client must account for the server that is able to
 perform I/O and non-reclaim locking requests within the grace period
 as well as those that can not do so.
 A reclaim-type locking request outside the server's grace period can
 only succeed if the server can guarantee that no conflicting lock or
 I/O request has been granted since reboot or restart.
 A server may, upon restart, establish a new value for the lease
 period.  Therefore, clients should, once a new clientid is
 established, refetch the lease_time attribute and use it as the basis
 for lease renewal for the lease associated with that server.
 However, the server must establish, for this restart event, a grace
 period at least as long as the lease period for the previous server
 instantiation.  This allows the client state obtained during the
 previous server instance to be reliably re-established.

8.6.3. Network Partitions and Recovery

 If the duration of a network partition is greater than the lease
 period provided by the server, the server will have not received a
 lease renewal from the client.  If this occurs, the server may free
 all locks held for the client.  As a result, all stateids held by the
 client will become invalid or stale.  Once the client is able to
 reach the server after such a network partition, all I/O submitted by
 the client with the now invalid stateids will fail with the server
 returning the error NFS4ERR_EXPIRED.  Once this error is received,
 the client will suitably notify the application that held the lock.
 As a courtesy to the client or as an optimization, the server may
 continue to hold locks on behalf of a client for which recent
 communication has extended beyond the lease period.  If the server
 receives a lock or I/O request that conflicts with one of these
 courtesy locks, the server must free the courtesy lock and grant the
 new request.
 When a network partition is combined with a server reboot, there are
 edge conditions that place requirements on the server in order to
 avoid silent data corruption following the server reboot.  Two of
 these edge conditions are known, and are discussed below.

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 The first edge condition has the following scenario:
    1. Client A acquires a lock.
    2. Client A and server experience mutual network partition, such
       that client A is unable to renew its lease.
    3. Client A's lease expires, so server releases lock.
    4. Client B acquires a lock that would have conflicted with that
       of Client A.
    5. Client B releases the lock
    6. Server reboots
    7. Network partition between client A and server heals.
    8. Client A issues a RENEW operation, and gets back a
       NFS4ERR_STALE_CLIENTID.
    9. Client A reclaims its lock within the server's grace period.
 Thus, at the final step, the server has erroneously granted client
 A's lock reclaim.  If client B modified the object the lock was
 protecting, client A will experience object corruption.
 The second known edge condition follows:
    1. Client A acquires a lock.
    2. Server reboots.
    3. Client A and server experience mutual network partition, such
       that client A is unable to reclaim its lock within the grace
       period.
    4. Server's reclaim grace period ends.  Client A has no locks
       recorded on server.
    5. Client B acquires a lock that would have conflicted with that
       of Client A.
    6. Client B releases the lock.
    7. Server reboots a second time.
    8. Network partition between client A and server heals.

Shepler, et al. Standards Track [Page 82] RFC 3530 NFS version 4 Protocol April 2003

    9. Client A issues a RENEW operation, and gets back a
       NFS4ERR_STALE_CLIENTID.
   10. Client A reclaims its lock within the server's grace period.
 As with the first edge condition, the final step of the scenario of
 the second edge condition has the server erroneously granting client
 A's lock reclaim.
 Solving the first and second edge conditions requires that the server
 either assume after it reboots that edge condition occurs, and thus
 return NFS4ERR_NO_GRACE for all reclaim attempts, or that the server
 record some information stable storage.  The amount of information
 the server records in stable storage is in inverse proportion to how
 harsh the server wants to be whenever the edge conditions occur.  The
 server that is completely tolerant of all edge conditions will record
 in stable storage every lock that is acquired, removing the lock
 record from stable storage only when the lock is unlocked by the
 client and the lock's lockowner advances the sequence number such
 that the lock release is not the last stateful event for the
 lockowner's sequence.  For the two aforementioned edge conditions,
 the harshest a server can be, and still support a grace period for
 reclaims, requires that the server record in stable storage
 information some minimal information.  For example, a server
 implementation could, for each client, save in stable storage a
 record containing:
 o  the client's id string
 o  a boolean that indicates if the client's lease expired or if there
    was administrative intervention (see the section, Server
    Revocation of Locks) to revoke a record lock, share reservation,
    or delegation
 o  a timestamp that is updated the first time after a server boot or
    reboot the client acquires record locking, share reservation, or
    delegation state on the server.  The timestamp need not be updated
    on subsequent lock requests until the server reboots.
 The server implementation would also record in the stable storage the
 timestamps from the two most recent server reboots.
 Assuming the above record keeping, for the first edge condition,
 after the server reboots, the record that client A's lease expired
 means that another client could have acquired a conflicting record
 lock, share reservation, or delegation.  Hence the server must reject
 a reclaim from client A with the error NFS4ERR_NO_GRACE.

Shepler, et al. Standards Track [Page 83] RFC 3530 NFS version 4 Protocol April 2003

 For the second edge condition, after the server reboots for a second
 time, the record that the client had an unexpired record lock, share
 reservation, or delegation established before the server's previous
 incarnation means that the server must reject a reclaim from client A
 with the error NFS4ERR_NO_GRACE.
 Regardless of the level and approach to record keeping, the server
 MUST implement one of the following strategies (which apply to
 reclaims of share reservations, record locks, and delegations):
    1. Reject all reclaims with NFS4ERR_NO_GRACE.  This is superharsh,
       but necessary if the server does not want to record lock state
       in stable storage.
    2. Record sufficient state in stable storage such that all known
       edge conditions involving server reboot, including the two
       noted in this section, are detected.  False positives are
       acceptable.  Note that at this time, it is not known if there
       are other edge conditions.
       In the event, after a server reboot, the server determines that
       there is unrecoverable damage or corruption to the the stable
       storage, then for all clients and/or locks affected, the server
       MUST return NFS4ERR_NO_GRACE.
 A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
 outside the scope of this specification, since the strategies for
 such handling are very dependent on the client's operating
 environment.  However, one potential approach is described below.
 When the client receives NFS4ERR_NO_GRACE, it could examine the
 change attribute of the objects the client is trying to reclaim state
 for, and use that to determine whether to re-establish the state via
 normal OPEN or LOCK requests.  This is acceptable provided the
 client's operating environment allows it.  In otherwords, the client
 implementor is advised to document for his users the behavior.  The
 client could also inform the application that its record lock or
 share reservations (whether they were delegated or not) have been
 lost, such as via a UNIX signal, a GUI pop-up window, etc.  See the
 section, "Data Caching and Revocation" for a discussion of what the
 client should do for dealing with unreclaimed delegations on client
 state.
 For further discussion of revocation of locks see the section "Server
 Revocation of Locks".

Shepler, et al. Standards Track [Page 84] RFC 3530 NFS version 4 Protocol April 2003

8.7. Recovery from a Lock Request Timeout or Abort

 In the event a lock request times out, a client may decide to not
 retry the request.  The client may also abort the request when the
 process for which it was issued is terminated (e.g., in UNIX due to a
 signal).  It is possible though that the server received the request
 and acted upon it.  This would change the state on the server without
 the client being aware of the change.  It is paramount that the
 client re-synchronize state with server before it attempts any other
 operation that takes a seqid and/or a stateid with the same
 lock_owner.  This is straightforward to do without a special re-
 synchronize operation.
 Since the server maintains the last lock request and response
 received on the lock_owner, for each lock_owner, the client should
 cache the last lock request it sent such that the lock request did
 not receive a response.  From this, the next time the client does a
 lock operation for the lock_owner, it can send the cached request, if
 there is one, and if the request was one that established state
 (e.g., a LOCK or OPEN operation), the server will return the cached
 result or if never saw the request, perform it.  The client can
 follow up with a request to remove the state (e.g., a LOCKU or CLOSE
 operation).  With this approach, the sequencing and stateid
 information on the client and server for the given lock_owner will
 re-synchronize and in turn the lock state will re-synchronize.

8.8. Server Revocation of Locks

 At any point, the server can revoke locks held by a client and the
 client must be prepared for this event.  When the client detects that
 its locks have been or may have been revoked, the client is
 responsible for validating the state information between itself and
 the server.  Validating locking state for the client means that it
 must verify or reclaim state for each lock currently held.
 The first instance of lock revocation is upon server reboot or re-
 initialization.  In this instance the client will receive an error
 (NFS4ERR_STALE_STATEID or NFS4ERR_STALE_CLIENTID) and the client will
 proceed with normal crash recovery as described in the previous
 section.
 The second lock revocation event is the inability to renew the lease
 before expiration.  While this is considered a rare or unusual event,
 the client must be prepared to recover.  Both the server and client
 will be able to detect the failure to renew the lease and are capable
 of recovering without data corruption.  For the server, it tracks the
 last renewal event serviced for the client and knows when the lease
 will expire.  Similarly, the client must track operations which will

Shepler, et al. Standards Track [Page 85] RFC 3530 NFS version 4 Protocol April 2003

 renew the lease period.  Using the time that each such request was
 sent and the time that the corresponding reply was received, the
 client should bound the time that the corresponding renewal could
 have occurred on the server and thus determine if it is possible that
 a lease period expiration could have occurred.
 The third lock revocation event can occur as a result of
 administrative intervention within the lease period.  While this is
 considered a rare event, it is possible that the server's
 administrator has decided to release or revoke a particular lock held
 by the client.  As a result of revocation, the client will receive an
 error of NFS4ERR_ADMIN_REVOKED.  In this instance the client may
 assume that only the lock_owner's locks have been lost.  The client
 notifies the lock holder appropriately.  The client may not assume
 the lease period has been renewed as a result of failed operation.
 When the client determines the lease period may have expired, the
 client must mark all locks held for the associated lease as
 "unvalidated".  This means the client has been unable to re-establish
 or confirm the appropriate lock state with the server.  As described
 in the previous section on crash recovery, there are scenarios in
 which the server may grant conflicting locks after the lease period
 has expired for a client.  When it is possible that the lease period
 has expired, the client must validate each lock currently held to
 ensure that a conflicting lock has not been granted.  The client may
 accomplish this task by issuing an I/O request, either a pending I/O
 or a zero-length read, specifying the stateid associated with the
 lock in question.  If the response to the request is success, the
 client has validated all of the locks governed by that stateid and
 re-established the appropriate state between itself and the server.
 If the I/O request is not successful, then one or more of the locks
 associated with the stateid was revoked by the server and the client
 must notify the owner.

8.9. Share Reservations

 A share reservation is a mechanism to control access to a file.  It
 is a separate and independent mechanism from record locking.  When a
 client opens a file, it issues an OPEN operation to the server
 specifying the type of access required (READ, WRITE, or BOTH) and the
 type of access to deny others (deny NONE, READ, WRITE, or BOTH).  If
 the OPEN fails the client will fail the application's open request.
 Pseudo-code definition of the semantics:
 if (request.access == 0)
    return (NFS4ERR_INVAL)

Shepler, et al. Standards Track [Page 86] RFC 3530 NFS version 4 Protocol April 2003

 else
    if ((request.access & file_state.deny)) ||
          (request.deny & file_state.access))
                  return (NFS4ERR_DENIED)
 This checking of share reservations on OPEN is done with no exception
 for an existing OPEN for the same open_owner.
 The constants used for the OPEN and OPEN_DOWNGRADE operations for the
 access and deny fields are as follows:
 const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
 const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
 const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;
 const OPEN4_SHARE_DENY_NONE     = 0x00000000;
 const OPEN4_SHARE_DENY_READ     = 0x00000001;
 const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
 const OPEN4_SHARE_DENY_BOTH     = 0x00000003;

8.10. OPEN/CLOSE Operations

 To provide correct share semantics, a client MUST use the OPEN
 operation to obtain the initial filehandle and indicate the desired
 access and what if any access to deny.  Even if the client intends to
 use a stateid of all 0's or all 1's, it must still obtain the
 filehandle for the regular file with the OPEN operation so the
 appropriate share semantics can be applied.  For clients that do not
 have a deny mode built into their open programming interfaces, deny
 equal to NONE should be used.
 The OPEN operation with the CREATE flag, also subsumes the CREATE
 operation for regular files as used in previous versions of the NFS
 protocol.  This allows a create with a share to be done atomically.
 The CLOSE operation removes all share reservations held by the
 lock_owner on that file.  If record locks are held, the client SHOULD
 release all locks before issuing a CLOSE.  The server MAY free all
 outstanding locks on CLOSE but some servers may not support the CLOSE
 of a file that still has record locks held.  The server MUST return
 failure, NFS4ERR_LOCKS_HELD, if any locks would exist after the
 CLOSE.
 The LOOKUP operation will return a filehandle without establishing
 any lock state on the server.  Without a valid stateid, the server
 will assume the client has the least access.  For example, a file

Shepler, et al. Standards Track [Page 87] RFC 3530 NFS version 4 Protocol April 2003

 opened with deny READ/WRITE cannot be accessed using a filehandle
 obtained through LOOKUP because it would not have a valid stateid
 (i.e., using a stateid of all bits 0 or all bits 1).

8.10.1. Close and Retention of State Information

 Since a CLOSE operation requests deallocation of a stateid, dealing
 with retransmission of the CLOSE, may pose special difficulties,
 since the state information, which normally would be used to
 determine the state of the open file being designated, might be
 deallocated, resulting in an NFS4ERR_BAD_STATEID error.
 Servers may deal with this problem in a number of ways.  To provide
 the greatest degree assurance that the protocol is being used
 properly, a server should, rather than deallocate the stateid, mark
 it as close-pending, and retain the stateid with this status, until
 later deallocation.  In this way, a retransmitted CLOSE can be
 recognized since the stateid points to state information with this
 distinctive status, so that it can be handled without error.
 When adopting this strategy, a server should retain the state
 information until the earliest of:
 o  Another validly sequenced request for the same lockowner, that is
    not a retransmission.
 o  The time that a lockowner is freed by the server due to period
    with no activity.
 o  All locks for the client are freed as a result of a SETCLIENTID.
 Servers may avoid this complexity, at the cost of less complete
 protocol error checking, by simply responding NFS4_OK in the event of
 a CLOSE for a deallocated stateid, on the assumption that this case
 must be caused by a retransmitted close.  When adopting this
 approach, it is desirable to at least log an error when returning a
 no-error indication in this situation.  If the server maintains a
 reply-cache mechanism, it can verify the CLOSE is indeed a
 retransmission and avoid error logging in most cases.

8.11. Open Upgrade and Downgrade

 When an OPEN is done for a file and the lockowner for which the open
 is being done already has the file open, the result is to upgrade the
 open file status maintained on the server to include the access and
 deny bits specified by the new OPEN as well as those for the existing
 OPEN.  The result is that there is one open file, as far as the
 protocol is concerned, and it includes the union of the access and

Shepler, et al. Standards Track [Page 88] RFC 3530 NFS version 4 Protocol April 2003

 deny bits for all of the OPEN requests completed.  Only a single
 CLOSE will be done to reset the effects of both OPENs.  Note that the
 client, when issuing the OPEN, may not know that the same file is in
 fact being opened.  The above only applies if both OPENs result in
 the OPENed object being designated by the same filehandle.
 When the server chooses to export multiple filehandles corresponding
 to the same file object and returns different filehandles on two
 different OPENs of the same file object, the server MUST NOT "OR"
 together the access and deny bits and coalesce the two open files.
 Instead the server must maintain separate OPENs with separate
 stateids and will require separate CLOSEs to free them.
 When multiple open files on the client are merged into a single open
 file object on the server, the close of one of the open files (on the
 client) may necessitate change of the access and deny status of the
 open file on the server.  This is because the union of the access and
 deny bits for the remaining opens may be smaller (i.e., a proper
 subset) than previously.  The OPEN_DOWNGRADE operation is used to
 make the necessary change and the client should use it to update the
 server so that share reservation requests by other clients are
 handled properly.

8.12. Short and Long Leases

 When determining the time period for the server lease, the usual
 lease tradeoffs apply.  Short leases are good for fast server
 recovery at a cost of increased RENEW or READ (with zero length)
 requests.  Longer leases are certainly kinder and gentler to servers
 trying to handle very large numbers of clients.  The number of RENEW
 requests drop in proportion to the lease time.  The disadvantages of
 long leases are slower recovery after server failure (the server must
 wait for the leases to expire and the grace period to elapse before
 granting new lock requests) and increased file contention (if client
 fails to transmit an unlock request then server must wait for lease
 expiration before granting new locks).
 Long leases are usable if the server is able to store lease state in
 non-volatile memory.  Upon recovery, the server can reconstruct the
 lease state from its non-volatile memory and continue operation with
 its clients and therefore long leases would not be an issue.

8.13. Clocks, Propagation Delay, and Calculating Lease Expiration

 To avoid the need for synchronized clocks, lease times are granted by
 the server as a time delta.  However, there is a requirement that the
 client and server clocks do not drift excessively over the duration
 of the lock.  There is also the issue of propagation delay across the

Shepler, et al. Standards Track [Page 89] RFC 3530 NFS version 4 Protocol April 2003

 network which could easily be several hundred milliseconds as well as
 the possibility that requests will be lost and need to be
 retransmitted.
 To take propagation delay into account, the client should subtract it
 from lease times (e.g., if the client estimates the one-way
 propagation delay as 200 msec, then it can assume that the lease is
 already 200 msec old when it gets it).  In addition, it will take
 another 200 msec to get a response back to the server.  So the client
 must send a lock renewal or write data back to the server 400 msec
 before the lease would expire.
 The server's lease period configuration should take into account the
 network distance of the clients that will be accessing the server's
 resources.  It is expected that the lease period will take into
 account the network propagation delays and other network delay
 factors for the client population.  Since the protocol does not allow
 for an automatic method to determine an appropriate lease period, the
 server's administrator may have to tune the lease period.

8.14. Migration, Replication and State

 When responsibility for handling a given file system is transferred
 to a new server (migration) or the client chooses to use an alternate
 server (e.g., in response to server unresponsiveness) in the context
 of file system replication, the appropriate handling of state shared
 between the client and server (i.e., locks, leases, stateids, and
 clientids) is as described below.  The handling differs between
 migration and replication.  For related discussion of file server
 state and recover of such see the sections under "File Locking and
 Share Reservations".
 If server replica or a server immigrating a filesystem agrees to, or
 is expected to, accept opaque values from the client that originated
 from another server, then it is a wise implementation practice for
 the servers to encode the "opaque" values in network byte order.
 This way, servers acting as replicas or immigrating filesystems will
 be able to parse values like stateids, directory cookies,
 filehandles, etc. even if their native byte order is different from
 other servers cooperating in the replication and migration of the
 filesystem.

8.14.1. Migration and State

 In the case of migration, the servers involved in the migration of a
 filesystem SHOULD transfer all server state from the original to the
 new server.  This must be done in a way that is transparent to the
 client.  This state transfer will ease the client's transition when a

Shepler, et al. Standards Track [Page 90] RFC 3530 NFS version 4 Protocol April 2003

 filesystem migration occurs.  If the servers are successful in
 transferring all state, the client will continue to use stateids
 assigned by the original server.  Therefore the new server must
 recognize these stateids as valid.  This holds true for the clientid
 as well.  Since responsibility for an entire filesystem is
 transferred with a migration event, there is no possibility that
 conflicts will arise on the new server as a result of the transfer of
 locks.
 As part of the transfer of information between servers, leases would
 be transferred as well.  The leases being transferred to the new
 server will typically have a different expiration time from those for
 the same client, previously on the old server.  To maintain the
 property that all leases on a given server for a given client expire
 at the same time, the server should advance the expiration time to
 the later of the leases being transferred or the leases already
 present.  This allows the client to maintain lease renewal of both
 classes without special effort.
 The servers may choose not to transfer the state information upon
 migration.  However, this choice is discouraged.  In this case, when
 the client presents state information from the original server, the
 client must be prepared to receive either NFS4ERR_STALE_CLIENTID or
 NFS4ERR_STALE_STATEID from the new server.  The client should then
 recover its state information as it normally would in response to a
 server failure.  The new server must take care to allow for the
 recovery of state information as it would in the event of server
 restart.

8.14.2. Replication and State

 Since client switch-over in the case of replication is not under
 server control, the handling of state is different.  In this case,
 leases, stateids and clientids do not have validity across a
 transition from one server to another.  The client must re-establish
 its locks on the new server.  This can be compared to the re-
 establishment of locks by means of reclaim-type requests after a
 server reboot.  The difference is that the server has no provision to
 distinguish requests reclaiming locks from those obtaining new locks
 or to defer the latter.  Thus, a client re-establishing a lock on the
 new server (by means of a LOCK or OPEN request), may have the
 requests denied due to a conflicting lock.  Since replication is
 intended for read-only use of filesystems, such denial of locks
 should not pose large difficulties in practice.  When an attempt to
 re-establish a lock on a new server is denied, the client should
 treat the situation as if his original lock had been revoked.

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8.14.3. Notification of Migrated Lease

 In the case of lease renewal, the client may not be submitting
 requests for a filesystem that has been migrated to another server.
 This can occur because of the implicit lease renewal mechanism.  The
 client renews leases for all filesystems when submitting a request to
 any one filesystem at the server.
 In order for the client to schedule renewal of leases that may have
 been relocated to the new server, the client must find out about
 lease relocation before those leases expire.  To accomplish this, all
 operations which implicitly renew leases for a client (i.e., OPEN,
 CLOSE, READ, WRITE, RENEW, LOCK, LOCKT, LOCKU), will return the error
 NFS4ERR_LEASE_MOVED if responsibility for any of the leases to be
 renewed has been transferred to a new server.  This condition will
 continue until the client receives an NFS4ERR_MOVED error and the
 server receives the subsequent GETATTR(fs_locations) for an access to
 each filesystem for which a lease has been moved to a new server.
 When a client receives an NFS4ERR_LEASE_MOVED error, it should
 perform an operation on each filesystem associated with the server in
 question.  When the client receives an NFS4ERR_MOVED error, the
 client can follow the normal process to obtain the new server
 information (through the fs_locations attribute) and perform renewal
 of those leases on the new server.  If the server has not had state
 transferred to it transparently, the client will receive either
 NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID from the new server,
 as described above, and the client can then recover state information
 as it does in the event of server failure.

8.14.4. Migration and the Lease_time Attribute

 In order that the client may appropriately manage its leases in the
 case of migration, the destination server must establish proper
 values for the lease_time attribute.
 When state is transferred transparently, that state should include
 the correct value of the lease_time attribute.  The lease_time
 attribute on the destination server must never be less than that on
 the source since this would result in premature expiration of leases
 granted by the source server.  Upon migration in which state is
 transferred transparently, the client is under no obligation to re-
 fetch the lease_time attribute and may continue to use the value
 previously fetched (on the source server).
 If state has not been transferred transparently (i.e., the client
 sees a real or simulated server reboot), the client should fetch the
 value of lease_time on the new (i.e., destination) server, and use it

Shepler, et al. Standards Track [Page 92] RFC 3530 NFS version 4 Protocol April 2003

 for subsequent locking requests.  However the server must respect a
 grace period at least as long as the lease_time on the source server,
 in order to ensure that clients have ample time to reclaim their
 locks before potentially conflicting non-reclaimed locks are granted.
 The means by which the new server obtains the value of lease_time on
 the old server is left to the server implementations.  It is not
 specified by the NFS version 4 protocol.

9. Client-Side Caching

 Client-side caching of data, of file attributes, and of file names is
 essential to providing good performance with the NFS protocol.
 Providing distributed cache coherence is a difficult problem and
 previous versions of the NFS protocol have not attempted it.
 Instead, several NFS client implementation techniques have been used
 to reduce the problems that a lack of coherence poses for users.
 These techniques have not been clearly defined by earlier protocol
 specifications and it is often unclear what is valid or invalid
 client behavior.
 The NFS version 4 protocol uses many techniques similar to those that
 have been used in previous protocol versions.  The NFS version 4
 protocol does not provide distributed cache coherence.  However, it
 defines a more limited set of caching guarantees to allow locks and
 share reservations to be used without destructive interference from
 client side caching.
 In addition, the NFS version 4 protocol introduces a delegation
 mechanism which allows many decisions normally made by the server to
 be made locally by clients.  This mechanism provides efficient
 support of the common cases where sharing is infrequent or where
 sharing is read-only.

9.1. Performance Challenges for Client-Side Caching

 Caching techniques used in previous versions of the NFS protocol have
 been successful in providing good performance.  However, several
 scalability challenges can arise when those techniques are used with
 very large numbers of clients.  This is particularly true when
 clients are geographically distributed which classically increases
 the latency for cache revalidation requests.
 The previous versions of the NFS protocol repeat their file data
 cache validation requests at the time the file is opened.  This
 behavior can have serious performance drawbacks.  A common case is
 one in which a file is only accessed by a single client.  Therefore,
 sharing is infrequent.

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 In this case, repeated reference to the server to find that no
 conflicts exist is expensive.  A better option with regards to
 performance is to allow a client that repeatedly opens a file to do
 so without reference to the server.  This is done until potentially
 conflicting operations from another client actually occur.
 A similar situation arises in connection with file locking.  Sending
 file lock and unlock requests to the server as well as the read and
 write requests necessary to make data caching consistent with the
 locking semantics (see the section "Data Caching and File Locking")
 can severely limit performance.  When locking is used to provide
 protection against infrequent conflicts, a large penalty is incurred.
 This penalty may discourage the use of file locking by applications.
 The NFS version 4 protocol provides more aggressive caching
 strategies with the following design goals:
 o  Compatibility with a large range of server semantics.
 o  Provide the same caching benefits as previous versions of the NFS
    protocol when unable to provide the more aggressive model.
 o  Requirements for aggressive caching are organized so that a large
    portion of the benefit can be obtained even when not all of the
    requirements can be met.
 The appropriate requirements for the server are discussed in later
 sections in which specific forms of caching are covered.  (see the
 section "Open Delegation").

9.2. Delegation and Callbacks

 Recallable delegation of server responsibilities for a file to a
 client improves performance by avoiding repeated requests to the
 server in the absence of inter-client conflict.  With the use of a
 "callback" RPC from server to client, a server recalls delegated
 responsibilities when another client engages in sharing of a
 delegated file.
 A delegation is passed from the server to the client, specifying the
 object of the delegation and the type of delegation.  There are
 different types of delegations but each type contains a stateid to be
 used to represent the delegation when performing operations that
 depend on the delegation.  This stateid is similar to those
 associated with locks and share reservations but differs in that the
 stateid for a delegation is associated with a clientid and may be

Shepler, et al. Standards Track [Page 94] RFC 3530 NFS version 4 Protocol April 2003

 used on behalf of all the open_owners for the given client.  A
 delegation is made to the client as a whole and not to any specific
 process or thread of control within it.
 Because callback RPCs may not work in all environments (due to
 firewalls, for example), correct protocol operation does not depend
 on them.  Preliminary testing of callback functionality by means of a
 CB_NULL procedure determines whether callbacks can be supported.  The
 CB_NULL procedure checks the continuity of the callback path.  A
 server makes a preliminary assessment of callback availability to a
 given client and avoids delegating responsibilities until it has
 determined that callbacks are supported.  Because the granting of a
 delegation is always conditional upon the absence of conflicting
 access, clients must not assume that a delegation will be granted and
 they must always be prepared for OPENs to be processed without any
 delegations being granted.
 Once granted, a delegation behaves in most ways like a lock.  There
 is an associated lease that is subject to renewal together with all
 of the other leases held by that client.
 Unlike locks, an operation by a second client to a delegated file
 will cause the server to recall a delegation through a callback.
 On recall, the client holding the delegation must flush modified
 state (such as modified data) to the server and return the
 delegation.  The conflicting request will not receive a response
 until the recall is complete.  The recall is considered complete when
 the client returns the delegation or the server times out on the
 recall and revokes the delegation as a result of the timeout.
 Following the resolution of the recall, the server has the
 information necessary to grant or deny the second client's request.
 At the time the client receives a delegation recall, it may have
 substantial state that needs to be flushed to the server.  Therefore,
 the server should allow sufficient time for the delegation to be
 returned since it may involve numerous RPCs to the server.  If the
 server is able to determine that the client is diligently flushing
 state to the server as a result of the recall, the server may extend
 the usual time allowed for a recall.  However, the time allowed for
 recall completion should not be unbounded.
 An example of this is when responsibility to mediate opens on a given
 file is delegated to a client (see the section "Open Delegation").
 The server will not know what opens are in effect on the client.
 Without this knowledge the server will be unable to determine if the
 access and deny state for the file allows any particular open until
 the delegation for the file has been returned.

Shepler, et al. Standards Track [Page 95] RFC 3530 NFS version 4 Protocol April 2003

 A client failure or a network partition can result in failure to
 respond to a recall callback.  In this case, the server will revoke
 the delegation which in turn will render useless any modified state
 still on the client.

9.2.1. Delegation Recovery

 There are three situations that delegation recovery must deal with:
 o   Client reboot or restart
 o   Server reboot or restart
 o   Network partition (full or callback-only)
 In the event the client reboots or restarts, the failure to renew
 leases will result in the revocation of record locks and share
 reservations.  Delegations, however, may be treated a bit
 differently.
 There will be situations in which delegations will need to be
 reestablished after a client reboots or restarts.  The reason for
 this is the client may have file data stored locally and this data
 was associated with the previously held delegations.  The client will
 need to reestablish the appropriate file state on the server.
 To allow for this type of client recovery, the server MAY extend the
 period for delegation recovery beyond the typical lease expiration
 period.  This implies that requests from other clients that conflict
 with these delegations will need to wait.  Because the normal recall
 process may require significant time for the client to flush changed
 state to the server, other clients need be prepared for delays that
 occur because of a conflicting delegation.  This longer interval
 would increase the window for clients to reboot and consult stable
 storage so that the delegations can be reclaimed.  For open
 delegations, such delegations are reclaimed using OPEN with a claim
 type of CLAIM_DELEGATE_PREV.  (See the sections on "Data Caching and
 Revocation" and "Operation 18: OPEN" for discussion of open
 delegation and the details of OPEN respectively).
 A server MAY support a claim type of CLAIM_DELEGATE_PREV, but if it
 does, it MUST NOT remove delegations upon SETCLIENTID_CONFIRM, and
 instead MUST, for a period of time no less than that of the value of
 the lease_time attribute, maintain the client's delegations to allow
 time for the client to issue CLAIM_DELEGATE_PREV requests.  The
 server that supports CLAIM_DELEGATE_PREV MUST support the DELEGPURGE
 operation.

Shepler, et al. Standards Track [Page 96] RFC 3530 NFS version 4 Protocol April 2003

 When the server reboots or restarts, delegations are reclaimed (using
 the OPEN operation with CLAIM_PREVIOUS) in a similar fashion to
 record locks and share reservations.  However, there is a slight
 semantic difference.  In the normal case if the server decides that a
 delegation should not be granted, it performs the requested action
 (e.g., OPEN) without granting any delegation.  For reclaim, the
 server grants the delegation but a special designation is applied so
 that the client treats the delegation as having been granted but
 recalled by the server.  Because of this, the client has the duty to
 write all modified state to the server and then return the
 delegation.  This process of handling delegation reclaim reconciles
 three principles of the NFS version 4 protocol:
 o  Upon reclaim, a client reporting resources assigned to it by an
    earlier server instance must be granted those resources.
 o  The server has unquestionable authority to determine whether
    delegations are to be granted and, once granted, whether they are
    to be continued.
 o  The use of callbacks is not to be depended upon until the client
    has proven its ability to receive them.
 When a network partition occurs, delegations are subject to freeing
 by the server when the lease renewal period expires.  This is similar
 to the behavior for locks and share reservations.  For delegations,
 however, the server may extend the period in which conflicting
 requests are held off.  Eventually the occurrence of a conflicting
 request from another client will cause revocation of the delegation.
 A loss of the callback path (e.g., by later network configuration
 change) will have the same effect.  A recall request will fail and
 revocation of the delegation will result.
 A client normally finds out about revocation of a delegation when it
 uses a stateid associated with a delegation and receives the error
 NFS4ERR_EXPIRED.  It also may find out about delegation revocation
 after a client reboot when it attempts to reclaim a delegation and
 receives that same error.  Note that in the case of a revoked write
 open delegation, there are issues because data may have been modified
 by the client whose delegation is revoked and separately by other
 clients.  See the section "Revocation Recovery for Write Open
 Delegation" for a discussion of such issues.  Note also that when
 delegations are revoked, information about the revoked delegation
 will be written by the server to stable storage (as described in the
 section "Crash Recovery").  This is done to deal with the case in
 which a server reboots after revoking a delegation but before the
 client holding the revoked delegation is notified about the
 revocation.

Shepler, et al. Standards Track [Page 97] RFC 3530 NFS version 4 Protocol April 2003

9.3. Data Caching

 When applications share access to a set of files, they need to be
 implemented so as to take account of the possibility of conflicting
 access by another application.  This is true whether the applications
 in question execute on different clients or reside on the same
 client.
 Share reservations and record locks are the facilities the NFS
 version 4 protocol provides to allow applications to coordinate
 access by providing mutual exclusion facilities.  The NFS version 4
 protocol's data caching must be implemented such that it does not
 invalidate the assumptions that those using these facilities depend
 upon.

9.3.1. Data Caching and OPENs

 In order to avoid invalidating the sharing assumptions that
 applications rely on, NFS version 4 clients should not provide cached
 data to applications or modify it on behalf of an application when it
 would not be valid to obtain or modify that same data via a READ or
 WRITE operation.
 Furthermore, in the absence of open delegation (see the section "Open
 Delegation") two additional rules apply.  Note that these rules are
 obeyed in practice by many NFS version 2 and version 3 clients.
 o  First, cached data present on a client must be revalidated after
    doing an OPEN.  Revalidating means that the client fetches the
    change attribute from the server, compares it with the cached
    change attribute, and if different, declares the cached data (as
    well as the cached attributes) as invalid.  This is to ensure that
    the data for the OPENed file is still correctly reflected in the
    client's cache.  This validation must be done at least when the
    client's OPEN operation includes DENY=WRITE or BOTH thus
    terminating a period in which other clients may have had the
    opportunity to open the file with WRITE access.  Clients may
    choose to do the revalidation more often (i.e., at OPENs
    specifying DENY=NONE) to parallel the NFS version 3 protocol's
    practice for the benefit of users assuming this degree of cache
    revalidation.
    Since the change attribute is updated for data and metadata
    modifications, some client implementors may be tempted to use the
    time_modify attribute and not change to validate cached data, so
    that metadata changes do not spuriously invalidate clean data.
    The implementor is cautioned in this approach.  The change
    attribute is guaranteed to change for each update to the file,

Shepler, et al. Standards Track [Page 98] RFC 3530 NFS version 4 Protocol April 2003

    whereas time_modify is guaranteed to change only at the
    granularity of the time_delta attribute.  Use by the client's data
    cache validation logic of time_modify and not change runs the risk
    of the client incorrectly marking stale data as valid.
 o  Second, modified data must be flushed to the server before closing
    a file OPENed for write.  This is complementary to the first rule.
    If the data is not flushed at CLOSE, the revalidation done after
    client OPENs as file is unable to achieve its purpose.  The other
    aspect to flushing the data before close is that the data must be
    committed to stable storage, at the server, before the CLOSE
    operation is requested by the client.  In the case of a server
    reboot or restart and a CLOSEd file, it may not be possible to
    retransmit the data to be written to the file.  Hence, this
    requirement.

9.3.2. Data Caching and File Locking

 For those applications that choose to use file locking instead of
 share reservations to exclude inconsistent file access, there is an
 analogous set of constraints that apply to client side data caching.
 These rules are effective only if the file locking is used in a way
 that matches in an equivalent way the actual READ and WRITE
 operations executed.  This is as opposed to file locking that is
 based on pure convention.  For example, it is possible to manipulate
 a two-megabyte file by dividing the file into two one-megabyte
 regions and protecting access to the two regions by file locks on
 bytes zero and one.  A lock for write on byte zero of the file would
 represent the right to do READ and WRITE operations on the first
 region.  A lock for write on byte one of the file would represent the
 right to do READ and WRITE operations on the second region.  As long
 as all applications manipulating the file obey this convention, they
 will work on a local filesystem.  However, they may not work with the
 NFS version 4 protocol unless clients refrain from data caching.
 The rules for data caching in the file locking environment are:
 o  First, when a client obtains a file lock for a particular region,
    the data cache corresponding to that region (if any cached data
    exists) must be revalidated.  If the change attribute indicates
    that the file may have been updated since the cached data was
    obtained, the client must flush or invalidate the cached data for
    the newly locked region.  A client might choose to invalidate all
    of non-modified cached data that it has for the file but the only
    requirement for correct operation is to invalidate all of the data
    in the newly locked region.

Shepler, et al. Standards Track [Page 99] RFC 3530 NFS version 4 Protocol April 2003

 o  Second, before releasing a write lock for a region, all modified
    data for that region must be flushed to the server.  The modified
    data must also be written to stable storage.
 Note that flushing data to the server and the invalidation of cached
 data must reflect the actual byte ranges locked or unlocked.
 Rounding these up or down to reflect client cache block boundaries
 will cause problems if not carefully done.  For example, writing a
 modified block when only half of that block is within an area being
 unlocked may cause invalid modification to the region outside the
 unlocked area.  This, in turn, may be part of a region locked by
 another client.  Clients can avoid this situation by synchronously
 performing portions of write operations that overlap that portion
 (initial or final) that is not a full block.  Similarly, invalidating
 a locked area which is not an integral number of full buffer blocks
 would require the client to read one or two partial blocks from the
 server if the revalidation procedure shows that the data which the
 client possesses may not be valid.
 The data that is written to the server as a prerequisite to the
 unlocking of a region must be written, at the server, to stable
 storage.  The client may accomplish this either with synchronous
 writes or by following asynchronous writes with a COMMIT operation.
 This is required because retransmission of the modified data after a
 server reboot might conflict with a lock held by another client.
 A client implementation may choose to accommodate applications which
 use record locking in non-standard ways (e.g., using a record lock as
 a global semaphore) by flushing to the server more data upon an LOCKU
 than is covered by the locked range.  This may include modified data
 within files other than the one for which the unlocks are being done.
 In such cases, the client must not interfere with applications whose
 READs and WRITEs are being done only within the bounds of record
 locks which the application holds.  For example, an application locks
 a single byte of a file and proceeds to write that single byte.  A
 client that chose to handle a LOCKU by flushing all modified data to
 the server could validly write that single byte in response to an
 unrelated unlock.  However, it would not be valid to write the entire
 block in which that single written byte was located since it includes
 an area that is not locked and might be locked by another client.
 Client implementations can avoid this problem by dividing files with
 modified data into those for which all modifications are done to
 areas covered by an appropriate record lock and those for which there
 are modifications not covered by a record lock.  Any writes done for
 the former class of files must not include areas not locked and thus
 not modified on the client.

Shepler, et al. Standards Track [Page 100] RFC 3530 NFS version 4 Protocol April 2003

9.3.3. Data Caching and Mandatory File Locking

 Client side data caching needs to respect mandatory file locking when
 it is in effect.  The presence of mandatory file locking for a given
 file is indicated when the client gets back NFS4ERR_LOCKED from a
 READ or WRITE on a file it has an appropriate share reservation for.
 When mandatory locking is in effect for a file, the client must check
 for an appropriate file lock for data being read or written.  If a
 lock exists for the range being read or written, the client may
 satisfy the request using the client's validated cache.  If an
 appropriate file lock is not held for the range of the read or write,
 the read or write request must not be satisfied by the client's cache
 and the request must be sent to the server for processing.  When a
 read or write request partially overlaps a locked region, the request
 should be subdivided into multiple pieces with each region (locked or
 not) treated appropriately.

9.3.4. Data Caching and File Identity

 When clients cache data, the file data needs to be organized
 according to the filesystem object to which the data belongs.  For
 NFS version 3 clients, the typical practice has been to assume for
 the purpose of caching that distinct filehandles represent distinct
 filesystem objects.  The client then has the choice to organize and
 maintain the data cache on this basis.
 In the NFS version 4 protocol, there is now the possibility to have
 significant deviations from a "one filehandle per object" model
 because a filehandle may be constructed on the basis of the object's
 pathname.  Therefore, clients need a reliable method to determine if
 two filehandles designate the same filesystem object.  If clients
 were simply to assume that all distinct filehandles denote distinct
 objects and proceed to do data caching on this basis, caching
 inconsistencies would arise between the distinct client side objects
 which mapped to the same server side object.
 By providing a method to differentiate filehandles, the NFS version 4
 protocol alleviates a potential functional regression in comparison
 with the NFS version 3 protocol.  Without this method, caching
 inconsistencies within the same client could occur and this has not
 been present in previous versions of the NFS protocol.  Note that it
 is possible to have such inconsistencies with applications executing
 on multiple clients but that is not the issue being addressed here.
 For the purposes of data caching, the following steps allow an NFS
 version 4 client to determine whether two distinct filehandles denote
 the same server side object:

Shepler, et al. Standards Track [Page 101] RFC 3530 NFS version 4 Protocol April 2003

 o  If GETATTR directed to two filehandles returns different values of
    the fsid attribute, then the filehandles represent distinct
    objects.
 o  If GETATTR for any file with an fsid that matches the fsid of the
    two filehandles in question returns a unique_handles attribute
    with a value of TRUE, then the two objects are distinct.
 o  If GETATTR directed to the two filehandles does not return the
    fileid attribute for both of the handles, then it cannot be
    determined whether the two objects are the same.  Therefore,
    operations which depend on that knowledge (e.g., client side data
    caching) cannot be done reliably.
 o  If GETATTR directed to the two filehandles returns different
    values for the fileid attribute, then they are distinct objects.
 o  Otherwise they are the same object.

9.4. Open Delegation

 When a file is being OPENed, the server may delegate further handling
 of opens and closes for that file to the opening client.  Any such
 delegation is recallable, since the circumstances that allowed for
 the delegation are subject to change.  In particular, the server may
 receive a conflicting OPEN from another client, the server must
 recall the delegation before deciding whether the OPEN from the other
 client may be granted.  Making a delegation is up to the server and
 clients should not assume that any particular OPEN either will or
 will not result in an open delegation.  The following is a typical
 set of conditions that servers might use in deciding whether OPEN
 should be delegated:
 o  The client must be able to respond to the server's callback
    requests.  The server will use the CB_NULL procedure for a test of
    callback ability.
 o  The client must have responded properly to previous recalls.
 o  There must be no current open conflicting with the requested
    delegation.
 o  There should be no current delegation that conflicts with the
    delegation being requested.
 o  The probability of future conflicting open requests should be low
    based on the recent history of the file.

Shepler, et al. Standards Track [Page 102] RFC 3530 NFS version 4 Protocol April 2003

 o  The existence of any server-specific semantics of OPEN/CLOSE that
    would make the required handling incompatible with the prescribed
    handling that the delegated client would apply (see below).
 There are two types of open delegations, read and write.  A read open
 delegation allows a client to handle, on its own, requests to open a
 file for reading that do not deny read access to others.  Multiple
 read open delegations may be outstanding simultaneously and do not
 conflict.  A write open delegation allows the client to handle, on
 its own, all opens.  Only one write open delegation may exist for a
 given file at a given time and it is inconsistent with any read open
 delegations.
 When a client has a read open delegation, it may not make any changes
 to the contents or attributes of the file but it is assured that no
 other client may do so.  When a client has a write open delegation,
 it may modify the file data since no other client will be accessing
 the file's data.  The client holding a write delegation may only
 affect file attributes which are intimately connected with the file
 data:  size, time_modify, change.
 When a client has an open delegation, it does not send OPENs or
 CLOSEs to the server but updates the appropriate status internally.
 For a read open delegation, opens that cannot be handled locally
 (opens for write or that deny read access) must be sent to the
 server.
 When an open delegation is made, the response to the OPEN contains an
 open delegation structure which specifies the following:
 o  the type of delegation (read or write)
 o  space limitation information to control flushing of data on close
    (write open delegation only, see the section "Open Delegation and
    Data Caching")
 o  an nfsace4 specifying read and write permissions
 o  a stateid to represent the delegation for READ and WRITE
 The delegation stateid is separate and distinct from the stateid for
 the OPEN proper.  The standard stateid, unlike the delegation
 stateid, is associated with a particular lock_owner and will continue
 to be valid after the delegation is recalled and the file remains
 open.

Shepler, et al. Standards Track [Page 103] RFC 3530 NFS version 4 Protocol April 2003

 When a request internal to the client is made to open a file and open
 delegation is in effect, it will be accepted or rejected solely on
 the basis of the following conditions.  Any requirement for other
 checks to be made by the delegate should result in open delegation
 being denied so that the checks can be made by the server itself.
 o  The access and deny bits for the request and the file as described
    in the section "Share Reservations".
 o  The read and write permissions as determined below.
 The nfsace4 passed with delegation can be used to avoid frequent
 ACCESS calls.  The permission check should be as follows:
 o  If the nfsace4 indicates that the open may be done, then it should
    be granted without reference to the server.
 o  If the nfsace4 indicates that the open may not be done, then an
    ACCESS request must be sent to the server to obtain the definitive
    answer.
 The server may return an nfsace4 that is more restrictive than the
 actual ACL of the file.  This includes an nfsace4 that specifies
 denial of all access.  Note that some common practices such as
 mapping the traditional user "root" to the user "nobody" may make it
 incorrect to return the actual ACL of the file in the delegation
 response.
 The use of delegation together with various other forms of caching
 creates the possibility that no server authentication will ever be
 performed for a given user since all of the user's requests might be
 satisfied locally.  Where the client is depending on the server for
 authentication, the client should be sure authentication occurs for
 each user by use of the ACCESS operation.  This should be the case
 even if an ACCESS operation would not be required otherwise.  As
 mentioned before, the server may enforce frequent authentication by
 returning an nfsace4 denying all access with every open delegation.

9.4.1. Open Delegation and Data Caching

 OPEN delegation allows much of the message overhead associated with
 the opening and closing files to be eliminated.  An open when an open
 delegation is in effect does not require that a validation message be
 sent to the server.  The continued endurance of the "read open
 delegation" provides a guarantee that no OPEN for write and thus no
 write has occurred.  Similarly, when closing a file opened for write
 and if write open delegation is in effect, the data written does not
 have to be flushed to the server until the open delegation is

Shepler, et al. Standards Track [Page 104] RFC 3530 NFS version 4 Protocol April 2003

 recalled.  The continued endurance of the open delegation provides a
 guarantee that no open and thus no read or write has been done by
 another client.
 For the purposes of open delegation, READs and WRITEs done without an
 OPEN are treated as the functional equivalents of a corresponding
 type of OPEN.  This refers to the READs and WRITEs that use the
 special stateids consisting of all zero bits or all one bits.
 Therefore, READs or WRITEs with a special stateid done by another
 client will force the server to recall a write open delegation.  A
 WRITE with a special stateid done by another client will force a
 recall of read open delegations.
 With delegations, a client is able to avoid writing data to the
 server when the CLOSE of a file is serviced.  The file close system
 call is the usual point at which the client is notified of a lack of
 stable storage for the modified file data generated by the
 application.  At the close, file data is written to the server and
 through normal accounting the server is able to determine if the
 available filesystem space for the data has been exceeded (i.e.,
 server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT).  This accounting
 includes quotas.  The introduction of delegations requires that a
 alternative method be in place for the same type of communication to
 occur between client and server.
 In the delegation response, the server provides either the limit of
 the size of the file or the number of modified blocks and associated
 block size.  The server must ensure that the client will be able to
 flush data to the server of a size equal to that provided in the
 original delegation.  The server must make this assurance for all
 outstanding delegations.  Therefore, the server must be careful in
 its management of available space for new or modified data taking
 into account available filesystem space and any applicable quotas.
 The server can recall delegations as a result of managing the
 available filesystem space.  The client should abide by the server's
 state space limits for delegations.  If the client exceeds the stated
 limits for the delegation, the server's behavior is undefined.
 Based on server conditions, quotas or available filesystem space, the
 server may grant write open delegations with very restrictive space
 limitations.  The limitations may be defined in a way that will
 always force modified data to be flushed to the server on close.
 With respect to authentication, flushing modified data to the server
 after a CLOSE has occurred may be problematic.  For example, the user
 of the application may have logged off the client and unexpired
 authentication credentials may not be present.  In this case, the
 client may need to take special care to ensure that local unexpired

Shepler, et al. Standards Track [Page 105] RFC 3530 NFS version 4 Protocol April 2003

 credentials will in fact be available.  This may be accomplished by
 tracking the expiration time of credentials and flushing data well in
 advance of their expiration or by making private copies of
 credentials to assure their availability when needed.

9.4.2. Open Delegation and File Locks

 When a client holds a write open delegation, lock operations may be
 performed locally.  This includes those required for mandatory file
 locking.  This can be done since the delegation implies that there
 can be no conflicting locks.  Similarly, all of the revalidations
 that would normally be associated with obtaining locks and the
 flushing of data associated with the releasing of locks need not be
 done.
 When a client holds a read open delegation, lock operations are not
 performed locally.  All lock operations, including those requesting
 non-exclusive locks, are sent to the server for resolution.

9.4.3. Handling of CB_GETATTR

 The server needs to employ special handling for a GETATTR where the
 target is a file that has a write open delegation in effect.  The
 reason for this is that the client holding the write delegation may
 have modified the data and the server needs to reflect this change to
 the second client that submitted the GETATTR.  Therefore, the client
 holding the write delegation needs to be interrogated.  The server
 will use the CB_GETATTR operation.  The only attributes that the
 server can reliably query via CB_GETATTR are size and change.
 Since CB_GETATTR is being used to satisfy another client's GETATTR
 request, the server only needs to know if the client holding the
 delegation has a modified version of the file.  If the client's copy
 of the delegated file is not modified (data or size), the server can
 satisfy the second client's GETATTR request from the attributes
 stored locally at the server.  If the file is modified, the server
 only needs to know about this modified state.  If the server
 determines that the file is currently modified, it will respond to
 the second client's GETATTR as if the file had been modified locally
 at the server.
 Since the form of the change attribute is determined by the server
 and is opaque to the client, the client and server need to agree on a
 method of communicating the modified state of the file.  For the size
 attribute, the client will report its current view of the file size.
 For the change attribute, the handling is more involved.

Shepler, et al. Standards Track [Page 106] RFC 3530 NFS version 4 Protocol April 2003

 For the client, the following steps will be taken when receiving a
 write delegation:
 o  The value of the change attribute will be obtained from the server
    and cached.  Let this value be represented by c.
 o  The client will create a value greater than c that will be used
    for communicating modified data is held at the client.  Let this
    value be represented by d.
 o  When the client is queried via CB_GETATTR for the change
    attribute, it checks to see if it holds modified data.  If the
    file is modified, the value d is returned for the change attribute
    value.  If this file is not currently modified, the client returns
    the value c for the change attribute.
 For simplicity of implementation, the client MAY for each CB_GETATTR
 return the same value d.  This is true even if, between successive
 CB_GETATTR operations, the client again modifies in the file's data
 or metadata in its cache.  The client can return the same value
 because the only requirement is that the client be able to indicate
 to the server that the client holds modified data.  Therefore, the
 value of d may always be c + 1.
 While the change attribute is opaque to the client in the sense that
 it has no idea what units of time, if any, the server is counting
 change with, it is not opaque in that the client has to treat it as
 an unsigned integer, and the server has to be able to see the results
 of the client's changes to that integer.  Therefore, the server MUST
 encode the change attribute in network order when sending it to the
 client.  The client MUST decode it from network order to its native
 order when receiving it and the client MUST encode it network order
 when sending it to the server.  For this reason, change is defined as
 an unsigned integer rather than an opaque array of octets.
 For the server, the following steps will be taken when providing a
 write delegation:
 o  Upon providing a write delegation, the server will cache a copy of
    the change attribute in the data structure it uses to record the
    delegation.  Let this value be represented by sc.
 o  When a second client sends a GETATTR operation on the same file to
    the server, the server obtains the change attribute from the first
    client.  Let this value be cc.

Shepler, et al. Standards Track [Page 107] RFC 3530 NFS version 4 Protocol April 2003

 o  If the value cc is equal to sc, the file is not modified and the
    server returns the current values for change, time_metadata, and
    time_modify (for example) to the second client.
 o  If the value cc is NOT equal to sc, the file is currently modified
    at the first client and most likely will be modified at the server
    at a future time.  The server then uses its current time to
    construct attribute values for time_metadata and time_modify.  A
    new value of sc, which we will call nsc, is computed by the
    server, such that nsc >= sc + 1.  The server then returns the
    constructed time_metadata, time_modify, and nsc values to the
    requester.  The server replaces sc in the delegation record with
    nsc.  To prevent the possibility of time_modify, time_metadata,
    and change from appearing to go backward (which would happen if
    the client holding the delegation fails to write its modified data
    to the server before the delegation is revoked or returned), the
    server SHOULD update the file's metadata record with the
    constructed attribute values.  For reasons of reasonable
    performance, committing the constructed attribute values to stable
    storage is OPTIONAL.
    As discussed earlier in this section, the client MAY return the
    same cc value on subsequent CB_GETATTR calls, even if the file was
    modified in the client's cache yet again between successive
    CB_GETATTR calls.  Therefore, the server must assume that the file
    has been modified yet again, and MUST take care to ensure that the
    new nsc it constructs and returns is greater than the previous nsc
    it returned.  An example implementation's delegation record would
    satisfy this mandate by including a boolean field (let us call it
    "modified") that is set to false when the delegation is granted,
    and an sc value set at the time of grant to the change attribute
    value.  The modified field would be set to true the first time cc
    != sc, and would stay true until the delegation is returned or
    revoked.  The processing for constructing nsc, time_modify, and
    time_metadata would use this pseudo code:
    if (!modified) {
        do CB_GETATTR for change and size;
           if (cc != sc)
               modified = TRUE;
       } else {
               do CB_GETATTR for size;
       }
       if (modified) {
           sc = sc + 1;
        time_modify = time_metadata = current_time;

Shepler, et al. Standards Track [Page 108] RFC 3530 NFS version 4 Protocol April 2003

        update sc, time_modify, time_metadata into file's metadata;
    }
    return to client (that sent GETATTR) the attributes
       it requested, but make sure size comes from what
       CB_GETATTR returned.  Do not update the file's metadata
       with the client's modified size.
 o  In the case that the file attribute size is different than the
    server's current value, the server treats this as a modification
    regardless of the value of the change attribute retrieved via
    CB_GETATTR and responds to the second client as in the last step.
 This methodology resolves issues of clock differences between client
 and server and other scenarios where the use of CB_GETATTR break
 down.
 It should be noted that the server is under no obligation to use
 CB_GETATTR and therefore the server MAY simply recall the delegation
 to avoid its use.

9.4.4. Recall of Open Delegation

 The following events necessitate recall of an open delegation:
 o  Potentially conflicting OPEN request (or READ/WRITE done with
    "special" stateid)
 o  SETATTR issued by another client
 o  REMOVE request for the file
 o  RENAME request for the file as either source or target of the
    RENAME
 Whether a RENAME of a directory in the path leading to the file
 results in recall of an open delegation depends on the semantics of
 the server filesystem.  If that filesystem denies such RENAMEs when a
 file is open, the recall must be performed to determine whether the
 file in question is, in fact, open.
 In addition to the situations above, the server may choose to recall
 open delegations at any time if resource constraints make it
 advisable to do so.  Clients should always be prepared for the
 possibility of recall.

Shepler, et al. Standards Track [Page 109] RFC 3530 NFS version 4 Protocol April 2003

 When a client receives a recall for an open delegation, it needs to
 update state on the server before returning the delegation.  These
 same updates must be done whenever a client chooses to return a
 delegation voluntarily.  The following items of state need to be
 dealt with:
 o  If the file associated with the delegation is no longer open and
    no previous CLOSE operation has been sent to the server, a CLOSE
    operation must be sent to the server.
 o  If a file has other open references at the client, then OPEN
    operations must be sent to the server.  The appropriate stateids
    will be provided by the server for subsequent use by the client
    since the delegation stateid will not longer be valid.  These OPEN
    requests are done with the claim type of CLAIM_DELEGATE_CUR.  This
    will allow the presentation of the delegation stateid so that the
    client can establish the appropriate rights to perform the OPEN.
    (see the section "Operation 18: OPEN" for details.)
 o  If there are granted file locks, the corresponding LOCK operations
    need to be performed.  This applies to the write open delegation
    case only.
 o  For a write open delegation, if at the time of recall the file is
    not open for write, all modified data for the file must be flushed
    to the server.  If the delegation had not existed, the client
    would have done this data flush before the CLOSE operation.
 o  For a write open delegation when a file is still open at the time
    of recall, any modified data for the file needs to be flushed to
    the server.
 o  With the write open delegation in place, it is possible that the
    file was truncated during the duration of the delegation.  For
    example, the truncation could have occurred as a result of an OPEN
    UNCHECKED with a size attribute value of zero.  Therefore, if a
    truncation of the file has occurred and this operation has not
    been propagated to the server, the truncation must occur before
    any modified data is written to the server.
 In the case of write open delegation, file locking imposes some
 additional requirements.  To precisely maintain the associated
 invariant, it is required to flush any modified data in any region
 for which a write lock was released while the write delegation was in
 effect.  However, because the write open delegation implies no other
 locking by other clients, a simpler implementation is to flush all
 modified data for the file (as described just above) if any write
 lock has been released while the write open delegation was in effect.

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 An implementation need not wait until delegation recall (or deciding
 to voluntarily return a delegation) to perform any of the above
 actions, if implementation considerations (e.g., resource
 availability constraints) make that desirable.  Generally, however,
 the fact that the actual open state of the file may continue to
 change makes it not worthwhile to send information about opens and
 closes to the server, except as part of delegation return.  Only in
 the case of closing the open that resulted in obtaining the
 delegation would clients be likely to do this early, since, in that
 case, the close once done will not be undone.  Regardless of the
 client's choices on scheduling these actions, all must be performed
 before the delegation is returned, including (when applicable) the
 close that corresponds to the open that resulted in the delegation.
 These actions can be performed either in previous requests or in
 previous operations in the same COMPOUND request.

9.4.5. Clients that Fail to Honor Delegation Recalls

 A client may fail to respond to a recall for various reasons, such as
 a failure of the callback path from server to the client.  The client
 may be unaware of a failure in the callback path.  This lack of
 awareness could result in the client finding out long after the
 failure that its delegation has been revoked, and another client has
 modified the data for which the client had a delegation.  This is
 especially a problem for the client that held a write delegation.
 The server also has a dilemma in that the client that fails to
 respond to the recall might also be sending other NFS requests,
 including those that renew the lease before the lease expires.
 Without returning an error for those lease renewing operations, the
 server leads the client to believe that the delegation it has is in
 force.
 This difficulty is solved by the following rules:
 o  When the callback path is down, the server MUST NOT revoke the
    delegation if one of the following occurs:
  1. The client has issued a RENEW operation and the server has

returned an NFS4ERR_CB_PATH_DOWN error. The server MUST renew

       the lease for any record locks and share reservations the
       client has that the server has known about (as opposed to those
       locks and share reservations the client has established but not
       yet sent to the server, due to the delegation).  The server
       SHOULD give the client a reasonable time to return its
       delegations to the server before revoking the client's
       delegations.

Shepler, et al. Standards Track [Page 111] RFC 3530 NFS version 4 Protocol April 2003

  1. The client has not issued a RENEW operation for some period of

time after the server attempted to recall the delegation. This

       period of time MUST NOT be less than the value of the
       lease_time attribute.
 o  When the client holds a delegation, it can not rely on operations,
    except for RENEW, that take a stateid, to renew delegation leases
    across callback path failures.  The client that wants to keep
    delegations in force across callback path failures must use RENEW
    to do so.

9.4.6. Delegation Revocation

 At the point a delegation is revoked, if there are associated opens
 on the client, the applications holding these opens need to be
 notified.  This notification usually occurs by returning errors for
 READ/WRITE operations or when a close is attempted for the open file.
 If no opens exist for the file at the point the delegation is
 revoked, then notification of the revocation is unnecessary.
 However, if there is modified data present at the client for the
 file, the user of the application should be notified.  Unfortunately,
 it may not be possible to notify the user since active applications
 may not be present at the client.  See the section "Revocation
 Recovery for Write Open Delegation" for additional details.

9.5. Data Caching and Revocation

 When locks and delegations are revoked, the assumptions upon which
 successful caching depend are no longer guaranteed.  For any locks or
 share reservations that have been revoked, the corresponding owner
 needs to be notified.  This notification includes applications with a
 file open that has a corresponding delegation which has been revoked.
 Cached data associated with the revocation must be removed from the
 client.  In the case of modified data existing in the client's cache,
 that data must be removed from the client without it being written to
 the server.  As mentioned, the assumptions made by the client are no
 longer valid at the point when a lock or delegation has been revoked.
 For example, another client may have been granted a conflicting lock
 after the revocation of the lock at the first client.  Therefore, the
 data within the lock range may have been modified by the other
 client.  Obviously, the first client is unable to guarantee to the
 application what has occurred to the file in the case of revocation.
 Notification to a lock owner will in many cases consist of simply
 returning an error on the next and all subsequent READs/WRITEs to the
 open file or on the close.  Where the methods available to a client
 make such notification impossible because errors for certain

Shepler, et al. Standards Track [Page 112] RFC 3530 NFS version 4 Protocol April 2003

 operations may not be returned, more drastic action such as signals
 or process termination may be appropriate.  The justification for
 this is that an invariant for which an application depends on may be
 violated.  Depending on how errors are typically treated for the
 client operating environment, further levels of notification
 including logging, console messages, and GUI pop-ups may be
 appropriate.

9.5.1. Revocation Recovery for Write Open Delegation

 Revocation recovery for a write open delegation poses the special
 issue of modified data in the client cache while the file is not
 open.  In this situation, any client which does not flush modified
 data to the server on each close must ensure that the user receives
 appropriate notification of the failure as a result of the
 revocation.  Since such situations may require human action to
 correct problems, notification schemes in which the appropriate user
 or administrator is notified may be necessary.  Logging and console
 messages are typical examples.
 If there is modified data on the client, it must not be flushed
 normally to the server.  A client may attempt to provide a copy of
 the file data as modified during the delegation under a different
 name in the filesystem name space to ease recovery.  Note that when
 the client can determine that the file has not been modified by any
 other client, or when the client has a complete cached copy of file
 in question, such a saved copy of the client's view of the file may
 be of particular value for recovery.  In other case, recovery using a
 copy of the file based partially on the client's cached data and
 partially on the server copy as modified by other clients, will be
 anything but straightforward, so clients may avoid saving file
 contents in these situations or mark the results specially to warn
 users of possible problems.
 Saving of such modified data in delegation revocation situations may
 be limited to files of a certain size or might be used only when
 sufficient disk space is available within the target filesystem.
 Such saving may also be restricted to situations when the client has
 sufficient buffering resources to keep the cached copy available
 until it is properly stored to the target filesystem.

9.6. Attribute Caching

 The attributes discussed in this section do not include named
 attributes.  Individual named attributes are analogous to files and
 caching of the data for these needs to be handled just as data

Shepler, et al. Standards Track [Page 113] RFC 3530 NFS version 4 Protocol April 2003

 caching is for ordinary files.  Similarly, LOOKUP results from an
 OPENATTR directory are to be cached on the same basis as any other
 pathnames and similarly for directory contents.
 Clients may cache file attributes obtained from the server and use
 them to avoid subsequent GETATTR requests.  Such caching is write
 through in that modification to file attributes is always done by
 means of requests to the server and should not be done locally and
 cached.  The exception to this are modifications to attributes that
 are intimately connected with data caching.  Therefore, extending a
 file by writing data to the local data cache is reflected immediately
 in the size as seen on the client without this change being
 immediately reflected on the server.  Normally such changes are not
 propagated directly to the server but when the modified data is
 flushed to the server, analogous attribute changes are made on the
 server.  When open delegation is in effect, the modified attributes
 may be returned to the server in the response to a CB_RECALL call.
 The result of local caching of attributes is that the attribute
 caches maintained on individual clients will not be coherent.
 Changes made in one order on the server may be seen in a different
 order on one client and in a third order on a different client.
 The typical filesystem application programming interfaces do not
 provide means to atomically modify or interrogate attributes for
 multiple files at the same time.  The following rules provide an
 environment where the potential incoherences mentioned above can be
 reasonably managed.  These rules are derived from the practice of
 previous NFS protocols.
 o  All attributes for a given file (per-fsid attributes excepted) are
    cached as a unit at the client so that no non-serializability can
    arise within the context of a single file.
 o  An upper time boundary is maintained on how long a client cache
    entry can be kept without being refreshed from the server.
 o  When operations are performed that change attributes at the
    server, the updated attribute set is requested as part of the
    containing RPC.  This includes directory operations that update
    attributes indirectly.  This is accomplished by following the
    modifying operation with a GETATTR operation and then using the
    results of the GETATTR to update the client's cached attributes.
 Note that if the full set of attributes to be cached is requested by
 READDIR, the results can be cached by the client on the same basis as
 attributes obtained via GETATTR.

Shepler, et al. Standards Track [Page 114] RFC 3530 NFS version 4 Protocol April 2003

 A client may validate its cached version of attributes for a file by
 fetching just both the change and time_access attributes and assuming
 that if the change attribute has the same value as it did when the
 attributes were cached, then no attributes other than time_access
 have changed.  The reason why time_access is also fetched is because
 many servers operate in environments where the operation that updates
 change does not update time_access.  For example, POSIX file
 semantics do not update access time when a file is modified by the
 write system call.  Therefore, the client that wants a current
 time_access value should fetch it with change during the attribute
 cache validation processing and update its cached time_access.
 The client may maintain a cache of modified attributes for those
 attributes intimately connected with data of modified regular files
 (size, time_modify, and change).  Other than those three attributes,
 the client MUST NOT maintain a cache of modified attributes.
 Instead, attribute changes are immediately sent to the server.
 In some operating environments, the equivalent to time_access is
 expected to be implicitly updated by each read of the content of the
 file object.  If an NFS client is caching the content of a file
 object, whether it is a regular file, directory, or symbolic link,
 the client SHOULD NOT update the time_access attribute (via SETATTR
 or a small READ or READDIR request) on the server with each read that
 is satisfied from cache.  The reason is that this can defeat the
 performance benefits of caching content, especially since an explicit
 SETATTR of time_access may alter the change attribute on the server.
 If the change attribute changes, clients that are caching the content
 will think the content has changed, and will re-read unmodified data
 from the server.  Nor is the client encouraged to maintain a modified
 version of time_access in its cache, since this would mean that the
 client will either eventually have to write the access time to the
 server with bad performance effects, or it would never update the
 server's time_access, thereby resulting in a situation where an
 application that caches access time between a close and open of the
 same file observes the access time oscillating between the past and
 present.  The time_access attribute always means the time of last
 access to a file by a read that was satisfied by the server.  This
 way clients will tend to see only time_access changes that go forward
 in time.

9.7. Data and Metadata Caching and Memory Mapped Files

 Some operating environments include the capability for an application
 to map a file's content into the application's address space.  Each
 time the application accesses a memory location that corresponds to a
 block that has not been loaded into the address space, a page fault
 occurs and the file is read (or if the block does not exist in the

Shepler, et al. Standards Track [Page 115] RFC 3530 NFS version 4 Protocol April 2003

 file, the block is allocated and then instantiated in the
 application's address space).
 As long as each memory mapped access to the file requires a page
 fault, the relevant attributes of the file that are used to detect
 access and modification (time_access, time_metadata, time_modify, and
 change) will be updated.  However, in many operating environments,
 when page faults are not required these attributes will not be
 updated on reads or updates to the file via memory access (regardless
 whether the file is local file or is being access remotely).  A
 client or server MAY fail to update attributes of a file that is
 being accessed via memory mapped I/O.  This has several implications:
 o  If there is an application on the server that has memory mapped a
    file that a client is also accessing, the client may not be able
    to get a consistent value of the change attribute to determine
    whether its cache is stale or not.  A server that knows that the
    file is memory mapped could always pessimistically return updated
    values for change so as to force the application to always get the
    most up to date data and metadata for the file.  However, due to
    the negative performance implications of this, such behavior is
    OPTIONAL.
 o  If the memory mapped file is not being modified on the server, and
    instead is just being read by an application via the memory mapped
    interface, the client will not see an updated time_access
    attribute.  However, in many operating environments, neither will
    any process running on the server.  Thus NFS clients are at no
    disadvantage with respect to local processes.
 o  If there is another client that is memory mapping the file, and if
    that client is holding a write delegation, the same set of issues
    as discussed in the previous two bullet items apply.  So, when a
    server does a CB_GETATTR to a file that the client has modified in
    its cache, the response from CB_GETATTR will not necessarily be
    accurate.  As discussed earlier, the client's obligation is to
    report that the file has been modified since the delegation was
    granted, not whether it has been modified again between successive
    CB_GETATTR calls, and the server MUST assume that any file the
    client has modified in cache has been modified again between
    successive CB_GETATTR calls.  Depending on the nature of the
    client's memory management system, this weak obligation may not be
    possible.  A client MAY return stale information in CB_GETATTR
    whenever the file is memory mapped.
 o  The mixture of memory mapping and file locking on the same file is
    problematic.  Consider the following scenario, where the page size
    on each client is 8192 bytes.

Shepler, et al. Standards Track [Page 116] RFC 3530 NFS version 4 Protocol April 2003

  1. Client A memory maps first page (8192 bytes) of file X
  1. Client B memory maps first page (8192 bytes) of file X
  1. Client A write locks first 4096 bytes
  1. Client B write locks second 4096 bytes
  1. Client A, via a STORE instruction modifies part of its locked

region.

  1. Simultaneous to client A, client B issues a STORE on part of

its locked region.

 Here the challenge is for each client to resynchronize to get a
 correct view of the first page.  In many operating environments, the
 virtual memory management systems on each client only know a page is
 modified, not that a subset of the page corresponding to the
 respective lock regions has been modified.  So it is not possible for
 each client to do the right thing, which is to only write to the
 server that portion of the page that is locked. For example, if
 client A simply writes out the page, and then client B writes out the
 page, client A's data is lost.
 Moreover, if mandatory locking is enabled on the file, then we have a
 different problem.  When clients A and B issue the STORE
 instructions, the resulting page faults require a record lock on the
 entire page.  Each client then tries to extend their locked range to
 the entire page, which results in a deadlock.
 Communicating the NFS4ERR_DEADLOCK error to a STORE instruction is
 difficult at best.
 If a client is locking the entire memory mapped file, there is no
 problem with advisory or mandatory record locking, at least until the
 client unlocks a region in the middle of the file.
 Given the above issues the following are permitted:
  1. Clients and servers MAY deny memory mapping a file they know there

are record locks for.

  1. Clients and servers MAY deny a record lock on a file they know is

memory mapped.

Shepler, et al. Standards Track [Page 117] RFC 3530 NFS version 4 Protocol April 2003

  1. A client MAY deny memory mapping a file that it knows requires

mandatory locking for I/O. If mandatory locking is enabled after

    the file is opened and mapped, the client MAY deny the application
    further access to its mapped file.

9.8. Name Caching

 The results of LOOKUP and READDIR operations may be cached to avoid
 the cost of subsequent LOOKUP operations.  Just as in the case of
 attribute caching, inconsistencies may arise among the various client
 caches.  To mitigate the effects of these inconsistencies and given
 the context of typical filesystem APIs, an upper time boundary is
 maintained on how long a client name cache entry can be kept without
 verifying that the entry has not been made invalid by a directory
 change operation performed by another client.
 When a client is not making changes to a directory for which there
 exist name cache entries, the client needs to periodically fetch
 attributes for that directory to ensure that it is not being
 modified.  After determining that no modification has occurred, the
 expiration time for the associated name cache entries may be updated
 to be the current time plus the name cache staleness bound.
 When a client is making changes to a given directory, it needs to
 determine whether there have been changes made to the directory by
 other clients.  It does this by using the change attribute as
 reported before and after the directory operation in the associated
 change_info4 value returned for the operation.  The server is able to
 communicate to the client whether the change_info4 data is provided
 atomically with respect to the directory operation.  If the change
 values are provided atomically, the client is then able to compare
 the pre-operation change value with the change value in the client's
 name cache.  If the comparison indicates that the directory was
 updated by another client, the name cache associated with the
 modified directory is purged from the client.  If the comparison
 indicates no modification, the name cache can be updated on the
 client to reflect the directory operation and the associated timeout
 extended.  The post-operation change value needs to be saved as the
 basis for future change_info4 comparisons.
 As demonstrated by the scenario above, name caching requires that the
 client revalidate name cache data by inspecting the change attribute
 of a directory at the point when the name cache item was cached.
 This requires that the server update the change attribute for
 directories when the contents of the corresponding directory is
 modified.  For a client to use the change_info4 information
 appropriately and correctly, the server must report the pre and post
 operation change attribute values atomically.  When the server is

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 unable to report the before and after values atomically with respect
 to the directory operation, the server must indicate that fact in the
 change_info4 return value.  When the information is not atomically
 reported, the client should not assume that other clients have not
 changed the directory.

9.9. Directory Caching

 The results of READDIR operations may be used to avoid subsequent
 READDIR operations.  Just as in the cases of attribute and name
 caching, inconsistencies may arise among the various client caches.
 To mitigate the effects of these inconsistencies, and given the
 context of typical filesystem APIs, the following rules should be
 followed:
 o  Cached READDIR information for a directory which is not obtained
    in a single READDIR operation must always be a consistent snapshot
    of directory contents.  This is determined by using a GETATTR
    before the first READDIR and after the last of READDIR that
    contributes to the cache.
 o  An upper time boundary is maintained to indicate the length of
    time a directory cache entry is considered valid before the client
    must revalidate the cached information.
 The revalidation technique parallels that discussed in the case of
 name caching.  When the client is not changing the directory in
 question, checking the change attribute of the directory with GETATTR
 is adequate.  The lifetime of the cache entry can be extended at
 these checkpoints.  When a client is modifying the directory, the
 client needs to use the change_info4 data to determine whether there
 are other clients modifying the directory.  If it is determined that
 no other client modifications are occurring, the client may update
 its directory cache to reflect its own changes.
 As demonstrated previously, directory caching requires that the
 client revalidate directory cache data by inspecting the change
 attribute of a directory at the point when the directory was cached.
 This requires that the server update the change attribute for
 directories when the contents of the corresponding directory is
 modified.  For a client to use the change_info4 information
 appropriately and correctly, the server must report the pre and post
 operation change attribute values atomically.  When the server is
 unable to report the before and after values atomically with respect
 to the directory operation, the server must indicate that fact in the
 change_info4 return value.  When the information is not atomically
 reported, the client should not assume that other clients have not
 changed the directory.

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10. Minor Versioning

 To address the requirement of an NFS protocol that can evolve as the
 need arises, the NFS version 4 protocol contains the rules and
 framework to allow for future minor changes or versioning.
 The base assumption with respect to minor versioning is that any
 future accepted minor version must follow the IETF process and be
 documented in a standards track RFC.  Therefore, each minor version
 number will correspond to an RFC.  Minor version zero of the NFS
 version 4 protocol is represented by this RFC.  The COMPOUND
 procedure will support the encoding of the minor version being
 requested by the client.
 The following items represent the basic rules for the development of
 minor versions.  Note that a future minor version may decide to
 modify or add to the following rules as part of the minor version
 definition.
  1.  Procedures are not added or deleted
      To maintain the general RPC model, NFS version 4 minor versions
      will not add to or delete procedures from the NFS program.
  2.  Minor versions may add operations to the COMPOUND and
      CB_COMPOUND procedures.
      The addition of operations to the COMPOUND and CB_COMPOUND
      procedures does not affect the RPC model.
  2.1 Minor versions may append attributes to GETATTR4args, bitmap4,
      and GETATTR4res.
      This allows for the expansion of the attribute model to allow
      for future growth or adaptation.
  2.2 Minor version X must append any new attributes after the last
      documented attribute.
      Since attribute results are specified as an opaque array of
      per-attribute XDR encoded results, the complexity of adding new
      attributes in the midst of the current definitions will be too
      burdensome.
  3.  Minor versions must not modify the structure of an existing
      operation's arguments or results.

Shepler, et al. Standards Track [Page 120] RFC 3530 NFS version 4 Protocol April 2003

      Again the complexity of handling multiple structure definitions
      for a single operation is too burdensome.  New operations should
      be added instead of modifying existing structures for a minor
      version.
      This rule does not preclude the following adaptations in a minor
      version.
    o  adding bits to flag fields such as new attributes to GETATTR's
       bitmap4 data type
    o  adding bits to existing attributes like ACLs that have flag
       words
    o  extending enumerated types (including NFS4ERR_*) with new
       values
  4.  Minor versions may not modify the structure of existing
      attributes.
  5.  Minor versions may not delete operations.
      This prevents the potential reuse of a particular operation
      "slot" in a future minor version.
  6.  Minor versions may not delete attributes.
  7.  Minor versions may not delete flag bits or enumeration values.
  8.  Minor versions may declare an operation as mandatory to NOT
      implement.
      Specifying an operation as "mandatory to not implement" is
      equivalent to obsoleting an operation.  For the client, it means
      that the operation should not be sent to the server.  For the
      server, an NFS error can be returned as opposed to "dropping"
      the request as an XDR decode error.  This approach allows for
      the obsolescence of an operation while maintaining its structure
      so that a future minor version can reintroduce the operation.
  8.1 Minor versions may declare attributes mandatory to NOT
      implement.
  8.2 Minor versions may declare flag bits or enumeration values as
      mandatory to NOT implement.
  9.  Minor versions may downgrade features from mandatory to
      recommended, or recommended to optional.

Shepler, et al. Standards Track [Page 121] RFC 3530 NFS version 4 Protocol April 2003

  10. Minor versions may upgrade features from optional to recommended
      or recommended to mandatory.
  11. A client and server that support minor version X must support
      minor versions 0 (zero) through X-1 as well.
  12. No new features may be introduced as mandatory in a minor
      version.
      This rule allows for the introduction of new functionality and
      forces the use of implementation experience before designating a
      feature as mandatory.
  13. A client MUST NOT attempt to use a stateid, filehandle, or
      similar returned object from the COMPOUND procedure with minor
      version X for another COMPOUND procedure with minor version Y,
      where X != Y.

11. Internationalization

 The primary issue in which NFS version 4 needs to deal with
 internationalization, or I18N, is with respect to file names and
 other strings as used within the protocol.  The choice of string
 representation must allow reasonable name/string access to clients
 which use various languages.  The UTF-8 encoding of the UCS as
 defined by [ISO10646] allows for this type of access and follows the
 policy described in "IETF Policy on Character Sets and Languages",
 [RFC2277].
 [RFC3454], otherwise know as "stringprep", documents a framework for
 using Unicode/UTF-8 in networking protocols, so as "to increase the
 likelihood that string input and string comparison work in ways that
 make sense for typical users throughout the world."  A protocol must
 define a profile of stringprep "in order to fully specify the
 processing options."  The remainder of this Internationalization
 section defines the NFS version 4 stringprep profiles.  Much of
 terminology used for the remainder of this section comes from
 stringprep.
 There are three UTF-8 string types defined for NFS version 4:
 utf8str_cs, utf8str_cis, and utf8str_mixed.  Separate profiles are
 defined for each. Each profile defines the following, as required by
 stringprep:
 o  The intended applicability of the profile

Shepler, et al. Standards Track [Page 122] RFC 3530 NFS version 4 Protocol April 2003

 o  The character repertoire that is the input and output to
    stringprep (which is Unicode 3.2 for referenced version of
    stringprep)
 o  The mapping tables from stringprep used (as described in section 3
    of stringprep)
 o  Any additional mapping tables specific to the profile
 o  The Unicode normalization used, if any (as described in section 4
    of stringprep)
 o  The tables from stringprep listing of characters that are
    prohibited as output (as described in section 5 of stringprep)
 o  The bidirectional string testing used, if any (as described in
    section 6 of stringprep)
 o  Any additional characters that are prohibited as output specific
    to the profile
 Stringprep discusses Unicode characters, whereas NFS version 4
 renders UTF-8 characters.  Since there is a one to one mapping from
 UTF-8 to Unicode, where ever the remainder of this document refers to
 to Unicode, the reader should assume UTF-8.
 Much of the text for the profiles comes from [RFC3454].

11.1. Stringprep profile for the utf8str_cs type

 Every use of the utf8str_cs type definition in the NFS version 4
 protocol specification follows the profile named nfs4_cs_prep.

11.1.1. Intended applicability of the nfs4_cs_prep profile

 The utf8str_cs type is a case sensitive string of UTF-8 characters.
 Its primary use in NFS Version 4 is for naming components and
 pathnames.  Components and pathnames are stored on the server's
 filesystem.  Two valid distinct UTF-8 strings might be the same after
 processing via the utf8str_cs profile.  If the strings are two names
 inside a directory, the NFS version 4 server will need to either:
 o  disallow the creation of a second name if it's post processed form
    collides with that of an existing name, or
 o  allow the creation of the second name, but arrange so that after
    post processing, the second name is different than the post
    processed form of the first name.

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11.1.2. Character repertoire of nfs4_cs_prep

 The nfs4_cs_prep profile uses Unicode 3.2, as defined in stringprep's
 Appendix A.1

11.1.3. Mapping used by nfs4_cs_prep

 The nfs4_cs_prep profile specifies mapping using the following tables
 from stringprep:
    Table B.1
 Table B.2 is normally not part of the nfs4_cs_prep profile as it is
 primarily for dealing with case-insensitive comparisons.  However, if
 the NFS version 4 file server supports the case_insensitive
 filesystem attribute, and if case_insensitive is true, the NFS
 version 4 server MUST use Table B.2 (in addition to Table B1) when
 processing utf8str_cs strings, and the NFS version 4 client MUST
 assume Table B.2 (in addition to Table B.1) are being used.
 If the case_preserving attribute is present and set to false, then
 the NFS version 4 server MUST use table B.2 to map case when
 processing utf8str_cs strings.  Whether the server maps from lower to
 upper case or the upper to lower case is an implementation
 dependency.

11.1.4. Normalization used by nfs4_cs_prep

 The nfs4_cs_prep profile does not specify a normalization form.  A
 later revision of this specification may specify a particular
 normalization form.  Therefore, the server and client can expect that
 they may receive unnormalized characters within protocol requests and
 responses.  If the operating environment requires normalization, then
 the implementation must normalize utf8str_cs strings within the
 protocol before presenting the information to an application (at the
 client) or local filesystem (at the server).

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11.1.5. Prohibited output for nfs4_cs_prep

 The nfs4_cs_prep profile specifies prohibiting using the following
 tables from stringprep:
    Table C.3
    Table C.4
    Table C.5
    Table C.6
    Table C.7
    Table C.8
    Table C.9

11.1.6. Bidirectional output for nfs4_cs_prep

 The nfs4_cs_prep profile does not specify any checking of
 bidirectional strings.

11.2. Stringprep profile for the utf8str_cis type

 Every use of the utf8str_cis type definition in the NFS version 4
 protocol specification follows the profile named nfs4_cis_prep.

11.2.1. Intended applicability of the nfs4_cis_prep profile

 The utf8str_cis type is a case insensitive string of UTF-8
 characters.  Its primary use in NFS Version 4 is for naming NFS
 servers.

11.2.2. Character repertoire of nfs4_cis_prep

 The nfs4_cis_prep profile uses Unicode 3.2, as defined in
 stringprep's Appendix A.1

11.2.3. Mapping used by nfs4_cis_prep

 The nfs4_cis_prep profile specifies mapping using the following
 tables from stringprep:
    Table B.1
    Table B.2

11.2.4. Normalization used by nfs4_cis_prep

 The nfs4_cis_prep profile specifies using Unicode normalization form
 KC, as described in stringprep.

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11.2.5. Prohibited output for nfs4_cis_prep

 The nfs4_cis_prep profile specifies prohibiting using the following
 tables from stringprep:
    Table C.1.2
    Table C.2.2
    Table C.3
    Table C.4
    Table C.5
    Table C.6
    Table C.7
    Table C.8
    Table C.9

11.2.6. Bidirectional output for nfs4_cis_prep

 The nfs4_cis_prep profile specifies checking bidirectional strings as
 described in stringprep's section 6.

11.3. Stringprep profile for the utf8str_mixed type

 Every use of the utf8str_mixed type definition in the NFS version 4
 protocol specification follows the profile named nfs4_mixed_prep.

11.3.1. Intended applicability of the nfs4_mixed_prep profile

 The utf8str_mixed type is a string of UTF-8 characters, with a prefix
 that is case sensitive, a separator equal to '@', and a suffix that
 is fully qualified domain name.  Its primary use in NFS Version 4 is
 for naming principals identified in an Access Control Entry.

11.3.2. Character repertoire of nfs4_mixed_prep

 The nfs4_mixed_prep profile uses Unicode 3.2, as defined in
 stringprep's Appendix A.1

11.3.3. Mapping used by nfs4_cis_prep

 For the prefix and the separator of a utf8str_mixed string, the
 nfs4_mixed_prep profile specifies mapping using the following table
 from stringprep:
    Table B.1
 For the suffix of a utf8str_mixed string, the nfs4_mixed_prep profile
 specifies mapping using the following tables from stringprep:

Shepler, et al. Standards Track [Page 126] RFC 3530 NFS version 4 Protocol April 2003

    Table B.1
    Table B.2

11.3.4. Normalization used by nfs4_mixed_prep

 The nfs4_mixed_prep profile specifies using Unicode normalization
 form KC, as described in stringprep.

11.3.5. Prohibited output for nfs4_mixed_prep

 The nfs4_mixed_prep profile specifies prohibiting using the following
 tables from stringprep:
    Table C.1.2
    Table C.2.2
    Table C.3
    Table C.4
    Table C.5
    Table C.6
    Table C.7
    Table C.8
    Table C.9

11.3.6. Bidirectional output for nfs4_mixed_prep

 The nfs4_mixed_prep profile specifies checking bidirectional strings
 as described in stringprep's section 6.

11.4. UTF-8 Related Errors

 Where the client sends an invalid UTF-8 string, the server should
 return an NFS4ERR_INVAL error.  This includes cases in which
 inappropriate prefixes are detected and where the count includes
 trailing bytes that do not constitute a full UCS character.
 Where the client supplied string is valid UTF-8 but contains
 characters that are not supported by the server as a value for that
 string (e.g., names containing characters that have more than two
 octets on a filesystem that supports Unicode characters only), the
 server should return an NFS4ERR_BADCHAR error.
 Where a UTF-8 string is used as a file name, and the filesystem,
 while supporting all of the characters within the name, does not
 allow that particular name to be used, the server should return the
 error NFS4ERR_BADNAME.  This includes situations in which the server
 filesystem imposes a normalization constraint on name strings, but

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 will also include such situations as filesystem prohibitions of "."
 and ".." as file names for certain operations, and other such
 constraints.

12. Error Definitions

 NFS error numbers are assigned to failed operations within a compound
 request.  A compound request contains a number of NFS operations that
 have their results encoded in sequence in a compound reply.  The
 results of successful operations will consist of an NFS4_OK status
 followed by the encoded results of the operation.  If an NFS
 operation fails, an error status will be entered in the reply and the
 compound request will be terminated.
 A description of each defined error follows:
 NFS4_OK               Indicates the operation completed successfully.
 NFS4ERR_ACCESS        Permission denied. The caller does not have the
                       correct permission to perform the requested
                       operation. Contrast this with NFS4ERR_PERM,
                       which restricts itself to owner or privileged
                       user permission failures.
 NFS4ERR_ATTRNOTSUPP   An attribute specified is not supported by the
                       server.  Does not apply to the GETATTR
                       operation.
 NFS4ERR_ADMIN_REVOKED Due to administrator intervention, the
                       lockowner's record locks, share reservations,
                       and delegations have been revoked by the
                       server.
 NFS4ERR_BADCHAR       A UTF-8 string contains a character which is
                       not supported by the server in the context in
                       which it being used.
 NFS4ERR_BAD_COOKIE    READDIR cookie is stale.
 NFS4ERR_BADHANDLE     Illegal NFS filehandle. The filehandle failed
                       internal consistency checks.
 NFS4ERR_BADNAME       A name string in a request consists of valid
                       UTF-8 characters supported by the server but
                       the name is not supported by the server as a
                       valid name for current operation.

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 NFS4ERR_BADOWNER      An owner, owner_group, or ACL attribute value
                       can not be translated to local representation.
 NFS4ERR_BADTYPE       An attempt was made to create an object of a
                       type not supported by the server.
 NFS4ERR_BAD_RANGE     The range for a LOCK, LOCKT, or LOCKU operation
                       is not appropriate to the allowable range of
                       offsets for the server.
 NFS4ERR_BAD_SEQID     The sequence number in a locking request is
                       neither the next expected number or the last
                       number processed.
 NFS4ERR_BAD_STATEID   A stateid generated by the current server
                       instance, but which does not designate any
                       locking state (either current or superseded)
                       for a current lockowner-file pair, was used.
 NFS4ERR_BADXDR        The server encountered an XDR decoding error
                       while processing an operation.
 NFS4ERR_CLID_INUSE    The SETCLIENTID operation has found that a
                       client id is already in use by another client.
 NFS4ERR_DEADLOCK      The server has been able to determine a file
                       locking deadlock condition for a blocking lock
                       request.
 NFS4ERR_DELAY         The server initiated the request, but was not
                       able to complete it in a timely fashion. The
                       client should wait and then try the request
                       with a new RPC transaction ID.  For example,
                       this error should be returned from a server
                       that supports hierarchical storage and receives
                       a request to process a file that has been
                       migrated. In this case, the server should start
                       the immigration process and respond to client
                       with this error.  This error may also occur
                       when a necessary delegation recall makes
                       processing a request in a timely fashion
                       impossible.
 NFS4ERR_DENIED        An attempt to lock a file is denied.  Since
                       this may be a temporary condition, the client
                       is encouraged to retry the lock request until
                       the lock is accepted.

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 NFS4ERR_DQUOT         Resource (quota) hard limit exceeded. The
                       user's resource limit on the server has been
                       exceeded.
 NFS4ERR_EXIST         File exists. The file specified already exists.
 NFS4ERR_EXPIRED       A lease has expired that is being used in the
                       current operation.
 NFS4ERR_FBIG          File too large. The operation would have caused
                       a file to grow beyond the server's limit.
 NFS4ERR_FHEXPIRED     The filehandle provided is volatile and has
                       expired at the server.
 NFS4ERR_FILE_OPEN     The operation can not be successfully processed
                       because a file involved in the operation is
                       currently open.
 NFS4ERR_GRACE         The server is in its recovery or grace period
                       which should match the lease period of the
                       server.
 NFS4ERR_INVAL         Invalid argument or unsupported argument for an
                       operation. Two examples are attempting a
                       READLINK on an object other than a symbolic
                       link or specifying a value for an enum field
                       that is not defined in the protocol (e.g.,
                       nfs_ftype4).
 NFS4ERR_IO            I/O error. A hard error (for example, a disk
                       error) occurred while processing the requested
                       operation.
 NFS4ERR_ISDIR         Is a directory. The caller specified a
                       directory in a non-directory operation.
 NFS4ERR_LEASE_MOVED   A lease being renewed is associated with a
                       filesystem that has been migrated to a new
                       server.
 NFS4ERR_LOCKED        A read or write operation was attempted on a
                       locked file.
 NFS4ERR_LOCK_NOTSUPP  Server does not support atomic upgrade or
                       downgrade of locks.

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 NFS4ERR_LOCK_RANGE    A lock request is operating on a sub-range of a
                       current lock for the lock owner and the server
                       does not support this type of request.
 NFS4ERR_LOCKS_HELD    A CLOSE was attempted and file locks would
                       exist after the CLOSE.
 NFS4ERR_MINOR_VERS_MISMATCH
                       The server has received a request that
                       specifies an unsupported minor version.  The
                       server must return a COMPOUND4res with a zero
                       length operations result array.
 NFS4ERR_MLINK         Too many hard links.
 NFS4ERR_MOVED         The filesystem which contains the current
                       filehandle object has been relocated or
                       migrated to another server.  The client may
                       obtain the new filesystem location by obtaining
                       the "fs_locations" attribute for the current
                       filehandle.  For further discussion, refer to
                       the section "Filesystem Migration or
                       Relocation".
 NFS4ERR_NAMETOOLONG   The filename in an operation was too long.
 NFS4ERR_NOENT         No such file or directory. The file or
                       directory name specified does not exist.
 NFS4ERR_NOFILEHANDLE  The logical current filehandle value (or, in
                       the case of RESTOREFH, the saved filehandle
                       value) has not been set properly.  This may be
                       a result of a malformed COMPOUND operation
                       (i.e., no PUTFH or PUTROOTFH before an
                       operation that requires the current filehandle
                       be set).
 NFS4ERR_NO_GRACE      A reclaim of client state has fallen outside of
                       the grace period of the server.  As a result,
                       the server can not guarantee that conflicting
                       state has not been provided to another client.
 NFS4ERR_NOSPC         No space left on device. The operation would
                       have caused the server's filesystem to exceed
                       its limit.
 NFS4ERR_NOTDIR        Not a directory. The caller specified a non-
                       directory in a directory operation.

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 NFS4ERR_NOTEMPTY      An attempt was made to remove a directory that
                       was not empty.
 NFS4ERR_NOTSUPP       Operation is not supported.
 NFS4ERR_NOT_SAME      This error is returned by the VERIFY operation
                       to signify that the attributes compared were
                       not the same as provided in the client's
                       request.
 NFS4ERR_NXIO          I/O error. No such device or address.
 NFS4ERR_OLD_STATEID   A stateid which designates the locking state
                       for a lockowner-file at an earlier time was
                       used.
 NFS4ERR_OPENMODE      The client attempted a READ, WRITE, LOCK or
                       SETATTR operation not sanctioned by the stateid
                       passed (e.g., writing to a file opened only for
                       read).
 NFS4ERR_OP_ILLEGAL    An illegal operation value has been specified
                       in the argop field of a COMPOUND or CB_COMPOUND
                       procedure.
 NFS4ERR_PERM          Not owner. The operation was not allowed
                       because the caller is either not a privileged
                       user (root) or not the owner of the target of
                       the operation.
 NFS4ERR_RECLAIM_BAD   The reclaim provided by the client does not
                       match any of the server's state consistency
                       checks and is bad.
 NFS4ERR_RECLAIM_CONFLICT
                       The reclaim provided by the client has
                       encountered a conflict and can not be provided.
                       Potentially indicates a misbehaving client.
 NFS4ERR_RESOURCE      For the processing of the COMPOUND procedure,
                       the server may exhaust available resources and
                       can not continue processing operations within
                       the COMPOUND procedure.  This error will be
                       returned from the server in those instances of
                       resource exhaustion related to the processing
                       of the COMPOUND procedure.

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 NFS4ERR_RESTOREFH     The RESTOREFH operation does not have a saved
                       filehandle (identified by SAVEFH) to operate
                       upon.
 NFS4ERR_ROFS          Read-only filesystem. A modifying operation was
                       attempted on a read-only filesystem.
 NFS4ERR_SAME          This error is returned by the NVERIFY operation
                       to signify that the attributes compared were
                       the same as provided in the client's request.
 NFS4ERR_SERVERFAULT   An error occurred on the server which does not
                       map to any of the legal NFS version 4 protocol
                       error values.  The client should translate this
                       into an appropriate error.  UNIX clients may
                       choose to translate this to EIO.
 NFS4ERR_SHARE_DENIED  An attempt to OPEN a file with a share
                       reservation has failed because of a share
                       conflict.
 NFS4ERR_STALE         Invalid filehandle. The filehandle given in the
                       arguments was invalid. The file referred to by
                       that filehandle no longer exists or access to
                       it has been revoked.
 NFS4ERR_STALE_CLIENTID A clientid not recognized by the server was
                        used in a locking or SETCLIENTID_CONFIRM
                        request.
 NFS4ERR_STALE_STATEID A stateid generated by an earlier server
                       instance was used.
 NFS4ERR_SYMLINK       The current filehandle provided for a LOOKUP is
                       not a directory but a symbolic link.  Also used
                       if the final component of the OPEN path is a
                       symbolic link.
 NFS4ERR_TOOSMALL      The encoded response to a READDIR request
                       exceeds the size limit set by the initial
                       request.
 NFS4ERR_WRONGSEC      The security mechanism being used by the client
                       for the operation does not match the server's
                       security policy.  The client should change the
                       security mechanism being used and retry the
                       operation.

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 NFS4ERR_XDEV          Attempt to do an operation between different
                       fsids.

13. NFS version 4 Requests

 For the NFS version 4 RPC program, there are two traditional RPC
 procedures: NULL and COMPOUND.  All other functionality is defined as
 a set of operations and these operations are defined in normal
 XDR/RPC syntax and semantics.  However, these operations are
 encapsulated within the COMPOUND procedure.  This requires that the
 client combine one or more of the NFS version 4 operations into a
 single request.
 The NFS4_CALLBACK program is used to provide server to client
 signaling and is constructed in a similar fashion as the NFS version
 4 program.  The procedures CB_NULL and CB_COMPOUND are defined in the
 same way as NULL and COMPOUND are within the NFS program.  The
 CB_COMPOUND request also encapsulates the remaining operations of the
 NFS4_CALLBACK program.  There is no predefined RPC program number for
 the NFS4_CALLBACK program.  It is up to the client to specify a
 program number in the "transient" program range.  The program and
 port number of the NFS4_CALLBACK program are provided by the client
 as part of the SETCLIENTID/SETCLIENTID_CONFIRM sequence. The program
 and port can be changed by another SETCLIENTID/SETCLIENTID_CONFIRM
 sequence, and it is possible to use the sequence to change them
 within a client incarnation without removing relevant leased client
 state.

13.1. Compound Procedure

 The COMPOUND procedure provides the opportunity for better
 performance within high latency networks.  The client can avoid
 cumulative latency of multiple RPCs by combining multiple dependent
 operations into a single COMPOUND procedure.  A compound operation
 may provide for protocol simplification by allowing the client to
 combine basic procedures into a single request that is customized for
 the client's environment.
 The CB_COMPOUND procedure precisely parallels the features of
 COMPOUND as described above.
 The basic structure of the COMPOUND procedure is:
 +-----+--------------+--------+-----------+-----------+-----------+--
 | tag | minorversion | numops | op + args | op + args | op + args |
 +-----+--------------+--------+-----------+-----------+-----------+--

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 and the reply's structure is:
    +------------+-----+--------+-----------------------+--
    |last status | tag | numres | status + op + results |
    +------------+-----+--------+-----------------------+--
 The numops and numres fields, used in the depiction above, represent
 the count for the counted array encoding use to signify the number of
 arguments or results encoded in the request and response.  As per the
 XDR encoding, these counts must match exactly the number of operation
 arguments or results encoded.

13.2. Evaluation of a Compound Request

 The server will process the COMPOUND procedure by evaluating each of
 the operations within the COMPOUND procedure in order.  Each
 component operation consists of a 32 bit operation code, followed by
 the argument of length determined by the type of operation. The
 results of each operation are encoded in sequence into a reply
 buffer.  The results of each operation are preceded by the opcode and
 a status code (normally zero).  If an operation results in a non-zero
 status code, the status will be encoded and evaluation of the
 compound sequence will halt and the reply will be returned.  Note
 that evaluation stops even in the event of "non error" conditions
 such as NFS4ERR_SAME.
 There are no atomicity requirements for the operations contained
 within the COMPOUND procedure.  The operations being evaluated as
 part of a COMPOUND request may be evaluated simultaneously with other
 COMPOUND requests that the server receives.
 It is the client's responsibility for recovering from any partially
 completed COMPOUND procedure.  Partially completed COMPOUND
 procedures may occur at any point due to errors such as
 NFS4ERR_RESOURCE and NFS4ERR_DELAY.  This may occur even given an
 otherwise valid operation string.  Further, a server reboot which
 occurs in the middle of processing a COMPOUND procedure may leave the
 client with the difficult task of determining how far COMPOUND
 processing has proceeded.  Therefore, the client should avoid overly
 complex COMPOUND procedures in the event of the failure of an
 operation within the procedure.
 Each operation assumes a "current" and "saved" filehandle that is
 available as part of the execution context of the compound request.
 Operations may set, change, or return the current filehandle.  The
 "saved" filehandle is used for temporary storage of a filehandle
 value and as operands for the RENAME and LINK operations.

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13.3. Synchronous Modifying Operations

 NFS version 4 operations that modify the filesystem are synchronous.
 When an operation is successfully completed at the server, the client
 can depend that any data associated with the request is now on stable
 storage (the one exception is in the case of the file data in a WRITE
 operation with the UNSTABLE option specified).
 This implies that any previous operations within the same compound
 request are also reflected in stable storage.  This behavior enables
 the client's ability to recover from a partially executed compound
 request which may resulted from the failure of the server.  For
 example, if a compound request contains operations A and B and the
 server is unable to send a response to the client, depending on the
 progress the server made in servicing the request the result of both
 operations may be reflected in stable storage or just operation A may
 be reflected.  The server must not have just the results of operation
 B in stable storage.

13.4. Operation Values

 The operations encoded in the COMPOUND procedure are identified by
 operation values.  To avoid overlap with the RPC procedure numbers,
 operations 0 (zero) and 1 are not defined.  Operation 2 is not
 defined but reserved for future use with minor versioning.

14. NFS version 4 Procedures

14.1. Procedure 0: NULL - No Operation

 SYNOPSIS
    <null>
 ARGUMENT
    void;
 RESULT
    void;

Shepler, et al. Standards Track [Page 136] RFC 3530 NFS version 4 Protocol April 2003

 DESCRIPTION
    Standard NULL procedure.  Void argument, void response.  This
    procedure has no functionality associated with it.  Because of
    this it is sometimes used to measure the overhead of processing a
    service request.  Therefore, the server should ensure that no
    unnecessary work is done in servicing this procedure.
 ERRORS
    None.

14.2. Procedure 1: COMPOUND - Compound Operations

 SYNOPSIS
   compoundargs -> compoundres
 ARGUMENT
   union nfs_argop4 switch (nfs_opnum4 argop) {
           case <OPCODE>: <argument>;
           ...
   };
   struct COMPOUND4args {
           utf8str_cs      tag;
           uint32_t        minorversion;
           nfs_argop4      argarray<>;
   };
 RESULT
   union nfs_resop4 switch (nfs_opnum4 resop){
           case <OPCODE>: <result>;
           ...
   };
   struct COMPOUND4res {
           nfsstat4        status;
           utf8str_cs      tag;
           nfs_resop4      resarray<>;
   };

Shepler, et al. Standards Track [Page 137] RFC 3530 NFS version 4 Protocol April 2003

 DESCRIPTION
 The COMPOUND procedure is used to combine one or more of the NFS
 operations into a single RPC request.  The main NFS RPC program has
 two main procedures: NULL and COMPOUND.  All other operations use the
 COMPOUND procedure as a wrapper.
 The COMPOUND procedure is used to combine individual operations into
 a single RPC request.  The server interprets each of the operations
 in turn.  If an operation is executed by the server and the status of
 that operation is NFS4_OK, then the next operation in the COMPOUND
 procedure is executed.  The server continues this process until there
 are no more operations to be executed or one of the operations has a
 status value other than NFS4_OK.
 In the processing of the COMPOUND procedure, the server may find that
 it does not have the available resources to execute any or all of the
 operations within the COMPOUND sequence.  In this case, the error
 NFS4ERR_RESOURCE will be returned for the particular operation within
 the COMPOUND procedure where the resource exhaustion occurred.  This
 assumes that all previous operations within the COMPOUND sequence
 have been evaluated successfully.  The results for all of the
 evaluated operations must be returned to the client.
 The server will generally choose between two methods of decoding the
 client's request.  The first would be the traditional one-pass XDR
 decode, in which decoding of the entire COMPOUND precedes execution
 of any operation within it.  If there is an XDR decoding error in
 this case, an RPC XDR decode error would be returned.  The second
 method would be to make an initial pass to decode the basic COMPOUND
 request and then to XDR decode each of the individual operations, as
 the server is ready to execute it.  In this case, the server may
 encounter an XDR decode error during such an operation decode, after
 previous operations within the COMPOUND have been executed.  In this
 case, the server would return the error NFS4ERR_BADXDR to signify the
 decode error.
 The COMPOUND arguments contain a "minorversion" field.  The initial
 and default value for this field is 0 (zero).  This field will be
 used by future minor versions such that the client can communicate to
 the server what minor version is being requested.  If the server
 receives a COMPOUND procedure with a minorversion field value that it
 does not support, the server MUST return an error of
 NFS4ERR_MINOR_VERS_MISMATCH and a zero length resultdata array.
 Contained within the COMPOUND results is a "status" field.  If the
 results array length is non-zero, this status must be equivalent to
 the status of the last operation that was executed within the

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 COMPOUND procedure.  Therefore, if an operation incurred an error
 then the "status" value will be the same error value as is being
 returned for the operation that failed.
 Note that operations, 0 (zero) and 1 (one) are not defined for the
 COMPOUND procedure.  Operation 2 is not defined but reserved for
 future definition and use with minor versioning.  If the server
 receives a operation array that contains operation 2 and the
 minorversion field has a value of 0 (zero), an error of
 NFS4ERR_OP_ILLEGAL, as described in the next paragraph, is returned
 to the client.  If an operation array contains an operation 2 and the
 minorversion field is non-zero and the server does not support the
 minor version, the server returns an error of
 NFS4ERR_MINOR_VERS_MISMATCH.  Therefore, the
 NFS4ERR_MINOR_VERS_MISMATCH error takes precedence over all other
 errors.
 It is possible that the server receives a request that contains an
 operation that is less than the first legal operation (OP_ACCESS) or
 greater than the last legal operation (OP_RELEASE_LOCKOWNER).
 In this case, the server's response will encode the opcode OP_ILLEGAL
 rather than the illegal opcode of the request. The status field in
 the ILLEGAL return results will set to NFS4ERR_OP_ILLEGAL.  The
 COMPOUND procedure's return results will also be NFS4ERR_OP_ILLEGAL.
 The definition of the "tag" in the request is left to the
 implementor.  It may be used to summarize the content of the compound
 request for the benefit of packet sniffers and engineers debugging
 implementations.  However, the value of "tag" in the response SHOULD
 be the same value as provided in the request.  This applies to the
 tag field of the CB_COMPOUND procedure as well.
 IMPLEMENTATION
 Since an error of any type may occur after only a portion of the
 operations have been evaluated, the client must be prepared to
 recover from any failure.  If the source of an NFS4ERR_RESOURCE error
 was a complex or lengthy set of operations, it is likely that if the
 number of operations were reduced the server would be able to
 evaluate them successfully.  Therefore, the client is responsible for
 dealing with this type of complexity in recovery.
 ERRORS
 All errors defined in the protocol

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14.2.1. Operation 3: ACCESS - Check Access Rights

 SYNOPSIS
   (cfh), accessreq -> supported, accessrights
 ARGUMENT
   const ACCESS4_READ      = 0x00000001;
   const ACCESS4_LOOKUP    = 0x00000002;
   const ACCESS4_MODIFY    = 0x00000004;
   const ACCESS4_EXTEND    = 0x00000008;
   const ACCESS4_DELETE    = 0x00000010;
   const ACCESS4_EXECUTE   = 0x00000020;
   struct ACCESS4args {
           /* CURRENT_FH: object */
           uint32_t        access;
   };
 RESULT
   struct ACCESS4resok {
           uint32_t        supported;
           uint32_t        access;
   };
   union ACCESS4res switch (nfsstat4 status) {
    case NFS4_OK:
            ACCESS4resok   resok4;
    default:
            void;
   };
 DESCRIPTION
 ACCESS determines the access rights that a user, as identified by the
 credentials in the RPC request, has with respect to the file system
 object specified by the current filehandle.  The client encodes the
 set of access rights that are to be checked in the bit mask "access".
 The server checks the permissions encoded in the bit mask.  If a
 status of NFS4_OK is returned, two bit masks are included in the
 response.  The first, "supported", represents the access rights for
 which the server can verify reliably.  The second, "access",
 represents the access rights available to the user for the filehandle
 provided.  On success, the current filehandle retains its value.

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 Note that the supported field will contain only as many values as
 were originally sent in the arguments.  For example, if the client
 sends an ACCESS operation with only the ACCESS4_READ value set and
 the server supports this value, the server will return only
 ACCESS4_READ even if it could have reliably checked other values.
 The results of this operation are necessarily advisory in nature.  A
 return status of NFS4_OK and the appropriate bit set in the bit mask
 does not imply that such access will be allowed to the file system
 object in the future. This is because access rights can be revoked by
 the server at any time.
 The following access permissions may be requested:
 ACCESS4_READ    Read data from file or read a directory.
 ACCESS4_LOOKUP  Look up a name in a directory (no meaning for non-
                 directory objects).
 ACCESS4_MODIFY  Rewrite existing file data or modify existing
                 directory entries.
 ACCESS4_EXTEND  Write new data or add directory entries.
 ACCESS4_DELETE  Delete an existing directory entry.
 ACCESS4_EXECUTE Execute file (no meaning for a directory).
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 In general, it is not sufficient for the client to attempt to deduce
 access permissions by inspecting the uid, gid, and mode fields in the
 file attributes or by attempting to interpret the contents of the ACL
 attribute.  This is because the server may perform uid or gid mapping
 or enforce additional access control restrictions.  It is also
 possible that the server may not be in the same ID space as the
 client.  In these cases (and perhaps others), the client can not
 reliably perform an access check with only current file attributes.
 In the NFS version 2 protocol, the only reliable way to determine
 whether an operation was allowed was to try it and see if it
 succeeded or failed.  Using the ACCESS operation in the NFS version 4
 protocol, the client can ask the server to indicate whether or not
 one or more classes of operations are permitted.  The ACCESS
 operation is provided to allow clients to check before doing a series
 of operations which will result in an access failure.  The OPEN

Shepler, et al. Standards Track [Page 141] RFC 3530 NFS version 4 Protocol April 2003

 operation provides a point where the server can verify access to the
 file object and method to return that information to the client.  The
 ACCESS operation is still useful for directory operations or for use
 in the case the UNIX API "access" is used on the client.
 The information returned by the server in response to an ACCESS call
 is not permanent.  It was correct at the exact time that the server
 performed the checks, but not necessarily afterwards.  The server can
 revoke access permission at any time.
 The client should use the effective credentials of the user to build
 the authentication information in the ACCESS request used to
 determine access rights.  It is the effective user and group
 credentials that are used in subsequent read and write operations.
 Many implementations do not directly support the ACCESS4_DELETE
 permission.  Operating systems like UNIX will ignore the
 ACCESS4_DELETE bit if set on an access request on a non-directory
 object.  In these systems, delete permission on a file is determined
 by the access permissions on the directory in which the file resides,
 instead of being determined by the permissions of the file itself.
 Therefore, the mask returned enumerating which access rights can be
 determined will have the ACCESS4_DELETE value set to 0.  This
 indicates to the client that the server was unable to check that
 particular access right.  The ACCESS4_DELETE bit in the access mask
 returned will then be ignored by the client.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADHANDLE
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

14.2.2. Operation 4: CLOSE - Close File

 SYNOPSIS
   (cfh), seqid, open_stateid -> open_stateid

Shepler, et al. Standards Track [Page 142] RFC 3530 NFS version 4 Protocol April 2003

 ARGUMENT
   struct CLOSE4args {
           /* CURRENT_FH: object */
           seqid4          seqid
           stateid4        open_stateid;
   };
 RESULT
   union CLOSE4res switch (nfsstat4 status) {
    case NFS4_OK:
            stateid4       open_stateid;
    default:
            void;
   };
 DESCRIPTION
 The CLOSE operation releases share reservations for the regular or
 named attribute file as specified by the current filehandle.  The
 share reservations and other state information released at the server
 as a result of this CLOSE is only associated with the supplied
 stateid.  The sequence id provides for the correct ordering. State
 associated with other OPENs is not affected.
 If record locks are held, the client SHOULD release all locks before
 issuing a CLOSE.  The server MAY free all outstanding locks on CLOSE
 but some servers may not support the CLOSE of a file that still has
 record locks held.  The server MUST return failure if any locks would
 exist after the CLOSE.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 Even though CLOSE returns a stateid, this stateid is not useful to
 the client and should be treated as deprecated.  CLOSE "shuts down"
 the state associated with all OPENs for the file by a single
 open_owner.  As noted above, CLOSE will either release all file
 locking state or return an error.  Therefore, the stateid returned by
 CLOSE is not useful for operations that follow.
 ERRORS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_SEQID

Shepler, et al. Standards Track [Page 143] RFC 3530 NFS version 4 Protocol April 2003

    NFS4ERR_BAD_STATEID
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_EXPIRED
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_ISDIR
    NFS4ERR_LEASE_MOVED
    NFS4ERR_LOCKS_HELD
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_OLD_STATEID
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_STATEID

14.2.3. Operation 5: COMMIT - Commit Cached Data

 SYNOPSIS
   (cfh), offset, count -> verifier
 ARGUMENT
   struct COMMIT4args {
           /* CURRENT_FH: file */
           offset4         offset;
           count4          count;
   };
 RESULT
   struct COMMIT4resok {
           verifier4       writeverf;
   };
   union COMMIT4res switch (nfsstat4 status) {
    case NFS4_OK:
            COMMIT4resok   resok4;
    default:
            void;
   };

Shepler, et al. Standards Track [Page 144] RFC 3530 NFS version 4 Protocol April 2003

 DESCRIPTION
 The COMMIT operation forces or flushes data to stable storage for the
 file specified by the current filehandle.  The flushed data is that
 which was previously written with a WRITE operation which had the
 stable field set to UNSTABLE4.
 The offset specifies the position within the file where the flush is
 to begin.  An offset value of 0 (zero) means to flush data starting
 at the beginning of the file.  The count specifies the number of
 bytes of data to flush.  If count is 0 (zero), a flush from offset to
 the end of the file is done.
 The server returns a write verifier upon successful completion of the
 COMMIT.  The write verifier is used by the client to determine if the
 server has restarted or rebooted between the initial WRITE(s) and the
 COMMIT.  The client does this by comparing the write verifier
 returned from the initial writes and the verifier returned by the
 COMMIT operation.  The server must vary the value of the write
 verifier at each server event or instantiation that may lead to a
 loss of uncommitted data.  Most commonly this occurs when the server
 is rebooted; however, other events at the server may result in
 uncommitted data loss as well.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 The COMMIT operation is similar in operation and semantics to the
 POSIX fsync(2) system call that synchronizes a file's state with the
 disk (file data and metadata is flushed to disk or stable storage).
 COMMIT performs the same operation for a client, flushing any
 unsynchronized data and metadata on the server to the server's disk
 or stable storage for the specified file.  Like fsync(2), it may be
 that there is some modified data or no modified data to synchronize.
 The data may have been synchronized by the server's normal periodic
 buffer synchronization activity.  COMMIT should return NFS4_OK,
 unless there has been an unexpected error.
 COMMIT differs from fsync(2) in that it is possible for the client to
 flush a range of the file (most likely triggered by a buffer-
 reclamation scheme on the client before file has been completely
 written).
 The server implementation of COMMIT is reasonably simple.  If the
 server receives a full file COMMIT request, that is starting at
 offset 0 and count 0, it should do the equivalent of fsync()'ing the
 file.  Otherwise, it should arrange to have the cached data in the

Shepler, et al. Standards Track [Page 145] RFC 3530 NFS version 4 Protocol April 2003

 range specified by offset and count to be flushed to stable storage.
 In both cases, any metadata associated with the file must be flushed
 to stable storage before returning.  It is not an error for there to
 be nothing to flush on the server.  This means that the data and
 metadata that needed to be flushed have already been flushed or lost
 during the last server failure.
 The client implementation of COMMIT is a little more complex.  There
 are two reasons for wanting to commit a client buffer to stable
 storage.  The first is that the client wants to reuse a buffer.  In
 this case, the offset and count of the buffer are sent to the server
 in the COMMIT request.  The server then flushes any cached data based
 on the offset and count, and flushes any metadata associated with the
 file.  It then returns the status of the flush and the write
 verifier.  The other reason for the client to generate a COMMIT is
 for a full file flush, such as may be done at close.  In this case,
 the client would gather all of the buffers for this file that contain
 uncommitted data, do the COMMIT operation with an offset of 0 and
 count of 0, and then free all of those buffers.  Any other dirty
 buffers would be sent to the server in the normal fashion.
 After a buffer is written by the client with the stable parameter set
 to UNSTABLE4, the buffer must be considered as modified by the client
 until the buffer has either been flushed via a COMMIT operation or
 written via a WRITE operation with stable parameter set to FILE_SYNC4
 or DATA_SYNC4. This is done to prevent the buffer from being freed
 and reused before the data can be flushed to stable storage on the
 server.
 When a response is returned from either a WRITE or a COMMIT operation
 and it contains a write verifier that is different than previously
 returned by the server, the client will need to retransmit all of the
 buffers containing uncommitted cached data to the server.  How this
 is to be done is up to the implementor.  If there is only one buffer
 of interest, then it should probably be sent back over in a WRITE
 request with the appropriate stable parameter.  If there is more than
 one buffer, it might be worthwhile retransmitting all of the buffers
 in WRITE requests with the stable parameter set to UNSTABLE4 and then
 retransmitting the COMMIT operation to flush all of the data on the
 server to stable storage.  The timing of these retransmissions is
 left to the implementor.
 The above description applies to page-cache-based systems as well as
 buffer-cache-based systems.  In those systems, the virtual memory
 system will need to be modified instead of the buffer cache.

Shepler, et al. Standards Track [Page 146] RFC 3530 NFS version 4 Protocol April 2003

 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADHANDLE
    NFS4ERR_BADXDR
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_ISDIR
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

14.2.4. Operation 6: CREATE - Create a Non-Regular File Object

 SYNOPSIS
   (cfh), name, type, attrs -> (cfh), change_info, attrs_set
 ARGUMENT
   union createtype4 switch (nfs_ftype4 type) {
    case NF4LNK:
            linktext4      linkdata;
    case NF4BLK:
    case NF4CHR:
            specdata4      devdata;
    case NF4SOCK:
    case NF4FIFO:
    case NF4DIR:
            void;
   };
   struct CREATE4args {
           /* CURRENT_FH: directory for creation */
           createtype4     objtype;
           component4      objname;
           fattr4          createattrs;
   };
 RESULT
   struct CREATE4resok {
           change_info4    cinfo;
           bitmap4         attrset;        /* attributes set */

Shepler, et al. Standards Track [Page 147] RFC 3530 NFS version 4 Protocol April 2003

   };
   union CREATE4res switch (nfsstat4 status) {
    case NFS4_OK:
            CREATE4resok resok4;
    default:
            void;
   };
 DESCRIPTION
 The CREATE operation creates a non-regular file object in a directory
 with a given name.  The OPEN operation MUST be used to create a
 regular file.
 The objname specifies the name for the new object.  The objtype
 determines the type of object to be created: directory, symlink, etc.
 If an object of the same name already exists in the directory, the
 server will return the error NFS4ERR_EXIST.
 For the directory where the new file object was created, the server
 returns change_info4 information in cinfo.  With the atomic field of
 the change_info4 struct, the server will indicate if the before and
 after change attributes were obtained atomically with respect to the
 file object creation.
 If the objname has a length of 0 (zero), or if objname does not obey
 the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
 The current filehandle is replaced by that of the new object.
 The createattrs specifies the initial set of attributes for the
 object.  The set of attributes may include any writable attribute
 valid for the object type. When the operation is successful, the
 server will return to the client an attribute mask signifying which
 attributes were successfully set for the object.
 If createattrs includes neither the owner attribute nor an ACL with
 an ACE for the owner, and if the server's filesystem both supports
 and requires an owner attribute (or an owner ACE) then the server
 MUST derive the owner (or the owner ACE). This would typically be
 from the principal indicated in the RPC credentials of the call, but
 the server's operating environment or filesystem semantics may
 dictate other methods of derivation. Similarly, if createattrs
 includes neither the group attribute nor a group ACE, and if the
 server's filesystem both supports and requires the notion of a group
 attribute (or group ACE), the server MUST derive the group attribute

Shepler, et al. Standards Track [Page 148] RFC 3530 NFS version 4 Protocol April 2003

 (or the corresponding owner ACE) for the file. This could be from the
 RPC call's credentials, such as the group principal if the
 credentials include it (such as with AUTH_SYS), from the group
 identifier associated with the principal in the credentials (for
 e.g., POSIX systems have a passwd database that has the group
 identifier for every user identifier), inherited from directory the
 object is created in, or whatever else the server's operating
 environment or filesystem semantics dictate. This applies to the OPEN
 operation too.
 Conversely, it is possible the client will specify in createattrs an
 owner attribute or group attribute or ACL that the principal
 indicated the RPC call's credentials does not have permissions to
 create files for. The error to be returned in this instance is
 NFS4ERR_PERM. This applies to the OPEN operation too.
 IMPLEMENTATION
 If the client desires to set attribute values after the create, a
 SETATTR operation can be added to the COMPOUND request so that the
 appropriate attributes will be set.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_ATTRNOTSUPP
    NFS4ERR_BADCHAR
    NFS4ERR_BADHANDLE
    NFS4ERR_BADNAME
    NFS4ERR_BADOWNER
    NFS4ERR_BADTYPE
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_DQUOT
    NFS4ERR_EXIST
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NAMETOOLONG
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOSPC
    NFS4ERR_NOTDIR
    NFS4ERR_PERM
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

Shepler, et al. Standards Track [Page 149] RFC 3530 NFS version 4 Protocol April 2003

14.2.5. Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery

 SYNOPSIS
   clientid ->
 ARGUMENT
   struct DELEGPURGE4args {
           clientid4       clientid;
   };
 RESULT
   struct DELEGPURGE4res {
           nfsstat4        status;
   };
 DESCRIPTION
 Purges all of the delegations awaiting recovery for a given client.
 This is useful for clients which do not commit delegation information
 to stable storage to indicate that conflicting requests need not be
 delayed by the server awaiting recovery of delegation information.
 This operation should be used by clients that record delegation
 information on stable storage on the client.  In this case,
 DELEGPURGE should be issued immediately after doing delegation
 recovery on all delegations known to the client.  Doing so will
 notify the server that no additional delegations for the client will
 be recovered allowing it to free resources, and avoid delaying other
 clients who make requests that conflict with the unrecovered
 delegations.  The set of delegations known to the server and the
 client may be different.  The reason for this is that a client may
 fail after making a request which resulted in delegation but before
 it received the results and committed them to the client's stable
 storage.
 The server MAY support DELEGPURGE, but if it does not, it MUST NOT
 support CLAIM_DELEGATE_PREV.
 ERRORS
    NFS4ERR_BADXDR
    NFS4ERR_NOTSUPP
    NFS4ERR_LEASE_MOVED
    NFS4ERR_MOVED
    NFS4ERR_RESOURCE

Shepler, et al. Standards Track [Page 150] RFC 3530 NFS version 4 Protocol April 2003

    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE_CLIENTID

14.2.6. Operation 8: DELEGRETURN - Return Delegation

 SYNOPSIS
   (cfh), stateid ->
 ARGUMENT
   struct DELEGRETURN4args {
           /* CURRENT_FH: delegated file */
           stateid4        stateid;
   };
 RESULT
   struct DELEGRETURN4res {
           nfsstat4        status;
   };
 DESCRIPTION
 Returns the delegation represented by the current filehandle and
 stateid.
 Delegations may be returned when recalled or voluntarily (i.e.,
 before the server has recalled them).  In either case the client must
 properly propagate state changed under the context of the delegation
 to the server before returning the delegation.
 ERRORS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_BAD_STATEID
    NFS4ERR_BADXDR
    NFS4ERR_EXPIRED
    NFS4ERR_INVAL
    NFS4ERR_LEASE_MOVED
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTSUPP
    NFS4ERR_OLD_STATEID
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_STATEID

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14.2.7. Operation 9: GETATTR - Get Attributes

 SYNOPSIS
   (cfh), attrbits -> attrbits, attrvals
 ARGUMENT
   struct GETATTR4args {
           /* CURRENT_FH: directory or file */
           bitmap4         attr_request;
   };
 RESULT
   struct GETATTR4resok {
           fattr4          obj_attributes;
   };
   union GETATTR4res switch (nfsstat4 status) {
    case NFS4_OK:
            GETATTR4resok  resok4;
    default:
            void;
   };
 DESCRIPTION
 The GETATTR operation will obtain attributes for the filesystem
 object specified by the current filehandle.  The client sets a bit in
 the bitmap argument for each attribute value that it would like the
 server to return.  The server returns an attribute bitmap that
 indicates the attribute values for which it was able to return,
 followed by the attribute values ordered lowest attribute number
 first.
 The server must return a value for each attribute that the client
 requests if the attribute is supported by the server.  If the server
 does not support an attribute or cannot approximate a useful value
 then it must not return the attribute value and must not set the
 attribute bit in the result bitmap.  The server must return an error
 if it supports an attribute but cannot obtain its value.  In that
 case no attribute values will be returned.
 All servers must support the mandatory attributes as specified in the
 section "File Attributes".
 On success, the current filehandle retains its value.

Shepler, et al. Standards Track [Page 152] RFC 3530 NFS version 4 Protocol April 2003

 IMPLEMENTATION
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADHANDLE
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

14.2.8. Operation 10: GETFH - Get Current Filehandle

 SYNOPSIS
   (cfh) -> filehandle
 ARGUMENT
   /* CURRENT_FH: */
   void;
 RESULT
   struct GETFH4resok {
           nfs_fh4         object;
   };
   union GETFH4res switch (nfsstat4 status) {
    case NFS4_OK:
           GETFH4resok     resok4;
    default:
           void;
   };
 DESCRIPTION
 This operation returns the current filehandle value.
 On success, the current filehandle retains its value.

Shepler, et al. Standards Track [Page 153] RFC 3530 NFS version 4 Protocol April 2003

 IMPLEMENTATION
 Operations that change the current filehandle like LOOKUP or CREATE
 do not automatically return the new filehandle as a result.  For
 instance, if a client needs to lookup a directory entry and obtain
 its filehandle then the following request is needed.
    PUTFH  (directory filehandle)
    LOOKUP (entry name)
    GETFH
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_FHEXPIRED
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

14.2.9. Operation 11: LINK - Create Link to a File

 SYNOPSIS
   (sfh), (cfh), newname -> (cfh), change_info
 ARGUMENT
   struct LINK4args {
           /* SAVED_FH: source object */
           /* CURRENT_FH: target directory */
           component4      newname;
   };
 RESULT
   struct LINK4resok {
           change_info4    cinfo;
   };
   union LINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            LINK4resok resok4;
    default:
            void;
   };

Shepler, et al. Standards Track [Page 154] RFC 3530 NFS version 4 Protocol April 2003

 DESCRIPTION
 The LINK operation creates an additional newname for the file
 represented by the saved filehandle, as set by the SAVEFH operation,
 in the directory represented by the current filehandle.  The existing
 file and the target directory must reside within the same filesystem
 on the server.  On success, the current filehandle will continue to
 be the target directory.  If an object exists in the target directory
 with the same name as newname, the server must return NFS4ERR_EXIST.
 For the target directory, the server returns change_info4 information
 in cinfo.  With the atomic field of the change_info4 struct, the
 server will indicate if the before and after change attributes were
 obtained atomically with respect to the link creation.
 If the newname has a length of 0 (zero), or if newname does not obey
 the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
 IMPLEMENTATION
 Changes to any property of the "hard" linked files are reflected in
 all of the linked files.  When a link is made to a file, the
 attributes for the file should have a value for numlinks that is one
 greater than the value before the LINK operation.
 The statement "file and the target directory must reside within the
 same filesystem on the server" means that the fsid fields in the
 attributes for the objects are the same. If they reside on different
 filesystems, the error, NFS4ERR_XDEV, is returned.  On some servers,
 the filenames, "." and "..", are illegal as newname.
 In the case that newname is already linked to the file represented by
 the saved filehandle, the server will return NFS4ERR_EXIST.
 Note that symbolic links are created with the CREATE operation.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADCHAR
    NFS4ERR_BADHANDLE
    NFS4ERR_BADNAME
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_DQUOT
    NFS4ERR_EXIST
    NFS4ERR_FHEXPIRED
    NFS4ERR_FILE_OPEN

Shepler, et al. Standards Track [Page 155] RFC 3530 NFS version 4 Protocol April 2003

    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_ISDIR
    NFS4ERR_MLINK
    NFS4ERR_MOVED
    NFS4ERR_NAMETOOLONG
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOSPC
    NFS4ERR_NOTDIR
    NFS4ERR_NOTSUPP
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC
    NFS4ERR_XDEV

14.2.10. Operation 12: LOCK - Create Lock

 SYNOPSIS
   (cfh) locktype, reclaim, offset, length, locker -> stateid
 ARGUMENT
   struct open_to_lock_owner4 {
           seqid4          open_seqid;
           stateid4        open_stateid;
           seqid4          lock_seqid;
           lock_owner4     lock_owner;
   };
   struct exist_lock_owner4 {
           stateid4        lock_stateid;
           seqid4          lock_seqid;
   };
   union locker4 switch (bool new_lock_owner) {
    case TRUE:
           open_to_lock_owner4     open_owner;
    case FALSE:
           exist_lock_owner4       lock_owner;
   };
   enum nfs_lock_type4 {
           READ_LT         = 1,
           WRITE_LT        = 2,

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           READW_LT        = 3,    /* blocking read */
           WRITEW_LT       = 4     /* blocking write */
   };
   struct LOCK4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           bool            reclaim;
           offset4         offset;
           length4         length;
           locker4         locker;
   };
 RESULT
   struct LOCK4denied {
           offset4         offset;
           length4         length;
           nfs_lock_type4  locktype;
           lock_owner4     owner;
   };
   struct LOCK4resok {
           stateid4        lock_stateid;
   };
   union LOCK4res switch (nfsstat4 status) {
    case NFS4_OK:
            LOCK4resok     resok4;
    case NFS4ERR_DENIED:
            LOCK4denied    denied;
    default:
            void;
   };
 DESCRIPTION
 The LOCK operation requests a record lock for the byte range
 specified by the offset and length parameters.  The lock type is also
 specified to be one of the nfs_lock_type4s.  If this is a reclaim
 request, the reclaim parameter will be TRUE;
 Bytes in a file may be locked even if those bytes are not currently
 allocated to the file.  To lock the file from a specific offset
 through the end-of-file (no matter how long the file actually is) use
 a length field with all bits set to 1 (one).  If the length is zero,

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 or if a length which is not all bits set to one is specified, and
 length when added to the offset exceeds the maximum 64-bit unsigned
 integer value, the error NFS4ERR_INVAL will result.
 Some servers may only support locking for byte offsets that fit
 within 32 bits.  If the client specifies a range that includes a byte
 beyond the last byte offset of the 32-bit range, but does not include
 the last byte offset of the 32-bit and all of the byte offsets beyond
 it, up to the end of the valid 64-bit range, such a 32-bit server
 MUST return the error NFS4ERR_BAD_RANGE.
 In the case that the lock is denied, the owner, offset, and length of
 a conflicting lock are returned.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 If the server is unable to determine the exact offset and length of
 the conflicting lock, the same offset and length that were provided
 in the arguments should be returned in the denied results.  The File
 Locking section contains a full description of this and the other
 file locking operations.
 LOCK operations are subject to permission checks and to checks
 against the access type of the associated file.  However, the
 specific right and modes required for various type of locks, reflect
 the semantics of the server-exported filesystem, and are not
 specified by the protocol.  For example, Windows 2000 allows a write
 lock of a file open for READ, while a POSIX-compliant system does
 not.
 When the client makes a lock request that corresponds to a range that
 the lockowner has locked already (with the same or different lock
 type), or to a sub-region of such a range, or to a region which
 includes multiple locks already granted to that lockowner, in whole
 or in part, and the server does not support such locking operations
 (i.e., does not support POSIX locking semantics), the server will
 return the error NFS4ERR_LOCK_RANGE.  In that case, the client may
 return an error, or it may emulate the required operations, using
 only LOCK for ranges that do not include any bytes already locked by
 that lock_owner and LOCKU of locks held by that lock_owner
 (specifying an exactly-matching range and type).  Similarly, when the
 client makes a lock request that amounts to upgrading (changing from
 a read lock to a write lock) or downgrading (changing from write lock
 to a read lock) an existing record lock, and the server does not

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 support such a lock, the server will return NFS4ERR_LOCK_NOTSUPP.
 Such operations may not perfectly reflect the required semantics in
 the face of conflicting lock requests from other clients.
 The locker argument specifies the lock_owner that is associated with
 the LOCK request.  The locker4 structure is a switched union that
 indicates whether the lock_owner is known to the server or if the
 lock_owner is new to the server.  In the case that the lock_owner is
 known to the server and has an established lock_seqid, the argument
 is just the lock_owner and lock_seqid.  In the case that the
 lock_owner is not known to the server, the argument contains not only
 the lock_owner and lock_seqid but also the open_stateid and
 open_seqid.  The new lock_owner case covers the very first lock done
 by the lock_owner and offers a method to use the established state of
 the open_stateid to transition to the use of the lock_owner.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_RANGE
    NFS4ERR_BAD_SEQID
    NFS4ERR_BAD_STATEID
    NFS4ERR_BADXDR
    NFS4ERR_DEADLOCK
    NFS4ERR_DELAY
    NFS4ERR_DENIED
    NFS4ERR_EXPIRED
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_INVAL
    NFS4ERR_ISDIR
    NFS4ERR_LEASE_MOVED
    NFS4ERR_LOCK_NOTSUPP
    NFS4ERR_LOCK_RANGE
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NO_GRACE
    NFS4ERR_OLD_STATEID
    NFS4ERR_OPENMODE
    NFS4ERR_RECLAIM_BAD
    NFS4ERR_RECLAIM_CONFLICT
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_CLIENTID
    NFS4ERR_STALE_STATEID

Shepler, et al. Standards Track [Page 159] RFC 3530 NFS version 4 Protocol April 2003

14.2.11. Operation 13: LOCKT - Test For Lock

 SYNOPSIS
   (cfh) locktype, offset, length owner -> {void, NFS4ERR_DENIED ->
   owner}
 ARGUMENT
   struct LOCKT4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           offset4         offset;
           length4         length;
           lock_owner4     owner;
   };
 RESULT
   struct LOCK4denied {
           offset4         offset;
           length4         length;
           nfs_lock_type4  locktype;
           lock_owner4     owner;
   };
   union LOCKT4res switch (nfsstat4 status) {
    case NFS4ERR_DENIED:
            LOCK4denied    denied;
    case NFS4_OK:
            void;
    default:
            void;
   };
 DESCRIPTION
 The LOCKT operation tests the lock as specified in the arguments.  If
 a conflicting lock exists, the owner, offset, length, and type of the
 conflicting lock are returned; if no lock is held, nothing other than
 NFS4_OK is returned.  Lock types READ_LT and READW_LT are processed
 in the same way in that a conflicting lock test is done without
 regard to blocking or non-blocking.  The same is true for WRITE_LT
 and WRITEW_LT.
 The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
 NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
 for LOCK.

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 On success, the current filehandle retains its value.
 IMPLEMENTATION
 If the server is unable to determine the exact offset and length of
 the conflicting lock, the same offset and length that were provided
 in the arguments should be returned in the denied results.  The File
 Locking section contains further discussion of the file locking
 mechanisms.
 LOCKT uses a lock_owner4 rather a stateid4, as is used in LOCK to
 identify the owner.  This is because the client does not have to open
 the file to test for the existence of a lock, so a stateid may not be
 available.
 The test for conflicting locks should exclude locks for the current
 lockowner.  Note that since such locks are not examined the possible
 existence of overlapping ranges may not affect the results of LOCKT.
 If the server does examine locks that match the lockowner for the
 purpose of range checking, NFS4ERR_LOCK_RANGE may be returned..  In
 the event that it returns NFS4_OK, clients may do a LOCK and receive
 NFS4ERR_LOCK_RANGE on the LOCK request because of the flexibility
 provided to the server.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_RANGE
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_DENIED
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_INVAL
    NFS4ERR_ISDIR
    NFS4ERR_LEASE_MOVED
    NFS4ERR_LOCK_RANGE
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_CLIENTID

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14.2.12. Operation 14: LOCKU - Unlock File

 SYNOPSIS
   (cfh) type, seqid, stateid, offset, length -> stateid
 ARGUMENT
   struct LOCKU4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           seqid4          seqid;
           stateid4        stateid;
           offset4         offset;
           length4         length;
   };
 RESULT
   union LOCKU4res switch (nfsstat4 status) {
    case   NFS4_OK:
            stateid4       stateid;
    default:
            void;
   };
 DESCRIPTION
 The LOCKU operation unlocks the record lock specified by the
 parameters. The client may set the locktype field to any value that
 is legal for the nfs_lock_type4 enumerated type, and the server MUST
 accept any legal value for locktype. Any legal value for locktype has
 no effect on the success or failure of the LOCKU operation.
 The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
 NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
 for LOCK.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 If the area to be unlocked does not correspond exactly to a lock
 actually held by the lockowner the server may return the error
 NFS4ERR_LOCK_RANGE.  This includes the case in which the area is not
 locked, where the area is a sub-range of the area locked, where it
 overlaps the area locked without matching exactly or the area
 specified includes multiple locks held by the lockowner.  In all of

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 these cases, allowed by POSIX locking semantics, a client receiving
 this error, should if it desires support for such operations,
 simulate the operation using LOCKU on ranges corresponding to locks
 it actually holds, possibly followed by LOCK requests for the sub-
 ranges not being unlocked.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_RANGE
    NFS4ERR_BAD_SEQID
    NFS4ERR_BAD_STATEID
    NFS4ERR_BADXDR
    NFS4ERR_EXPIRED
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_INVAL
    NFS4ERR_ISDIR
    NFS4ERR_LEASE_MOVED
    NFS4ERR_LOCK_RANGE
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_OLD_STATEID
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_STATEID

14.2.13. Operation 15: LOOKUP - Lookup Filename

 SYNOPSIS
   (cfh), component -> (cfh)
 ARGUMENT
   struct LOOKUP4args {
           /* CURRENT_FH: directory */
           component4      objname;
   };

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 RESULT
   struct LOOKUP4res {
           /* CURRENT_FH: object */
           nfsstat4        status;
   };
 DESCRIPTION
 This operation LOOKUPs or finds a filesystem object using the
 directory specified by the current filehandle.  LOOKUP evaluates the
 component and if the object exists the current filehandle is replaced
 with the component's filehandle.
 If the component cannot be evaluated either because it does not exist
 or because the client does not have permission to evaluate the
 component, then an error will be returned and the current filehandle
 will be unchanged.
 If the component is a zero length string or if any component does not
 obey the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
 IMPLEMENTATION
 If the client wants to achieve the effect of a multi-component
 lookup, it may construct a COMPOUND request such as (and obtain each
 filehandle):
    PUTFH  (directory filehandle)
    LOOKUP "pub"
    GETFH
    LOOKUP "foo"
    GETFH
    LOOKUP "bar"
    GETFH
 NFS version 4 servers depart from the semantics of previous NFS
 versions in allowing LOOKUP requests to cross mountpoints on the
 server.  The client can detect a mountpoint crossing by comparing the
 fsid attribute of the directory with the fsid attribute of the
 directory looked up.  If the fsids are different then the new
 directory is a server mountpoint.  UNIX clients that detect a
 mountpoint crossing will need to mount the server's filesystem.  This
 needs to be done to maintain the file object identity checking
 mechanisms common to UNIX clients.

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 Servers that limit NFS access to "shares" or "exported" filesystems
 should provide a pseudo-filesystem into which the exported
 filesystems can be integrated, so that clients can browse the
 server's name space.  The clients' view of a pseudo filesystem will
 be limited to paths that lead to exported filesystems.
 Note: previous versions of the protocol assigned special semantics to
 the names "." and "..".  NFS version 4 assigns no special semantics
 to these names.  The LOOKUPP operator must be used to lookup a parent
 directory.
 Note that this operation does not follow symbolic links.  The client
 is responsible for all parsing of filenames including filenames that
 are modified by symbolic links encountered during the lookup process.
 If the current filehandle supplied is not a directory but a symbolic
 link, the error NFS4ERR_SYMLINK is returned as the error.  For all
 other non-directory file types, the error NFS4ERR_NOTDIR is returned.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADCHAR
    NFS4ERR_BADHANDLE
    NFS4ERR_BADNAME
    NFS4ERR_BADXDR
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NAMETOOLONG
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTDIR
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_SYMLINK
    NFS4ERR_WRONGSEC

14.2.14. Operation 16: LOOKUPP - Lookup Parent Directory

 SYNOPSIS
   (cfh) -> (cfh)

Shepler, et al. Standards Track [Page 165] RFC 3530 NFS version 4 Protocol April 2003

 ARGUMENT
   /* CURRENT_FH: object */
   void;
 RESULT
   struct LOOKUPP4res {
           /* CURRENT_FH: directory */
           nfsstat4        status;
   };
 DESCRIPTION
 The current filehandle is assumed to refer to a regular directory
 or a named attribute directory.  LOOKUPP assigns the filehandle for
 its parent directory to be the current filehandle.  If there is no
 parent directory an NFS4ERR_NOENT error must be returned.
 Therefore, NFS4ERR_NOENT will be returned by the server when the
 current filehandle is at the root or top of the server's file tree.
 IMPLEMENTATION
 As for LOOKUP, LOOKUPP will also cross mountpoints.
 If the current filehandle is not a directory or named attribute
 directory, the error NFS4ERR_NOTDIR is returned.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADHANDLE
    NFS4ERR_FHEXPIRED
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTDIR
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

14.2.15. Operation 17: NVERIFY - Verify Difference in Attributes

 SYNOPSIS
   (cfh), fattr -> -

Shepler, et al. Standards Track [Page 166] RFC 3530 NFS version 4 Protocol April 2003

 ARGUMENT
   struct NVERIFY4args {
           /* CURRENT_FH: object */
           fattr4          obj_attributes;
   };
 RESULT
   struct NVERIFY4res {
           nfsstat4        status;
   };
 DESCRIPTION
 This operation is used to prefix a sequence of operations to be
 performed if one or more attributes have changed on some filesystem
 object.  If all the attributes match then the error NFS4ERR_SAME must
 be returned.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 This operation is useful as a cache validation operator.  If the
 object to which the attributes belong has changed then the following
 operations may obtain new data associated with that object.  For
 instance, to check if a file has been changed and obtain new data if
 it has:
    PUTFH  (public)
    LOOKUP "foobar"
    NVERIFY attrbits attrs
    READ 0 32767
 In the case that a recommended attribute is specified in the NVERIFY
 operation and the server does not support that attribute for the
 filesystem object, the error NFS4ERR_ATTRNOTSUPP is returned to the
 client.
 When the attribute rdattr_error or any write-only attribute (e.g.,
 time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
 the client.

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 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_ATTRNOTSUPP
    NFS4ERR_BADCHAR
    NFS4ERR_BADHANDLE
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_RESOURCE
    NFS4ERR_SAME
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

14.2.16. Operation 18: OPEN - Open a Regular File

 SYNOPSIS
   (cfh), seqid, share_access, share_deny, owner, openhow, claim ->
   (cfh), stateid, cinfo, rflags, open_confirm, attrset delegation
 ARGUMENT
   struct OPEN4args {
           seqid4          seqid;
           uint32_t        share_access;
           uint32_t        share_deny;
           open_owner4     owner;
           openflag4       openhow;
           open_claim4     claim;
   };
   enum createmode4 {
           UNCHECKED4      = 0,
           GUARDED4        = 1,
           EXCLUSIVE4      = 2
   };
   union createhow4 switch (createmode4 mode) {
    case UNCHECKED4:
    case GUARDED4:
            fattr4         createattrs;
    case EXCLUSIVE4:
            verifier4      createverf;

Shepler, et al. Standards Track [Page 168] RFC 3530 NFS version 4 Protocol April 2003

   };
   enum opentype4 {
           OPEN4_NOCREATE  = 0,
           OPEN4_CREATE    = 1
   };
   union openflag4 switch (opentype4 opentype) {
    case OPEN4_CREATE:
            createhow4     how;
    default:
            void;
   };
   /* Next definitions used for OPEN delegation */
   enum limit_by4 {
           NFS_LIMIT_SIZE          = 1,
           NFS_LIMIT_BLOCKS        = 2
           /* others as needed */
   };
   struct nfs_modified_limit4 {
           uint32_t        num_blocks;
           uint32_t        bytes_per_block;
   };
   union nfs_space_limit4 switch (limit_by4 limitby) {
    /* limit specified as file size */
    case NFS_LIMIT_SIZE:
            uint64_t               filesize;
    /* limit specified by number of blocks */
    case NFS_LIMIT_BLOCKS:
            nfs_modified_limit4    mod_blocks;
   } ;
   enum open_delegation_type4 {
           OPEN_DELEGATE_NONE      = 0,
           OPEN_DELEGATE_READ      = 1,
           OPEN_DELEGATE_WRITE     = 2
   };
   enum open_claim_type4 {
           CLAIM_NULL              = 0,
           CLAIM_PREVIOUS          = 1,
           CLAIM_DELEGATE_CUR      = 2,
           CLAIM_DELEGATE_PREV     = 3
   };

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   struct open_claim_delegate_cur4 {
           stateid4        delegate_stateid;
           component4      file;
   };
   union open_claim4 switch (open_claim_type4 claim) {
    /*
     * No special rights to file. Ordinary OPEN of the specified file.
     */
    case CLAIM_NULL:
            /* CURRENT_FH: directory */
            component4     file;
    /*
     * Right to the file established by an open previous to server
     * reboot.  File identified by filehandle obtained at that time
     * rather than by name.
     */
    case CLAIM_PREVIOUS:
            /* CURRENT_FH: file being reclaimed */
            open_delegation_type4   delegate_type;
    /*
     * Right to file based on a delegation granted by the server.
     * File is specified by name.
     */
    case CLAIM_DELEGATE_CUR:
            /* CURRENT_FH: directory */
            open_claim_delegate_cur4       delegate_cur_info;
    /* Right to file based on a delegation granted to a previous boot
     * instance of the client.  File is specified by name.
     */
    case CLAIM_DELEGATE_PREV:
            /* CURRENT_FH: directory */
            component4     file_delegate_prev;
   };
 RESULT
 struct open_read_delegation4 {
         stateid4        stateid;        /* Stateid for delegation*/
         bool            recall;         /* Pre-recalled flag for
                                            delegations obtained
                                            by reclaim
                                            (CLAIM_PREVIOUS) */
         nfsace4         permissions;    /* Defines users who don't
                                            need an ACCESS call to

Shepler, et al. Standards Track [Page 170] RFC 3530 NFS version 4 Protocol April 2003

                                            open for read */
 };
 struct open_write_delegation4 {
         stateid4        stateid;        /* Stateid for delegation*/
         bool            recall;         /* Pre-recalled flag for
                                            delegations obtained
                                            by reclaim
                                            (CLAIM_PREVIOUS) */
         nfs_space_limit4 space_limit;   /* Defines condition that
                                            the client must check to
                                            determine whether the
                                            file needs to be flushed
                                            to the server on close.
                                            */
         nfsace4         permissions;    /* Defines users who don't
                                            need an ACCESS call as
                                            part of a delegated
                                            open. */
 };
 union open_delegation4
 switch (open_delegation_type4 delegation_type) {
         case OPEN_DELEGATE_NONE:
                 void;
         case OPEN_DELEGATE_READ:
                 open_read_delegation4 read;
         case OPEN_DELEGATE_WRITE:
                 open_write_delegation4 write;
 };
 const OPEN4_RESULT_CONFIRM      = 0x00000002;
 const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;
 struct OPEN4resok {
         stateid4        stateid;        /* Stateid for open */
         change_info4    cinfo;          /* Directory Change Info */
         uint32_t        rflags;         /* Result flags */
         bitmap4         attrset;        /* attributes on create */
         open_delegation4 delegation;    /* Info on any open
                                            delegation */
 };
 union OPEN4res switch (nfsstat4 status) {
  case NFS4_OK:
         /* CURRENT_FH: opened file */
         OPEN4resok      resok4;
  default:

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         void;
 };
 WARNING TO CLIENT IMPLEMENTORS
 OPEN resembles LOOKUP in that it generates a filehandle for the
 client to use.  Unlike LOOKUP though, OPEN creates server state on
 the filehandle.  In normal circumstances, the client can only release
 this state with a CLOSE operation.  CLOSE uses the current filehandle
 to determine which file to close.  Therefore the client MUST follow
 every OPEN operation with a GETFH operation in the same COMPOUND
 procedure.  This will supply the client with the filehandle such that
 CLOSE can be used appropriately.
 Simply waiting for the lease on the file to expire is insufficient
 because the server may maintain the state indefinitely as long as
 another client does not attempt to make a conflicting access to the
 same file.
 DESCRIPTION
 The OPEN operation creates and/or opens a regular file in a directory
 with the provided name.  If the file does not exist at the server and
 creation is desired, specification of the method of creation is
 provided by the openhow parameter.  The client has the choice of
 three creation methods: UNCHECKED, GUARDED, or EXCLUSIVE.
 If the current filehandle is a named attribute directory, OPEN will
 then create or open a named attribute file.  Note that exclusive
 create of a named attribute is not supported.  If the createmode is
 EXCLUSIVE4 and the current filehandle is a named attribute directory,
 the server will return EINVAL.
 UNCHECKED means that the file should be created if a file of that
 name does not exist and encountering an existing regular file of that
 name is not an error.  For this type of create, createattrs specifies
 the initial set of attributes for the file.  The set of attributes
 may include any writable attribute valid for regular files.  When an
 UNCHECKED create encounters an existing file, the attributes
 specified by createattrs are not used, except that when an size of
 zero is specified, the existing file is truncated.  If GUARDED is
 specified, the server checks for the presence of a duplicate object
 by name before performing the create.  If a duplicate exists, an
 error of NFS4ERR_EXIST is returned as the status.  If the object does
 not exist, the request is performed as described for UNCHECKED.  For

Shepler, et al. Standards Track [Page 172] RFC 3530 NFS version 4 Protocol April 2003

 each of these cases (UNCHECKED and GUARDED) where the operation is
 successful, the server will return to the client an attribute mask
 signifying which attributes were successfully set for the object.
 EXCLUSIVE specifies that the server is to follow exclusive creation
 semantics, using the verifier to ensure exclusive creation of the
 target.  The server should check for the presence of a duplicate
 object by name.  If the object does not exist, the server creates the
 object and stores the verifier with the object.  If the object does
 exist and the stored verifier matches the client provided verifier,
 the server uses the existing object as the newly created object.  If
 the stored verifier does not match, then an error of NFS4ERR_EXIST is
 returned.  No attributes may be provided in this case, since the
 server may use an attribute of the target object to store the
 verifier.  If the server uses an attribute to store the exclusive
 create verifier, it will signify which attribute by setting the
 appropriate bit in the attribute mask that is returned in the
 results.
 For the target directory, the server returns change_info4 information
 in cinfo.  With the atomic field of the change_info4 struct, the
 server will indicate if the before and after change attributes were
 obtained atomically with respect to the link creation.
 Upon successful creation, the current filehandle is replaced by that
 of the new object.
 The OPEN operation provides for Windows share reservation capability
 with the use of the share_access and share_deny fields of the OPEN
 arguments.  The client specifies at OPEN the required share_access
 and share_deny modes.  For clients that do not directly support
 SHAREs (i.e., UNIX), the expected deny value is DENY_NONE.  In the
 case that there is a existing SHARE reservation that conflicts with
 the OPEN request, the server returns the error NFS4ERR_SHARE_DENIED.
 For a complete SHARE request, the client must provide values for the
 owner and seqid fields for the OPEN argument.  For additional
 discussion of SHARE semantics see the section on 'Share
 Reservations'.
 In the case that the client is recovering state from a server
 failure, the claim field of the OPEN argument is used to signify that
 the request is meant to reclaim state previously held.
 The "claim" field of the OPEN argument is used to specify the file to
 be opened and the state information which the client claims to
 possess.  There are four basic claim types which cover the various
 situations for an OPEN.  They are as follows:

Shepler, et al. Standards Track [Page 173] RFC 3530 NFS version 4 Protocol April 2003

 CLAIM_NULL
                       For the client, this is a new OPEN
                       request and there is no previous state
                       associate with the file for the client.
 CLAIM_PREVIOUS
                       The client is claiming basic OPEN state
                       for a file that was held previous to a
                       server reboot.  Generally used when a
                       server is returning persistent
                       filehandles; the client may not have the
                       file name to reclaim the OPEN.
 CLAIM_DELEGATE_CUR
                       The client is claiming a delegation for
                       OPEN as granted by the server.
                       Generally this is done as part of
                       recalling a delegation.
 CLAIM_DELEGATE_PREV
                       The client is claiming a delegation
                       granted to a previous client instance;
                       used after the client reboots. The
                       server MAY support CLAIM_DELEGATE_PREV.
                       If it does support CLAIM_DELEGATE_PREV,
                       SETCLIENTID_CONFIRM MUST NOT remove the
                       client's delegation state, and the
                       server MUST support the DELEGPURGE
                       operation.
 For OPEN requests whose claim type is other than CLAIM_PREVIOUS
 (i.e., requests other than those devoted to reclaiming opens after a
 server reboot) that reach the server during its grace or lease
 expiration period, the server returns an error of NFS4ERR_GRACE.
 For any OPEN request, the server may return an open delegation, which
 allows further opens and closes to be handled locally on the client
 as described in the section Open Delegation.  Note that delegation is
 up to the server to decide.  The client should never assume that
 delegation will or will not be granted in a particular instance.  It
 should always be prepared for either case.  A partial exception is
 the reclaim (CLAIM_PREVIOUS) case, in which a delegation type is
 claimed.  In this case, delegation will always be granted, although
 the server may specify an immediate recall in the delegation
 structure.
 The rflags returned by a successful OPEN allow the server to return
 information governing how the open file is to be handled.

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 OPEN4_RESULT_CONFIRM indicates that the client MUST execute an
 OPEN_CONFIRM operation before using the open file.
 OPEN4_RESULT_LOCKTYPE_POSIX indicates the server's file locking
 behavior supports the complete set of Posix locking techniques.  From
 this the client can choose to manage file locking state in a way to
 handle a mis-match of file locking management.
 If the component is of zero length, NFS4ERR_INVAL will be returned.
 The component is also subject to the normal UTF-8, character support,
 and name checks.  See the section "UTF-8 Related Errors" for further
 discussion.
 When an OPEN is done and the specified lockowner already has the
 resulting filehandle open, the result is to "OR" together the new
 share and deny status together with the existing status.  In this
 case, only a single CLOSE need be done, even though multiple OPENs
 were completed.  When such an OPEN is done, checking of share
 reservations for the new OPEN proceeds normally, with no exception
 for the existing OPEN held by the same lockowner.
 If the underlying filesystem at the server is only accessible in a
 read-only mode and the OPEN request has specified ACCESS_WRITE or
 ACCESS_BOTH, the server will return NFS4ERR_ROFS to indicate a read-
 only filesystem.
 As with the CREATE operation, the server MUST derive the owner, owner
 ACE, group, or group ACE if any of the four attributes are required
 and supported by the server's filesystem.  For an OPEN with the
 EXCLUSIVE4 createmode, the server has no choice, since such OPEN
 calls do not include the createattrs field.  Conversely, if
 createattrs is specified, and includes owner or group (or
 corresponding ACEs) that the principal in the RPC call's credentials
 does not have authorization to create files for, then the server may
 return NFS4ERR_PERM.
 In the case of a OPEN which specifies a size of zero (e.g.,
 truncation) and the file has named attributes, the named attributes
 are left as is.  They are not removed.
 IMPLEMENTATION
 The OPEN operation contains support for EXCLUSIVE create.  The
 mechanism is similar to the support in NFS version 3 [RFC1813].  As
 in NFS version 3, this mechanism provides reliable exclusive
 creation.  Exclusive create is invoked when the how parameter is
 EXCLUSIVE.  In this case, the client provides a verifier that can
 reasonably be expected to be unique.  A combination of a client

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 identifier, perhaps the client network address, and a unique number
 generated by the client, perhaps the RPC transaction identifier, may
 be appropriate.
 If the object does not exist, the server creates the object and
 stores the verifier in stable storage. For filesystems that do not
 provide a mechanism for the storage of arbitrary file attributes, the
 server may use one or more elements of the object meta-data to store
 the verifier. The verifier must be stored in stable storage to
 prevent erroneous failure on retransmission of the request. It is
 assumed that an exclusive create is being performed because exclusive
 semantics are critical to the application. Because of the expected
 usage, exclusive CREATE does not rely solely on the normally volatile
 duplicate request cache for storage of the verifier. The duplicate
 request cache in volatile storage does not survive a crash and may
 actually flush on a long network partition, opening failure windows.
 In the UNIX local filesystem environment, the expected storage
 location for the verifier on creation is the meta-data (time stamps)
 of the object. For this reason, an exclusive object create may not
 include initial attributes because the server would have nowhere to
 store the verifier.
 If the server can not support these exclusive create semantics,
 possibly because of the requirement to commit the verifier to stable
 storage, it should fail the OPEN request with the error,
 NFS4ERR_NOTSUPP.
 During an exclusive CREATE request, if the object already exists, the
 server reconstructs the object's verifier and compares it with the
 verifier in the request. If they match, the server treats the request
 as a success. The request is presumed to be a duplicate of an
 earlier, successful request for which the reply was lost and that the
 server duplicate request cache mechanism did not detect.  If the
 verifiers do not match, the request is rejected with the status,
 NFS4ERR_EXIST.
 Once the client has performed a successful exclusive create, it must
 issue a SETATTR to set the correct object attributes.  Until it does
 so, it should not rely upon any of the object attributes, since the
 server implementation may need to overload object meta-data to store
 the verifier.  The subsequent SETATTR must not occur in the same
 COMPOUND request as the OPEN.  This separation will guarantee that
 the exclusive create mechanism will continue to function properly in
 the face of retransmission of the request.
 Use of the GUARDED attribute does not provide exactly-once semantics.
 In particular, if a reply is lost and the server does not detect the
 retransmission of the request, the operation can fail with

Shepler, et al. Standards Track [Page 176] RFC 3530 NFS version 4 Protocol April 2003

 NFS4ERR_EXIST, even though the create was performed successfully.
 The client would use this behavior in the case that the application
 has not requested an exclusive create but has asked to have the file
 truncated when the file is opened.  In the case of the client timing
 out and retransmitting the create request, the client can use GUARDED
 to prevent against a sequence like: create, write, create
 (retransmitted) from occurring.
 For SHARE reservations, the client must specify a value for
 share_access that is one of READ, WRITE, or BOTH.  For share_deny,
 the client must specify one of NONE, READ, WRITE, or BOTH.  If the
 client fails to do this, the server must return NFS4ERR_INVAL.
 Based on the share_access value (READ, WRITE, or BOTH) the client
 should check that the requester has the proper access rights to
 perform the specified operation.  This would generally be the results
 of applying the ACL access rules to the file for the current
 requester.  However, just as with the ACCESS operation, the client
 should not attempt to second-guess the server's decisions, as access
 rights may change and may be subject to server administrative
 controls outside the ACL framework.  If the requester is not
 authorized to READ or WRITE (depending on the share_access value),
 the server must return NFS4ERR_ACCESS.  Note that since the NFS
 version 4 protocol does not impose any requirement that READs and
 WRITEs issued for an open file have the same credentials as the OPEN
 itself, the server still must do appropriate access checking on the
 READs and WRITEs themselves.
 If the component provided to OPEN is a symbolic link, the error
 NFS4ERR_SYMLINK will be returned to the client.  If the current
 filehandle is not a directory, the error NFS4ERR_NOTDIR will be
 returned.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_ATTRNOTSUPP
    NFS4ERR_BADCHAR
    NFS4ERR_BADHANDLE
    NFS4ERR_BADNAME
    NFS4ERR_BADOWNER
    NFS4ERR_BAD_SEQID
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_DQUOT
    NFS4ERR_EXIST
    NFS4ERR_EXPIRED

Shepler, et al. Standards Track [Page 177] RFC 3530 NFS version 4 Protocol April 2003

    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_IO
    NFS4ERR_INVAL
    NFS4ERR_ISDIR
    NFS4ERR_LEASE_MOVED
    NFS4ERR_MOVED
    NFS4ERR_NAMETOOLONG
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOSPC
    NFS4ERR_NOTDIR
    NFS4ERR_NOTSUPP
    NFS4ERR_NO_GRACE
    NFS4ERR_PERM
    NFS4ERR_RECLAIM_BAD
    NFS4ERR_RECLAIM_CONFLICT
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_SHARE_DENIED
    NFS4ERR_STALE
    NFS4ERR_STALE_CLIENTID
    NFS4ERR_SYMLINK
    NFS4ERR_WRONGSEC

14.2.17. Operation 19: OPENATTR - Open Named Attribute Directory

 SYNOPSIS
   (cfh) createdir -> (cfh)
 ARGUMENT
   struct OPENATTR4args {
           /* CURRENT_FH: object */
           bool    createdir;
   };
 RESULT
   struct OPENATTR4res {
           /* CURRENT_FH: named attr directory*/
           nfsstat4        status;
   };

Shepler, et al. Standards Track [Page 178] RFC 3530 NFS version 4 Protocol April 2003

 DESCRIPTION
 The OPENATTR operation is used to obtain the filehandle of the named
 attribute directory associated with the current filehandle.  The
 result of the OPENATTR will be a filehandle to an object of type
 NF4ATTRDIR.  From this filehandle, READDIR and LOOKUP operations can
 be used to obtain filehandles for the various named attributes
 associated with the original filesystem object.  Filehandles returned
 within the named attribute directory will have a type of
 NF4NAMEDATTR.
 The createdir argument allows the client to signify if a named
 attribute directory should be created as a result of the OPENATTR
 operation.  Some clients may use the OPENATTR operation with a value
 of FALSE for createdir to determine if any named attributes exist for
 the object.  If none exist, then NFS4ERR_NOENT will be returned.  If
 createdir has a value of TRUE and no named attribute directory
 exists, one is created.  The creation of a named attribute directory
 assumes that the server has implemented named attribute support in
 this fashion and is not required to do so by this definition.
 IMPLEMENTATION
 If the server does not support named attributes for the current
 filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
 client.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADHANDLE
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_DQUOT
    NFS4ERR_FHEXPIRED
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOSPC
    NFS4ERR_NOTSUPP
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

Shepler, et al. Standards Track [Page 179] RFC 3530 NFS version 4 Protocol April 2003

14.2.18. Operation 20: OPEN_CONFIRM - Confirm Open

 SYNOPSIS
   (cfh), seqid, stateid-> stateid
 ARGUMENT
   struct OPEN_CONFIRM4args {
           /* CURRENT_FH: opened file */
           stateid4        open_stateid;
           seqid4          seqid;
   };
 RESULT
   struct OPEN_CONFIRM4resok {
           stateid4        open_stateid;
   };
   union OPEN_CONFIRM4res switch (nfsstat4 status) {
    case NFS4_OK:
            OPEN_CONFIRM4resok     resok4;
    default:
            void;
   };
 DESCRIPTION
 This operation is used to confirm the sequence id usage for the first
 time that a open_owner is used by a client.  The stateid returned
 from the OPEN operation is used as the argument for this operation
 along with the next sequence id for the open_owner.  The sequence id
 passed to the OPEN_CONFIRM must be 1 (one) greater than the seqid
 passed to the OPEN operation from which the open_confirm value was
 obtained.  If the server receives an unexpected sequence id with
 respect to the original open, then the server assumes that the client
 will not confirm the original OPEN and all state associated with the
 original OPEN is released by the server.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 A given client might generate many open_owner4 data structures for a
 given clientid.  The client will periodically either dispose of its
 open_owner4s or stop using them for indefinite periods of time.  The
 latter situation is why the NFS version 4 protocol does not have an

Shepler, et al. Standards Track [Page 180] RFC 3530 NFS version 4 Protocol April 2003

 explicit operation to exit an open_owner4: such an operation is of no
 use in that situation.  Instead, to avoid unbounded memory use, the
 server needs to implement a strategy for disposing of open_owner4s
 that have no current lock, open, or delegation state for any files
 and have not been used recently.  The time period used to determine
 when to dispose of open_owner4s is an implementation choice.  The
 time period should certainly be no less than the lease time plus any
 grace period the server wishes to implement beyond a lease time.  The
 OPEN_CONFIRM operation allows the server to safely dispose of unused
 open_owner4 data structures.
 In the case that a client issues an OPEN operation and the server no
 longer has a record of the open_owner4, the server needs to ensure
 that this is a new OPEN and not a replay or retransmission.
 Servers must not require confirmation on OPENs that grant delegations
 or are doing reclaim operations.  See section "Use of Open
 Confirmation" for details.  The server can easily avoid this by
 noting whether it has disposed of one open_owner4 for the given
 clientid.  If the server does not support delegation, it might simply
 maintain a single bit that notes whether any open_owner4 (for any
 client) has been disposed of.
 The server must hold unconfirmed OPEN state until one of three events
 occur.  First, the client sends an OPEN_CONFIRM request with the
 appropriate sequence id and stateid within the lease period.  In this
 case, the OPEN state on the server goes to confirmed, and the
 open_owner4 on the server is fully established.
 Second, the client sends another OPEN request with a sequence id that
 is incorrect for the open_owner4 (out of sequence).  In this case,
 the server assumes the second OPEN request is valid and the first one
 is a replay.  The server cancels the OPEN state of the first OPEN
 request, establishes an unconfirmed OPEN state for the second OPEN
 request, and responds to the second OPEN request with an indication
 that an OPEN_CONFIRM is needed.  The process then repeats itself.
 While there is a potential for a denial of service attack on the
 client, it is mitigated if the client and server require the use of a
 security flavor based on Kerberos V5, LIPKEY, or some other flavor
 that uses cryptography.
 What if the server is in the unconfirmed OPEN state for a given
 open_owner4, and it receives an operation on the open_owner4 that has
 a stateid but the operation is not OPEN, or it is OPEN_CONFIRM but
 with the wrong stateid?  Then, even if the seqid is correct, the

Shepler, et al. Standards Track [Page 181] RFC 3530 NFS version 4 Protocol April 2003

 server returns NFS4ERR_BAD_STATEID, because the server assumes the
 operation is a replay: if the server has no established OPEN state,
 then there is no way, for example, a LOCK operation could be valid.
 Third, neither of the two aforementioned events occur for the
 open_owner4 within the lease period.  In this case, the OPEN state is
 canceled and disposal of the open_owner4 can occur.
 ERRORS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_SEQID
    NFS4ERR_BAD_STATEID
    NFS4ERR_BADXDR
    NFS4ERR_EXPIRED
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_ISDIR
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_OLD_STATEID
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_STATEID

14.2.19. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access

 SYNOPSIS
   (cfh), stateid, seqid, access, deny -> stateid
 ARGUMENT
   struct OPEN_DOWNGRADE4args {
           /* CURRENT_FH: opened file */
           stateid4        open_stateid;
           seqid4          seqid;
           uint32_t        share_access;
           uint32_t        share_deny;
   };
 RESULT
   struct OPEN_DOWNGRADE4resok {
           stateid4        open_stateid;
   };

Shepler, et al. Standards Track [Page 182] RFC 3530 NFS version 4 Protocol April 2003

   union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
    case NFS4_OK:
           OPEN_DOWNGRADE4resok    resok4;
    default:
           void;
   };
 DESCRIPTION
 This operation is used to adjust the share_access and share_deny bits
 for a given open.  This is necessary when a given openowner opens the
 same file multiple times with different share_access and share_deny
 flags.  In this situation, a close of one of the opens may change the
 appropriate share_access and share_deny flags to remove bits
 associated with opens no longer in effect.
 The share_access and share_deny bits specified in this operation
 replace the current ones for the specified open file.  The
 share_access and share_deny bits specified must be exactly equal to
 the union of the share_access and share_deny bits specified for some
 subset of the OPENs in effect for current openowner on the current
 file.  If that constraint is not respected, the error NFS4ERR_INVAL
 should be returned.  Since share_access and share_deny bits are
 subsets of those already granted, it is not possible for this request
 to be denied because of conflicting share reservations.
 On success, the current filehandle retains its value.
 ERRORS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_SEQID
    NFS4ERR_BAD_STATEID
    NFS4ERR_BADXDR
    NFS4ERR_EXPIRED
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_OLD_STATEID
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_STATEID

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14.2.20. Operation 22: PUTFH - Set Current Filehandle

 SYNOPSIS
   filehandle -> (cfh)
 ARGUMENT
   struct PUTFH4args {
           nfs_fh4         object;
   };
 RESULT
   struct PUTFH4res {
           /* CURRENT_FH: */
           nfsstat4        status;
   };
 DESCRIPTION
 Replaces the current filehandle with the filehandle provided as an
 argument.
 If the security mechanism used by the requester does not meet the
 requirements of the filehandle provided to this operation, the server
 MUST return NFS4ERR_WRONGSEC.
 IMPLEMENTATION
 Commonly used as the first operator in an NFS request to set the
 context for following operations.
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_BADXDR
    NFS4ERR_FHEXPIRED
    NFS4ERR_MOVED
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

Shepler, et al. Standards Track [Page 184] RFC 3530 NFS version 4 Protocol April 2003

14.2.21. Operation 23: PUTPUBFH - Set Public Filehandle

 SYNOPSIS
  1. → (cfh)
 ARGUMENT
   void;
 RESULT
   struct PUTPUBFH4res {
           /* CURRENT_FH: public fh */
           nfsstat4        status;
   };
 DESCRIPTION
 Replaces the current filehandle with the filehandle that represents
 the public filehandle of the server's name space.  This filehandle
 may be different from the "root" filehandle which may be associated
 with some other directory on the server.
 The public filehandle represents the concepts embodied in [RFC2054],
 [RFC2055], [RFC2224].  The intent for NFS version 4 is that the
 public filehandle (represented by the PUTPUBFH operation) be used as
 a method of providing WebNFS server compatibility with NFS versions 2
 and 3.
 The public filehandle and the root filehandle (represented by the
 PUTROOTFH operation) should be equivalent.  If the public and root
 filehandles are not equivalent, then the public filehandle MUST be a
 descendant of the root filehandle.
 IMPLEMENTATION
 Used as the first operator in an NFS request to set the context for
 following operations.
 With the NFS version 2 and 3 public filehandle, the client is able to
 specify whether the path name provided in the LOOKUP should be
 evaluated as either an absolute path relative to the server's root or
 relative to the public filehandle.  [RFC2224] contains further
 discussion of the functionality.  With NFS version 4, that type of
 specification is not directly available in the LOOKUP operation.  The
 reason for this is because the component separators needed to specify
 absolute vs. relative are not allowed in NFS version 4.  Therefore,

Shepler, et al. Standards Track [Page 185] RFC 3530 NFS version 4 Protocol April 2003

 the client is responsible for constructing its request such that the
 use of either PUTROOTFH or PUTPUBFH are used to signify absolute or
 relative evaluation of an NFS URL respectively.
 Note that there are warnings mentioned in [RFC2224] with respect to
 the use of absolute evaluation and the restrictions the server may
 place on that evaluation with respect to how much of its namespace
 has been made available.  These same warnings apply to NFS version 4.
 It is likely, therefore that because of server implementation
 details, an NFS version 3 absolute public filehandle lookup may
 behave differently than an NFS version 4 absolute resolution.
 There is a form of security negotiation as described in [RFC2755]
 that uses the public filehandle a method of employing SNEGO.  This
 method is not available with NFS version 4 as filehandles are not
 overloaded with special meaning and therefore do not provide the same
 framework as NFS versions 2 and 3.  Clients should therefore use the
 security negotiation mechanisms described in this RFC.
 ERRORS
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_WRONGSEC

14.2.22. Operation 24: PUTROOTFH - Set Root Filehandle

 SYNOPSIS
  1. → (cfh)
 ARGUMENT
   void;
 RESULT
   struct PUTROOTFH4res {
           /* CURRENT_FH: root fh */
           nfsstat4        status;
   };

Shepler, et al. Standards Track [Page 186] RFC 3530 NFS version 4 Protocol April 2003

 DESCRIPTION
 Replaces the current filehandle with the filehandle that represents
 the root of the server's name space.  From this filehandle a LOOKUP
 operation can locate any other filehandle on the server. This
 filehandle may be different from the "public" filehandle which may be
 associated with some other directory on the server.
 IMPLEMENTATION
 Commonly used as the first operator in an NFS request to set the
 context for following operations.
 ERRORS
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_WRONGSEC

14.2.23. Operation 25: READ - Read from File

 SYNOPSIS
   (cfh), stateid, offset, count -> eof, data
 ARGUMENT
   struct READ4args {
           /* CURRENT_FH: file */
           stateid4        stateid;
           offset4         offset;
           count4          count;
   };
 RESULT
   struct READ4resok {
           bool            eof;
           opaque          data<>;
   };
   union READ4res switch (nfsstat4 status) {
    case NFS4_OK:
            READ4resok     resok4;
    default:
            void;
   };

Shepler, et al. Standards Track [Page 187] RFC 3530 NFS version 4 Protocol April 2003

 DESCRIPTION
 The READ operation reads data from the regular file identified by the
 current filehandle.
 The client provides an offset of where the READ is to start and a
 count of how many bytes are to be read.  An offset of 0 (zero) means
 to read data starting at the beginning of the file.  If offset is
 greater than or equal to the size of the file, the status, NFS4_OK,
 is returned with a data length set to 0 (zero) and eof is set to
 TRUE.  The READ is subject to access permissions checking.
 If the client specifies a count value of 0 (zero), the READ succeeds
 and returns 0 (zero) bytes of data again subject to access
 permissions checking.  The server may choose to return fewer bytes
 than specified by the client.  The client needs to check for this
 condition and handle the condition appropriately.
 The stateid value for a READ request represents a value returned from
 a previous record lock or share reservation request.  The stateid is
 used by the server to verify that the associated share reservation
 and any record locks are still valid and to update lease timeouts for
 the client.
 If the read ended at the end-of-file (formally, in a correctly formed
 READ request, if offset + count is equal to the size of the file), or
 the read request extends beyond the size of the file (if offset +
 count is greater than the size of the file), eof is returned as TRUE;
 otherwise it is FALSE.  A successful READ of an empty file will
 always return eof as TRUE.
 If the current filehandle is not a regular file, an error will be
 returned to the client.  In the case the current filehandle
 represents a directory, NFS4ERR_ISDIR is return; otherwise,
 NFS4ERR_INVAL is returned.
 For a READ with a stateid value of all bits 0, the server MAY allow
 the READ to be serviced subject to mandatory file locks or the
 current share deny modes for the file.  For a READ with a stateid
 value of all bits 1, the server MAY allow READ operations to bypass
 locking checks at the server.
 On success, the current filehandle retains its value.

Shepler, et al. Standards Track [Page 188] RFC 3530 NFS version 4 Protocol April 2003

 IMPLEMENTATION
 It is possible for the server to return fewer than count bytes of
 data.  If the server returns less than the count requested and eof is
 set to FALSE, the client should issue another READ to get the
 remaining data.  A server may return less data than requested under
 several circumstances.  The file may have been truncated by another
 client or perhaps on the server itself, changing the file size from
 what the requesting client believes to be the case.  This would
 reduce the actual amount of data available to the client.  It is
 possible that the server may back off the transfer size and reduce
 the read request return.  Server resource exhaustion may also occur
 necessitating a smaller read return.
 If mandatory file locking is on for the file, and if the region
 corresponding to the data to be read from file is write locked by an
 owner not associated the stateid, the server will return the
 NFS4ERR_LOCKED error.  The client should try to get the appropriate
 read record lock via the LOCK operation before re-attempting the
 READ.  When the READ completes, the client should release the record
 lock via LOCKU.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_STATEID
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_EXPIRED
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_IO
    NFS4ERR_INVAL
    NFS4ERR_ISDIR
    NFS4ERR_LEASE_MOVED
    NFS4ERR_LOCKED
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NXIO
    NFS4ERR_OLD_STATEID
    NFS4ERR_OPENMODE
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_STATEID

Shepler, et al. Standards Track [Page 189] RFC 3530 NFS version 4 Protocol April 2003

14.2.24. Operation 26: READDIR - Read Directory

 SYNOPSIS
    (cfh), cookie, cookieverf, dircount, maxcount, attr_request ->
    cookieverf { cookie, name, attrs }
 ARGUMENT
   struct READDIR4args {
           /* CURRENT_FH: directory */
           nfs_cookie4     cookie;
           verifier4       cookieverf;
           count4          dircount;
           count4          maxcount;
           bitmap4         attr_request;
   };
 RESULT
   struct entry4 {
           nfs_cookie4     cookie;
           component4      name;
           fattr4          attrs;
           entry4          *nextentry;
   };
   struct dirlist4 {
           entry4          *entries;
           bool            eof;
   };
   struct READDIR4resok {
           verifier4       cookieverf;
           dirlist4        reply;
   };
   union READDIR4res switch (nfsstat4 status) {
    case NFS4_OK:
            READDIR4resok  resok4;
    default:
            void;
   };

Shepler, et al. Standards Track [Page 190] RFC 3530 NFS version 4 Protocol April 2003

 DESCRIPTION
 The READDIR operation retrieves a variable number of entries from a
 filesystem directory and returns client requested attributes for each
 entry along with information to allow the client to request
 additional directory entries in a subsequent READDIR.
 The arguments contain a cookie value that represents where the
 READDIR should start within the directory.  A value of 0 (zero) for
 the cookie is used to start reading at the beginning of the
 directory.  For subsequent READDIR requests, the client specifies a
 cookie value that is provided by the server on a previous READDIR
 request.
 The cookieverf value should be set to 0 (zero) when the cookie value
 is 0 (zero) (first directory read).  On subsequent requests, it
 should be a cookieverf as returned by the server.  The cookieverf
 must match that returned by the READDIR in which the cookie was
 acquired.  If the server determines that the cookieverf is no longer
 valid for the directory, the error NFS4ERR_NOT_SAME must be returned.
 The dircount portion of the argument is a hint of the maximum number
 of bytes of directory information that should be returned.  This
 value represents the length of the names of the directory entries and
 the cookie value for these entries.  This length represents the XDR
 encoding of the data (names and cookies) and not the length in the
 native format of the server.
 The maxcount value of the argument is the maximum number of bytes for
 the result.  This maximum size represents all of the data being
 returned within the READDIR4resok structure and includes the XDR
 overhead.  The server may return less data.  If the server is unable
 to return a single directory entry within the maxcount limit, the
 error NFS4ERR_TOOSMALL will be returned to the client.
 Finally, attr_request represents the list of attributes to be
 returned for each directory entry supplied by the server.
 On successful return, the server's response will provide a list of
 directory entries.  Each of these entries contains the name of the
 directory entry, a cookie value for that entry, and the associated
 attributes as requested.  The "eof" flag has a value of TRUE if there
 are no more entries in the directory.
 The cookie value is only meaningful to the server and is used as a
 "bookmark" for the directory entry.  As mentioned, this cookie is
 used by the client for subsequent READDIR operations so that it may
 continue reading a directory.  The cookie is similar in concept to a

Shepler, et al. Standards Track [Page 191] RFC 3530 NFS version 4 Protocol April 2003

 READ offset but should not be interpreted as such by the client.
 Ideally, the cookie value should not change if the directory is
 modified since the client may be caching these values.
 In some cases, the server may encounter an error while obtaining the
 attributes for a directory entry.  Instead of returning an error for
 the entire READDIR operation, the server can instead return the
 attribute 'fattr4_rdattr_error'.  With this, the server is able to
 communicate the failure to the client and not fail the entire
 operation in the instance of what might be a transient failure.
 Obviously, the client must request the fattr4_rdattr_error attribute
 for this method to work properly.  If the client does not request the
 attribute, the server has no choice but to return failure for the
 entire READDIR operation.
 For some filesystem environments, the directory entries "." and ".."
 have special meaning and in other environments, they may not.  If the
 server supports these special entries within a directory, they should
 not be returned to the client as part of the READDIR response.  To
 enable some client environments, the cookie values of 0, 1, and 2 are
 to be considered reserved.  Note that the UNIX client will use these
 values when combining the server's response and local representations
 to enable a fully formed UNIX directory presentation to the
 application.
 For READDIR arguments, cookie values of 1 and 2 should not be used
 and for READDIR results cookie values of 0, 1, and 2 should not be
 returned.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 The server's filesystem directory representations can differ greatly.
 A client's programming interfaces may also be bound to the local
 operating environment in a way that does not translate well into the
 NFS protocol.  Therefore the use of the dircount and maxcount fields
 are provided to allow the client the ability to provide guidelines to
 the server.  If the client is aggressive about attribute collection
 during a READDIR, the server has an idea of how to limit the encoded
 response.  The dircount field provides a hint on the number of
 entries based solely on the names of the directory entries.  Since it
 is a hint, it may be possible that a dircount value is zero.  In this
 case, the server is free to ignore the dircount value and return
 directory information based on the specified maxcount value.

Shepler, et al. Standards Track [Page 192] RFC 3530 NFS version 4 Protocol April 2003

 The cookieverf may be used by the server to help manage cookie values
 that may become stale.  It should be a rare occurrence that a server
 is unable to continue properly reading a directory with the provided
 cookie/cookieverf pair.  The server should make every effort to avoid
 this condition since the application at the client may not be able to
 properly handle this type of failure.
 The use of the cookieverf will also protect the client from using
 READDIR cookie values that may be stale.  For example, if the file
 system has been migrated, the server may or may not be able to use
 the same cookie values to service READDIR as the previous server
 used.  With the client providing the cookieverf, the server is able
 to provide the appropriate response to the client.  This prevents the
 case where the server may accept a cookie value but the underlying
 directory has changed and the response is invalid from the client's
 context of its previous READDIR.
 Since some servers will not be returning "." and ".." entries as has
 been done with previous versions of the NFS protocol, the client that
 requires these entries be present in READDIR responses must fabricate
 them.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_COOKIE
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTDIR
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_TOOSMALL

14.2.25. Operation 27: READLINK - Read Symbolic Link

 SYNOPSIS
   (cfh) -> linktext

Shepler, et al. Standards Track [Page 193] RFC 3530 NFS version 4 Protocol April 2003

 ARGUMENT
   /* CURRENT_FH: symlink */
   void;
 RESULT
   struct READLINK4resok {
           linktext4       link;
   };
   union READLINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            READLINK4resok resok4;
    default:
            void;
   };
 DESCRIPTION
 READLINK reads the data associated with a symbolic link.  The data is
 a UTF-8 string that is opaque to the server.  That is, whether
 created by an NFS client or created locally on the server, the data
 in a symbolic link is not interpreted when created, but is simply
 stored.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 A symbolic link is nominally a pointer to another file.  The data is
 not necessarily interpreted by the server, just stored in the file.
 It is possible for a client implementation to store a path name that
 is not meaningful to the server operating system in a symbolic link.
 A READLINK operation returns the data to the client for
 interpretation. If different implementations want to share access to
 symbolic links, then they must agree on the interpretation of the
 data in the symbolic link.
 The READLINK operation is only allowed on objects of type NF4LNK.
 The server should return the error, NFS4ERR_INVAL, if the object is
 not of type, NF4LNK.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADHANDLE
    NFS4ERR_DELAY

Shepler, et al. Standards Track [Page 194] RFC 3530 NFS version 4 Protocol April 2003

    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_ISDIR
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTSUPP
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

14.2.26. Operation 28: REMOVE - Remove Filesystem Object

 SYNOPSIS
   (cfh), filename -> change_info
 ARGUMENT
   struct REMOVE4args {
           /* CURRENT_FH: directory */
           component4       target;
   };
 RESULT
   struct REMOVE4resok {
           change_info4    cinfo;
   }
   union REMOVE4res switch (nfsstat4 status) {
    case NFS4_OK:
            REMOVE4resok   resok4;
    default:
            void;
   }
 DESCRIPTION
 The REMOVE operation removes (deletes) a directory entry named by
 filename from the directory corresponding to the current filehandle.
 If the entry in the directory was the last reference to the
 corresponding filesystem object, the object may be destroyed.

Shepler, et al. Standards Track [Page 195] RFC 3530 NFS version 4 Protocol April 2003

 For the directory where the filename was removed, the server returns
 change_info4 information in cinfo.  With the atomic field of the
 change_info4 struct, the server will indicate if the before and after
 change attributes were obtained atomically with respect to the
 removal.
 If the target has a length of 0 (zero), or if target does not obey
 the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 NFS versions 2 and 3 required a different operator RMDIR for
 directory removal and REMOVE for non-directory removal. This allowed
 clients to skip checking the file type when being passed a non-
 directory delete system call (e.g., unlink() in POSIX) to remove a
 directory, as well as the converse (e.g., a rmdir() on a non-
 directory) because they knew the server would check the file type.
 NFS version 4 REMOVE can be used to delete any directory entry
 independent of its file type. The implementor of an NFS version 4
 client's entry points from the unlink() and rmdir() system calls
 should first check the file type against the types the system call is
 allowed to remove before issuing a REMOVE. Alternatively, the
 implementor can produce a COMPOUND call that includes a LOOKUP/VERIFY
 sequence to verify the file type before a REMOVE operation in the
 same COMPOUND call.
 The concept of last reference is server specific.  However, if the
 numlinks field in the previous attributes of the object had the value
 1, the client should not rely on referring to the object via a
 filehandle.  Likewise, the client should not rely on the resources
 (disk space, directory entry, and so on) formerly associated with the
 object becoming immediately available.  Thus, if a client needs to be
 able to continue to access a file after using REMOVE to remove it,
 the client should take steps to make sure that the file will still be
 accessible.  The usual mechanism used is to RENAME the file from its
 old name to a new hidden name.
 If the server finds that the file is still open when the REMOVE
 arrives:
 o  The server SHOULD NOT delete the file's directory entry if the
    file was opened with OPEN4_SHARE_DENY_WRITE or
    OPEN4_SHARE_DENY_BOTH.

Shepler, et al. Standards Track [Page 196] RFC 3530 NFS version 4 Protocol April 2003

 o  If the file was not opened with OPEN4_SHARE_DENY_WRITE or
    OPEN4_SHARE_DENY_BOTH, the server SHOULD delete the file's
    directory entry.  However, until last CLOSE of the file, the
    server MAY continue to allow access to the file via its
    filehandle.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADCHAR
    NFS4ERR_BADHANDLE
    NFS4ERR_BADNAME
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_FILE_OPEN
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NAMETOOLONG
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTDIR
    NFS4ERR_NOTEMPTY
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

14.2.27. Operation 29: RENAME - Rename Directory Entry

 SYNOPSIS
   (sfh), oldname, (cfh), newname -> source_change_info,
   target_change_info
 ARGUMENT
   struct RENAME4args {
           /* SAVED_FH: source directory */
           component4      oldname;
           /* CURRENT_FH: target directory */
           component4      newname;
   };

Shepler, et al. Standards Track [Page 197] RFC 3530 NFS version 4 Protocol April 2003

 RESULT
   struct RENAME4resok {
           change_info4    source_cinfo;
           change_info4    target_cinfo;
   };
   union RENAME4res switch (nfsstat4 status) {
    case NFS4_OK:
            RENAME4resok   resok4;
    default:
            void;
   };
 DESCRIPTION
 The RENAME operation renames the object identified by oldname in the
 source directory corresponding to the saved filehandle, as set by the
 SAVEFH operation, to newname in the target directory corresponding to
 the current filehandle.  The operation is required to be atomic to
 the client.  Source and target directories must reside on the same
 filesystem on the server.  On success, the current filehandle will
 continue to be the target directory.
 If the target directory already contains an entry with the name,
 newname, the source object must be compatible with the target:
 either both are non-directories or both are directories and the
 target must be empty.  If compatible, the existing target is removed
 before the rename occurs (See the IMPLEMENTATION subsection of the
 section "Operation 28: REMOVE - Remove Filesystem Object" for client
 and server actions whenever a target is removed).  If they are not
 compatible or if the target is a directory but not empty, the server
 will return the error, NFS4ERR_EXIST.
 If oldname and newname both refer to the same file (they might be
 hard links of each other), then RENAME should perform no action and
 return success.
 For both directories involved in the RENAME, the server returns
 change_info4 information.  With the atomic field of the change_info4
 struct, the server will indicate if the before and after change
 attributes were obtained atomically with respect to the rename.
 If the oldname refers to a named attribute and the saved and current
 filehandles refer to different filesystem objects, the server will
 return NFS4ERR_XDEV just as if the saved and current filehandles
 represented directories on different filesystems.

Shepler, et al. Standards Track [Page 198] RFC 3530 NFS version 4 Protocol April 2003

 If the oldname or newname has a length of 0 (zero), or if oldname or
 newname does not obey the UTF-8 definition, the error NFS4ERR_INVAL
 will be returned.
 IMPLEMENTATION
 The RENAME operation must be atomic to the client.  The statement
 "source and target directories must reside on the same filesystem on
 the server" means that the fsid fields in the attributes for the
 directories are the same. If they reside on different filesystems,
 the error, NFS4ERR_XDEV, is returned.
 Based on the value of the fh_expire_type attribute for the object,
 the filehandle may or may not expire on a RENAME.  However, server
 implementors are strongly encouraged to attempt to keep filehandles
 from expiring in this fashion.
 On some servers, the file names "." and ".." are illegal as either
 oldname or newname, and will result in the error NFS4ERR_BADNAME.  In
 addition, on many servers the case of oldname or newname being an
 alias for the source directory will be checked for.  Such servers
 will return the error NFS4ERR_INVAL in these cases.
 If either of the source or target filehandles are not directories,
 the server will return NFS4ERR_NOTDIR.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADCHAR
    NFS4ERR_BADHANDLE
    NFS4ERR_BADNAME
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_DQUOT
    NFS4ERR_EXIST
    NFS4ERR_FHEXPIRED
    NFS4ERR_FILE_OPEN
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NAMETOOLONG
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOSPC
    NFS4ERR_NOTDIR
    NFS4ERR_NOTEMPTY
    NFS4ERR_RESOURCE

Shepler, et al. Standards Track [Page 199] RFC 3530 NFS version 4 Protocol April 2003

    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC
    NFS4ERR_XDEV

14.2.28. Operation 30: RENEW - Renew a Lease

 SYNOPSIS
   clientid -> ()
 ARGUMENT
   struct RENEW4args {
           clientid4       clientid;
   };
 RESULT
   struct RENEW4res {
           nfsstat4        status;
   };
 DESCRIPTION
 The RENEW operation is used by the client to renew leases which it
 currently holds at a server.  In processing the RENEW request, the
 server renews all leases associated with the client.  The associated
 leases are determined by the clientid provided via the SETCLIENTID
 operation.
 IMPLEMENTATION
 When the client holds delegations, it needs to use RENEW to detect
 when the server has determined that the callback path is down.  When
 the server has made such a determination, only the RENEW operation
 will renew the lease on delegations.  If the server determines the
 callback path is down, it returns NFS4ERR_CB_PATH_DOWN.  Even though
 it returns NFS4ERR_CB_PATH_DOWN, the server MUST renew the lease on
 the record locks and share reservations that the client has
 established on the server.  If for some reason the lock and share
 reservation lease cannot be renewed, then the server MUST return an
 error other than NFS4ERR_CB_PATH_DOWN, even if the callback path is
 also down.

Shepler, et al. Standards Track [Page 200] RFC 3530 NFS version 4 Protocol April 2003

 The client that issues RENEW MUST choose the principal, RPC security
 flavor, and if applicable, GSS-API mechanism and service via one of
 the following algorithms:
 o  The client uses the same principal, RPC security flavor -- and if
    the flavor was RPCSEC_GSS -- the same mechanism and service that
    was used when the client id was established via
    SETCLIENTID_CONFIRM.
 o  The client uses any principal, RPC security flavor mechanism and
    service combination that currently has an OPEN file on the server.
    I.e.,  the same principal had a successful OPEN operation, the
    file is still open by that principal, and the flavor, mechanism,
    and service of RENEW match that of the previous OPEN.
 The server MUST reject a RENEW that does not use one the
 aforementioned algorithms, with the error NFS4ERR_ACCESS.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_BADXDR
    NFS4ERR_CB_PATH_DOWN
    NFS4ERR_EXPIRED
    NFS4ERR_LEASE_MOVED
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE_CLIENTID

14.2.29. Operation 31: RESTOREFH - Restore Saved Filehandle

 SYNOPSIS
   (sfh) -> (cfh)
 ARGUMENT
   /* SAVED_FH: */
   void;
 RESULT
   struct RESTOREFH4res {
           /* CURRENT_FH: value of saved fh */
           nfsstat4        status;
   };

Shepler, et al. Standards Track [Page 201] RFC 3530 NFS version 4 Protocol April 2003

 DESCRIPTION
 Set the current filehandle to the value in the saved filehandle.  If
 there is no saved filehandle then return the error NFS4ERR_RESTOREFH.
 IMPLEMENTATION
 Operations like OPEN and LOOKUP use the current filehandle to
 represent a directory and replace it with a new filehandle.  Assuming
 the previous filehandle was saved with a SAVEFH operator, the
 previous filehandle can be restored as the current filehandle.  This
 is commonly used to obtain post-operation attributes for the
 directory, e.g.,
       PUTFH (directory filehandle)
       SAVEFH
       GETATTR attrbits     (pre-op dir attrs)
       CREATE optbits "foo" attrs
       GETATTR attrbits     (file attributes)
       RESTOREFH
       GETATTR attrbits     (post-op dir attrs)
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_FHEXPIRED
    NFS4ERR_MOVED
    NFS4ERR_RESOURCE
    NFS4ERR_RESTOREFH
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

14.2.30. Operation 32: SAVEFH - Save Current Filehandle

 SYNOPSIS
   (cfh) -> (sfh)
 ARGUMENT
   /* CURRENT_FH: */
   void;

Shepler, et al. Standards Track [Page 202] RFC 3530 NFS version 4 Protocol April 2003

 RESULT
   struct SAVEFH4res {
           /* SAVED_FH: value of current fh */
           nfsstat4        status;
   };
 DESCRIPTION
 Save the current filehandle.  If a previous filehandle was saved then
 it is no longer accessible.  The saved filehandle can be restored as
 the current filehandle with the RESTOREFH operator.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_FHEXPIRED
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

14.2.31. Operation 33: SECINFO - Obtain Available Security

 SYNOPSIS
   (cfh), name -> { secinfo }
 ARGUMENT
   struct SECINFO4args {
           /* CURRENT_FH: directory */
           component4     name;
   };
 RESULT
   enum rpc_gss_svc_t {/* From RFC 2203 */
           RPC_GSS_SVC_NONE        = 1,
           RPC_GSS_SVC_INTEGRITY   = 2,
           RPC_GSS_SVC_PRIVACY     = 3
   };

Shepler, et al. Standards Track [Page 203] RFC 3530 NFS version 4 Protocol April 2003

   struct rpcsec_gss_info {
           sec_oid4        oid;
           qop4            qop;
           rpc_gss_svc_t   service;
   };
   union secinfo4 switch (uint32_t flavor) {
    case RPCSEC_GSS:
            rpcsec_gss_info        flavor_info;
    default:
            void;
   };
   typedef secinfo4 SECINFO4resok<>;
   union SECINFO4res switch (nfsstat4 status) {
    case NFS4_OK:
            SECINFO4resok resok4;
    default:
            void;
   };
 DESCRIPTION
 The SECINFO operation is used by the client to obtain a list of valid
 RPC authentication flavors for a specific directory filehandle, file
 name pair.  SECINFO should apply the same access methodology used for
 LOOKUP when evaluating the name.  Therefore, if the requester does
 not have the appropriate access to LOOKUP the name then SECINFO must
 behave the same way and return NFS4ERR_ACCESS.
 The result will contain an array which represents the security
 mechanisms available, with an order corresponding to server's
 preferences, the most preferred being first in the array. The client
 is free to pick whatever security mechanism it both desires and
 supports, or to pick in the server's preference order the first one
 it supports.  The array entries are represented by the secinfo4
 structure.  The field 'flavor' will contain a value of AUTH_NONE,
 AUTH_SYS (as defined in [RFC1831]), or RPCSEC_GSS (as defined in
 [RFC2203]).
 For the flavors AUTH_NONE and AUTH_SYS, no additional security
 information is returned.  For a return value of RPCSEC_GSS, a
 security triple is returned that contains the mechanism object id (as
 defined in [RFC2743]), the quality of protection (as defined in
 [RFC2743]) and the service type (as defined in [RFC2203]).  It is
 possible for SECINFO to return multiple entries with flavor equal to
 RPCSEC_GSS with different security triple values.

Shepler, et al. Standards Track [Page 204] RFC 3530 NFS version 4 Protocol April 2003

 On success, the current filehandle retains its value.
 If the name has a length of 0 (zero), or if name does not obey the
 UTF-8 definition, the error NFS4ERR_INVAL will be returned.
 IMPLEMENTATION
 The SECINFO operation is expected to be used by the NFS client when
 the error value of NFS4ERR_WRONGSEC is returned from another NFS
 operation.  This signifies to the client that the server's security
 policy is different from what the client is currently using.  At this
 point, the client is expected to obtain a list of possible security
 flavors and choose what best suits its policies.
 As mentioned, the server's security policies will determine when a
 client request receives NFS4ERR_WRONGSEC.  The operations which may
 receive this error are: LINK, LOOKUP, OPEN, PUTFH, PUTPUBFH,
 PUTROOTFH, RESTOREFH, RENAME, and indirectly READDIR.  LINK and
 RENAME will only receive this error if the security used for the
 operation is inappropriate for saved filehandle.  With the exception
 of READDIR, these operations represent the point at which the client
 can instantiate a filehandle into the "current filehandle" at the
 server.  The filehandle is either provided by the client (PUTFH,
 PUTPUBFH, PUTROOTFH) or generated as a result of a name to filehandle
 translation (LOOKUP and OPEN).  RESTOREFH is different because the
 filehandle is a result of a previous SAVEFH.  Even though the
 filehandle, for RESTOREFH, might have previously passed the server's
 inspection for a security match, the server will check it again on
 RESTOREFH to ensure that the security policy has not changed.
 If the client wants to resolve an error return of NFS4ERR_WRONGSEC,
 the following will occur:
 o  For LOOKUP and OPEN, the client will use SECINFO with the same
    current filehandle and name as provided in the original LOOKUP or
    OPEN to enumerate the available security triples.
 o  For LINK, PUTFH, RENAME, and RESTOREFH, the client will use
    SECINFO and provide the parent directory filehandle and object
    name which corresponds to the filehandle originally provided by
    the PUTFH RESTOREFH, or for LINK and RENAME, the SAVEFH.
 o  For PUTROOTFH and PUTPUBFH, the client will be unable to use the
    SECINFO operation since SECINFO requires a current filehandle and
    none exist for these two operations.  Therefore, the client must
    iterate through the security triples available at the client and
    reattempt the PUTROOTFH or PUTPUBFH operation. In the unfortunate
    event none of the MANDATORY security triples are supported by the

Shepler, et al. Standards Track [Page 205] RFC 3530 NFS version 4 Protocol April 2003

    client and server, the client SHOULD try using others that support
    integrity. Failing that, the client can try using AUTH_NONE, but
    because such forms lack integrity checks, this puts the client at
    risk.  Nonetheless, the server SHOULD allow the client to use
    whatever security form the client requests and the server
    supports, since the risks of doing so are on the client.
 The READDIR operation will not directly return the NFS4ERR_WRONGSEC
 error.  However, if the READDIR request included a request for
 attributes, it is possible that the READDIR request's security triple
 does not match that of a directory entry.  If this is the case and
 the client has requested the rdattr_error attribute, the server will
 return the NFS4ERR_WRONGSEC error in rdattr_error for the entry.
 See the section "Security Considerations" for a discussion on the
 recommendations for security flavor used by SECINFO.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_BADCHAR
    NFS4ERR_BADHANDLE
    NFS4ERR_BADNAME
    NFS4ERR_BADXDR
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_MOVED
    NFS4ERR_NAMETOOLONG
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTDIR
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

14.2.32. Operation 34: SETATTR - Set Attributes

 SYNOPSIS
   (cfh), stateid, attrmask, attr_vals -> attrsset
 ARGUMENT
   struct SETATTR4args {
           /* CURRENT_FH: target object */
           stateid4        stateid;
           fattr4          obj_attributes;
   };

Shepler, et al. Standards Track [Page 206] RFC 3530 NFS version 4 Protocol April 2003

 RESULT
   struct SETATTR4res {
           nfsstat4        status;
           bitmap4         attrsset;
   };
 DESCRIPTION
 The SETATTR operation changes one or more of the attributes of a
 filesystem object.  The new attributes are specified with a bitmap
 and the attributes that follow the bitmap in bit order.
 The stateid argument for SETATTR is used to provide file locking
 context that is necessary for SETATTR requests that set the size
 attribute.  Since setting the size attribute modifies the file's
 data, it has the same locking requirements as a corresponding WRITE.
 Any SETATTR that sets the size attribute is incompatible with a share
 reservation that specifies DENY_WRITE.  The area between the old
 end-of-file and the new end-of-file is considered to be modified just
 as would have been the case had the area in question been specified
 as the target of WRITE, for the purpose of checking conflicts with
 record locks, for those cases in which a server is implementing
 mandatory record locking behavior.  A valid stateid should always be
 specified.  When the file size attribute is not set, the special
 stateid consisting of all bits zero should be passed.
 On either success or failure of the operation, the server will return
 the attrsset bitmask to represent what (if any) attributes were
 successfully set.  The attrsset in the response is a subset of the
 bitmap4 that is part of the obj_attributes in the argument.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 If the request specifies the owner attribute to be set, the server
 should allow the operation to succeed if the current owner of the
 object matches the value specified in the request.  Some servers may
 be implemented in a way as to prohibit the setting of the owner
 attribute unless the requester has privilege to do so.  If the server
 is lenient in this one case of matching owner values, the client
 implementation may be simplified in cases of creation of an object
 followed by a SETATTR.
 The file size attribute is used to request changes to the size of a
 file. A value of 0 (zero) causes the file to be truncated, a value
 less than the current size of the file causes data from new size to

Shepler, et al. Standards Track [Page 207] RFC 3530 NFS version 4 Protocol April 2003

 the end of the file to be discarded, and a size greater than the
 current size of the file causes logically zeroed data bytes to be
 added to the end of the file.  Servers are free to implement this
 using holes or actual zero data bytes. Clients should not make any
 assumptions regarding a server's implementation of this feature,
 beyond that the bytes returned will be zeroed.  Servers must support
 extending the file size via SETATTR.
 SETATTR is not guaranteed atomic.  A failed SETATTR may partially
 change a file's attributes.
 Changing the size of a file with SETATTR indirectly changes the
 time_modify.  A client must account for this as size changes can
 result in data deletion.
 The attributes time_access_set and time_modify_set are write-only
 attributes constructed as a switched union so the client can direct
 the server in setting the time values.  If the switched union
 specifies SET_TO_CLIENT_TIME4, the client has provided an nfstime4 to
 be used for the operation.  If the switch union does not specify
 SET_TO_CLIENT_TIME4, the server is to use its current time for the
 SETATTR operation.
 If server and client times differ, programs that compare client time
 to file times can break. A time maintenance protocol should be used
 to limit client/server time skew.
 Use of a COMPOUND containing a VERIFY operation specifying only the
 change attribute, immediately followed by a SETATTR, provides a means
 whereby a client may specify a request that emulates the
 functionality of the SETATTR guard mechanism of NFS version 3.  Since
 the function of the guard mechanism is to avoid changes to the file
 attributes based on stale information, delays between checking of the
 guard condition and the setting of the attributes have the potential
 to compromise this function, as would the corresponding delay in the
 NFS version 4 emulation.  Therefore, NFS version 4 servers should
 take care to avoid such delays, to the degree possible, when
 executing such a request.
 If the server does not support an attribute as requested by the
 client, the server should return NFS4ERR_ATTRNOTSUPP.
 A mask of the attributes actually set is returned by SETATTR in all
 cases.  That mask must not include attributes bits not requested to
 be set by the client, and must be equal to the mask of attributes
 requested to be set only if the SETATTR completes without error.

Shepler, et al. Standards Track [Page 208] RFC 3530 NFS version 4 Protocol April 2003

 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_ATTRNOTSUPP
    NFS4ERR_BADCHAR
    NFS4ERR_BADHANDLE
    NFS4ERR_BADOWNER
    NFS4ERR_BAD_STATEID
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_DQUOT
    NFS4ERR_EXPIRED
    NFS4ERR_FBIG
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_ISDIR
    NFS4ERR_LOCKED
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOSPC
    NFS4ERR_OLD_STATEID
    NFS4ERR_OPENMODE
    NFS4ERR_PERM
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_STATEID

14.2.33. Operation 35: SETCLIENTID - Negotiate Clientid

 SYNOPSIS
   client, callback, callback_ident -> clientid, setclientid_confirm
 ARGUMENT
   struct SETCLIENTID4args {
           nfs_client_id4  client;
           cb_client4      callback;
           uint32_t        callback_ident;
   };

Shepler, et al. Standards Track [Page 209] RFC 3530 NFS version 4 Protocol April 2003

 RESULT
   struct SETCLIENTID4resok {
           clientid4       clientid;
           verifier4       setclientid_confirm;
   };
   union SETCLIENTID4res switch (nfsstat4 status) {
    case NFS4_OK:
            SETCLIENTID4resok      resok4;
    case NFS4ERR_CLID_INUSE:
            clientaddr4    client_using;
    default:
            void;
   };
 DESCRIPTION
 The client uses the SETCLIENTID operation to notify the server of its
 intention to use a particular client identifier, callback, and
 callback_ident for subsequent requests that entail creating lock,
 share reservation, and delegation state on the server.  Upon
 successful completion the server will return a shorthand clientid
 which, if confirmed via a separate step, will be used in subsequent
 file locking and file open requests. Confirmation of the clientid
 must be done via the SETCLIENTID_CONFIRM operation to return the
 clientid and setclientid_confirm values, as verifiers, to the server.
 The reason why two verifiers are necessary is that it is possible to
 use SETCLIENTID and SETCLIENTID_CONFIRM to modify the callback and
 callback_ident information but not the shorthand clientid.  In that
 event, the setclientid_confirm value is effectively the only
 verifier.
 The callback information provided in this operation will be used if
 the client is provided an open delegation at a future point.
 Therefore, the client must correctly reflect the program and port
 numbers for the callback program at the time SETCLIENTID is used.
 The callback_ident value is used by the server on the callback.  The
 client can leverage the callback_ident to eliminate the need for more
 than one callback RPC program number, while still being able to
 determine which server is initiating the callback.

Shepler, et al. Standards Track [Page 210] RFC 3530 NFS version 4 Protocol April 2003

 IMPLEMENTATION
 To understand how to implement SETCLIENTID, make the following
 notations. Let:
 x be the value of the client.id subfield of the SETCLIENTID4args
   structure.
 v be the value of the client.verifier subfield of the
   SETCLIENTID4args structure.
 c be the value of the clientid field returned in the
   SETCLIENTID4resok structure.
 k represent the value combination of the fields callback and
   callback_ident fields of the SETCLIENTID4args structure.
 s be the setclientid_confirm value returned in the
   SETCLIENTID4resok structure.
 { v, x, c, k, s }
   be a quintuple for a client record. A client record is
   confirmed if there has been a SETCLIENTID_CONFIRM operation to
   confirm it.  Otherwise it is unconfirmed. An unconfirmed
   record is established by a SETCLIENTID call.
 Since SETCLIENTID is a non-idempotent operation, let us assume that
 the server is implementing the duplicate request cache (DRC).
 When the server gets a SETCLIENTID { v, x, k } request, it processes
 it in the following manner.
 o  It first looks up the request in the DRC. If there is a hit, it
    returns the result cached in the DRC.  The server does NOT remove
    client state (locks, shares, delegations) nor does it modify any
    recorded callback and callback_ident information for client { x }.
    For any DRC miss, the server takes the client id string x, and
    searches for client records for x that the server may have
    recorded from previous SETCLIENTID calls. For any confirmed record
    with the same id string x, if the recorded principal does not
    match that of SETCLIENTID call, then the server returns a
    NFS4ERR_CLID_INUSE error.
    For brevity of discussion, the remaining description of the
    processing assumes that there was a DRC miss, and that where the
    server has previously recorded a confirmed record for client x,
    the aforementioned principal check has successfully passed.

Shepler, et al. Standards Track [Page 211] RFC 3530 NFS version 4 Protocol April 2003

 o  The server checks if it has recorded a confirmed record for { v,
    x, c, l, s }, where l may or may not equal k. If so, and since the
    id verifier v of the request matches that which is confirmed and
    recorded, the server treats this as a probable callback
    information update and records an unconfirmed { v, x, c, k, t }
    and leaves the confirmed { v, x, c, l, s } in place, such that t
    != s. It does not matter if k equals l or not.  Any pre-existing
    unconfirmed { v, x, c, *, * } is removed.
    The server returns { c, t }. It is indeed returning the old
    clientid4 value c, because the client apparently only wants to
    update callback value k to value l.  It's possible this request is
    one from the Byzantine router that has stale callback information,
    but this is not a problem.  The callback information update is
    only confirmed if followed up by a SETCLIENTID_CONFIRM { c, t }.
    The server awaits confirmation of k via
    SETCLIENTID_CONFIRM { c, t }.
    The server does NOT remove client (lock/share/delegation) state
    for x.
 o  The server has previously recorded a confirmed { u, x, c, l, s }
    record such that v != u, l may or may not equal k, and has not
    recorded any unconfirmed { *, x, *, *, * } record for x.  The
    server records an unconfirmed { v, x, d, k, t } (d != c, t != s).
    The server returns { d, t }.
    The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM
    { d, t }.
    The server does NOT remove client (lock/share/delegation) state
    for x.
 o  The server has previously recorded a confirmed { u, x, c, l, s }
    record such that v != u, l may or may not equal k, and recorded an
    unconfirmed { w, x, d, m, t } record such that c != d, t != s, m
    may or may not equal k, m may or may not equal l, and k may or may
    not equal l. Whether w == v or w != v makes no difference.  The
    server simply removes the unconfirmed { w, x, d, m, t } record and
    replaces it with an unconfirmed { v, x, e, k, r } record, such
    that e != d, e != c, r != t, r != s.
    The server returns { e, r }.
    The server awaits confirmation of { e, k } via
    SETCLIENTID_CONFIRM { e, r }.

Shepler, et al. Standards Track [Page 212] RFC 3530 NFS version 4 Protocol April 2003

    The server does NOT remove client (lock/share/delegation) state
    for x.
 o  The server has no confirmed { *, x, *, *, * } for x. It may or may
    not have recorded an unconfirmed { u, x, c, l, s }, where l may or
    may not equal k, and u may or may not equal v.  Any unconfirmed
    record { u, x, c, l, * }, regardless whether u == v or l == k, is
    replaced with an unconfirmed record { v, x, d, k, t } where d !=
    c, t != s.
    The server returns { d, t }.
    The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM
    { d, t }.  The server does NOT remove client
    (lock/share/delegation) state for x.
 The server generates the clientid and setclientid_confirm values and
 must take care to ensure that these values are extremely unlikely to
 ever be regenerated.
 ERRORS
    NFS4ERR_BADXDR
    NFS4ERR_CLID_INUSE
    NFS4ERR_INVAL
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT

14.2.34. Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid

 SYNOPSIS
   clientid, verifier -> -
 ARGUMENT
   struct SETCLIENTID_CONFIRM4args {
           clientid4       clientid;
           verifier4       setclientid_confirm;
   };
 RESULT
   struct SETCLIENTID_CONFIRM4res {
           nfsstat4        status;
   };

Shepler, et al. Standards Track [Page 213] RFC 3530 NFS version 4 Protocol April 2003

 DESCRIPTION
 This operation is used by the client to confirm the results from a
 previous call to SETCLIENTID.  The client provides the server
 supplied (from a SETCLIENTID response) clientid.  The server responds
 with a simple status of success or failure.
 IMPLEMENTATION
 The client must use the SETCLIENTID_CONFIRM operation to confirm the
 following two distinct cases:
 o  The client's use of a new shorthand client identifier (as returned
    from the server in the response to SETCLIENTID), a new callback
    value (as specified in the arguments to SETCLIENTID) and a new
    callback_ident (as specified in the arguments to SETCLIENTID)
    value.  The client's use of SETCLIENTID_CONFIRM in this case also
    confirms the removal of any of the client's previous relevant
    leased state. Relevant leased client state includes record locks,
    share reservations, and where the server does not support the
    CLAIM_DELEGATE_PREV claim type, delegations.  If the server
    supports CLAIM_DELEGATE_PREV, then SETCLIENTID_CONFIRM MUST NOT
    remove delegations for this client; relevant leased client state
    would then just include record locks and share reservations.
 o  The client's re-use of an old, previously confirmed, shorthand
    client identifier, a new callback value, and a new callback_ident
    value.  The client's use of SETCLIENTID_CONFIRM in this case MUST
    NOT result in the removal of any previous leased state (locks,
    share reservations, and delegations)
 We use the same notation and definitions for v, x, c, k, s, and
 unconfirmed and confirmed client records as introduced in the
 description of the SETCLIENTID operation. The arguments to
 SETCLIENTID_CONFIRM are indicated by the notation { c, s }, where c
 is a value of type clientid4, and s is a value of type verifier4
 corresponding to the setclientid_confirm field.
 As with SETCLIENTID, SETCLIENTID_CONFIRM is a non-idempotent
 operation, and we assume that the server is implementing the
 duplicate request cache (DRC).
 When the server gets a SETCLIENTID_CONFIRM { c, s } request, it
 processes it in the following manner.

Shepler, et al. Standards Track [Page 214] RFC 3530 NFS version 4 Protocol April 2003

 o  It first looks up the request in the DRC. If there is a hit, it
    returns the result cached in the DRC.  The server does not remove
    any relevant leased client state nor does it modify any recorded
    callback and callback_ident information for client { x } as
    represented by the shorthand value c.
 For a DRC miss, the server checks for client records that match the
 shorthand value c.  The processing cases are as follows:
 o  The server has recorded an unconfirmed { v, x, c, k, s } record
    and a confirmed { v, x, c, l, t } record, such that s != t.  If
    the principals of the records do not match that of the
    SETCLIENTID_CONFIRM, the server returns NFS4ERR_CLID_INUSE, and no
    relevant leased client state is removed and no recorded callback
    and callback_ident information for client { x } is changed.
    Otherwise, the confirmed { v, x, c, l, t } record is removed and
    the unconfirmed { v, x, c, k, s } is marked as confirmed, thereby
    modifying recorded and confirmed callback and callback_ident
    information for client { x }.
    The server does not remove any relevant leased client state.
    The server returns NFS4_OK.
 o  The server has not recorded an unconfirmed { v, x, c, *, * } and
    has recorded a confirmed { v, x, c, *, s }. If the principals of
    the record and of SETCLIENTID_CONFIRM do not match, the server
    returns NFS4ERR_CLID_INUSE without removing any relevant leased
    client state and without changing recorded callback and
    callback_ident values for client { x }.
    If the principals match, then what has likely happened is that the
    client never got the response from the SETCLIENTID_CONFIRM, and
    the DRC entry has been purged. Whatever the scenario, since the
    principals match, as well as { c, s } matching a confirmed record,
    the server leaves client x's relevant leased client state intact,
    leaves its callback and callback_ident values unmodified, and
    returns NFS4_OK.
 o  The server has not recorded a confirmed { *, *, c, *, * }, and has
    recorded an unconfirmed { *, x, c, k, s }.  Even if this is a
    retry from client, nonetheless the client's first
    SETCLIENTID_CONFIRM attempt was not received by the server.  Retry
    or not, the server doesn't know, but it processes it as if were a
    first try.  If the principal of the unconfirmed { *, x, c, k, s }
    record mismatches that of the SETCLIENTID_CONFIRM request the
    server returns NFS4ERR_CLID_INUSE without removing any relevant
    leased client state.

Shepler, et al. Standards Track [Page 215] RFC 3530 NFS version 4 Protocol April 2003

    Otherwise, the server records a confirmed { *, x, c, k, s }. If
    there is also a confirmed { *, x, d, *, t }, the server MUST
    remove the client x's relevant leased client state, and overwrite
    the callback state with k. The confirmed record { *, x, d, *, t }
    is removed.
    Server returns NFS4_OK.
 o  The server has no record of a confirmed or unconfirmed { *, *, c,
    *, s }.  The server returns NFS4ERR_STALE_CLIENTID.  The server
    does not remove any relevant leased client state, nor does it
    modify any recorded callback and callback_ident information for
    any client.
 The server needs to cache unconfirmed { v, x, c, k, s } client
 records and await for some time their confirmation.  As should be
 clear from the record processing discussions for SETCLIENTID and
 SETCLIENTID_CONFIRM, there are cases where the server does not
 deterministically remove unconfirmed client records.  To avoid
 running out of resources, the server is not required to hold
 unconfirmed records indefinitely.  One strategy the server might use
 is to set a limit on how many unconfirmed client records it will
 maintain, and then when the limit would be exceeded, remove the
 oldest record. Another strategy might be to remove an unconfirmed
 record when some amount of time has elapsed. The choice of the amount
 of time is fairly arbitrary but it is surely no higher than the
 server's lease time period. Consider that leases need to be renewed
 before the lease time expires via an operation from the client.  If
 the client cannot issue a SETCLIENTID_CONFIRM after a SETCLIENTID
 before a period of time equal to that of a lease expires, then the
 client is unlikely to be able maintain state on the server during
 steady state operation.
 If the client does send a SETCLIENTID_CONFIRM for an unconfirmed
 record that the server has already deleted, the client will get
 NFS4ERR_STALE_CLIENTID back.  If so, the client should then start
 over, and send SETCLIENTID to reestablish an unconfirmed client
 record and get back an unconfirmed clientid and setclientid_confirm
 verifier.  The client should then send the SETCLIENTID_CONFIRM to
 confirm the clientid.
 SETCLIENTID_CONFIRM does not establish or renew a lease.  However, if
 SETCLIENTID_CONFIRM removes relevant leased client state, and that
 state does not include existing delegations, the server MUST allow
 the client a period of time no less than the value of lease_time
 attribute, to reclaim, (via the CLAIM_DELEGATE_PREV claim type of the
 OPEN operation) its delegations before removing unreclaimed
 delegations.

Shepler, et al. Standards Track [Page 216] RFC 3530 NFS version 4 Protocol April 2003

 ERRORS
    NFS4ERR_BADXDR
    NFS4ERR_CLID_INUSE
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE_CLIENTID

14.2.35. Operation 37: VERIFY - Verify Same Attributes

 SYNOPSIS
   (cfh), fattr -> -
 ARGUMENT
   struct VERIFY4args {
           /* CURRENT_FH: object */
           fattr4          obj_attributes;
   };
 RESULT
   struct VERIFY4res {
           nfsstat4        status;
   };
 DESCRIPTION
 The VERIFY operation is used to verify that attributes have a value
 assumed by the client before proceeding with following operations in
 the compound request.  If any of the attributes do not match then the
 error NFS4ERR_NOT_SAME must be returned.  The current filehandle
 retains its value after successful completion of the operation.
 IMPLEMENTATION
 One possible use of the VERIFY operation is the following compound
 sequence.  With this the client is attempting to verify that the file
 being removed will match what the client expects to be removed.  This
 sequence can help prevent the unintended deletion of a file.
       PUTFH (directory filehandle)
       LOOKUP (file name)
       VERIFY (filehandle == fh)
       PUTFH (directory filehandle)
       REMOVE (file name)

Shepler, et al. Standards Track [Page 217] RFC 3530 NFS version 4 Protocol April 2003

 This sequence does not prevent a second client from removing and
 creating a new file in the middle of this sequence but it does help
 avoid the unintended result.
 In the case that a recommended attribute is specified in the VERIFY
 operation and the server does not support that attribute for the
 filesystem object, the error NFS4ERR_ATTRNOTSUPP is returned to the
 client.
 When the attribute rdattr_error or any write-only attribute (e.g.,
 time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
 the client.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_ATTRNOTSUPP
    NFS4ERR_BADCHAR
    NFS4ERR_BADHANDLE
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOT_SAME
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE

14.2.36. Operation 38: WRITE - Write to File

 SYNOPSIS
   (cfh), stateid, offset, stable, data -> count, committed, writeverf
 ARGUMENT
   enum stable_how4 {
           UNSTABLE4       = 0,
           DATA_SYNC4      = 1,
           FILE_SYNC4      = 2
   };
   struct WRITE4args {
           /* CURRENT_FH: file */
           stateid4        stateid;
           offset4         offset;

Shepler, et al. Standards Track [Page 218] RFC 3530 NFS version 4 Protocol April 2003

           stable_how4     stable;
           opaque          data<>;
   };
 RESULT
   struct WRITE4resok {
           count4          count;
           stable_how4     committed;
           verifier4       writeverf;
   };
   union WRITE4res switch (nfsstat4 status) {
    case NFS4_OK:
            WRITE4resok    resok4;
    default:
            void;
   };
 DESCRIPTION
 The WRITE operation is used to write data to a regular file.  The
 target file is specified by the current filehandle.  The offset
 specifies the offset where the data should be written.  An offset of
 0 (zero) specifies that the write should start at the beginning of
 the file.  The count, as encoded as part of the opaque data
 parameter, represents the number of bytes of data that are to be
 written.  If the count is 0 (zero), the WRITE will succeed and return
 a count of 0 (zero) subject to permissions checking.  The server may
 choose to write fewer bytes than requested by the client.
 Part of the write request is a specification of how the write is to
 be performed.  The client specifies with the stable parameter the
 method of how the data is to be processed by the server.  If stable
 is FILE_SYNC4, the server must commit the data written plus all
 filesystem metadata to stable storage before returning results.  This
 corresponds to the NFS version 2 protocol semantics.  Any other
 behavior constitutes a protocol violation.  If stable is DATA_SYNC4,
 then the server must commit all of the data to stable storage and
 enough of the metadata to retrieve the data before returning.  The
 server implementor is free to implement DATA_SYNC4 in the same
 fashion as FILE_SYNC4, but with a possible performance drop.  If
 stable is UNSTABLE4, the server is free to commit any part of the
 data and the metadata to stable storage, including all or none,
 before returning a reply to the client. There is no guarantee whether
 or when any uncommitted data will subsequently be committed to stable
 storage. The only guarantees made by the server are that it will not

Shepler, et al. Standards Track [Page 219] RFC 3530 NFS version 4 Protocol April 2003

 destroy any data without changing the value of verf and that it will
 not commit the data and metadata at a level less than that requested
 by the client.
 The stateid value for a WRITE request represents a value returned
 from a previous record lock or share reservation request.  The
 stateid is used by the server to verify that the associated share
 reservation and any record locks are still valid and to update lease
 timeouts for the client.
 Upon successful completion, the following results are returned.  The
 count result is the number of bytes of data written to the file. The
 server may write fewer bytes than requested. If so, the actual number
 of bytes written starting at location, offset, is returned.
 The server also returns an indication of the level of commitment of
 the data and metadata via committed. If the server committed all data
 and metadata to stable storage, committed should be set to
 FILE_SYNC4. If the level of commitment was at least as strong as
 DATA_SYNC4, then committed should be set to DATA_SYNC4.  Otherwise,
 committed must be returned as UNSTABLE4. If stable was FILE4_SYNC,
 then committed must also be FILE_SYNC4: anything else constitutes a
 protocol violation. If stable was DATA_SYNC4, then committed may be
 FILE_SYNC4 or DATA_SYNC4: anything else constitutes a protocol
 violation. If stable was UNSTABLE4, then committed may be either
 FILE_SYNC4, DATA_SYNC4, or UNSTABLE4.
 The final portion of the result is the write verifier.  The write
 verifier is a cookie that the client can use to determine whether the
 server has changed instance (boot) state between a call to WRITE and
 a subsequent call to either WRITE or COMMIT.  This cookie must be
 consistent during a single instance of the NFS version 4 protocol
 service and must be unique between instances of the NFS version 4
 protocol server, where uncommitted data may be lost.
 If a client writes data to the server with the stable argument set to
 UNSTABLE4 and the reply yields a committed response of DATA_SYNC4 or
 UNSTABLE4, the client will follow up some time in the future with a
 COMMIT operation to synchronize outstanding asynchronous data and
 metadata with the server's stable storage, barring client error. It
 is possible that due to client crash or other error that a subsequent
 COMMIT will not be received by the server.
 For a WRITE with a stateid value of all bits 0, the server MAY allow
 the WRITE to be serviced subject to mandatory file locks or the
 current share deny modes for the file.  For a WRITE with a stateid

Shepler, et al. Standards Track [Page 220] RFC 3530 NFS version 4 Protocol April 2003

 value of all bits 1, the server MUST NOT allow the WRITE operation to
 bypass locking checks at the server and are treated exactly the same
 as if a stateid of all bits 0 were used.
 On success, the current filehandle retains its value.
 IMPLEMENTATION
 It is possible for the server to write fewer bytes of data than
 requested by the client.  In this case, the server should not return
 an error unless no data was written at all.  If the server writes
 less than the number of bytes specified, the client should issue
 another WRITE to write the remaining data.
 It is assumed that the act of writing data to a file will cause the
 time_modified of the file to be updated.  However, the time_modified
 of the file should not be changed unless the contents of the file are
 changed.  Thus, a WRITE request with count set to 0 should not cause
 the time_modified of the file to be updated.
 The definition of stable storage has been historically a point of
 contention.  The following expected properties of stable storage may
 help in resolving design issues in the implementation. Stable storage
 is persistent storage that survives:
    1. Repeated power failures.
    2. Hardware failures (of any board, power supply, etc.).
    3. Repeated software crashes, including reboot cycle.
 This definition does not address failure of the stable storage module
 itself.
 The verifier is defined to allow a client to detect different
 instances of an NFS version 4 protocol server over which cached,
 uncommitted data may be lost. In the most likely case, the verifier
 allows the client to detect server reboots.  This information is
 required so that the client can safely determine whether the server
 could have lost cached data.  If the server fails unexpectedly and
 the client has uncommitted data from previous WRITE requests (done
 with the stable argument set to UNSTABLE4 and in which the result
 committed was returned as UNSTABLE4 as well) it may not have flushed
 cached data to stable storage. The burden of recovery is on the
 client and the client will need to retransmit the data to the server.
 A suggested verifier would be to use the time that the server was
 booted or the time the server was last started (if restarting the
 server without a reboot results in lost buffers).

Shepler, et al. Standards Track [Page 221] RFC 3530 NFS version 4 Protocol April 2003

 The committed field in the results allows the client to do more
 effective caching.  If the server is committing all WRITE requests to
 stable storage, then it should return with committed set to
 FILE_SYNC4, regardless of the value of the stable field in the
 arguments. A server that uses an NVRAM accelerator may choose to
 implement this policy.  The client can use this to increase the
 effectiveness of the cache by discarding cached data that has already
 been committed on the server.
 Some implementations may return NFS4ERR_NOSPC instead of
 NFS4ERR_DQUOT when a user's quota is exceeded.  In the case that the
 current filehandle is a directory, the server will return
 NFS4ERR_ISDIR.  If the current filehandle is not a regular file or a
 directory, the server will return NFS4ERR_INVAL.
 If mandatory file locking is on for the file, and corresponding
 record of the data to be written file is read or write locked by an
 owner that is not associated with the stateid, the server will return
 NFS4ERR_LOCKED. If so, the client must check if the owner
 corresponding to the stateid used with the WRITE operation has a
 conflicting read lock that overlaps with the region that was to be
 written. If the stateid's owner has no conflicting read lock, then
 the client should try to get the appropriate write record lock via
 the LOCK operation before re-attempting the WRITE. When the WRITE
 completes, the client should release the record lock via LOCKU.
 If the stateid's owner had a conflicting read lock, then the client
 has no choice but to return an error to the application that
 attempted the WRITE. The reason is that since the stateid's owner had
 a read lock, the server either attempted to temporarily effectively
 upgrade this read lock to a write lock, or the server has no upgrade
 capability. If the server attempted to upgrade the read lock and
 failed, it is pointless for the client to re-attempt the upgrade via
 the LOCK operation, because there might be another client also trying
 to upgrade.  If two clients are blocked trying upgrade the same lock,
 the clients deadlock.  If the server has no upgrade capability, then
 it is pointless to try a LOCK operation to upgrade.
 ERRORS
    NFS4ERR_ACCESS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_STATEID
    NFS4ERR_BADXDR
    NFS4ERR_DELAY
    NFS4ERR_DQUOT
    NFS4ERR_EXPIRED

Shepler, et al. Standards Track [Page 222] RFC 3530 NFS version 4 Protocol April 2003

    NFS4ERR_FBIG
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_ISDIR
    NFS4ERR_LEASE_MOVED
    NFS4ERR_LOCKED
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOSPC
    NFS4ERR_NXIO
    NFS4ERR_OLD_STATEID
    NFS4ERR_OPENMODE
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_STATEID

14.2.37. Operation 39: RELEASE_LOCKOWNER - Release Lockowner State

 SYNOPSIS
   lockowner -> ()
 ARGUMENT
   struct RELEASE_LOCKOWNER4args {
           lock_owner4     lock_owner;
   };
 RESULT
   struct RELEASE_LOCKOWNER4res {
           nfsstat4        status;
   };
 DESCRIPTION
 This operation is used to notify the server that the lock_owner is no
 longer in use by the client.  This allows the server to release
 cached state related to the specified lock_owner.  If file locks,
 associated with the lock_owner, are held at the server, the error
 NFS4ERR_LOCKS_HELD will be returned and no further action will be
 taken.

Shepler, et al. Standards Track [Page 223] RFC 3530 NFS version 4 Protocol April 2003

 IMPLEMENTATION
 The client may choose to use this operation to ease the amount of
 server state that is held.  Depending on behavior of applications at
 the client, it may be important for the client to use this operation
 since the server has certain obligations with respect to holding a
 reference to a lock_owner as long as the associated file is open.
 Therefore, if the client knows for certain that the lock_owner will
 no longer be used under the context of the associated open_owner4, it
 should use RELEASE_LOCKOWNER.
 ERRORS
    NFS4ERR_ADMIN_REVOKED
    NFS4ERR_BADXDR
    NFS4ERR_EXPIRED
    NFS4ERR_LEASE_MOVED
    NFS4ERR_LOCKS_HELD
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE_CLIENTID

14.2.38. Operation 10044: ILLEGAL - Illegal operation

 SYNOPSIS
   <null> -> ()
 ARGUMENT
           void;
 RESULT
           struct ILLEGAL4res {
                   nfsstat4        status;
           };
 DESCRIPTION
 This operation is a placeholder for encoding a result to handle the
 case of the client sending an operation code within COMPOUND that is
 not supported. See the COMPOUND procedure description for more
 details.
 The status field of ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.

Shepler, et al. Standards Track [Page 224] RFC 3530 NFS version 4 Protocol April 2003

 IMPLEMENTATION
 A client will probably not send an operation with code OP_ILLEGAL but
 if it does, the response will be ILLEGAL4res just as it would be with
 any other invalid operation code. Note that if the server gets an
 illegal operation code that is not OP_ILLEGAL, and if the server
 checks for legal operation codes during the XDR decode phase, then
 the ILLEGAL4res would not be returned.
 ERRORS
 NFS4ERR_OP_ILLEGAL

15. NFS version 4 Callback Procedures

 The procedures used for callbacks are defined in the following
 sections.  In the interest of clarity, the terms "client" and
 "server" refer to NFS clients and servers, despite the fact that for
 an individual callback RPC, the sense of these terms would be
 precisely the opposite.

15.1. Procedure 0: CB_NULL - No Operation

 SYNOPSIS
   <null>
 ARGUMENT
   void;
 RESULT
   void;
 DESCRIPTION
 Standard NULL procedure.  Void argument, void response.  Even though
 there is no direct functionality associated with this procedure, the
 server will use CB_NULL to confirm the existence of a path for RPCs
 from server to client.
 ERRORS
 None.

Shepler, et al. Standards Track [Page 225] RFC 3530 NFS version 4 Protocol April 2003

15.2. Procedure 1: CB_COMPOUND - Compound Operations

 SYNOPSIS
   compoundargs -> compoundres
 ARGUMENT
   enum nfs_cb_opnum4 {
           OP_CB_GETATTR           = 3,
           OP_CB_RECALL            = 4,
           OP_CB_ILLEGAL           = 10044
   };
   union nfs_cb_argop4 switch (unsigned argop) {
    case OP_CB_GETATTR:    CB_GETATTR4args opcbgetattr;
    case OP_CB_RECALL:     CB_RECALL4args  opcbrecall;
    case OP_CB_ILLEGAL:    void            opcbillegal;
   };
   struct CB_COMPOUND4args {
           utf8str_cs      tag;
           uint32_t        minorversion;
           uint32_t        callback_ident;
           nfs_cb_argop4   argarray<>;
   };
 RESULT
   union nfs_cb_resop4 switch (unsigned resop){
    case OP_CB_GETATTR:    CB_GETATTR4res  opcbgetattr;
    case OP_CB_RECALL:     CB_RECALL4res   opcbrecall;
   };
   struct CB_COMPOUND4res {
           nfsstat4 status;
           utf8str_cs      tag;
           nfs_cb_resop4   resarray<>;
   };
 DESCRIPTION
 The CB_COMPOUND procedure is used to combine one or more of the
 callback procedures into a single RPC request.  The main callback RPC
 program has two main procedures: CB_NULL and CB_COMPOUND.  All other
 operations use the CB_COMPOUND procedure as a wrapper.

Shepler, et al. Standards Track [Page 226] RFC 3530 NFS version 4 Protocol April 2003

 In the processing of the CB_COMPOUND procedure, the client may find
 that it does not have the available resources to execute any or all
 of the operations within the CB_COMPOUND sequence.  In this case, the
 error NFS4ERR_RESOURCE will be returned for the particular operation
 within the CB_COMPOUND procedure where the resource exhaustion
 occurred.  This assumes that all previous operations within the
 CB_COMPOUND sequence have been evaluated successfully.
 Contained within the CB_COMPOUND results is a 'status' field.  This
 status must be equivalent to the status of the last operation that
 was executed within the CB_COMPOUND procedure.  Therefore, if an
 operation incurred an error then the 'status' value will be the same
 error value as is being returned for the operation that failed.
 For the definition of the "tag" field, see the section "Procedure 1:
 COMPOUND - Compound Operations".
 The value of callback_ident is supplied by the client during
 SETCLIENTID.  The server must use the client supplied callback_ident
 during the CB_COMPOUND to allow the client to properly identify the
 server.
 Illegal operation codes are handled in the same way as they are
 handled for the COMPOUND procedure.
 IMPLEMENTATION
 The CB_COMPOUND procedure is used to combine individual operations
 into a single RPC request.  The client interprets each of the
 operations in turn.  If an operation is executed by the client and
 the status of that operation is NFS4_OK, then the next operation in
 the CB_COMPOUND procedure is executed.  The client continues this
 process until there are no more operations to be executed or one of
 the operations has a status value other than NFS4_OK.
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_STATEID
    NFS4ERR_BADXDR
    NFS4ERR_OP_ILLEGAL
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT

Shepler, et al. Standards Track [Page 227] RFC 3530 NFS version 4 Protocol April 2003

15.2.1. Operation 3: CB_GETATTR - Get Attributes

 SYNOPSIS
   fh, attr_request -> attrmask, attr_vals
 ARGUMENT
   struct CB_GETATTR4args {
           nfs_fh4 fh;
           bitmap4 attr_request;
   };
 RESULT
   struct CB_GETATTR4resok {
           fattr4  obj_attributes;
   };
   union CB_GETATTR4res switch (nfsstat4 status) {
    case NFS4_OK:
            CB_GETATTR4resok       resok4;
    default:
            void;
   };

DESCRIPTION

 The CB_GETATTR operation is used by the server to obtain the
 current modified state of a file that has been write delegated.
 The attributes size and change are the only ones guaranteed to be
 serviced by the client.  See the section "Handling of CB_GETATTR"
 for a full description of how the client and server are to interact
 with the use of CB_GETATTR.
 If the filehandle specified is not one for which the client holds a
 write open delegation, an NFS4ERR_BADHANDLE error is returned.
 IMPLEMENTATION
 The client returns attrmask bits and the associated attribute
 values only for the change attribute, and attributes that it may
 change (time_modify, and size).

Shepler, et al. Standards Track [Page 228] RFC 3530 NFS version 4 Protocol April 2003

 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_BADXDR
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT

15.2.2. Operation 4: CB_RECALL - Recall an Open Delegation

 SYNOPSIS
   stateid, truncate, fh -> ()
 ARGUMENT
   struct CB_RECALL4args {
           stateid4        stateid;
           bool            truncate;
           nfs_fh4         fh;
   };
 RESULT
   struct CB_RECALL4res {
           nfsstat4        status;
   };
 DESCRIPTION
 The CB_RECALL operation is used to begin the process of recalling an
 open delegation and returning it to the server.
 The truncate flag is used to optimize recall for a file which is
 about to be truncated to zero.  When it is set, the client is freed
 of obligation to propagate modified data for the file to the server,
 since this data is irrelevant.
 If the handle specified is not one for which the client holds an open
 delegation, an NFS4ERR_BADHANDLE error is returned.
 If the stateid specified is not one corresponding to an open
 delegation for the file specified by the filehandle, an
 NFS4ERR_BAD_STATEID is returned.

Shepler, et al. Standards Track [Page 229] RFC 3530 NFS version 4 Protocol April 2003

 IMPLEMENTATION
 The client should reply to the callback immediately.  Replying does
 not complete the recall except when an error was returned.  The
 recall is not complete until the delegation is returned using a
 DELEGRETURN.
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_STATEID
    NFS4ERR_BADXDR
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT

15.2.3. Operation 10044: CB_ILLEGAL - Illegal Callback Operation

 SYNOPSIS
   <null> -> ()
 ARGUMENT
     void;
 RESULT
           struct CB_ILLEGAL4res {
                   nfsstat4        status;
           };
 DESCRIPTION
 This operation is a placeholder for encoding a result to handle the
 case of the client sending an operation code within COMPOUND that is
 not supported. See the COMPOUND procedure description for more
 details.
 The status field of CB_ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.
 IMPLEMENTATION
 A server will probably not send an operation with code OP_CB_ILLEGAL
 but if it does, the response will be CB_ILLEGAL4res just as it would
 be with any other invalid operation code. Note that if the client

Shepler, et al. Standards Track [Page 230] RFC 3530 NFS version 4 Protocol April 2003

 gets an illegal operation code that is not OP_ILLEGAL, and if the
 client checks for legal operation codes during the XDR decode phase,
 then the CB_ILLEGAL4res would not be returned.
 ERRORS
 NFS4ERR_OP_ILLEGAL

16. Security Considerations

 NFS has historically used a model where, from an authentication
 perspective, the client was the entire machine, or at least the
 source IP address of the machine.  The NFS server relied on the NFS
 client to make the proper authentication of the end-user.  The NFS
 server in turn shared its files only to specific clients, as
 identified by the client's source IP address.  Given this model, the
 AUTH_SYS RPC security flavor simply identified the end-user using the
 client to the NFS server.  When processing NFS responses, the client
 ensured that the responses came from the same IP address and port
 number that the request was sent to.  While such a model is easy to
 implement and simple to deploy and use, it is certainly not a safe
 model.  Thus, NFSv4 mandates that implementations support a security
 model that uses end to end authentication, where an end-user on a
 client mutually authenticates (via cryptographic schemes that do not
 expose passwords or keys in the clear on the network) to a principal
 on an NFS server.  Consideration should also be given to the
 integrity and privacy of NFS requests and responses.  The issues of
 end to end mutual authentication, integrity, and privacy are
 discussed as part of the section on "RPC and Security Flavor".
 Note that while NFSv4 mandates an end to end mutual authentication
 model, the "classic" model of machine authentication via IP address
 checking and AUTH_SYS identification can still be supported with the
 caveat that the AUTH_SYS flavor is neither MANDATORY nor RECOMMENDED
 by this specification, and so interoperability via AUTH_SYS is not
 assured.
 For reasons of reduced administration overhead, better performance
 and/or reduction of CPU utilization, users of NFS version 4
 implementations may choose to not use security mechanisms that enable
 integrity protection on each remote procedure call and response. The
 use of mechanisms without integrity leaves the customer vulnerable to
 an attacker in between the NFS client and server that modifies the
 RPC request and/or the response. While implementations are free to
 provide the option to use weaker security mechanisms, there are two
 operations in particular that warrant the implementation overriding
 user choices.

Shepler, et al. Standards Track [Page 231] RFC 3530 NFS version 4 Protocol April 2003

 The first such operation is SECINFO.  It is recommended that the
 client issue the SECINFO call such that it is protected with a
 security flavor that has integrity protection, such as RPCSEC_GSS
 with a security triple that uses either rpc_gss_svc_integrity or
 rpc_gss_svc_privacy (rpc_gss_svc_privacy includes integrity
 protection) service. Without integrity protection encapsulating
 SECINFO and therefore its results, an attacker in the middle could
 modify results such that the client might select a weaker algorithm
 in the set allowed by server, making the client and/or server
 vulnerable to further attacks.
 The second operation that should definitely use integrity protection
 is any GETATTR for the fs_locations attribute. The attack has two
 steps.  First the attacker modifies the unprotected results of some
 operation to return NFS4ERR_MOVED. Second, when the client follows up
 with a GETATTR for the fs_locations attribute, the attacker modifies
 the results to cause the client migrate its traffic to a server
 controlled by the attacker.
 Because the operations SETCLIENTID/SETCLIENTID_CONFIRM are
 responsible for the release of client state, it is imperative that
 the principal used for these operations is checked against and match
 the previous use of these operations.  See the section "Client ID"
 for further discussion.

17. IANA Considerations

17.1. Named Attribute Definition

 The NFS version 4 protocol provides for the association of named
 attributes to files.  The name space identifiers for these attributes
 are defined as string names.  The protocol does not define the
 specific assignment of the name space for these file attributes.
 Even though the name space is not specifically controlled to prevent
 collisions, an IANA registry has been created for the registration of
 NFS version 4 named attributes.  Registration will be achieved
 through the publication of an Informational RFC and will require not
 only the name of the attribute but the syntax and semantics of the
 named attribute contents; the intent is to promote interoperability
 where common interests exist.  While application developers are
 allowed to define and use attributes as needed, they are encouraged
 to register the attributes with IANA.

17.2. ONC RPC Network Identifiers (netids)

 The section "Structured Data Types" discussed the r_netid field and
 the corresponding r_addr field of a clientaddr4 structure.  The NFS
 version 4 protocol depends on the syntax and semantics of these

Shepler, et al. Standards Track [Page 232] RFC 3530 NFS version 4 Protocol April 2003

 fields to effectively communicate callback information between client
 and server.  Therefore, an IANA registry has been created to include
 the values defined in this document and to allow for future expansion
 based on transport usage/availability.  Additions to this ONC RPC
 Network Identifier registry must be done with the publication of an
 RFC.
 The initial values for this registry are as follows (some of this
 text is replicated from section 2.2 for clarity):
 The Network Identifier (or r_netid for short) is used to specify a
 transport protocol and associated universal address (or r_addr for
 short).  The syntax of the Network Identifier is a US-ASCII string.
 The initial definitions for r_netid are:
    "tcp"   - TCP over IP version 4
    "udp"   - UDP over IP version 4
    "tcp6"  - TCP over IP version 6
    "udp6"  - UDP over IP version 6
 Note: the '"' marks are used for delimiting the strings for this
 document and are not part of the Network Identifier string.
 For the "tcp" and "udp" Network Identifiers the Universal Address or
 r_addr (for IPv4) is a US-ASCII string and is of the form:
 h1.h2.h3.h4.p1.p2
 The prefix, "h1.h2.h3.h4", is the standard textual form for
 representing an IPv4 address, which is always four octets long.
 Assuming big-endian ordering, h1, h2, h3, and h4, are respectively,
 the first through fourth octets each converted to ASCII-decimal.
 Assuming big-endian ordering, p1 and p2 are, respectively, the first
 and second octets each converted to ASCII-decimal.  For example, if a
 host, in big-endian order, has an address of 0x0A010307 and there is
 a service listening on, in big endian order, port 0x020F (decimal
 527), then complete universal address is "10.1.3.7.2.15".
 For the "tcp6" and "udp6" Network Identifiers the Universal Address
 or r_addr (for IPv6) is a US-ASCII string and is of the form:
    x1:x2:x3:x4:x5:x6:x7:x8.p1.p2

Shepler, et al. Standards Track [Page 233] RFC 3530 NFS version 4 Protocol April 2003

 The suffix "p1.p2" is the service port, and is computed the same way
 as with universal addresses for "tcp" and "udp".  The prefix,
 "x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for
 representing an IPv6 address as defined in Section 2.2 of [RFC2373].
 Additionally, the two alternative forms specified in Section 2.2 of
 [RFC2373] are also acceptable.
 As mentioned, the registration of new Network Identifiers will
 require the publication of an Information RFC with similar detail as
 listed above for the Network Identifier itself and corresponding
 Universal Address.

18. RPC definition file

 /*
  *  Copyright (C) The Internet Society (1998,1999,2000,2001,2002).
  *  All Rights Reserved.
  */
 /*
  *      nfs4_prot.x
  *
  */
 %#pragma ident  "%W%"
 /*
  * Basic typedefs for RFC 1832 data type definitions
  */
 typedef int             int32_t;
 typedef unsigned int    uint32_t;
 typedef hyper           int64_t;
 typedef unsigned hyper  uint64_t;
 /*
  * Sizes
  */
 const NFS4_FHSIZE               = 128;
 const NFS4_VERIFIER_SIZE        = 8;
 const NFS4_OPAQUE_LIMIT         = 1024;
 /*
  * File types
  */
 enum nfs_ftype4 {
         NF4REG          = 1,    /* Regular File */
         NF4DIR          = 2,    /* Directory */
         NF4BLK          = 3,    /* Special File - block device */

Shepler, et al. Standards Track [Page 234] RFC 3530 NFS version 4 Protocol April 2003

         NF4CHR          = 4,    /* Special File - character device */
         NF4LNK          = 5,    /* Symbolic Link */
         NF4SOCK         = 6,    /* Special File - socket */
         NF4FIFO         = 7,    /* Special File - fifo */
         NF4ATTRDIR      = 8,    /* Attribute Directory */
         NF4NAMEDATTR    = 9     /* Named Attribute */
 };
 /*
  * Error status
  */
 enum nfsstat4 {
         NFS4_OK                 = 0,    /* everything is okay      */
         NFS4ERR_PERM            = 1,    /* caller not privileged   */
         NFS4ERR_NOENT           = 2,    /* no such file/directory  */
         NFS4ERR_IO              = 5,    /* hard I/O error          */
         NFS4ERR_NXIO            = 6,    /* no such device          */
         NFS4ERR_ACCESS          = 13,   /* access denied           */
         NFS4ERR_EXIST           = 17,   /* file already exists     */
         NFS4ERR_XDEV            = 18,   /* different filesystems   */
         /* Unused/reserved        19 */
         NFS4ERR_NOTDIR          = 20,   /* should be a directory   */
         NFS4ERR_ISDIR           = 21,   /* should not be directory */
         NFS4ERR_INVAL           = 22,   /* invalid argument        */
         NFS4ERR_FBIG            = 27,   /* file exceeds server max */
         NFS4ERR_NOSPC           = 28,   /* no space on filesystem  */
         NFS4ERR_ROFS            = 30,   /* read-only filesystem    */
         NFS4ERR_MLINK           = 31,   /* too many hard links     */
         NFS4ERR_NAMETOOLONG     = 63,   /* name exceeds server max */
         NFS4ERR_NOTEMPTY        = 66,   /* directory not empty     */
         NFS4ERR_DQUOT           = 69,   /* hard quota limit reached*/
         NFS4ERR_STALE           = 70,   /* file no longer exists   */
         NFS4ERR_BADHANDLE       = 10001,/* Illegal filehandle      */
         NFS4ERR_BAD_COOKIE      = 10003,/* READDIR cookie is stale */
         NFS4ERR_NOTSUPP         = 10004,/* operation not supported */
         NFS4ERR_TOOSMALL        = 10005,/* response limit exceeded */
         NFS4ERR_SERVERFAULT     = 10006,/* undefined server error  */
         NFS4ERR_BADTYPE         = 10007,/* type invalid for CREATE */
         NFS4ERR_DELAY           = 10008,/* file "busy" - retry     */
         NFS4ERR_SAME            = 10009,/* nverify says attrs same */
         NFS4ERR_DENIED          = 10010,/* lock unavailable        */
         NFS4ERR_EXPIRED         = 10011,/* lock lease expired      */
         NFS4ERR_LOCKED          = 10012,/* I/O failed due to lock  */
         NFS4ERR_GRACE           = 10013,/* in grace period         */
         NFS4ERR_FHEXPIRED       = 10014,/* filehandle expired      */
         NFS4ERR_SHARE_DENIED    = 10015,/* share reserve denied    */
         NFS4ERR_WRONGSEC        = 10016,/* wrong security flavor   */
         NFS4ERR_CLID_INUSE      = 10017,/* clientid in use         */

Shepler, et al. Standards Track [Page 235] RFC 3530 NFS version 4 Protocol April 2003

         NFS4ERR_RESOURCE        = 10018,/* resource exhaustion     */
         NFS4ERR_MOVED           = 10019,/* filesystem relocated    */
         NFS4ERR_NOFILEHANDLE    = 10020,/* current FH is not set   */
         NFS4ERR_MINOR_VERS_MISMATCH = 10021,/* minor vers not supp */
         NFS4ERR_STALE_CLIENTID  = 10022,/* server has rebooted     */
         NFS4ERR_STALE_STATEID   = 10023,/* server has rebooted     */
         NFS4ERR_OLD_STATEID     = 10024,/* state is out of sync    */
         NFS4ERR_BAD_STATEID     = 10025,/* incorrect stateid       */
         NFS4ERR_BAD_SEQID       = 10026,/* request is out of seq.  */
         NFS4ERR_NOT_SAME        = 10027,/* verify - attrs not same */
         NFS4ERR_LOCK_RANGE      = 10028,/* lock range not supported*/
         NFS4ERR_SYMLINK         = 10029,/* should be file/directory*/
         NFS4ERR_RESTOREFH       = 10030,/* no saved filehandle     */
         NFS4ERR_LEASE_MOVED     = 10031,/* some filesystem moved   */
         NFS4ERR_ATTRNOTSUPP     = 10032,/* recommended attr not sup*/
         NFS4ERR_NO_GRACE        = 10033,/* reclaim outside of grace*/
         NFS4ERR_RECLAIM_BAD     = 10034,/* reclaim error at server */
         NFS4ERR_RECLAIM_CONFLICT = 10035,/* conflict on reclaim    */
         NFS4ERR_BADXDR          = 10036,/* XDR decode failed       */
         NFS4ERR_LOCKS_HELD      = 10037,/* file locks held at CLOSE*/
         NFS4ERR_OPENMODE        = 10038,/* conflict in OPEN and I/O*/
         NFS4ERR_BADOWNER        = 10039,/* owner translation bad   */
         NFS4ERR_BADCHAR         = 10040,/* utf-8 char not supported*/
         NFS4ERR_BADNAME         = 10041,/* name not supported      */
         NFS4ERR_BAD_RANGE       = 10042,/* lock range not supported*/
         NFS4ERR_LOCK_NOTSUPP    = 10043,/* no atomic up/downgrade  */
         NFS4ERR_OP_ILLEGAL      = 10044,/* undefined operation     */
         NFS4ERR_DEADLOCK        = 10045,/* file locking deadlock   */
         NFS4ERR_FILE_OPEN       = 10046,/* open file blocks op.    */
         NFS4ERR_ADMIN_REVOKED   = 10047,/* lockowner state revoked */
         NFS4ERR_CB_PATH_DOWN    = 10048 /* callback path down      */
 };
 /*
  * Basic data types
  */
 typedef uint32_t        bitmap4<>;
 typedef uint64_t        offset4;
 typedef uint32_t        count4;
 typedef uint64_t        length4;
 typedef uint64_t        clientid4;
 typedef uint32_t        seqid4;
 typedef opaque          utf8string<>;
 typedef utf8string      utf8str_cis;
 typedef utf8string      utf8str_cs;
 typedef utf8string      utf8str_mixed;
 typedef utf8str_cs      component4;
 typedef component4      pathname4<>;

Shepler, et al. Standards Track [Page 236] RFC 3530 NFS version 4 Protocol April 2003

 typedef uint64_t        nfs_lockid4;
 typedef uint64_t        nfs_cookie4;
 typedef utf8str_cs      linktext4;
 typedef opaque          sec_oid4<>;
 typedef uint32_t        qop4;
 typedef uint32_t        mode4;
 typedef uint64_t        changeid4;
 typedef opaque          verifier4[NFS4_VERIFIER_SIZE];
 /*
  * Timeval
  */
 struct nfstime4 {
         int64_t         seconds;
         uint32_t        nseconds;
 };
 enum time_how4 {
         SET_TO_SERVER_TIME4 = 0,
         SET_TO_CLIENT_TIME4 = 1
 };
 union settime4 switch (time_how4 set_it) {
  case SET_TO_CLIENT_TIME4:
          nfstime4       time;
  default:
          void;
 };
 /*
  * File access handle
  */
 typedef opaque  nfs_fh4<NFS4_FHSIZE>;
 /*
  * File attribute definitions
  */
 /*
  * FSID structure for major/minor
  */
 struct fsid4 {
         uint64_t        major;
         uint64_t        minor;
 };
 /*

Shepler, et al. Standards Track [Page 237] RFC 3530 NFS version 4 Protocol April 2003

  • Filesystem locations attribute for relocation/migration
  • /

struct fs_location4 {

         utf8str_cis     server<>;
         pathname4       rootpath;
 };
 struct fs_locations4 {
         pathname4       fs_root;
         fs_location4    locations<>;
 };
 /*
  * Various Access Control Entry definitions
  */
 /*
  * Mask that indicates which Access Control Entries are supported.
  * Values for the fattr4_aclsupport attribute.
  */
 const ACL4_SUPPORT_ALLOW_ACL    = 0x00000001;
 const ACL4_SUPPORT_DENY_ACL     = 0x00000002;
 const ACL4_SUPPORT_AUDIT_ACL    = 0x00000004;
 const ACL4_SUPPORT_ALARM_ACL    = 0x00000008;
 typedef uint32_t        acetype4;
 /*
  * acetype4 values, others can be added as needed.
  */
 const ACE4_ACCESS_ALLOWED_ACE_TYPE      = 0x00000000;
 const ACE4_ACCESS_DENIED_ACE_TYPE       = 0x00000001;
 const ACE4_SYSTEM_AUDIT_ACE_TYPE        = 0x00000002;
 const ACE4_SYSTEM_ALARM_ACE_TYPE        = 0x00000003;
 /*
  * ACE flag
  */
 typedef uint32_t aceflag4;
 /*
  * ACE flag values
  */
 const ACE4_FILE_INHERIT_ACE             = 0x00000001;
 const ACE4_DIRECTORY_INHERIT_ACE        = 0x00000002;
 const ACE4_NO_PROPAGATE_INHERIT_ACE     = 0x00000004;
 const ACE4_INHERIT_ONLY_ACE             = 0x00000008;

Shepler, et al. Standards Track [Page 238] RFC 3530 NFS version 4 Protocol April 2003

 const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG   = 0x00000010;
 const ACE4_FAILED_ACCESS_ACE_FLAG       = 0x00000020;
 const ACE4_IDENTIFIER_GROUP             = 0x00000040;
 /*
  * ACE mask
  */
 typedef uint32_t        acemask4;
 /*
  * ACE mask values
  */
 const ACE4_READ_DATA            = 0x00000001;
 const ACE4_LIST_DIRECTORY       = 0x00000001;
 const ACE4_WRITE_DATA           = 0x00000002;
 const ACE4_ADD_FILE             = 0x00000002;
 const ACE4_APPEND_DATA          = 0x00000004;
 const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
 const ACE4_READ_NAMED_ATTRS     = 0x00000008;
 const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
 const ACE4_EXECUTE              = 0x00000020;
 const ACE4_DELETE_CHILD         = 0x00000040;
 const ACE4_READ_ATTRIBUTES      = 0x00000080;
 const ACE4_WRITE_ATTRIBUTES     = 0x00000100;
 const ACE4_DELETE               = 0x00010000;
 const ACE4_READ_ACL             = 0x00020000;
 const ACE4_WRITE_ACL            = 0x00040000;
 const ACE4_WRITE_OWNER          = 0x00080000;
 const ACE4_SYNCHRONIZE          = 0x00100000;
 /*
  * ACE4_GENERIC_READ -- defined as combination of
  *      ACE4_READ_ACL |
  *      ACE4_READ_DATA |
  *      ACE4_READ_ATTRIBUTES |
  *      ACE4_SYNCHRONIZE
  */
 const ACE4_GENERIC_READ = 0x00120081;
 /*
  * ACE4_GENERIC_WRITE -- defined as combination of
  *      ACE4_READ_ACL |
  *      ACE4_WRITE_DATA |
  *      ACE4_WRITE_ATTRIBUTES |
  *      ACE4_WRITE_ACL |

Shepler, et al. Standards Track [Page 239] RFC 3530 NFS version 4 Protocol April 2003

  • ACE4_APPEND_DATA |
  • ACE4_SYNCHRONIZE
  • /

const ACE4_GENERIC_WRITE = 0x00160106;

 /*
  * ACE4_GENERIC_EXECUTE -- defined as combination of
  *      ACE4_READ_ACL
  *      ACE4_READ_ATTRIBUTES
  *      ACE4_EXECUTE
  *      ACE4_SYNCHRONIZE
  */
 const ACE4_GENERIC_EXECUTE = 0x001200A0;
 /*
  * Access Control Entry definition
  */
 struct nfsace4 {
         acetype4        type;
         aceflag4        flag;
         acemask4        access_mask;
         utf8str_mixed   who;
 };
 /*
  * Field definitions for the fattr4_mode attribute
  */
 const MODE4_SUID = 0x800;  /* set user id on execution */
 const MODE4_SGID = 0x400;  /* set group id on execution */
 const MODE4_SVTX = 0x200;  /* save text even after use */
 const MODE4_RUSR = 0x100;  /* read permission: owner */
 const MODE4_WUSR = 0x080;  /* write permission: owner */
 const MODE4_XUSR = 0x040;  /* execute permission: owner */
 const MODE4_RGRP = 0x020;  /* read permission: group */
 const MODE4_WGRP = 0x010;  /* write permission: group */
 const MODE4_XGRP = 0x008;  /* execute permission: group */
 const MODE4_ROTH = 0x004;  /* read permission: other */
 const MODE4_WOTH = 0x002;  /* write permission: other */
 const MODE4_XOTH = 0x001;  /* execute permission: other */
 /*
  * Special data/attribute associated with
  * file types NF4BLK and NF4CHR.
  */
 struct specdata4 {
         uint32_t        specdata1;      /* major device number */

Shepler, et al. Standards Track [Page 240] RFC 3530 NFS version 4 Protocol April 2003

         uint32_t        specdata2;      /* minor device number */
 };
 /*
  * Values for fattr4_fh_expire_type
  */
 const   FH4_PERSISTENT          = 0x00000000;
 const   FH4_NOEXPIRE_WITH_OPEN  = 0x00000001;
 const   FH4_VOLATILE_ANY        = 0x00000002;
 const   FH4_VOL_MIGRATION       = 0x00000004;
 const   FH4_VOL_RENAME          = 0x00000008;
 typedef bitmap4         fattr4_supported_attrs;
 typedef nfs_ftype4      fattr4_type;
 typedef uint32_t        fattr4_fh_expire_type;
 typedef changeid4       fattr4_change;
 typedef uint64_t        fattr4_size;
 typedef bool            fattr4_link_support;
 typedef bool            fattr4_symlink_support;
 typedef bool            fattr4_named_attr;
 typedef fsid4           fattr4_fsid;
 typedef bool            fattr4_unique_handles;
 typedef uint32_t        fattr4_lease_time;
 typedef nfsstat4        fattr4_rdattr_error;
 typedef nfsace4         fattr4_acl<>;
 typedef uint32_t        fattr4_aclsupport;
 typedef bool            fattr4_archive;
 typedef bool            fattr4_cansettime;
 typedef bool            fattr4_case_insensitive;
 typedef bool            fattr4_case_preserving;
 typedef bool            fattr4_chown_restricted;
 typedef uint64_t        fattr4_fileid;
 typedef uint64_t        fattr4_files_avail;
 typedef nfs_fh4         fattr4_filehandle;
 typedef uint64_t        fattr4_files_free;
 typedef uint64_t        fattr4_files_total;
 typedef fs_locations4   fattr4_fs_locations;
 typedef bool            fattr4_hidden;
 typedef bool            fattr4_homogeneous;
 typedef uint64_t        fattr4_maxfilesize;
 typedef uint32_t        fattr4_maxlink;
 typedef uint32_t        fattr4_maxname;
 typedef uint64_t        fattr4_maxread;
 typedef uint64_t        fattr4_maxwrite;
 typedef utf8str_cs      fattr4_mimetype;
 typedef mode4           fattr4_mode;

Shepler, et al. Standards Track [Page 241] RFC 3530 NFS version 4 Protocol April 2003

 typedef uint64_t        fattr4_mounted_on_fileid;
 typedef bool            fattr4_no_trunc;
 typedef uint32_t        fattr4_numlinks;
 typedef utf8str_mixed   fattr4_owner;
 typedef utf8str_mixed   fattr4_owner_group;
 typedef uint64_t        fattr4_quota_avail_hard;
 typedef uint64_t        fattr4_quota_avail_soft;
 typedef uint64_t        fattr4_quota_used;
 typedef specdata4       fattr4_rawdev;
 typedef uint64_t        fattr4_space_avail;
 typedef uint64_t        fattr4_space_free;
 typedef uint64_t        fattr4_space_total;
 typedef uint64_t        fattr4_space_used;
 typedef bool            fattr4_system;
 typedef nfstime4        fattr4_time_access;
 typedef settime4        fattr4_time_access_set;
 typedef nfstime4        fattr4_time_backup;
 typedef nfstime4        fattr4_time_create;
 typedef nfstime4        fattr4_time_delta;
 typedef nfstime4        fattr4_time_metadata;
 typedef nfstime4        fattr4_time_modify;
 typedef settime4        fattr4_time_modify_set;
 /*
  * Mandatory Attributes
  */
 const FATTR4_SUPPORTED_ATTRS    = 0;
 const FATTR4_TYPE               = 1;
 const FATTR4_FH_EXPIRE_TYPE     = 2;
 const FATTR4_CHANGE             = 3;
 const FATTR4_SIZE               = 4;
 const FATTR4_LINK_SUPPORT       = 5;
 const FATTR4_SYMLINK_SUPPORT    = 6;
 const FATTR4_NAMED_ATTR         = 7;
 const FATTR4_FSID               = 8;
 const FATTR4_UNIQUE_HANDLES     = 9;
 const FATTR4_LEASE_TIME         = 10;
 const FATTR4_RDATTR_ERROR       = 11;
 const FATTR4_FILEHANDLE         = 19;
 /*
  * Recommended Attributes
  */
 const FATTR4_ACL                = 12;
 const FATTR4_ACLSUPPORT         = 13;
 const FATTR4_ARCHIVE            = 14;
 const FATTR4_CANSETTIME         = 15;

Shepler, et al. Standards Track [Page 242] RFC 3530 NFS version 4 Protocol April 2003

 const FATTR4_CASE_INSENSITIVE   = 16;
 const FATTR4_CASE_PRESERVING    = 17;
 const FATTR4_CHOWN_RESTRICTED   = 18;
 const FATTR4_FILEID             = 20;
 const FATTR4_FILES_AVAIL        = 21;
 const FATTR4_FILES_FREE         = 22;
 const FATTR4_FILES_TOTAL        = 23;
 const FATTR4_FS_LOCATIONS       = 24;
 const FATTR4_HIDDEN             = 25;
 const FATTR4_HOMOGENEOUS        = 26;
 const FATTR4_MAXFILESIZE        = 27;
 const FATTR4_MAXLINK            = 28;
 const FATTR4_MAXNAME            = 29;
 const FATTR4_MAXREAD            = 30;
 const FATTR4_MAXWRITE           = 31;
 const FATTR4_MIMETYPE           = 32;
 const FATTR4_MODE               = 33;
 const FATTR4_NO_TRUNC           = 34;
 const FATTR4_NUMLINKS           = 35;
 const FATTR4_OWNER              = 36;
 const FATTR4_OWNER_GROUP        = 37;
 const FATTR4_QUOTA_AVAIL_HARD   = 38;
 const FATTR4_QUOTA_AVAIL_SOFT   = 39;
 const FATTR4_QUOTA_USED         = 40;
 const FATTR4_RAWDEV             = 41;
 const FATTR4_SPACE_AVAIL        = 42;
 const FATTR4_SPACE_FREE         = 43;
 const FATTR4_SPACE_TOTAL        = 44;
 const FATTR4_SPACE_USED         = 45;
 const FATTR4_SYSTEM             = 46;
 const FATTR4_TIME_ACCESS        = 47;
 const FATTR4_TIME_ACCESS_SET    = 48;
 const FATTR4_TIME_BACKUP        = 49;
 const FATTR4_TIME_CREATE        = 50;
 const FATTR4_TIME_DELTA         = 51;
 const FATTR4_TIME_METADATA      = 52;
 const FATTR4_TIME_MODIFY        = 53;
 const FATTR4_TIME_MODIFY_SET    = 54;
 const FATTR4_MOUNTED_ON_FILEID  = 55;
 typedef opaque  attrlist4<>;
 /*
  * File attribute container
  */
 struct fattr4 {
         bitmap4         attrmask;
         attrlist4       attr_vals;

Shepler, et al. Standards Track [Page 243] RFC 3530 NFS version 4 Protocol April 2003

 };
 /*
  * Change info for the client
  */
 struct change_info4 {
         bool            atomic;
         changeid4       before;
         changeid4       after;
 };
 struct clientaddr4 {
         /* see struct rpcb in RFC 1833 */
         string r_netid<>;               /* network id */
         string r_addr<>;                /* universal address */
 };
 /*
  * Callback program info as provided by the client
  */
 struct cb_client4 {
         uint32_t        cb_program;
         clientaddr4     cb_location;
 };
 /*
  * Stateid
  */
 struct stateid4 {
         uint32_t        seqid;
         opaque          other[12];
 };
 /*
  * Client ID
  */
 struct nfs_client_id4 {
         verifier4       verifier;
         opaque          id<NFS4_OPAQUE_LIMIT>;
 };
 struct open_owner4 {
         clientid4       clientid;
         opaque          owner<NFS4_OPAQUE_LIMIT>;
 };
 struct lock_owner4 {
         clientid4       clientid;

Shepler, et al. Standards Track [Page 244] RFC 3530 NFS version 4 Protocol April 2003

         opaque          owner<NFS4_OPAQUE_LIMIT>;
 };
 enum nfs_lock_type4 {
         READ_LT         = 1,
         WRITE_LT        = 2,
         READW_LT        = 3,    /* blocking read */
         WRITEW_LT       = 4     /* blocking write */
 };
 /*
  * ACCESS: Check access permission
  */
 const ACCESS4_READ      = 0x00000001;
 const ACCESS4_LOOKUP    = 0x00000002;
 const ACCESS4_MODIFY    = 0x00000004;
 const ACCESS4_EXTEND    = 0x00000008;
 const ACCESS4_DELETE    = 0x00000010;
 const ACCESS4_EXECUTE   = 0x00000020;
 struct ACCESS4args {
         /* CURRENT_FH: object */
         uint32_t        access;
 };
 struct ACCESS4resok {
         uint32_t        supported;
         uint32_t        access;
 };
 union ACCESS4res switch (nfsstat4 status) {
  case NFS4_OK:
          ACCESS4resok   resok4;
  default:
          void;
 };
 /*
  * CLOSE: Close a file and release share reservations
  */
 struct CLOSE4args {
         /* CURRENT_FH: object */
         seqid4          seqid;
         stateid4        open_stateid;
 };
 union CLOSE4res switch (nfsstat4 status) {
  case NFS4_OK:

Shepler, et al. Standards Track [Page 245] RFC 3530 NFS version 4 Protocol April 2003

          stateid4       open_stateid;
  default:
          void;
 };
 /*
  * COMMIT: Commit cached data on server to stable storage
  */
 struct COMMIT4args {
         /* CURRENT_FH: file */
         offset4         offset;
         count4          count;
 };
 struct COMMIT4resok {
         verifier4       writeverf;
 };
 union COMMIT4res switch (nfsstat4 status) {
  case NFS4_OK:
          COMMIT4resok   resok4;
  default:
          void;
 };
 /*
  * CREATE: Create a non-regular file
  */
 union createtype4 switch (nfs_ftype4 type) {
  case NF4LNK:
          linktext4      linkdata;
  case NF4BLK:
  case NF4CHR:
          specdata4      devdata;
  case NF4SOCK:
  case NF4FIFO:
  case NF4DIR:
          void;
  default:
          void;          /* server should return NFS4ERR_BADTYPE */
 };
 struct CREATE4args {
         /* CURRENT_FH: directory for creation */
         createtype4     objtype;
         component4      objname;
         fattr4          createattrs;

Shepler, et al. Standards Track [Page 246] RFC 3530 NFS version 4 Protocol April 2003

 };
 struct CREATE4resok {
         change_info4    cinfo;
         bitmap4         attrset;        /* attributes set */
 };
 union CREATE4res switch (nfsstat4 status) {
  case NFS4_OK:
          CREATE4resok resok4;
  default:
          void;
 };
 /*
  * DELEGPURGE: Purge Delegations Awaiting Recovery
  */
 struct DELEGPURGE4args {
         clientid4       clientid;
 };
 struct DELEGPURGE4res {
         nfsstat4        status;
 };
 /*
  * DELEGRETURN: Return a delegation
  */
 struct DELEGRETURN4args {
         /* CURRENT_FH: delegated file */
         stateid4        deleg_stateid;
 };
 struct DELEGRETURN4res {
         nfsstat4        status;
 };
 /*
  * GETATTR: Get file attributes
  */
 struct GETATTR4args {
         /* CURRENT_FH: directory or file */
         bitmap4         attr_request;
 };
 struct GETATTR4resok {
         fattr4          obj_attributes;
 };

Shepler, et al. Standards Track [Page 247] RFC 3530 NFS version 4 Protocol April 2003

 union GETATTR4res switch (nfsstat4 status) {
  case NFS4_OK:
          GETATTR4resok  resok4;
  default:
          void;
 };
 /*
  * GETFH: Get current filehandle
  */
 struct GETFH4resok {
         nfs_fh4         object;
 };
 union GETFH4res switch (nfsstat4 status) {
  case NFS4_OK:
         GETFH4resok     resok4;
  default:
         void;
 };
 /*
  * LINK: Create link to an object
  */
 struct LINK4args {
         /* SAVED_FH: source object */
         /* CURRENT_FH: target directory */
         component4      newname;
 };
 struct LINK4resok {
         change_info4    cinfo;
 };
 union LINK4res switch (nfsstat4 status) {
  case NFS4_OK:
          LINK4resok resok4;
  default:
          void;
 };
 /*
  * For LOCK, transition from open_owner to new lock_owner
  */
 struct open_to_lock_owner4 {
         seqid4          open_seqid;
         stateid4        open_stateid;
         seqid4          lock_seqid;

Shepler, et al. Standards Track [Page 248] RFC 3530 NFS version 4 Protocol April 2003

         lock_owner4     lock_owner;
 };
 /*
  * For LOCK, existing lock_owner continues to request file locks
  */
 struct exist_lock_owner4 {
         stateid4        lock_stateid;
         seqid4          lock_seqid;
 };
 union locker4 switch (bool new_lock_owner) {
  case TRUE:
         open_to_lock_owner4     open_owner;
  case FALSE:
         exist_lock_owner4       lock_owner;
 };
 /*
  * LOCK/LOCKT/LOCKU: Record lock management
  */
 struct LOCK4args {
         /* CURRENT_FH: file */
         nfs_lock_type4  locktype;
         bool            reclaim;
         offset4         offset;
         length4         length;
         locker4         locker;
 };
 struct LOCK4denied {
         offset4         offset;
         length4         length;
         nfs_lock_type4  locktype;
         lock_owner4     owner;
 };
 struct LOCK4resok {
         stateid4        lock_stateid;
 };
 union LOCK4res switch (nfsstat4 status) {
  case NFS4_OK:
          LOCK4resok     resok4;
  case NFS4ERR_DENIED:
          LOCK4denied    denied;
  default:
          void;

Shepler, et al. Standards Track [Page 249] RFC 3530 NFS version 4 Protocol April 2003

 };
 struct LOCKT4args {
         /* CURRENT_FH: file */
         nfs_lock_type4  locktype;
         offset4         offset;
         length4         length;
         lock_owner4     owner;
 };
 union LOCKT4res switch (nfsstat4 status) {
  case NFS4ERR_DENIED:
          LOCK4denied    denied;
  case NFS4_OK:
          void;
  default:
          void;
 };
 struct LOCKU4args {
         /* CURRENT_FH: file */
         nfs_lock_type4  locktype;
         seqid4          seqid;
         stateid4        lock_stateid;
         offset4         offset;
         length4         length;
 };
 union LOCKU4res switch (nfsstat4 status) {
  case   NFS4_OK:
          stateid4       lock_stateid;
  default:
          void;
 };
 /*
  * LOOKUP: Lookup filename
  */
 struct LOOKUP4args {
         /* CURRENT_FH: directory */
         component4      objname;
 };
 struct LOOKUP4res {
         /* CURRENT_FH: object */
         nfsstat4        status;
 };

Shepler, et al. Standards Track [Page 250] RFC 3530 NFS version 4 Protocol April 2003

 /*
  * LOOKUPP: Lookup parent directory
  */
 struct LOOKUPP4res {
         /* CURRENT_FH: directory */
         nfsstat4        status;
 };
 /*
  * NVERIFY: Verify attributes different
  */
 struct NVERIFY4args {
         /* CURRENT_FH: object */
         fattr4          obj_attributes;
 };
 struct NVERIFY4res {
         nfsstat4        status;
 };
 /*
  * Various definitions for OPEN
  */
 enum createmode4 {
         UNCHECKED4      = 0,
         GUARDED4        = 1,
         EXCLUSIVE4      = 2
 };
 union createhow4 switch (createmode4 mode) {
  case UNCHECKED4:
  case GUARDED4:
          fattr4         createattrs;
  case EXCLUSIVE4:
          verifier4      createverf;
 };
 enum opentype4 {
         OPEN4_NOCREATE  = 0,
         OPEN4_CREATE    = 1
 };
 union openflag4 switch (opentype4 opentype) {
  case OPEN4_CREATE:
          createhow4     how;
  default:
          void;
 };

Shepler, et al. Standards Track [Page 251] RFC 3530 NFS version 4 Protocol April 2003

 /* Next definitions used for OPEN delegation */
 enum limit_by4 {
         NFS_LIMIT_SIZE          = 1,
         NFS_LIMIT_BLOCKS        = 2
         /* others as needed */
 };
 struct nfs_modified_limit4 {
         uint32_t        num_blocks;
         uint32_t        bytes_per_block;
 };
 union nfs_space_limit4 switch (limit_by4 limitby) {
  /* limit specified as file size */
  case NFS_LIMIT_SIZE:
          uint64_t               filesize;
  /* limit specified by number of blocks */
  case NFS_LIMIT_BLOCKS:
          nfs_modified_limit4    mod_blocks;
 } ;
 /*
  * Share Access and Deny constants for open argument
  */
 const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
 const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
 const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;
 const OPEN4_SHARE_DENY_NONE     = 0x00000000;
 const OPEN4_SHARE_DENY_READ     = 0x00000001;
 const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
 const OPEN4_SHARE_DENY_BOTH     = 0x00000003;
 enum open_delegation_type4 {
         OPEN_DELEGATE_NONE      = 0,
         OPEN_DELEGATE_READ      = 1,
         OPEN_DELEGATE_WRITE     = 2
 };
 enum open_claim_type4 {
         CLAIM_NULL              = 0,
         CLAIM_PREVIOUS          = 1,
         CLAIM_DELEGATE_CUR      = 2,
         CLAIM_DELEGATE_PREV     = 3
 };
 struct open_claim_delegate_cur4 {
         stateid4        delegate_stateid;

Shepler, et al. Standards Track [Page 252] RFC 3530 NFS version 4 Protocol April 2003

         component4      file;
 };
 union open_claim4 switch (open_claim_type4 claim) {
  /*
   * No special rights to file. Ordinary OPEN of the specified file.
   */
  case CLAIM_NULL:
         /* CURRENT_FH: directory */
         component4      file;
  /*
   * Right to the file established by an open previous to server
   * reboot.  File identified by filehandle obtained at that time
   * rather than by name.
   */
  case CLAIM_PREVIOUS:
         /* CURRENT_FH: file being reclaimed */
         open_delegation_type4   delegate_type;
  /*
   * Right to file based on a delegation granted by the server.
   * File is specified by name.
   */
  case CLAIM_DELEGATE_CUR:
         /* CURRENT_FH: directory */
         open_claim_delegate_cur4        delegate_cur_info;
  /* Right to file based on a delegation granted to a previous boot
   * instance of the client.  File is specified by name.
   */
  case CLAIM_DELEGATE_PREV:
          /* CURRENT_FH: directory */
         component4      file_delegate_prev;
 };
 /*
  * OPEN: Open a file, potentially receiving an open delegation
  */
 struct OPEN4args {
         seqid4          seqid;
         uint32_t        share_access;
         uint32_t        share_deny;
         open_owner4     owner;
         openflag4       openhow;
         open_claim4     claim;
 };

Shepler, et al. Standards Track [Page 253] RFC 3530 NFS version 4 Protocol April 2003

 struct open_read_delegation4 {
         stateid4        stateid;        /* Stateid for delegation*/
         bool            recall;         /* Pre-recalled flag for
                                            delegations obtained
                                            by reclaim
                                            (CLAIM_PREVIOUS) */
         nfsace4         permissions;    /* Defines users who don't
                                            need an ACCESS call to
                                            open for read */
 };
 struct open_write_delegation4 {
         stateid4        stateid;        /* Stateid for delegation */
         bool            recall;         /* Pre-recalled flag for
                                            delegations obtained
                                            by reclaim
                                            (CLAIM_PREVIOUS) */
         nfs_space_limit4 space_limit;   /* Defines condition that
                                            the client must check to
                                            determine whether the
                                            file needs to be flushed
                                            to the server on close.
                                            */
         nfsace4         permissions;    /* Defines users who don't
                                            need an ACCESS call as
                                            part of a delegated
                                            open. */
 };
 union open_delegation4
 switch (open_delegation_type4 delegation_type) {
         case OPEN_DELEGATE_NONE:
                 void;
         case OPEN_DELEGATE_READ:
                 open_read_delegation4 read;
         case OPEN_DELEGATE_WRITE:
                 open_write_delegation4 write;
 };
 /*
  * Result flags
  */
 /* Client must confirm open */
 const OPEN4_RESULT_CONFIRM      = 0x00000002;
 /* Type of file locking behavior at the server */
 const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;
 struct OPEN4resok {
         stateid4        stateid;        /* Stateid for open */

Shepler, et al. Standards Track [Page 254] RFC 3530 NFS version 4 Protocol April 2003

         change_info4    cinfo;          /* Directory Change Info */
         uint32_t        rflags;         /* Result flags */
         bitmap4         attrset;        /* attribute set for create*/
         open_delegation4 delegation;    /* Info on any open
                                            delegation */
 };
 union OPEN4res switch (nfsstat4 status) {
  case NFS4_OK:
         /* CURRENT_FH: opened file */
         OPEN4resok      resok4;
  default:
         void;
 };
 /*
  * OPENATTR: open named attributes directory
  */
 struct OPENATTR4args {
         /* CURRENT_FH: object */
         bool    createdir;
 };
 struct OPENATTR4res {
         /* CURRENT_FH: named attr directory */
         nfsstat4        status;
 };
 /*
  * OPEN_CONFIRM: confirm the open
  */
 struct OPEN_CONFIRM4args {
         /* CURRENT_FH: opened file */
         stateid4        open_stateid;
         seqid4          seqid;
 };
 struct OPEN_CONFIRM4resok {
         stateid4        open_stateid;
 };
 union OPEN_CONFIRM4res switch (nfsstat4 status) {
     case NFS4_OK:
             OPEN_CONFIRM4resok     resok4;
  default:
          void;
 };

Shepler, et al. Standards Track [Page 255] RFC 3530 NFS version 4 Protocol April 2003

 /*
  * OPEN_DOWNGRADE: downgrade the access/deny for a file
  */
 struct OPEN_DOWNGRADE4args {
         /* CURRENT_FH: opened file */
         stateid4        open_stateid;
         seqid4          seqid;
         uint32_t        share_access;
         uint32_t        share_deny;
 };
 struct OPEN_DOWNGRADE4resok {
         stateid4        open_stateid;
 };
 union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
  case NFS4_OK:
         OPEN_DOWNGRADE4resok    resok4;
  default:
          void;
 };
 /*
  * PUTFH: Set current filehandle
  */
 struct PUTFH4args {
         nfs_fh4         object;
 };
 struct PUTFH4res {
         /* CURRENT_FH: */
         nfsstat4        status;
 };
 /*
  * PUTPUBFH: Set public filehandle
  */
 struct PUTPUBFH4res {
         /* CURRENT_FH: public fh */
         nfsstat4        status;
 };
 /*
  * PUTROOTFH: Set root filehandle
  */
 struct PUTROOTFH4res {
         /* CURRENT_FH: root fh */

Shepler, et al. Standards Track [Page 256] RFC 3530 NFS version 4 Protocol April 2003

         nfsstat4        status;
 };
 /*
  * READ: Read from file
  */
 struct READ4args {
         /* CURRENT_FH: file */
         stateid4        stateid;
         offset4         offset;
         count4          count;
 };
 struct READ4resok {
         bool            eof;
         opaque          data<>;
 };
 union READ4res switch (nfsstat4 status) {
  case NFS4_OK:
          READ4resok     resok4;
  default:
          void;
 };
 /*
  * READDIR: Read directory
  */
 struct READDIR4args {
         /* CURRENT_FH: directory */
         nfs_cookie4     cookie;
         verifier4       cookieverf;
         count4          dircount;
         count4          maxcount;
         bitmap4         attr_request;
 };
 struct entry4 {
         nfs_cookie4     cookie;
         component4      name;
         fattr4          attrs;
         entry4          *nextentry;
 };
 struct dirlist4 {
         entry4          *entries;
         bool            eof;
 };

Shepler, et al. Standards Track [Page 257] RFC 3530 NFS version 4 Protocol April 2003

 struct READDIR4resok {
         verifier4       cookieverf;
         dirlist4        reply;
 };
 union READDIR4res switch (nfsstat4 status) {
  case NFS4_OK:
          READDIR4resok  resok4;
  default:
          void;
 };
 /*
  * READLINK: Read symbolic link
  */
 struct READLINK4resok {
         linktext4       link;
 };
 union READLINK4res switch (nfsstat4 status) {
  case NFS4_OK:
          READLINK4resok resok4;
  default:
          void;
 };
 /*
  * REMOVE: Remove filesystem object
  */
 struct REMOVE4args {
         /* CURRENT_FH: directory */
         component4      target;
 };
 struct REMOVE4resok {
         change_info4    cinfo;
 };
 union REMOVE4res switch (nfsstat4 status) {
  case NFS4_OK:
          REMOVE4resok   resok4;
  default:
          void;
 };
 /*

Shepler, et al. Standards Track [Page 258] RFC 3530 NFS version 4 Protocol April 2003

  • RENAME: Rename directory entry
  • /

struct RENAME4args {

         /* SAVED_FH: source directory */
         component4      oldname;
         /* CURRENT_FH: target directory */
         component4      newname;
 };
 struct RENAME4resok {
         change_info4    source_cinfo;
         change_info4    target_cinfo;
 };
 union RENAME4res switch (nfsstat4 status) {
  case NFS4_OK:
         RENAME4resok    resok4;
  default:
         void;
 };
 /*
  * RENEW: Renew a Lease
  */
 struct RENEW4args {
         clientid4       clientid;
 };
 struct RENEW4res {
         nfsstat4        status;
 };
 /*
  * RESTOREFH: Restore saved filehandle
  */
 struct RESTOREFH4res {
         /* CURRENT_FH: value of saved fh */
         nfsstat4        status;
 };
 /*
  * SAVEFH: Save current filehandle
  */
 struct SAVEFH4res {
         /* SAVED_FH: value of current fh */
         nfsstat4        status;

Shepler, et al. Standards Track [Page 259] RFC 3530 NFS version 4 Protocol April 2003

 };
 /*
  * SECINFO: Obtain Available Security Mechanisms
  */
 struct SECINFO4args {
         /* CURRENT_FH: directory */
         component4      name;
 };
 /*
  • From RFC 2203
  • /

enum rpc_gss_svc_t {

         RPC_GSS_SVC_NONE        = 1,
         RPC_GSS_SVC_INTEGRITY   = 2,
         RPC_GSS_SVC_PRIVACY     = 3
 };
 struct rpcsec_gss_info {
         sec_oid4        oid;
         qop4            qop;
         rpc_gss_svc_t   service;
 };
 /* RPCSEC_GSS has a value of '6' - See RFC 2203 */
 union secinfo4 switch (uint32_t flavor) {
  case RPCSEC_GSS:
          rpcsec_gss_info        flavor_info;
  default:
          void;
 };
 typedef secinfo4 SECINFO4resok<>;
 union SECINFO4res switch (nfsstat4 status) {
  case NFS4_OK:
          SECINFO4resok resok4;
  default:
          void;
 };
 /*
  * SETATTR: Set attributes
  */
 struct SETATTR4args {
         /* CURRENT_FH: target object */

Shepler, et al. Standards Track [Page 260] RFC 3530 NFS version 4 Protocol April 2003

         stateid4        stateid;
         fattr4          obj_attributes;
 };
 struct SETATTR4res {
         nfsstat4        status;
         bitmap4         attrsset;
 };
 /*
  * SETCLIENTID
  */
 struct SETCLIENTID4args {
         nfs_client_id4  client;
         cb_client4      callback;
         uint32_t        callback_ident;
 };
 struct SETCLIENTID4resok {
         clientid4       clientid;
         verifier4       setclientid_confirm;
 };
 union SETCLIENTID4res switch (nfsstat4 status) {
  case NFS4_OK:
          SETCLIENTID4resok      resok4;
  case NFS4ERR_CLID_INUSE:
          clientaddr4    client_using;
  default:
          void;
 };
 struct SETCLIENTID_CONFIRM4args {
         clientid4       clientid;
         verifier4       setclientid_confirm;
 };
 struct SETCLIENTID_CONFIRM4res {
         nfsstat4        status;
 };
 /*
  * VERIFY: Verify attributes same
  */
 struct VERIFY4args {
         /* CURRENT_FH: object */
         fattr4          obj_attributes;

Shepler, et al. Standards Track [Page 261] RFC 3530 NFS version 4 Protocol April 2003

 };
 struct VERIFY4res {
         nfsstat4        status;
 };
 /*
  * WRITE: Write to file
  */
 enum stable_how4 {
         UNSTABLE4       = 0,
         DATA_SYNC4      = 1,
         FILE_SYNC4      = 2
 };
 struct WRITE4args {
         /* CURRENT_FH: file */
         stateid4        stateid;
         offset4         offset;
         stable_how4     stable;
         opaque          data<>;
 };
 struct WRITE4resok {
         count4          count;
         stable_how4     committed;
         verifier4       writeverf;
 };
 union WRITE4res switch (nfsstat4 status) {
  case NFS4_OK:
          WRITE4resok    resok4;
  default:
          void;
 };
 /*
  * RELEASE_LOCKOWNER: Notify server to release lockowner
  */
 struct RELEASE_LOCKOWNER4args {
         lock_owner4     lock_owner;
 };
 struct RELEASE_LOCKOWNER4res {
         nfsstat4        status;
 };
 /*

Shepler, et al. Standards Track [Page 262] RFC 3530 NFS version 4 Protocol April 2003

  • ILLEGAL: Response for illegal operation numbers
  • /

struct ILLEGAL4res {

         nfsstat4        status;
 };
 /*
  * Operation arrays
  */
 enum nfs_opnum4 {
         OP_ACCESS               = 3,
         OP_CLOSE                = 4,
         OP_COMMIT               = 5,
         OP_CREATE               = 6,
         OP_DELEGPURGE           = 7,
         OP_DELEGRETURN          = 8,
         OP_GETATTR              = 9,
         OP_GETFH                = 10,
         OP_LINK                 = 11,
         OP_LOCK                 = 12,
         OP_LOCKT                = 13,
         OP_LOCKU                = 14,
         OP_LOOKUP               = 15,
         OP_LOOKUPP              = 16,
         OP_NVERIFY              = 17,
         OP_OPEN                 = 18,
         OP_OPENATTR             = 19,
         OP_OPEN_CONFIRM         = 20,
         OP_OPEN_DOWNGRADE       = 21,
         OP_PUTFH                = 22,
         OP_PUTPUBFH             = 23,
         OP_PUTROOTFH            = 24,
         OP_READ                 = 25,
         OP_READDIR              = 26,
         OP_READLINK             = 27,
         OP_REMOVE               = 28,
         OP_RENAME               = 29,
         OP_RENEW                = 30,
         OP_RESTOREFH            = 31,
         OP_SAVEFH               = 32,
         OP_SECINFO              = 33,
         OP_SETATTR              = 34,
         OP_SETCLIENTID          = 35,
         OP_SETCLIENTID_CONFIRM  = 36,
         OP_VERIFY               = 37,
         OP_WRITE                = 38,
         OP_RELEASE_LOCKOWNER    = 39,

Shepler, et al. Standards Track [Page 263] RFC 3530 NFS version 4 Protocol April 2003

         OP_ILLEGAL              = 10044
 };
 union nfs_argop4 switch (nfs_opnum4 argop) {
  case OP_ACCESS:        ACCESS4args opaccess;
  case OP_CLOSE:         CLOSE4args opclose;
  case OP_COMMIT:        COMMIT4args opcommit;
  case OP_CREATE:        CREATE4args opcreate;
  case OP_DELEGPURGE:    DELEGPURGE4args opdelegpurge;
  case OP_DELEGRETURN:   DELEGRETURN4args opdelegreturn;
  case OP_GETATTR:       GETATTR4args opgetattr;
  case OP_GETFH:         void;
  case OP_LINK:          LINK4args oplink;
  case OP_LOCK:          LOCK4args oplock;
  case OP_LOCKT:         LOCKT4args oplockt;
  case OP_LOCKU:         LOCKU4args oplocku;
  case OP_LOOKUP:        LOOKUP4args oplookup;
  case OP_LOOKUPP:       void;
  case OP_NVERIFY:       NVERIFY4args opnverify;
  case OP_OPEN:          OPEN4args opopen;
  case OP_OPENATTR:      OPENATTR4args opopenattr;
  case OP_OPEN_CONFIRM:  OPEN_CONFIRM4args opopen_confirm;
  case OP_OPEN_DOWNGRADE:        OPEN_DOWNGRADE4args opopen_downgrade;
  case OP_PUTFH:         PUTFH4args opputfh;
  case OP_PUTPUBFH:      void;
  case OP_PUTROOTFH:     void;
  case OP_READ:          READ4args opread;
  case OP_READDIR:       READDIR4args opreaddir;
  case OP_READLINK:      void;
  case OP_REMOVE:        REMOVE4args opremove;
  case OP_RENAME:        RENAME4args oprename;
  case OP_RENEW:         RENEW4args oprenew;
  case OP_RESTOREFH:     void;
  case OP_SAVEFH:        void;
  case OP_SECINFO:       SECINFO4args opsecinfo;
  case OP_SETATTR:       SETATTR4args opsetattr;
  case OP_SETCLIENTID:   SETCLIENTID4args opsetclientid;
  case OP_SETCLIENTID_CONFIRM:   SETCLIENTID_CONFIRM4args
                                         opsetclientid_confirm;
  case OP_VERIFY:        VERIFY4args opverify;
  case OP_WRITE:         WRITE4args opwrite;
  case OP_RELEASE_LOCKOWNER:     RELEASE_LOCKOWNER4args
                                     oprelease_lockowner;
  case OP_ILLEGAL:       void;
 };
 union nfs_resop4 switch (nfs_opnum4 resop){
  case OP_ACCESS:        ACCESS4res opaccess;

Shepler, et al. Standards Track [Page 264] RFC 3530 NFS version 4 Protocol April 2003

  case OP_CLOSE:         CLOSE4res opclose;
  case OP_COMMIT:        COMMIT4res opcommit;
  case OP_CREATE:        CREATE4res opcreate;
  case OP_DELEGPURGE:    DELEGPURGE4res opdelegpurge;
  case OP_DELEGRETURN:   DELEGRETURN4res opdelegreturn;
  case OP_GETATTR:       GETATTR4res opgetattr;
  case OP_GETFH:         GETFH4res opgetfh;
  case OP_LINK:          LINK4res oplink;
  case OP_LOCK:          LOCK4res oplock;
  case OP_LOCKT:         LOCKT4res oplockt;
  case OP_LOCKU:         LOCKU4res oplocku;
  case OP_LOOKUP:        LOOKUP4res oplookup;
  case OP_LOOKUPP:       LOOKUPP4res oplookupp;
  case OP_NVERIFY:       NVERIFY4res opnverify;
  case OP_OPEN:          OPEN4res opopen;
  case OP_OPENATTR:      OPENATTR4res opopenattr;
  case OP_OPEN_CONFIRM:  OPEN_CONFIRM4res opopen_confirm;
  case OP_OPEN_DOWNGRADE:        OPEN_DOWNGRADE4res opopen_downgrade;
  case OP_PUTFH:         PUTFH4res opputfh;
  case OP_PUTPUBFH:      PUTPUBFH4res opputpubfh;
  case OP_PUTROOTFH:     PUTROOTFH4res opputrootfh;
  case OP_READ:          READ4res opread;
  case OP_READDIR:       READDIR4res opreaddir;
  case OP_READLINK:      READLINK4res opreadlink;
  case OP_REMOVE:        REMOVE4res opremove;
  case OP_RENAME:        RENAME4res oprename;
  case OP_RENEW:         RENEW4res oprenew;
  case OP_RESTOREFH:     RESTOREFH4res oprestorefh;
  case OP_SAVEFH:        SAVEFH4res opsavefh;
  case OP_SECINFO:       SECINFO4res opsecinfo;
  case OP_SETATTR:       SETATTR4res opsetattr;
  case OP_SETCLIENTID:   SETCLIENTID4res opsetclientid;
  case OP_SETCLIENTID_CONFIRM:   SETCLIENTID_CONFIRM4res
                                         opsetclientid_confirm;
  case OP_VERIFY:        VERIFY4res opverify;
  case OP_WRITE:         WRITE4res opwrite;
  case OP_RELEASE_LOCKOWNER:     RELEASE_LOCKOWNER4res
                                     oprelease_lockowner;
  case OP_ILLEGAL:       ILLEGAL4res opillegal;
 };
 struct COMPOUND4args {
         utf8str_cs      tag;
         uint32_t        minorversion;
         nfs_argop4      argarray<>;
 };
 struct COMPOUND4res {

Shepler, et al. Standards Track [Page 265] RFC 3530 NFS version 4 Protocol April 2003

         nfsstat4 status;
         utf8str_cs      tag;
         nfs_resop4      resarray<>;
 };
 /*
  * Remote file service routines
  */
 program NFS4_PROGRAM {
         version NFS_V4 {
                 void
                         NFSPROC4_NULL(void) = 0;
                 COMPOUND4res
                         NFSPROC4_COMPOUND(COMPOUND4args) = 1;
         } = 4;
 } = 100003;
 /*
  * NFS4 Callback Procedure Definitions and Program
  */
 /*
  * CB_GETATTR: Get Current Attributes
  */
 struct CB_GETATTR4args {
         nfs_fh4 fh;
         bitmap4 attr_request;
 };
 struct CB_GETATTR4resok {
         fattr4  obj_attributes;
 };
 union CB_GETATTR4res switch (nfsstat4 status) {
  case NFS4_OK:
          CB_GETATTR4resok       resok4;
  default:
          void;
 };
 /*
  * CB_RECALL: Recall an Open Delegation
  */
 struct CB_RECALL4args {

Shepler, et al. Standards Track [Page 266] RFC 3530 NFS version 4 Protocol April 2003

         stateid4        stateid;
         bool            truncate;
         nfs_fh4         fh;
 };
 struct CB_RECALL4res {
         nfsstat4        status;
 };
 /*
  * CB_ILLEGAL: Response for illegal operation numbers
  */
 struct CB_ILLEGAL4res {
         nfsstat4        status;
 };
 /*
  * Various definitions for CB_COMPOUND
  */
 enum nfs_cb_opnum4 {
         OP_CB_GETATTR           = 3,
         OP_CB_RECALL            = 4,
         OP_CB_ILLEGAL           = 10044
 };
 union nfs_cb_argop4 switch (unsigned argop) {
  case OP_CB_GETATTR:    CB_GETATTR4args opcbgetattr;
  case OP_CB_RECALL:     CB_RECALL4args  opcbrecall;
  case OP_CB_ILLEGAL:    void;
 };
 union nfs_cb_resop4 switch (unsigned resop){
  case OP_CB_GETATTR:    CB_GETATTR4res  opcbgetattr;
  case OP_CB_RECALL:     CB_RECALL4res   opcbrecall;
  case OP_CB_ILLEGAL:    CB_ILLEGAL4res  opcbillegal;
 };
 struct CB_COMPOUND4args {
         utf8str_cs      tag;
         uint32_t        minorversion;
         uint32_t        callback_ident;
         nfs_cb_argop4   argarray<>;
 };
 struct CB_COMPOUND4res {
         nfsstat4 status;
         utf8str_cs      tag;
         nfs_cb_resop4   resarray<>;

Shepler, et al. Standards Track [Page 267] RFC 3530 NFS version 4 Protocol April 2003

 };
 /*
  * Program number is in the transient range since the client
  * will assign the exact transient program number and provide
  * that to the server via the SETCLIENTID operation.
  */
 program NFS4_CALLBACK {
         version NFS_CB {
                 void
                         CB_NULL(void) = 0;
                 CB_COMPOUND4res
                         CB_COMPOUND(CB_COMPOUND4args) = 1;
         } = 1;
 } = 0x40000000;

19. Acknowledgements

 The authors thank and acknowledge:
 Neil Brown for his extensive review and comments of various
 documents. Rick Macklem at the University of Guelph, Mike Frisch,
 Sergey Klyushin, and Dan Trufasiu of Hummingbird Ltd., and Andy
 Adamson, Bruce Fields, Jim Rees, and Kendrick Smith from the CITI
 organization at the University of Michigan, for their implementation
 efforts and feedback on the protocol specification. Mike Kupfer for
 his review of the file locking and ACL mechanisms.  Alan Yoder for
 his input to ACL mechanisms. Peter Astrand for his close review of
 the protocol specification. Ran Atkinson for his constant reminder
 that users do matter.

20. Normative References

 [ISO10646]                "ISO/IEC 10646-1:1993. International
                           Standard -- Information technology --
                           Universal Multiple-Octet Coded Character
                           Set (UCS) -- Part 1: Architecture and Basic
                           Multilingual Plane."
 [RFC793]                  Postel, J., "Transmission Control
                           Protocol", STD 7, RFC 793, September 1981.
 [RFC1831]                 Srinivasan, R., "RPC: Remote Procedure Call
                           Protocol Specification Version 2", RFC
                           1831, August 1995.

Shepler, et al. Standards Track [Page 268] RFC 3530 NFS version 4 Protocol April 2003

 [RFC1832]                 Srinivasan, R., "XDR: External Data
                           Representation Standard", RFC 1832, August
                           1995.
 [RFC2373]                 Hinden, R. and S. Deering, "IP Version 6
                           Addressing Architecture", RFC 2373, July
                           1998.
 [RFC1964]                 Linn, J., "The Kerberos Version 5 GSS-API
                           Mechanism", RFC 1964, June 1996.
 [RFC2025]                 Adams, C., "The Simple Public-Key GSS-API
                           Mechanism (SPKM)", RFC 2025, October 1996.
 [RFC2119]                 Bradner, S., "Key words for use in RFCs to
                           Indicate Requirement Levels", BCP 14, RFC
                           2119, March 1997.
 [RFC2203]                 Eisler, M., Chiu, A. and L. Ling,
                           "RPCSEC_GSS Protocol Specification", RFC
                           2203, September 1997.
 [RFC2277]                 Alvestrand, H., "IETF Policy on Character
                           Sets and Languages", BCP 19, RFC 2277,
                           January 1998.
 [RFC2279]                 Yergeau, F., "UTF-8, a transformation
                           format of ISO 10646", RFC 2279, January
                           1998.
 [RFC2623]                 Eisler, M., "NFS Version 2 and Version 3
                           Security Issues and the NFS Protocol's Use
                           of RPCSEC_GSS and Kerberos V5", RFC 2623,
                           June 1999.
 [RFC2743]                 Linn, J., "Generic Security Service
                           Application Program Interface, Version 2,
                           Update 1", RFC 2743, January 2000.
 [RFC2847]                 Eisler, M., "LIPKEY - A Low Infrastructure
                           Public Key Mechanism Using SPKM", RFC 2847,
                           June 2000.
 [RFC3010]                 Shepler, S., Callaghan, B., Robinson, D.,
                           Thurlow, R., Beame, C., Eisler, M. and D.
                           Noveck, "NFS version 4 Protocol", RFC 3010,
                           December 2000.

Shepler, et al. Standards Track [Page 269] RFC 3530 NFS version 4 Protocol April 2003

 [RFC3454]                 Hoffman, P. and P. Blanchet, "Preparation
                           of Internationalized Strings
                           ("stringprep")", RFC 3454, December 2002.
 [Unicode1]                The Unicode Consortium, "The Unicode
                           Standard, Version 3.0", Addison-Wesley
                           Developers Press, Reading, MA, 2000. ISBN
                           0-201-61633-5.
                           More information available at:
                           http://www.unicode.org/
 [Unicode2]                "Unsupported Scripts" Unicode, Inc., The
                           Unicode Consortium, P.O. Box 700519, San
                           Jose, CA 95710-0519 USA, September 1999.
                           http://www.unicode.org/unicode/standard/
                           unsupported.html

21. Informative References

 [Floyd]                   S. Floyd, V. Jacobson, "The Synchronization
                           of Periodic Routing Messages," IEEE/ACM
                           Transactions on Networking, 2(2), pp. 122-
                           136, April 1994.
 [Gray]                    C. Gray, D. Cheriton, "Leases: An Efficient
                           Fault-Tolerant Mechanism for Distributed
                           File Cache Consistency," Proceedings of the
                           Twelfth Symposium on Operating Systems
                           Principles, p. 202-210, December 1989.
 [Juszczak]                Juszczak, Chet, "Improving the Performance
                           and Correctness of an NFS Server," USENIX
                           Conference Proceedings, USENIX Association,
                           Berkeley, CA, June 1990, pages 53-63.
                           Describes reply cache implementation that
                           avoids work in the server by handling
                           duplicate requests. More important, though
                           listed as a side-effect, the reply cache
                           aids in the avoidance of destructive non-
                           idempotent operation re-application --
                           improving correctness.

Shepler, et al. Standards Track [Page 270] RFC 3530 NFS version 4 Protocol April 2003

 [Kazar]                   Kazar, Michael Leon, "Synchronization and
                           Caching Issues in the Andrew File System,"
                           USENIX Conference Proceedings, USENIX
                           Association, Berkeley, CA, Dallas Winter
                           1988, pages 27-36.  A description of the
                           cache consistency scheme in AFS.
                           Contrasted with other distributed file
                           systems.
 [Macklem]                 Macklem, Rick, "Lessons Learned Tuning the
                           4.3BSD Reno Implementation of the NFS
                           Protocol," Winter USENIX Conference
                           Proceedings, USENIX Association, Berkeley,
                           CA, January 1991.  Describes performance
                           work in tuning the 4.3BSD Reno NFS
                           implementation. Describes performance
                           improvement (reduced CPU loading) through
                           elimination of data copies.
 [Mogul]                   Mogul, Jeffrey C., "A Recovery Protocol for
                           Spritely NFS," USENIX File System Workshop
                           Proceedings, Ann Arbor, MI, USENIX
                           Association, Berkeley, CA, May 1992.
                           Second paper on Spritely NFS proposes a
                           lease-based scheme for recovering state of
                           consistency protocol.
 [Nowicki]                 Nowicki, Bill, "Transport Issues in the
                           Network File System," ACM SIGCOMM
                           newsletter Computer Communication Review,
                           April 1989.  A brief description of the
                           basis for the dynamic retransmission work.
 [Pawlowski]               Pawlowski, Brian, Ron Hixon, Mark Stein,
                           Joseph Tumminaro, "Network Computing in the
                           UNIX and IBM Mainframe Environment,"
                           Uniforum `89 Conf.  Proc., (1989)
                           Description of an NFS server implementation
                           for IBM's MVS operating system.
 [RFC1094]                 Sun Microsystems, Inc., "NFS: Network File
                           System Protocol Specification", RFC 1094,
                           March 1989.
 [RFC1345]                 Simonsen, K., "Character Mnemonics &
                           Character Sets", RFC 1345, June 1992.

Shepler, et al. Standards Track [Page 271] RFC 3530 NFS version 4 Protocol April 2003

 [RFC1813]                 Callaghan, B., Pawlowski, B. and P.
                           Staubach, "NFS Version 3 Protocol
                           Specification", RFC 1813, June 1995.
 [RFC3232]                 Reynolds, J., Editor, "Assigned Numbers:
                           RFC 1700 is Replaced by an On-line
                           Database", RFC 3232, January 2002.
 [RFC1833]                 Srinivasan, R., "Binding Protocols for ONC
                           RPC Version 2", RFC 1833, August 1995.
 [RFC2054]                 Callaghan, B., "WebNFS Client
                           Specification", RFC 2054, October 1996.
 [RFC2055]                 Callaghan, B., "WebNFS Server
                           Specification", RFC 2055,  October 1996.
 [RFC2152]                 Goldsmith, D. and M. Davis, "UTF-7 A Mail-
                           Safe Transformation Format of Unicode", RFC
                           2152, May 1997.
 [RFC2224]                 Callaghan, B., "NFS URL Scheme", RFC 2224,
                           October 1997.
 [RFC2624]                 Shepler, S., "NFS Version 4 Design
                           Considerations", RFC 2624, June 1999.
 [RFC2755]                 Chiu, A., Eisler, M. and B. Callaghan,
                           "Security Negotiation for WebNFS" , RFC
                           2755, June 2000.
 [Sandberg]                Sandberg, R., D. Goldberg, S. Kleiman, D.
                           Walsh, B.  Lyon, "Design and Implementation
                           of the Sun Network Filesystem," USENIX
                           Conference Proceedings, USENIX Association,
                           Berkeley, CA, Summer 1985.  The basic paper
                           describing the SunOS implementation of the
                           NFS version 2 protocol, and discusses the
                           goals, protocol specification and trade-
                           offs.

Shepler, et al. Standards Track [Page 272] RFC 3530 NFS version 4 Protocol April 2003

 [Srinivasan]              Srinivasan, V., Jeffrey C. Mogul, "Spritely
                           NFS: Implementation and Performance of
                           Cache Consistency Protocols", WRL Research
                           Report 89/5, Digital Equipment Corporation
                           Western Research Laboratory, 100 Hamilton
                           Ave., Palo Alto, CA, 94301, May 1989.  This
                           paper analyzes the effect of applying a
                           Sprite-like consistency protocol applied to
                           standard NFS. The issues of recovery in a
                           stateful environment are covered in
                           [Mogul].
 [XNFS]                    The Open Group, Protocols for Interworking:
                           XNFS, Version 3W, The Open Group, 1010 El
                           Camino Real Suite 380, Menlo Park, CA
                           94025, ISBN 1-85912-184-5, February 1998.
                           HTML version available:
                           http://www.opengroup.org

22. Authors' Information

22.1. Editor's Address

 Spencer Shepler
 Sun Microsystems, Inc.
 7808 Moonflower Drive
 Austin, Texas  78750
 Phone: +1 512-349-9376
 EMail: spencer.shepler@sun.com

Shepler, et al. Standards Track [Page 273] RFC 3530 NFS version 4 Protocol April 2003

22.2. Authors' Addresses

 Carl Beame
 Hummingbird Ltd.
 EMail: beame@bws.com
 Brent Callaghan
 Sun Microsystems, Inc.
 17 Network Circle
 Menlo Park, CA  94025
 Phone: +1 650-786-5067
 EMail: brent.callaghan@sun.com
 Mike Eisler
 5765 Chase Point Circle
 Colorado Springs, CO  80919
 Phone: +1 719-599-9026
 EMail: mike@eisler.com
 David Noveck
 Network Appliance
 375 Totten Pond Road
 Waltham, MA  02451
 Phone: +1 781-768-5347
 EMail: dnoveck@netapp.com
 David Robinson
 Sun Microsystems, Inc.
 5300 Riata Park Court
 Austin, TX  78727
 Phone: +1 650-786-5088
 EMail: david.robinson@sun.com
 Robert Thurlow
 Sun Microsystems, Inc.
 500 Eldorado Blvd.
 Broomfield, CO  80021
 Phone: +1 650-786-5096
 EMail: robert.thurlow@sun.com

Shepler, et al. Standards Track [Page 274] RFC 3530 NFS version 4 Protocol April 2003

23. Full Copyright Statement

 Copyright (C) The Internet Society (2003).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
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 or assist in its implementation may be prepared, copied, published
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 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
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 The limited permissions granted above are perpetual and will not be
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 This document and the information contained herein is provided on an
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Shepler, et al. Standards Track [Page 275]

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