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rfc:rfc3010

Network Working Group S. Shepler Request for Comments: 3010 B. Callaghan Obsoletes: 1813, 1094 D. Robinson Category: Standards Track R. Thurlow

                                                 Sun Microsystems Inc.
                                                              C. Beame
                                                      Hummingbird Ltd.
                                                             M. Eisler
                                                         Zambeel, Inc.
                                                             D. Noveck
                                               Network Appliance, Inc.
                                                         December 2000
                       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 (2000).  All Rights Reserved.

Abstract

 NFS (Network File System) version 4 is a distributed file system
 protocol which owes heritage to NFS protocol versions 2 [RFC1094] and
 3 [RFC1813].  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.

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 RFC 2119.

Shepler, et al. Standards Track [Page 1] RFC 3010 NFS version 4 Protocol December 2000

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . .   5
 1.1.  Overview of NFS Version 4 Features . . . . . . . . . . . .   6
 1.1.1.  RPC and Security . . . . . . . . . . . . . . . . . . . .   6
 1.1.2.  Procedure and Operation Structure  . . . . . . . . . . .   7
 1.1.3.  File System Model  . . . . . . . . . . . . . . . . . . .   8
 1.1.3.1.  Filehandle Types . . . . . . . . . . . . . . . . . . .   8
 1.1.3.2.  Attribute Types  . . . . . . . . . . . . . . . . . . .   8
 1.1.3.3.  File System Replication and Migration  . . . . . . . .   9
 1.1.4.  OPEN and CLOSE . . . . . . . . . . . . . . . . . . . . .   9
 1.1.5.  File locking . . . . . . . . . . . . . . . . . . . . . .   9
 1.1.6.  Client Caching and Delegation  . . . . . . . . . . . . .  10
 1.2.  General Definitions  . . . . . . . . . . . . . . . . . . .  11
 2.  Protocol Data Types  . . . . . . . . . . . . . . . . . . . .  12
 2.1.  Basic Data Types . . . . . . . . . . . . . . . . . . . . .  12
 2.2.  Structured Data Types  . . . . . . . . . . . . . . . . . .  14
 3.  RPC and Security Flavor  . . . . . . . . . . . . . . . . . .  18
 3.1.  Ports and Transports . . . . . . . . . . . . . . . . . . .  18
 3.2.  Security Flavors . . . . . . . . . . . . . . . . . . . . .  18
 3.2.1.  Security mechanisms for NFS version 4  . . . . . . . . .  19
 3.2.1.1.  Kerberos V5 as security triple . . . . . . . . . . . .  19
 3.2.1.2.  LIPKEY as a security triple  . . . . . . . . . . . . .  19
 3.2.1.3.  SPKM-3 as a security triple  . . . . . . . . . . . . .  20
 3.3.  Security Negotiation . . . . . . . . . . . . . . . . . . .  21
 3.3.1.  Security Error . . . . . . . . . . . . . . . . . . . . .  21
 3.3.2.  SECINFO  . . . . . . . . . . . . . . . . . . . . . . . .  21
 3.4.  Callback RPC Authentication  . . . . . . . . . . . . . . .  22
 4.  Filehandles  . . . . . . . . . . . . . . . . . . . . . . . .  23
 4.1.  Obtaining the First Filehandle . . . . . . . . . . . . . .  24
 4.1.1.  Root Filehandle  . . . . . . . . . . . . . . . . . . . .  24
 4.1.2.  Public Filehandle  . . . . . . . . . . . . . . . . . . .  24
 4.2.  Filehandle Types . . . . . . . . . . . . . . . . . . . . .  25
 4.2.1.  General Properties of a Filehandle . . . . . . . . . . .  25
 4.2.2.  Persistent Filehandle  . . . . . . . . . . . . . . . . .  26
 4.2.3.  Volatile Filehandle  . . . . . . . . . . . . . . . . . .  26
 4.2.4.  One Method of Constructing a Volatile Filehandle . . . .  28
 4.3.  Client Recovery from Filehandle Expiration . . . . . . . .  28
 5.  File Attributes  . . . . . . . . . . . . . . . . . . . . . .  29
 5.1.  Mandatory Attributes . . . . . . . . . . . . . . . . . . .  30
 5.2.  Recommended Attributes . . . . . . . . . . . . . . . . . .  30
 5.3.  Named Attributes . . . . . . . . . . . . . . . . . . . . .  31
 5.4.  Mandatory Attributes - Definitions . . . . . . . . . . . .  31
 5.5.  Recommended Attributes - Definitions . . . . . . . . . . .  33
 5.6.  Interpreting owner and owner_group . . . . . . . . . . . .  38
 5.7.  Character Case Attributes  . . . . . . . . . . . . . . . .  39
 5.8.  Quota Attributes . . . . . . . . . . . . . . . . . . . . .  39
 5.9.  Access Control Lists . . . . . . . . . . . . . . . . . . .  40

Shepler, et al. Standards Track [Page 2] RFC 3010 NFS version 4 Protocol December 2000

 5.9.1.  ACE type . . . . . . . . . . . . . . . . . . . . . . . .  41
 5.9.2.  ACE flag . . . . . . . . . . . . . . . . . . . . . . . .  41
 5.9.3.  ACE Access Mask  . . . . . . . . . . . . . . . . . . . .  43
 5.9.4.  ACE who  . . . . . . . . . . . . . . . . . . . . . . . .  44
 6.  File System Migration and Replication  . . . . . . . . . . .  44
 6.1.  Replication  . . . . . . . . . . . . . . . . . . . . . . .  45
 6.2.  Migration  . . . . . . . . . . . . . . . . . . . . . . . .  45
 6.3.  Interpretation of the fs_locations Attribute . . . . . . .  46
 6.4.  Filehandle Recovery for Migration or Replication . . . . .  47
 7.  NFS Server Name Space  . . . . . . . . . . . . . . . . . . .  47
 7.1.  Server Exports . . . . . . . . . . . . . . . . . . . . . .  47
 7.2.  Browsing Exports . . . . . . . . . . . . . . . . . . . . .  48
 7.3.  Server Pseudo File System  . . . . . . . . . . . . . . . .  48
 7.4.  Multiple Roots . . . . . . . . . . . . . . . . . . . . . .  49
 7.5.  Filehandle Volatility  . . . . . . . . . . . . . . . . . .  49
 7.6.  Exported Root  . . . . . . . . . . . . . . . . . . . . . .  49
 7.7.  Mount Point Crossing . . . . . . . . . . . . . . . . . . .  49
 7.8.  Security Policy and Name Space Presentation  . . . . . . .  50
 8.  File Locking and Share Reservations  . . . . . . . . . . . .  50
 8.1.  Locking  . . . . . . . . . . . . . . . . . . . . . . . . .  51
 8.1.1.  Client ID  . . . . . . . . . . . . . . . . . . . . . . .  51
 8.1.2.  Server Release of Clientid . . . . . . . . . . . . . . .  53
 8.1.3.  nfs_lockowner and stateid Definition . . . . . . . . . .  54
 8.1.4.  Use of the stateid . . . . . . . . . . . . . . . . . . .  55
 8.1.5.  Sequencing of Lock Requests  . . . . . . . . . . . . . .  56
 8.1.6.  Recovery from Replayed Requests  . . . . . . . . . . . .  56
 8.1.7.  Releasing nfs_lockowner State  . . . . . . . . . . . . .  57
 8.2.  Lock Ranges  . . . . . . . . . . . . . . . . . . . . . . .  57
 8.3.  Blocking Locks . . . . . . . . . . . . . . . . . . . . . .  58
 8.4.  Lease Renewal  . . . . . . . . . . . . . . . . . . . . . .  58
 8.5.  Crash Recovery . . . . . . . . . . . . . . . . . . . . . .  59
 8.5.1.  Client Failure and Recovery  . . . . . . . . . . . . . .  59
 8.5.2.  Server Failure and Recovery  . . . . . . . . . . . . . .  60
 8.5.3.  Network Partitions and Recovery  . . . . . . . . . . . .  62
 8.6.  Recovery from a Lock Request Timeout or Abort  . . . . . .  63
 8.7.  Server Revocation of Locks . . . . . . . . . . . . . . . .  63
 8.8.  Share Reservations . . . . . . . . . . . . . . . . . . . .  65
 8.9.  OPEN/CLOSE Operations  . . . . . . . . . . . . . . . . . .  65
 8.10.  Open Upgrade and Downgrade  . . . . . . . . . . . . . . .  66
 8.11.  Short and Long Leases . . . . . . . . . . . . . . . . . .  66
 8.12.  Clocks and Calculating Lease Expiration . . . . . . . . .  67
 8.13.  Migration, Replication and State  . . . . . . . . . . . .  67
 8.13.1.  Migration and State . . . . . . . . . . . . . . . . . .  67
 8.13.2.  Replication and State . . . . . . . . . . . . . . . . .  68
 8.13.3.  Notification of Migrated Lease  . . . . . . . . . . . .  69
 9.  Client-Side Caching  . . . . . . . . . . . . . . . . . . . .  69
 9.1.  Performance Challenges for Client-Side Caching . . . . . .  70
 9.2.  Delegation and Callbacks . . . . . . . . . . . . . . . . .  71

Shepler, et al. Standards Track [Page 3] RFC 3010 NFS version 4 Protocol December 2000

 9.2.1.  Delegation Recovery  . . . . . . . . . . . . . . . . . .  72
 9.3.  Data Caching . . . . . . . . . . . . . . . . . . . . . . .  74
 9.3.1.  Data Caching and OPENs . . . . . . . . . . . . . . . . .  74
 9.3.2.  Data Caching and File Locking  . . . . . . . . . . . . .  75
 9.3.3.  Data Caching and Mandatory File Locking  . . . . . . . .  77
 9.3.4.  Data Caching and File Identity . . . . . . . . . . . . .  77
 9.4.  Open Delegation  . . . . . . . . . . . . . . . . . . . . .  78
 9.4.1.  Open Delegation and Data Caching . . . . . . . . . . . .  80
 9.4.2.  Open Delegation and File Locks . . . . . . . . . . . . .  82
 9.4.3.  Recall of Open Delegation  . . . . . . . . . . . . . . .  82
 9.4.4.  Delegation Revocation  . . . . . . . . . . . . . . . . .  84
 9.5.  Data Caching and Revocation  . . . . . . . . . . . . . . .  84
 9.5.1.  Revocation Recovery for Write Open Delegation  . . . . .  85
 9.6.  Attribute Caching  . . . . . . . . . . . . . . . . . . . .  85
 9.7.  Name Caching . . . . . . . . . . . . . . . . . . . . . . .  86
 9.8.  Directory Caching  . . . . . . . . . . . . . . . . . . . .  87
 10.  Minor Versioning  . . . . . . . . . . . . . . . . . . . . .  88
 11.  Internationalization  . . . . . . . . . . . . . . . . . . .  91
 11.1.  Universal Versus Local Character Sets . . . . . . . . . .  91
 11.2.  Overview of Universal Character Set Standards . . . . . .  92
 11.3.  Difficulties with UCS-4, UCS-2, Unicode . . . . . . . . .  93
 11.4.  UTF-8 and its solutions . . . . . . . . . . . . . . . . .  94
 11.5.  Normalization . . . . . . . . . . . . . . . . . . . . . .  94
 12.  Error Definitions . . . . . . . . . . . . . . . . . . . . .  95
 13.  NFS Version 4 Requests  . . . . . . . . . . . . . . . . . .  99
 13.1.  Compound Procedure  . . . . . . . . . . . . . . . . . . . 100
 13.2.  Evaluation of a Compound Request  . . . . . . . . . . . . 100
 13.3.  Synchronous Modifying Operations  . . . . . . . . . . . . 101
 13.4.  Operation Values  . . . . . . . . . . . . . . . . . . . . 102
 14.  NFS Version 4 Procedures  . . . . . . . . . . . . . . . . . 102
 14.1.  Procedure 0: NULL - No Operation  . . . . . . . . . . . . 102
 14.2.  Procedure 1: COMPOUND - Compound Operations . . . . . . . 102
 14.2.1.  Operation 3: ACCESS - Check Access Rights . . . . . . . 105
 14.2.2.  Operation 4: CLOSE - Close File . . . . . . . . . . . . 108
 14.2.3.  Operation 5: COMMIT - Commit Cached Data  . . . . . . . 109
 14.2.4.  Operation 6: CREATE - Create a Non-Regular File Object. 112
 14.2.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting
          Recovery  . . . . . . . . . . . . . . . . . . . . . . . 114
 14.2.6.  Operation 8: DELEGRETURN - Return Delegation  . . . . . 115
 14.2.7.  Operation 9: GETATTR - Get Attributes . . . . . . . . . 115
 14.2.8.  Operation 10: GETFH - Get Current Filehandle  . . . . . 117
 14.2.9.  Operation 11: LINK - Create Link to a File  . . . . . . 118
 14.2.10.  Operation 12: LOCK - Create Lock . . . . . . . . . . . 119
 14.2.11.  Operation 13: LOCKT - Test For Lock  . . . . . . . . . 121
 14.2.12.  Operation 14: LOCKU - Unlock File  . . . . . . . . . . 122
 14.2.13.  Operation 15: LOOKUP - Lookup Filename . . . . . . . . 123
 14.2.14.  Operation 16: LOOKUPP - Lookup Parent Directory  . . . 126

Shepler, et al. Standards Track [Page 4] RFC 3010 NFS version 4 Protocol December 2000

 14.2.15.  Operation 17: NVERIFY - Verify Difference in
           Attributes . . . . . . . . . . . . . . . . . . . . . . 127
 14.2.16.  Operation 18: OPEN - Open a Regular File . . . . . . . 128
 14.2.17.  Operation 19: OPENATTR - Open Named Attribute
           Directory  . . . . . . . . . . . . . . . . . . . . . . 137
 14.2.18.  Operation 20: OPEN_CONFIRM - Confirm Open  . . . . . . 138
 14.2.19.  Operation 21: OPEN_DOWNGRADE - Reduce Open File Access 140
 14.2.20.  Operation 22: PUTFH - Set Current Filehandle . . . . . 141
 14.2.21.  Operation 23: PUTPUBFH - Set Public Filehandle . . . . 142
 14.2.22.  Operation 24: PUTROOTFH - Set Root Filehandle  . . . . 143
 14.2.23.  Operation 25: READ - Read from File  . . . . . . . . . 144
 14.2.24.  Operation 26: READDIR - Read Directory . . . . . . . . 146
 14.2.25.  Operation 27: READLINK - Read Symbolic Link  . . . . . 150
 14.2.26.  Operation 28: REMOVE - Remove Filesystem Object  . . . 151
 14.2.27.  Operation 29: RENAME - Rename Directory Entry  . . . . 153
 14.2.28.  Operation 30: RENEW - Renew a Lease  . . . . . . . . . 155
 14.2.29.  Operation 31: RESTOREFH - Restore Saved Filehandle . . 156
 14.2.30.  Operation 32: SAVEFH - Save Current Filehandle . . . . 157
 14.2.31.  Operation 33: SECINFO - Obtain Available Security  . . 158
 14.2.32.  Operation 34: SETATTR - Set Attributes . . . . . . . . 160
 14.2.33.  Operation 35: SETCLIENTID - Negotiate Clientid . . . . 162
 14.2.34.  Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid . 163
 14.2.35.  Operation 37: VERIFY - Verify Same Attributes  . . . . 164
 14.2.36.  Operation 38: WRITE - Write to File  . . . . . . . . . 166
 15.  NFS Version 4 Callback Procedures . . . . . . . . . . . . . 170
 15.1.  Procedure 0: CB_NULL - No Operation . . . . . . . . . . . 170
 15.2.  Procedure 1: CB_COMPOUND - Compound Operations  . . . . . 171
 15.2.1.  Operation 3: CB_GETATTR - Get Attributes  . . . . . . . 172
 15.2.2.  Operation 4: CB_RECALL - Recall an Open Delegation  . . 173
 16.  Security Considerations . . . . . . . . . . . . . . . . . . 174
 17.  IANA Considerations . . . . . . . . . . . . . . . . . . . . 174
 17.1.  Named Attribute Definition  . . . . . . . . . . . . . . . 174
 18.  RPC definition file . . . . . . . . . . . . . . . . . . . . 175
 19.  Bibliography  . . . . . . . . . . . . . . . . . . . . . . . 206
 20.  Authors . . . . . . . . . . . . . . . . . . . . . . . . . . 210
 20.1.  Editor's Address  . . . . . . . . . . . . . . . . . . . . 210
 20.2.  Authors' Addresses  . . . . . . . . . . . . . . . . . . . 210
 20.3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . 211
 21.  Full Copyright Statement  . . . . . . . . . . . . . . . . . 212

1. Introduction

 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:

Shepler, et al. Standards Track [Page 5] RFC 3010 NFS version 4 Protocol December 2000

 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 file system model that provides a useful,
    common set of features that does not unduly favor one file system
    or operating system over another.
 o  Designed for protocol extensions.
    The protocol is designed to accept standard extensions that do not
    compromise backward compatibility.

1.1. 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 file systems and
 distributed file systems is expected as well.

1.1.1. 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

Shepler, et al. Standards Track [Page 6] RFC 3010 NFS version 4 Protocol December 2000

 [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 file system
 resources.  With this, the client can securely match the security
 mechanism that meets the policies specified at both the client and
 server.

1.1.2. 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.
 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 file system
 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 file system 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.

Shepler, et al. Standards Track [Page 7] RFC 3010 NFS version 4 Protocol December 2000

1.1.3. File System Model

 The general file system model used for the NFS version 4 protocol is
 the same as previous versions.  The server file system 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 file system tree provided by the server.  The server
 provides multiple file systems by gluing them together with pseudo
 file systems.  These pseudo file systems provide for potential gaps
 in the path names between real file systems.

1.1.3.1. 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 file system object to which it referred.  For some server
 implementations, this persistence requirement has been difficult to
 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 file system 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.

1.1.3.2. Attribute Types

 The NFS version 4 protocol introduces three classes of file system 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 file system 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.

Shepler, et al. Standards Track [Page 8] RFC 3010 NFS version 4 Protocol December 2000

 Mandatory attributes are the minimal set of file or file system
 attributes that must be provided by the server and must be properly
 represented by the server.  Recommended attributes represent
 different file system 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 file system
 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.

1.1.3.3. File System Replication and Migration

 With the use of a special file attribute, the ability to migrate or
 replicate server file systems is enabled within the protocol.  The
 file system locations attribute provides a method for the client to
 probe the server about the location of a file system.  In the event
 of a migration of a file system, the client will receive an error
 when operating on the file system 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 file system.  From this information, the
 client can use its own policies to access the appropriate file system
 location.

1.1.4. 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.

1.1.5. 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

Shepler, et al. Standards Track [Page 9] RFC 3010 NFS version 4 Protocol December 2000

 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).

1.1.6. 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 file system 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.
 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.

Shepler, et al. Standards Track [Page 10] RFC 3010 NFS version 4 Protocol December 2000

1.2. 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
           file system 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.
 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 file (share) locks unless
           specifically stated otherwise.
 Server    The "Server" is the entity responsible for coordinating
           client access to a set of file systems.
 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).

Shepler, et al. Standards Track [Page 11] RFC 3010 NFS version 4 Protocol December 2000

           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 64-bit quantity returned by a server that uniquely
           defines the locking state granted by the server for a
           specific lock owner for a specific file.
           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;

Shepler, et al. Standards Track [Page 12] RFC 3010 NFS version 4 Protocol December 2000

 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 utf8string      component4;
               Represents path name components
 count4        typedef uint32_t        count4;
               Various count parameters (READ, WRITE, COMMIT)
 length4       typedef uint64_t        length4;
               Describes LOCK lengths
 linktext4     typedef utf8string      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

Shepler, et al. Standards Track [Page 13] RFC 3010 NFS version 4 Protocol December 2000

 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 [RFC2078] for details.
 seqid4        typedef uint32_t        seqid4;
               Sequence identifier used for file locking
 stateid4      typedef uint64_t        stateid4;
               State identifier used for file locking and delegation
 utf8string    typedef opaque          utf8string<>;
               UTF-8 encoding for strings
 verifier4     typedef opaque        verifier4[NFS4_VERIFIER_SIZE];
               Verifier used for various operations (COMMIT, CREATE,
               OPEN, READDIR, SETCLIENTID, 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 file system object is

Shepler, et al. Standards Track [Page 14] RFC 3010 NFS version 4 Protocol December 2000

    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
                };
 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;
                        uint32_t specdata2;
                };
      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 file system identifier that is used as a
      mandatory attribute.

Shepler, et al. Standards Track [Page 15] RFC 3010 NFS version 4 Protocol December 2000

 fs_location4
                struct fs_location4 {
                        utf8string    server<>;
                        pathname4     rootpath;
                };
 fs_locations4
                struct fs_locations4 {
                        pathname4     fs_root;
                        fs_location4  locations<>;
                };
      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;
                };

Shepler, et al. Standards Track [Page 16] RFC 3010 NFS version 4 Protocol December 2000

      This structure is used with the CREATE, LINK, REMOVE, RENAME
      operations to let the client the know value of the change
      attribute for the directory in which the target file system
      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 SETCLIENT
      operation to either specify the address of the client that is
      using a clientid or as part of the call back registration.
 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.
 nfs_client_id4
                struct nfs_client_id4 {
                        verifier4     verifier;
                        opaque        id<>;
                };
      This structure is part of the arguments to the SETCLIENTID
      operation.
 nfs_lockowner4
                struct nfs_lockowner4 {
                        clientid4     clientid;
                        opaque        owner<>;
                };

Shepler, et al. Standards Track [Page 17] RFC 3010 NFS version 4 Protocol December 2000

      This structure is used to identify the owner of a OPEN share or
      file lock.

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 [RFC1700] 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.
 The transport used by the RPC service for the NFS version 4 protocol
 MUST provide congestion control comparable to that defined for TCP in
 [RFC2581].  If the operating environment implements TCP, the NFS
 version 4 protocol SHOULD be supported over TCP.  The NFS client and
 server may use other transports if they support congestion control as
 defined above and in those cases a mechanism may be provided to
 override TCP usage in favor of another transport.
 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.
 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].

3.2. 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 [RFC2078].  This allows for the use
 of varying 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

Shepler, et al. Standards Track [Page 18] RFC 3010 NFS version 4 Protocol December 2000

 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 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
 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].

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"

Shepler, et al. Standards Track [Page 19] RFC 3010 NFS version 4 Protocol December 2000

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 user.  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.

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.

Shepler, et al. Standards Track [Page 20] RFC 3010 NFS version 4 Protocol December 2000

 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 file system 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.

3.3.1. 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 file system
 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.

3.3.2. 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
 procedure 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.

Shepler, et al. Standards Track [Page 21] RFC 3010 NFS version 4 Protocol December 2000

3.4. Callback RPC Authentication

 The callback RPC (described later) must mutually authenticate the NFS
 server to the principal that acquired the clientid (also described
 later), using the same security flavor the original SETCLIENTID
 operation used. 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.
 For AUTH_NONE, there are no principals, so this is a non-issue.
 For AUTH_SYS, the server simply uses the AUTH_SYS credential that the
 user used when it 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.
 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.  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

Shepler, et al. Standards Track [Page 22] RFC 3010 NFS version 4 Protocol December 2000

 pair, and if the user that the NFS server is authenticating to has a
 public key certificate, then it works.
 In situations where 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
    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 file system 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 file system
 object.  Since the filehandle is the client's reference to an object
 and the client may cache this reference, the server SHOULD not reuse
 a filehandle for another file system object.  If the server needs to
 reuse a filehandle value, the time elapsed before reuse SHOULD be
 large enough such that it is unlikely the client has a cached copy of
 the reused filehandle value.  Note that a client may cache a
 filehandle for a very long time.  For example, a client may cache NFS
 data to local storage as a method to expand its effective cache size
 and as a means to survive client restarts.  Therefore, the lifetime
 of a cached filehandle may be extended.

Shepler, et al. Standards Track [Page 23] RFC 3010 NFS version 4 Protocol December 2000

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 file system 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 procedure 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.

4.1.1. Root Filehandle

 The first of the special filehandles is the ROOT filehandle.  The
 ROOT filehandle is the "conceptual" root of the file system 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 procedure.  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 file system 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 file system 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 file system object.  The client may not
 make any assumptions about this binding.

Shepler, et al. Standards Track [Page 24] RFC 3010 NFS version 4 Protocol December 2000

4.2. Filehandle Types

 In the NFS version 2 and 3 protocols, there was one type of
 filehandle with a single set of semantics.  The NFS version 4
 protocol introduces a new type of filehandle in an attempt to
 accommodate certain server environments.  The first type of
 filehandle is 'persistent'.  The semantics of a persistent filehandle
 are the same as the filehandles of the NFS version 2 and 3 protocols.
 The second or new type of filehandle is the "volatile" filehandle.
 The volatile filehandle type is being introduced to address server
 functionality or implementation issues which make correct
 implementation of a persistent filehandle infeasible.  Some server
 environments do not provide a file system level invariant that can be
 used to construct a persistent filehandle.  The underlying server
 file system may not provide the invariant or the server's file system
 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 file
 system reorganization or migration.  However, the volatile filehandle
 increases the implementation burden for the client.  However this
 increased burden is deemed acceptable based on the overall gains
 achieved by the protocol.
 Since the client will need to handle persistent and volatile
 filehandle 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.  If
 they are not equal, the client may use information provided by the
 server, in the form of file attributes, to determine whether they
 denote the same files or different files.  The client would do this
 as necessary for client side caching.  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.

Shepler, et al. Standards Track [Page 25] RFC 3010 NFS version 4 Protocol December 2000

 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 file system 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 file system object to which it refers.  Once the
 server creates the filehandle for a file system 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 file system is migrated, the new
 NFS server must honor the same file handle as the old NFS server.
 The persistent filehandle will be become stale or invalid when the
 file system 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
 file system containing the object is no longer available.  The file
 system may become unavailable if it exists on removable media and the
 media is no longer available at the server or the file system in
 whole has been destroyed or the file system 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.

Shepler, et al. Standards Track [Page 26] RFC 3010 NFS version 4 Protocol December 2000

 The mandatory attribute "fh_expire_type" is used by the client to
 determine what type of filehandle the server is providing for a
 particular file system.  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
       file system.  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_NOEXPIRE_WITH_OPEN
       The filehandle will not expire while client has the file open.
       If this bit is set, then the values FH4_VOLATILE_ANY or
       FH4_VOL_RENAME do not impact expiration while the file is open.
       Once the file is closed or if the FH4_NOEXPIRE_WITH_OPEN bit is
       false, the rest of the volatile related bits apply.
 FH4_VOLATILE_ANY
       The filehandle may expire at any time and will expire during
       system migration and rename.
 FH4_VOL_MIGRATION
       The filehandle will expire during file system migration.  May
       only be set if FH4_VOLATILE_ANY is not set.
 FH4_VOL_RENAME
       The filehandle may expire due to a rename.  This includes a
       rename by the requesting client or a rename by another client.
       May only be set if FH4_VOLATILE_ANY is not set.
 Servers which provide volatile filehandles should deny a RENAME or
 REMOVE that would affect an OPEN file or any of the components
 leading to the OPEN file.  In addition, the server should deny all
 RENAME or REMOVE requests during the grace or lease period upon
 server restart.
 The reader may be wondering why there are three FH4_VOL* bits and why
 FH4_VOLATILE_ANY is exclusive of FH4_VOL_MIGRATION and
 FH4_VOL_RENAME.  If the a filehandle is normally persistent but
 cannot persist across a file set migration, then the presence of the
 FH4_VOL_MIGRATION or FH4_VOL_RENAME tells the client that it can
 treat the file handle as persistent for purposes of maintaining a
 file name to file handle cache, except for the specific event
 described by the bit.  However, FH4_VOLATILE_ANY tells the client
 that it should not maintain such a cache for unopened files.  A
 server MUST not present FH4_VOLATILE_ANY with FH4_VOL_MIGRATION or

Shepler, et al. Standards Track [Page 27] RFC 3010 NFS version 4 Protocol December 2000

 FH4_VOL_RENAME as this will lead to confusion.  FH4_VOLATILE_ANY
 implies that the file handle will expire upon migration or rename, in
 addition to other events.

4.2.4. One Method of Constructing a Volatile Filehandle

 As mentioned, in some instances a filehandle is stale (no longer
 valid; perhaps because the file was removed from the server) or it is
 expired (the underlying file is valid but since the filehandle is
 volatile, it may have expired).  Thus the server needs to be able to
 return NFS4ERR_STALE in the former case and NFS4ERR_FHEXPIRED in the
 latter case. This can be done by careful construction of the volatile
 filehandle.  One possible implementation follows.
 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
 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.

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 file system
 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 file system name
 space.

Shepler, et al. Standards Track [Page 28] RFC 3010 NFS version 4 Protocol December 2000

 If the expired filehandle refers to an object that has been removed
 from the file system, 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

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 will be able to ask what
 attributes the server supports and will be able to request only those
 attributes in which it is interested.
 To this end, attributes will be 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

Shepler, et al. Standards Track [Page 29] RFC 3010 NFS version 4 Protocol December 2000

 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.  The recommended attributes may be unsupported; though a server
 should support as many as it can.  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.

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

Shepler, et al. Standards Track [Page 30] RFC 3010 NFS version 4 Protocol December 2000

 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 it seems that the client has a better ability to
 fabricate or construct an attribute or 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 file system 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.
 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 file system.  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. 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.
 type              1    nfs4_ftype   READ     The type of the object
                                              (file, directory,
                                              symlink)

Shepler, et al. Standards Track [Page 31] RFC 3010 NFS version 4 Protocol December 2000

 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_modify
                                              attribute for this
                                              attribute's value but
                                              only if the file
                                              system object can not
                                              be updated more
                                              frequently than the
                                              resolution of
                                              time_modify.
 size              4    uint64       R/W      The size of the object
                                              in bytes.
 link_support      5    boolean      READ     Does the object's file
                                              system supports hard
                                              links?
 symlink_support   6    boolean      READ     Does the object's file
                                              system supports
                                              symbolic links?
 named_attr        7    boolean      READ     Does this object have
                                              named attributes?
 fsid              8    fsid4        READ     Unique file system
                                              identifier for the
                                              file system holding
                                              this object.  fsid
                                              contains major and
                                              minor components each
                                              of which are uint64.

Shepler, et al. Standards Track [Page 32] RFC 3010 NFS version 4 Protocol December 2000

 unique_handles    9    boolean      READ     Are two distinct
                                              filehandles guaranteed
                                              to refer to two
                                              different file system
                                              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.

5.5. 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 file
                                                 system.
 archive            14   boolean        R/W      Whether or not this
                                                 file has been
                                                 archived since the
                                                 time of last
                                                 modification
                                                 (deprecated in favor
                                                 of time_backup).
 cansettime         15   boolean        READ     Is the server able to
                                                 change the times for
                                                 a file system object
                                                 as specified in a
                                                 SETATTR operation?
 case_insensitive   16   boolean        READ     Are filename
                                                 comparisons on this
                                                 file system case
                                                 insensitive?
 case_preserving    17   boolean        READ     Is filename case on
                                                 this file system
                                                 preserved?

Shepler, et al. Standards Track [Page 33] RFC 3010 NFS version 4 Protocol December 2000

 chown_restricted   18   boolean        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 NT
                                                 the "Take Ownership"
                                                 privilege)
 filehandle         19   nfs4_fh        READ     The filehandle of
                                                 this object
                                                 (primarily for
                                                 readdir requests).
 fileid             20   uint64         READ     A number uniquely
                                                 identifying the file
                                                 within the file
                                                 system.
 files_avail        21   uint64         READ     File slots available
                                                 to this user on the
                                                 file system
                                                 containing this
                                                 object - this should
                                                 be the smallest
                                                 relevant limit.
 files_free         22   uint64         READ     Free file slots on
                                                 the file system
                                                 containing this
                                                 object - this should
                                                 be the smallest
                                                 relevant limit.
 files_total        23   uint64         READ     Total file slots on
                                                 the file system
                                                 containing this
                                                 object.

Shepler, et al. Standards Track [Page 34] RFC 3010 NFS version 4 Protocol December 2000

 fs_locations       24   fs_locations   READ     Locations where this
                                                 file system may be
                                                 found.  If the server
                                                 returns NFS4ERR_MOVED
                                                 as an error, this
                                                 attribute must be
                                                 supported.
 hidden             25   boolean        R/W      Is file considered
                                                 hidden with respect
                                                 to the WIN32 API?
 homogeneous        26   boolean        READ     Whether or not this
                                                 object's file system
                                                 is homogeneous, i.e.
                                                 are per file system
                                                 attributes the same
                                                 for all file system's
                                                 objects.
 maxfilesize        27   uint64         READ     Maximum supported
                                                 file size for the
                                                 file system 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

Shepler, et al. Standards Track [Page 35] RFC 3010 NFS version 4 Protocol December 2000

                                                 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 permission
                                                 bits for this object
                                                 (deprecated in favor
                                                 of ACLs)
 no_trunc           34   boolean        READ     If a name longer than
                                                 name_max is used,
                                                 will an error be
                                                 returned or will the
                                                 name be truncated?
 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.

Shepler, et al. Standards Track [Page 36] RFC 3010 NFS version 4 Protocol December 2000

 space_avail        42   uint64         READ     Disk space in bytes
                                                 available to this
                                                 user on the file
                                                 system containing
                                                 this object - this
                                                 should be the
                                                 smallest relevant
                                                 limit.
 space_free         43   uint64         READ     Free disk space in
                                                 bytes on the file
                                                 system containing
                                                 this object - this
                                                 should be the
                                                 smallest relevant
                                                 limit.
 space_total        44   uint64         READ     Total disk space in
                                                 bytes on the file
                                                 system containing
                                                 this object.
 space_used         45   uint64         READ     Number of file system
                                                 bytes allocated to
                                                 this object.
 system             46   boolean        R/W      Is this file a system
                                                 file with respect to
                                                 the WIN32 API?
 time_access        47   nfstime4       READ     The time of last
                                                 access to the object.
 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".

Shepler, et al. Standards Track [Page 37] RFC 3010 NFS version 4 Protocol December 2000

 time_delta         51   nfstime4       READ     Smallest useful
                                                 server time
                                                 granularity.
 time_metadata      52   nfstime4       R/W      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.

5.6. Interpreting owner and owner_group

 The recommended attributes "owner" and "owner_group" 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.
 The translation 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.  The "dns_domain" portion of the owner
 string is meant to be a DNS domain name.  For example, user@ietf.org.
 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 and the
 receiver of the attribute should not place any special meaning with

Shepler, et al. Standards Track [Page 38] RFC 3010 NFS version 4 Protocol December 2000

 the attribute value.  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.

5.7. 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".

5.8. Quota Attributes

 For the attributes related to file system 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.

Shepler, et al. Standards Track [Page 39] RFC 3010 NFS version 4 Protocol December 2000

       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".

5.9. Access Control Lists

 The NFS ACL attribute is an array of access control entries (ACE).
 There are various access control entry types.  The server is able to
 communicate which ACE types are supported by returning the
 appropriate value within the aclsupport attribute.  The types of ACEs
 are defined as follows:
 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.
 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;
         utf8string      who;
 };
 To determine if an ACCESS or OPEN 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

Shepler, et al. Standards Track [Page 40] RFC 3010 NFS version 4 Protocol December 2000

 is no longer considered in the processing of later ACEs. If an
 ACCESS_DENIED_ACE is encountered where the requester's mode still has
 unALLOWED bits in common with the "access_mask" of the ACE, the
 request is denied.
 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;

5.9.1. ACE type

 The semantics of the "type" field follow the descriptions provided
 above.
 The bitmask constants used for the type field 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;

5.9.2. 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

Shepler, et al. Standards Track [Page 41] RFC 3010 NFS version 4 Protocol December 2000

 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
 Both indicate for AUDIT and ALARM which state to log the event.  On
 every ACCESS or OPEN call which occurs on a file or directory which
 has an ACL that is of type ACE4_SYSTEM_AUDIT_ACE_TYPE or
 ACE4_SYSTEM_ALARM_ACE_TYPE, the attempted access is compared to the
 ace4mask of these ACLs. If the access is a subset of ace4mask and the
 identifier match, an AUDIT trail or an ALARM is generated.  By
 default this happens regardless of the success or failure of the
 ACCESS or OPEN call.
 The flag ACE4_SUCCESSFUL_ACCESS_ACE_FLAG only produces the AUDIT or
 ALARM if the ACCESS or OPEN call is successful. The
 ACE4_FAILED_ACCESS_ACE_FLAG causes the ALARM or AUDIT if the ACCESS
 or OPEN call fails.
 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;

Shepler, et al. Standards Track [Page 42] RFC 3010 NFS version 4 Protocol December 2000

5.9.3. 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
                        (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;

Shepler, et al. Standards Track [Page 43] RFC 3010 NFS version 4 Protocol December 2000

 const ACE4_DELETE               = 0x00010000;
 const ACE4_READ_ACL             = 0x00020000;
 const ACE4_WRITE_ACL            = 0x00040000;
 const ACE4_WRITE_OWNER          = 0x00080000;
 const ACE4_SYNCHRONIZE          = 0x00100000;

5.9.4. ACE who

 There are several special identifiers ("who") which need to be
 understood universally. 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.
 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@.

6. File System Migration and Replication

 With the use of the recommended attribute "fs_locations", the NFS
 version 4 server has a method of providing file system migration or
 replication services.  For the purposes of migration and replication,
 a file system 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 file system 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 file system.  Depending on the type of service being provided,
 the list will provide a new location or a set of alternate locations
 for the file system.  The client will use this information to
 redirect its requests to the new server.

Shepler, et al. Standards Track [Page 44] RFC 3010 NFS version 4 Protocol December 2000

6.1. Replication

 It is expected that file system replication will be used in the case
 of read-only data.  Typically, the file system will be replicated on
 two or more servers.  The fs_locations attribute will provide the
 list of these locations to the client.  On first access of the file
 system, 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

 File system migration is used to move a file system from one server
 to another.  Migration is typically used for a file system 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 file system 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 file system, 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 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 file system 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

Shepler, et al. Standards Track [Page 45] RFC 3010 NFS version 4 Protocol December 2000

 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.

6.3. Interpretation of the fs_locations Attribute

 The fs_location attribute is structured in the following way:
 struct fs_location {
         utf8string      server<>;
         pathname4       rootpath;
 };
 struct fs_locations {
         pathname4       fs_root;
         fs_location     locations<>;
 };
 The fs_location struct is used to represent the location of a file
 system by providing a server name and the path to the root of the
 file system.  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 file system 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 file system
 at the various servers listed.
 As an example, there is a replicated file system located at two
 servers (servA and servB).  At servA the file system is located at
 path "/a/b/c".  At servB the file system is located at path "/x/y/z".
 In this example the client accesses the file system 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 file system'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

Shepler, et al. Standards Track [Page 46] RFC 3010 NFS version 4 Protocol December 2000

 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
 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.

6.4. Filehandle Recovery for Migration or Replication

 Filehandles for file systems that are replicated or migrated
 generally have the same semantics as for file systems that are not
 replicated or migrated.  For example, if a file system has persistent
 filehandles and it is migrated to another server, the filehandle
 values for the file system 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 file handle 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 file system 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 47] RFC 3010 NFS version 4 Protocol December 2000

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 file system.  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 file
 system" that allows the user to browse from one mounted file system
 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 File System

 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 file system" that provides a view of exported directories
 only.  A pseudo file system has a unique fsid and behaves like a
 normal, read only file system.
 Based on the construction of the server's name space, it is possible
 that multiple pseudo file systems may exist.  For example,
 /a         pseudo file system
 /a/b       real file system
 /a/b/c     pseudo file system
 /a/b/c/d   real file system
 Each of the pseudo file systems are consider separate entities and
 therefore will have a unique fsid.

Shepler, et al. Standards Track [Page 48] RFC 3010 NFS version 4 Protocol December 2000

7.4. Multiple Roots

 The DOS and Windows operating environments are sometimes described as
 having "multiple roots".  File systems are commonly represented as
 disk letters.  MacOS represents file systems 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 file system is that it is a logical
 representation of file system(s) available from the server.
 Therefore, the pseudo file system is most likely constructed
 dynamically when the server is first instantiated.  It is expected
 that the pseudo file system 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 file system, 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 file system is exported, one might conclude that
 a pseudo-file system is not needed.  This would be wrong.  Assume the
 following file systems 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-file system.

7.7. Mount Point Crossing

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

Shepler, et al. Standards Track [Page 49] RFC 3010 NFS version 4 Protocol December 2000

 The pseudo file system for this server may be constructed to look
 like:
          /               (place holder/not exported)
          /a/b            (file system 1)
          /a/b/c/d        (file system 2)
 It is the server's responsibility to present the pseudo file system
 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 file system "/a/b/c/d".  In previous versions of the NFS
 protocol, the server would respond with the directory "/a/b/c/d"
 within the file system "/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 file system 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 file system, the server
 may effectively hide file systems from a client that may otherwise
 have legitimate access.

8. File Locking and Share Reservations

 Integrating locking into the NFS protocol necessarily causes it to be
 state-full.  With the inclusion of "share" file locks 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

Shepler, et al. Standards Track [Page 50] RFC 3010 NFS version 4 Protocol December 2000

 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" locks 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 functionality 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.
 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.  Client identification is
 accomplished with two values.
 o  A verifier that is used to detect client reboots.
 o  A variable length opaque array to uniquely define a client.
       For an operating system this may be a fully qualified host name
       or IP address.  For a user level NFS client it may additionally
       contain a process id or other unique sequence.

Shepler, et al. Standards Track [Page 51] RFC 3010 NFS version 4 Protocol December 2000

 The data structure for the Client ID would then appear as:
          struct nfs_client_id {
                  opaque verifier[4];
                  opaque id<>;
          }
 It is possible through the mis-configuration of a client or the
 existence of a rogue client that two clients end up using the same
 nfs_client_id.  This situation is avoided by "negotiating" the
 nfs_client_id between client and server with the use of the
 SETCLIENTID and SETCLIENTID_CONFIRM operations.  The following
 describes the two scenarios of negotiation.
 1  Client has never connected to the server
    In this case the client generates an nfs_client_id and unless
    another client has the same nfs_client_id.id field, the server
    accepts the request. The server also records the principal (or
    principal to uid mapping) from the credential in the RPC request
    that contains the nfs_client_id negotiation request (SETCLIENTID
    operation).
    Two clients might still use the same nfs_client_id.id due to
    perhaps configuration error.  For example, a High Availability
    configuration where the nfs_client_id.id is derived from the
    ethernet controller address and both systems have the same
    address.  In this case, the result is a switched union that
    returns, in addition to NFS4ERR_CLID_INUSE, the network address
    (the rpcbind netid and universal address) of the client that is
    using the id.
 2  Client is re-connecting to the server after a client reboot
    In this case, the client still generates an nfs_client_id but the
    nfs_client_id.id field will be the same as the nfs_client_id.id
    generated prior to reboot.  If the server finds that the
    principal/uid is equal to the previously "registered"
    nfs_client_id.id, then locks associated with the old nfs_client_id
    are immediately released.  If the principal/uid is not equal, then
    this is a rogue client and the request is returned in error.  For
    more discussion of crash recovery semantics, see the section on
    "Crash Recovery".
    It is possible for a retransmission of request to be received by
    the server after the server has acted upon and responded to the
    original client request.  Therefore to mitigate effects of the
    retransmission of the SETCLIENTID operation, the client and server

Shepler, et al. Standards Track [Page 52] RFC 3010 NFS version 4 Protocol December 2000

    use a confirmation step.  The server returns a confirmation
    verifier that the client then sends to the server in the
    SETCLIENTID_CONFIRM operation.  Once the server receives the
    confirmation from the client, the locking state for the client is
    released.
 In both cases, upon success, NFS4_OK is returned.  To help reduce the
 amount of data transferred on OPEN and LOCK, the server will also
 return a unique 64-bit clientid value that is a shorthand reference
 to the nfs_client_id values presented by the client.  From this point
 forward, the client will use the clientid to refer to itself.
 The clientid assigned by the server 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
 "nfs_lockowner and stateid Definition" for details).

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.

Shepler, et al. Standards Track [Page 53] RFC 3010 NFS version 4 Protocol December 2000

8.1.3. nfs_lockowner 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 nfs_lockowner 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.
 When the server grants the lock, it responds with a unique 64-bit
 stateid.  The stateid is used as a shorthand reference to the
 nfs_lockowner, 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.

Shepler, et al. Standards Track [Page 54] RFC 3010 NFS version 4 Protocol December 2000

 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 divide stateids into three fields:
 o  A server verifier which uniquely designates a particular server
    instantiation.
 o  An index into a table of locking-state structures.
 o  A sequence value which is 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

 All READ and WRITE operations contain a stateid.  If the
 nfs_lockowner performs a READ or WRITE on a range of bytes within a
 locked range, the stateid (previously returned by the server) must be
 used to indicate that the appropriate lock (record or share) is held.
 If no state is established by the client, either record lock or share
 lock, a stateid of all bits 0 is used.  If no conflicting locks are
 held on the file, the server may service the READ or WRITE operation.
 If a conflict with an explicit lock occurs, an error is returned for
 the operation (NFS4ERR_LOCKED). This allows "mandatory locking" to be
 implemented.
 A stateid of all bits 1 (one) allows READ operations to bypass record
 locking checks at the server.  However, WRITE operations with stateid
 with bits all 1 (one) do not bypass record locking checks.  File
 locking checks are handled by the OPEN operation (see the section
 "OPEN/CLOSE Operations").
 An explicit lock may not be granted while a READ or WRITE operation
 with conflicting implicit locking is being performed.

Shepler, et al. Standards Track [Page 55] RFC 3010 NFS version 4 Protocol December 2000

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 nfs_lockowners have different sequences.  The
 server maintains the last sequence number (L) received and the
 response that was returned.
 Note that for requests that contain a sequence number, for each
 nfs_lockowner, there should be no more than one outstanding request.
 If a request 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 client verifier changes.
 Since the sequence number is represented with an unsigned 32-bit
 integer, the arithmetic involved with the sequence number is mod
 2^32.
 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 nfs_lockowner must be cached as long
 as the lock state exists on the server.

8.1.6. Recovery from Replayed Requests

 As described above, the sequence number is per nfs_lockowner.  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 nfs_lockowner, sequence number state as long as there
 are open files or closed files with locks outstanding.

Shepler, et al. Standards Track [Page 56] RFC 3010 NFS version 4 Protocol December 2000

 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 nfs_lockowner state.

8.1.7. Releasing nfs_lockowner State

 When a particular nfs_lockowner no longer holds open or file locking
 state at the server, the server may choose to release the sequence
 number state associated with the nfs_lockowner.  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 nfs_lockowner no
 longer is being utilized by the client.  The server may choose to
 hold the nfs_lockowner state in the event that retransmitted requests
 are received.  However, the period to hold this state is
 implementation specific.
 In the case that a LOCK, LOCKU, OPEN_DOWNGRADE, or CLOSE is
 retransmitted after the server has previously released the
 nfs_lockowner state, the server will find that the nfs_lockowner has
 no files open and an error will be returned to the client.  If the
 nfs_lockowner does have a file open, the stateid will not match and
 again an error is returned to the client.
 In the case that an OPEN is retransmitted and the nfs_lockowner is
 being used for the first time or the nfs_lockowner 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 nfs_lockowner 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 nfs_lockowner and associated
 sequence number.  See the section "OPEN_CONFIRM - Confirm Open" for
 further details.

8.2. Lock Ranges

 The protocol allows a lock owner to request a lock with one 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 file systems 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.

Shepler, et al. Standards Track [Page 57] RFC 3010 NFS version 4 Protocol December 2000

 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. 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.

8.4. 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.
 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

Shepler, et al. Standards Track [Page 58] RFC 3010 NFS version 4 Protocol December 2000

 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, DELEGRETURN, LOCK,
    LOCKU, OPEN, OPEN_CONFIRM, 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 operation.  The use of the SETCLIENTID operation
       (possibly with the addition of the optional SETCLIENTID_CONFIRM
       operation) notifies the server to drop the locking state
       associated with the client.
       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.

8.5. 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.

8.5.1. 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

Shepler, et al. Standards Track [Page 59] RFC 3010 NFS version 4 Protocol December 2000

 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 verifier 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.
 For secure environments, a change in the verifier must only cause the
 release of locks associated with the authenticated requester.  This
 is required to prevent a rogue entity from freeing otherwise valid
 locks.
 Note that the verifier must have the same uniqueness properties of
 the verifier for the COMMIT operation.

8.5.2. 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
 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.

Shepler, et al. Standards Track [Page 60] RFC 3010 NFS version 4 Protocol December 2000

 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.
 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 is included in

Shepler, et al. Standards Track [Page 61] RFC 3010 NFS version 4 Protocol December 2000

 [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.

8.5.3. 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.
 If the server continues to hold locks beyond the expiration of a
 client's lease, the server MUST employ a method of recording this
 fact in its stable storage.  Conflicting locks requests from another
 client may be serviced after the lease expiration.  There are various
 scenarios involving server failure after such an event that require
 the storage of these lease expirations or network partitions.  One
 scenario is as follows:
       A client holds a lock at the server and encounters a network
       partition and is unable to renew the associated lease.  A
       second client obtains a conflicting lock and then frees the
       lock.  After the unlock request by the second client, the
       server reboots or reinitializes.  Once the server recovers, the
       network partition heals and the original client attempts to
       reclaim the original lock.
 In this scenario and without any state information, the server will
 allow the reclaim and the client will be in an inconsistent state
 because the server or the client has no knowledge of the conflicting
 lock.

Shepler, et al. Standards Track [Page 62] RFC 3010 NFS version 4 Protocol December 2000

 The server may choose to store this lease expiration or network
 partitioning state in a way that will only identify the client as a
 whole.  Note that this may potentially lead to lock reclaims being
 denied unnecessarily because of a mix of conflicting and non-
 conflicting locks.  The server may also choose to store information
 about each lock that has an expired lease with an associated
 conflicting lock.  The choice of the amount and type of state
 information that is stored is left to the implementor.  In any case,
 the server must have enough state information to enable correct
 recovery from multiple partitions and multiple server failures.

8.6. 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
 nfs_lockowner. This is straightforward to do without a special re-
 synchronize operation.
 Since the server maintains the last lock request and response
 received on the nfs_lockowner, for each nfs_lockowner, 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 nfs_lockowner, 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 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 nfs_lockowner will re-synchronize and in
 turn the lock state will re-synchronize.

8.7. 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.

Shepler, et al. Standards Track [Page 63] RFC 3010 NFS version 4 Protocol December 2000

 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
 period.  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
 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_EXPIRED and the error is received within the lease
 period for the lock.  In this instance the client may assume that
 only the nfs_lockowner'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.

Shepler, et al. Standards Track [Page 64] RFC 3010 NFS version 4 Protocol December 2000

8.8. 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 & file_state.deny)) ||
                   (request.deny & file_state.access))
                           return (NFS4ERR_DENIED)
 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;

8.9. 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 locks held by the nfs_lockowner
 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 if any locks would exist after the CLOSE.

Shepler, et al. Standards Track [Page 65] RFC 3010 NFS version 4 Protocol December 2000

 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
 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. 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
 deny bits for all of the OPEN requests completed.  Only a single
 CLOSE will be done to reset the effects of both OPEN's.  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 OPEN's result
 in the OPEN'ed 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 OPEN's 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 OPEN's with separate
 stateid's and will require separate CLOSE's 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 open's 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.

8.11. 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 large
 internet 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
 (server must wait for leases to expire and grace period before

Shepler, et al. Standards Track [Page 66] RFC 3010 NFS version 4 Protocol December 2000

 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 are not an issue.

8.12. Clocks 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
 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.

8.13. 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, stateid's, and
 clientid's) 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"

8.13.1. Migration and State

 In the case of migration, the servers involved in the migration of a
 file system 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
 file system migration occurs.  If the servers are successful in
 transferring all state, the client will continue to use stateid's
 assigned by the original server.  Therefore the new server must

Shepler, et al. Standards Track [Page 67] RFC 3010 NFS version 4 Protocol December 2000

 recognize these stateid's as valid.  This holds true for the clientid
 as well.  Since responsibility for an entire file system 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 new 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.

8.13.2. 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, stateid's and clientid's 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.

Shepler, et al. Standards Track [Page 68] RFC 3010 NFS version 4 Protocol December 2000

8.13.3. Notification of Migrated Lease

 In the case of lease renewal, the client may not be submitting
 requests for a file system that has been migrated to another server.
 This can occur because of the implicit lease renewal mechanism.  The
 client renews leases for all file systems when submitting a request
 to any one file system 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 file system for which a lease has been moved to a new server.
 When a client receives an NFS4ERR_LEASE_MOVED error, it should
 perform some operation, such as a RENEW, on each file system
 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, it will
 receive either NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID from
 the new server, as described above, and can then recover state
 information as it does in the event of server failure.

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.

Shepler, et al. Standards Track [Page 69] RFC 3010 NFS version 4 Protocol December 2000

 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.
 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.

Shepler, et al. Standards Track [Page 70] RFC 3010 NFS version 4 Protocol December 2000

 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
 used on behalf of all the nfs_lockowners 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

Shepler, et al. Standards Track [Page 71] RFC 3010 NFS version 4 Protocol December 2000

 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.
 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.

Shepler, et al. Standards Track [Page 72] RFC 3010 NFS version 4 Protocol December 2000

 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).
 When the server reboots or restarts, delegations are reclaimed (using
 the OPEN operation with CLAIM_DELEGATE_PREV) 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.

Shepler, et al. Standards Track [Page 73] RFC 3010 NFS version 4 Protocol December 2000

 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.

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.  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

Shepler, et al. Standards Track [Page 74] RFC 3010 NFS version 4 Protocol December 2000

    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.
 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 file system.  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 cache 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 75] RFC 3010 NFS version 4 Protocol December 2000

 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 pre-requisite 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 76] RFC 3010 NFS version 4 Protocol December 2000

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 in the result flags for an OPEN.  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 organized according
 to the file system 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 file system
 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 file system 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 77] RFC 3010 NFS version 4 Protocol December 2000

 o  If GETATTR directed to two filehandles have 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 one or both of the handles, then the 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 78] RFC 3010 NFS version 4 Protocol December 2000

 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:  object_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 stateid is separate and distinct from the stateid for the OPEN
 proper.  The standard stateid, unlike the delegation stateid, is
 associated with a particular nfs_lockowner and will continue to be
 valid after the delegation is recalled and the file remains open.

Shepler, et al. Standards Track [Page 79] RFC 3010 NFS version 4 Protocol December 2000

 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 80] RFC 3010 NFS version 4 Protocol December 2000

 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 CLOSE operation 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 file
 system 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 file system space and any applicable quotas.
 The server can recall delegations as a result of managing the
 available file system 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 file system 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 of 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 81] RFC 3010 NFS version 4 Protocol December 2000

 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 are
 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.

9.4.3. 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 file system.  If that file system 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.
 The server needs to employ special handling for a GETATTR where the
 target is a file that has a write open delegation in effect.  In this
 case, the client holding the delegation needs to be interrogated.
 The server will use a CB_GETATTR callback, if the GETATTR attribute
 bits include any of the attributes that a write open delegate may
 modify (object_size, time_modify, change).

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 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 object_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.  The flushing of any modified data in any
 region for which a write lock was released while the write open
 delegation was in effect is what is required to precisely maintain
 the associated invariant.  However, because the write open delegation
 implies no other locking by other clients, a simpler implementation

Shepler, et al. Standards Track [Page 83] RFC 3010 NFS version 4 Protocol December 2000

 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.

9.4.4. 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.  The owner of the
 locks or share reservations which have been revoked 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
 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.

Shepler, et al. Standards Track [Page 84] RFC 3010 NFS version 4 Protocol December 2000

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 file system name space to ease recovery.  Unless the
 client can determine that the file has not modified by any other
 client, this technique must be limited to situations in which a
 client has a complete cached copy of the file in question.  Use of
 such a technique may be limited to files under a certain size or may
 only be used when sufficient disk space is guaranteed to be available
 within the target file system and when the client has sufficient
 buffering resources to keep the cached copy available until it is
 properly stored to the target file system.

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
 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 object_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.

Shepler, et al. Standards Track [Page 85] RFC 3010 NFS version 4 Protocol December 2000

 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 file system 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.
 A client may validate its cached version of attributes for a file by
 fetching only the change attribute and assuming that if the change
 attribute has the same value as it did when the attributes were
 cached, then no attributes have changed.  The possible exception is
 the attribute time_access.

9.7. 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 file system APIs, the following rules should
 be followed:
 o  The results of unsuccessful LOOKUPs should not be cached, unless
    they are specifically reverified at the point of use.

Shepler, et al. Standards Track [Page 86] RFC 3010 NFS version 4 Protocol December 2000

 o  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
 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.

9.8. 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.

Shepler, et al. Standards Track [Page 87] RFC 3010 NFS version 4 Protocol December 2000

 To mitigate the effects of these inconsistencies, and given the
 context of typical file system 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.

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

Shepler, et al. Standards Track [Page 88] RFC 3010 NFS version 4 Protocol December 2000

 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 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.
      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

Shepler, et al. Standards Track [Page 89] RFC 3010 NFS version 4 Protocol December 2000

      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.
 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.

Shepler, et al. Standards Track [Page 90] RFC 3010 NFS version 4 Protocol December 2000

      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, file handle, 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 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].  This choice is explained further in the following.

11.1. Universal Versus Local Character Sets

 [RFC1345] describes a table of 16 bit characters for many different
 languages (the bit encodings match Unicode, though of course RFC1345
 is somewhat out of date with respect to current Unicode assignments).
 Each character from each language has a unique 16 bit value in the 16
 bit character set.  Thus this table can be thought of as a universal
 character set.  [RFC1345] then talks about groupings of subsets of
 the entire 16 bit character set into "Charset Tables".  For example
 one might take all the Greek characters from the 16 bit table (which
 are consecutively allocated), and normalize their offsets to a table
 that fits in 7 bits.  Thus it is determined that "lower case alpha"
 is in the same position as "upper case a" in the US-ASCII table, and
 "upper case alpha" is in the same position as "lower case a" in the
 US-ASCII table.
 These normalized subset character sets can be thought of as "local
 character sets", suitable for an operating system locale.
 Local character sets are not suitable for the NFS protocol.  Consider
 someone who creates a file with a name in a Swedish character set.
 If someone else later goes to access the file with their locale set
 to the Swedish language, then there are no problems.  But if someone
 in say the US-ASCII locale goes to access the file, the file name
 will look very different, because the Swedish characters in the 7 bit
 table will now be represented in US-ASCII characters on the display.
 It would be preferable to give the US-ASCII user a way to display the

Shepler, et al. Standards Track [Page 91] RFC 3010 NFS version 4 Protocol December 2000

 file name using Swedish glyphs. In order to do that, the NFS protocol
 would have to include the locale with the file name on each operation
 to create a file.
 But then what of the situation when there is a path name on the
 server like:
       /component-1/component-2/component-3
 Each component could have been created with a different locale.  If
 one issues CREATE with multi-component path name, and if some of the
 leading components already exist, what is to be done with the
 existing components?  Is the current locale attribute replaced with
 the user's current one?  These types of situations quickly become too
 complex when there is an alternate solution.
 If the NFS version 4 protocol used a universal 16 bit or 32 bit
 character set (or an encoding of a 16 bit or 32 bit character set
 into octets), then the server and client need not care if the locale
 of the user accessing the file is different than the locale of the
 user who created the file.  The unique 16 bit or 32 bit encoding of
 the character allows for determination of what language the character
 is from and also how to display that character on the client.  The
 server need not know what locales are used.

11.2. Overview of Universal Character Set Standards

 The previous section makes a case for using a universal character
 set.  This section makes the case for using UTF-8 as the specific
 universal character set for the NFS version 4 protocol.
 [RFC2279] discusses UTF-* (UTF-8 and other UTF-XXX encodings),
 Unicode, and UCS-*.  There are two standards bodies managing
 universal code sets:
 o  ISO/IEC which has the standard 10646-1
 o  Unicode which has the Unicode standard
 Both standards bodies have pledged to track each other's assignments
 of character codes.
 The following is a brief analysis of the various standards.
 UCS       Universal Character Set.  This is ISO/IEC 10646-1: "a
           multi-octet character set called the Universal Character
           Set (UCS), which encompasses most of the world's writing
           systems."

Shepler, et al. Standards Track [Page 92] RFC 3010 NFS version 4 Protocol December 2000

 UCS-2     a two octet per character encoding that addresses the first
           2^16 characters of UCS. Currently there are no UCS
           characters beyond that range.
 UCS-4     a four octet per character encoding that permits the
           encoding of up to 2^31 characters.
 UTF       UTF is an abbreviation of the term "UCS transformation
           format" and is used in the naming of various standards for
           encoding of UCS characters as described below.
 UTF-1     Only historical interest; it has been removed from 10646-1
 UTF-7     Encodes the entire "repertoire" of UCS "characters using
           only octets with the higher order bit clear".  [RFC2152]
           describes UTF-7. UTF-7 accomplishes this by reserving one
           of the 7bit US-ASCII characters as a "shift" character to
           indicate non-US-ASCII characters.
 UTF-8     Unlike UTF-7, uses all 8 bits of the octets. US-ASCII
           characters are encoded as before unchanged. Any octet with
           the high bit cleared can only mean a US-ASCII character.
           The high bit set means that a UCS character is being
           encoded.
 UTF-16    Encodes UCS-4 characters into UCS-2 characters using a
           reserved range in UCS-2.
 Unicode   Unicode and UCS-2 are the same; [RFC2279] states:
           Up to the present time, changes in Unicode and amendments
           to ISO/IEC 10646 have tracked each other, so that the
           character repertoires and code point assignments have
           remained in sync.  The relevant standardization committees
           have committed to maintain this very useful synchronism.

11.3. Difficulties with UCS-4, UCS-2, Unicode

 Adapting existing applications, and file systems to multi-octet
 schemes like UCS and Unicode can be difficult.  A significant amount
 of code has been written to process streams of bytes. Also there are
 many existing stored objects described with 7 bit or 8 bit
 characters. Doubling or quadrupling the bandwidth and storage
 requirements seems like an expensive way to accomplish I18N.

Shepler, et al. Standards Track [Page 93] RFC 3010 NFS version 4 Protocol December 2000

 UCS-2 and Unicode are "only" 16 bits long.  That might seem to be
 enough but, according to [Unicode1], 49,194 Unicode characters are
 already assigned.  According to [Unicode2] there are still more
 languages that need to be added.

11.4. UTF-8 and its solutions

 UTF-8 solves problems for NFS that exist with the use of UCS and
 Unicode.  UTF-8 will encode 16 bit and 32 bit characters in a way
 that will be compact for most users. The encoding table from UCS-4 to
 UTF-8, as copied from [RFC2279]:
    UCS-4 range (hex.)           UTF-8 octet sequence (binary)
  0000 0000-0000 007F   0xxxxxxx
  0000 0080-0000 07FF   110xxxxx 10xxxxxx
  0000 0800-0000 FFFF   1110xxxx 10xxxxxx 10xxxxxx
  0001 0000-001F FFFF   11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
  0020 0000-03FF FFFF   111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
  0400 0000-7FFF FFFF   1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
                        10xxxxxx
 See [RFC2279] for precise encoding and decoding rules. Note because
 of UTF-16, the algorithm from Unicode/UCS-2 to UTF-8 needs to account
 for the reserved range between D800 and DFFF.
 Note that the 16 bit UCS or Unicode characters require no more than 3
 octets to encode into UTF-8
 Interestingly, UTF-8 has room to handle characters larger than 31
 bits, because the leading octet of form:
       1111111x
 is not defined. If needed, ISO could either use that octet to
 indicate a sequence of an encoded 8 octet character, or perhaps use
 11111110 to permit the next octet to indicate an even more expandable
 character set.
 So using UTF-8 to represent character encodings means never having to
 run out of room.

11.5. Normalization

 The client and server operating environments may differ in their
 policies and operational methods with respect to character
 normalization (See [Unicode1] for a discussion of normalization
 forms).  This difference may also exist between applications on the
 same client.  This adds to the difficulty of providing a single

Shepler, et al. Standards Track [Page 94] RFC 3010 NFS version 4 Protocol December 2000

 normalization policy for the protocol that allows for maximal
 interoperability.  This issue is similar to the character case issues
 where the server may or may not support case insensitive file name
 matching and may or may not preserve the character case when storing
 file names.  The protocol does not mandate a particular behavior but
 allows for the various permutations.
 The NFS version 4 protocol does not mandate the use of a particular
 normalization form at this time.  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 the various UTF-8 encoded strings
 within the protocol before presenting the information to an
 application (at the client) or local file system (at the server).

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_ACCES         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_BADHANDLE     Illegal NFS file handle. The file handle failed
                       internal consistency checks.
 NFS4ERR_BADTYPE       An attempt was made to create an object of a
                       type not supported by the server.
 NFS4ERR_BAD_COOKIE    READDIR cookie is stale.
 NFS4ERR_BAD_SEQID     The sequence number in a locking request is
                       neither the next expected number or the last
                       number processed.

Shepler, et al. Standards Track [Page 95] RFC 3010 NFS version 4 Protocol December 2000

 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_CLID_INUSE    The SETCLIENTID procedure has found that a
                       client id is already in use by another client.
 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.
 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 procedure.
 NFS4ERR_FBIG          File too large. The operation would have caused
                       a file to grow beyond the server's limit.
 NFS4ERR_FHEXPIRED     The file handle provided is volatile and has
                       expired at the server.
 NFS4ERR_GRACE         The server is in its recovery or grace period
                       which should match the lease period of the
                       server.

Shepler, et al. Standards Track [Page 96] RFC 3010 NFS version 4 Protocol December 2000

 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 attempting to SETATTR a time field on a
                       server that does not support this operation.
 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 file
                       system that has been migrated to a new server.
 NFS4ERR_LOCKED        A read or write operation was attempted on a
                       locked file.
 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_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_NODEV         No such device.
 NFS4ERR_NOENT         No such file or directory. The file or
                       directory name specified does not exist.

Shepler, et al. Standards Track [Page 97] RFC 3010 NFS version 4 Protocol December 2000

 NFS4ERR_NOFILEHANDLE  The logical current file handle 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 file handle be set).
 NFS4ERR_NOSPC         No space left on device. The operation would
                       have caused the server's file system to exceed
                       its limit.
 NFS4ERR_NOTDIR        Not a directory. The caller specified a non-
                       directory in a directory operation.
 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_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_READDIR_NOSPC The encoded response to a READDIR request
                       exceeds the size limit set by the initial
                       request.
 NFS4ERR_RESOURCE      For the processing of the COMPOUND procedure,
                       the server may exhaust available resources and
                       can not continue processing procedures within
                       the COMPOUND operation.  This error will be
                       returned from the server in those instances of
                       resource exhaustion related to the processing
                       of the COMPOUND procedure.
 NFS4ERR_ROFS          Read-only file system. A modifying operation
                       was attempted on a read-only file system.

Shepler, et al. Standards Track [Page 98] RFC 3010 NFS version 4 Protocol December 2000

 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 file handle. The file handle given in
                       the arguments was invalid. The file referred to
                       by that file handle 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 file handle 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      Buffer or request is too
                       small.
 NFS4ERR_WRONGSEC      The security mechanism being used by the client
                       for the procedure does not match the server's
                       security policy.  The client should change the
                       security mechanism being used and retry the
                       operation.
 NFS4ERR_XDEV          Attempt to do a cross-device hard link.

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

Shepler, et al. Standards Track [Page 99] RFC 3010 NFS version 4 Protocol December 2000

 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 operation and therefore is fixed for the
 life of the client instantiation.

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 basics of the COMPOUND procedures construction is:
                +-----------+-----------+-----------+--
                | op + args | op + args | op + args |
                +-----------+-----------+-----------+--
 and the reply looks like this:
    +------------+-----------------------+-----------------------+--
    |last status | status + op + results | status + op + results |
    +------------+-----------------------+-----------------------+--

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

Shepler, et al. Standards Track [Page 100] RFC 3010 NFS version 4 Protocol December 2000

 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_LONG_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.

13.3. Synchronous Modifying Operations

 NFS version 4 operations that modify the file system 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.

Shepler, et al. Standards Track [Page 101] RFC 3010 NFS version 4 Protocol December 2000

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;
 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>;
            ...
    };

Shepler, et al. Standards Track [Page 102] RFC 3010 NFS version 4 Protocol December 2000

    struct COMPOUND4args {
            utf8string      tag;
            uint32_t        minorversion;
            nfs_argop4      argarray<>;
    };
 RESULT
       union nfs_resop4 switch (nfs_opnum4 resop){
               case <OPCODE>: <result>;
               ...
       };
       struct COMPOUND4res {
               nfsstat4        status;
               utf8string      tag;
               nfs_resop4      resarray<>;
       };
 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 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.

Shepler, et al. Standards Track [Page 103] RFC 3010 NFS version 4 Protocol December 2000

    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
    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.  If the server receives an operation array
    with either of these included, an error of NFS4ERR_NOTSUPP must be
    returned.  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_NOTSUPP is
    returned.  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.
 IMPLEMENTATION
    Note that the definition of the "tag" in both the request and
    response are 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.
    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

Shepler, et al. Standards Track [Page 104] RFC 3010 NFS version 4 Protocol December 2000

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.

Shepler, et al. Standards Track [Page 105] RFC 3010 NFS version 4 Protocol December 2000

    Note that the supported field will contain only as many values as
    was 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 (no meaning for
                 non-directory objects).
 ACCESS4_EXECUTE Execute file (no meaning for a directory).
 On success, the current filehandle retains its value.
 IMPLEMENTATION
    For the NFS version 4 protocol, the use of the ACCESS procedure
    when opening a regular file is deprecated in favor of using OPEN.
    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.

Shepler, et al. Standards Track [Page 106] RFC 3010 NFS version 4 Protocol December 2000

    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 procedure 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 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_ACCES
       NFS4ERR_BADHANDLE
       NFS4ERR_DELAY
       NFS4ERR_FHEXPIRED
       NFS4ERR_IO
       NFS4ERR_MOVED
       NFS4ERR_NOFILEHANDLE
       NFS4ERR_RESOURCE
       NFS4ERR_SERVERFAULT
       NFS4ERR_STALE
       NFS4ERR_WRONGSEC

Shepler, et al. Standards Track [Page 107] RFC 3010 NFS version 4 Protocol December 2000

14.2.2. Operation 4: CLOSE - Close File

 SYNOPSIS
       (cfh), seqid, stateid -> stateid
 ARGUMENT
       struct CLOSE4args {
               /* CURRENT_FH: object */
               seqid4          seqid
               stateid4        stateid;
       };
 RESULT
       union CLOSE4res switch (nfsstat4 status) {
        case NFS4_OK:
                stateid4       stateid;
        default:
                void;
       };
 DESCRIPTION
    The CLOSE operation releases share reservations for the 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
    ERRORS
       NFS4ERR_BADHANDLE
       NFS4ERR_BAD_SEQID
       NFS4ERR_BAD_STATEID
       NFS4ERR_DELAY

Shepler, et al. Standards Track [Page 108] RFC 3010 NFS version 4 Protocol December 2000

       NFS4ERR_EXPIRED
       NFS4ERR_FHEXPIRED
       NFS4ERR_GRACE
       NFS4ERR_INVAL
       NFS4ERR_ISDIR
       NFS4ERR_LEASE_MOVED
       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;
       };
 DESCRIPTION
    The COMMIT operation forces or flushes data to stable storage for
    the file specified by the current file handle.  The flushed data
    is that which was previously written with a WRITE operation which
    had the stable field set to UNSTABLE4.

Shepler, et al. Standards Track [Page 109] RFC 3010 NFS version 4 Protocol December 2000

    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 procedure.  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 procedure 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 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.

Shepler, et al. Standards Track [Page 110] RFC 3010 NFS version 4 Protocol December 2000

    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.
 ERRORS
       NFS4ERR_ACCES
       NFS4ERR_BADHANDLE
       NFS4ERR_FHEXPIRED
       NFS4ERR_IO

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       NFS4ERR_ISDIR
       NFS4ERR_LOCKED
       NFS4ERR_MOVED
       NFS4ERR_NOFILEHANDLE
       NFS4ERR_RESOURCE
       NFS4ERR_ROFS
       NFS4ERR_SERVERFAULT
       NFS4ERR_STALE
       NFS4ERR_WRONGSEC

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

 SYNOPSIS
       (cfh), name, type -> (cfh), change_info
 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 */
               component4      objname;
               createtype4     objtype;
       };
 RESULT
       struct CREATE4resok {
               change_info4     cinfo;
       };
       union CREATE4res switch (nfsstat4 status) {
        case NFS4_OK:
                CREATE4resok resok4;
        default:
                void;
       };

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 DESCRIPTION
    The CREATE operation creates a non-regular file object in a
    directory with a given name.  The OPEN procedure MUST be used to
    create a regular file.
    The objname specifies the name for the new object.  If the objname
    has a length of 0 (zero), the error NFS4ERR_INVAL will be
    returned.  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.
 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_ACCES
       NFS4ERR_BADHANDLE
       NFS4ERR_BADTYPE
       NFS4ERR_DQUOT
       NFS4ERR_EXIST
       NFS4ERR_FHEXPIRED
       NFS4ERR_INVAL
       NFS4ERR_IO
       NFS4ERR_MOVED
       NFS4ERR_NAMETOOLONG
       NFS4ERR_NOFILEHANDLE
       NFS4ERR_NOSPC
       NFS4ERR_NOTDIR
       NFS4ERR_NOTSUPP

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       NFS4ERR_RESOURCE
       NFS4ERR_ROFS
       NFS4ERR_SERVERFAULT
       NFS4ERR_STALE
       NFS4ERR_WRONGSEC

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 know 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.
 ERRORS
    NFS4ERR_RESOURCE

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    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE_CLIENTID

14.2.6. Operation 8: DELEGRETURN - Return Delegation

 SYNOPSIS
       stateid ->
 ARGUMENT
       struct DELEGRETURN4args {
               stateid4        stateid;
       };
 RESULT
       struct DELEGRETURN4res {
               nfsstat4        status;
       };
 DESCRIPTION
    Returns the delegation represented by the given stateid.
 ERRORS
       NFS4ERR_BAD_STATEID
       NFS4ERR_OLD_STATEID
       NFS4ERR_RESOURCE
       NFS4ERR_SERVERFAULT
       NFS4ERR_STALE_STATEID

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

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       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 file system
    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.
 IMPLEMENTATION
 ERRORS
       NFS4ERR_ACCES
       NFS4ERR_BADHANDLE
       NFS4ERR_DELAY
       NFS4ERR_FHEXPIRED
       NFS4ERR_INVAL
       NFS4ERR_IO
       NFS4ERR_MOVED
       NFS4ERR_NOFILEHANDLE
       NFS4ERR_RESOURCE
       NFS4ERR_SERVERFAULT

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       NFS4ERR_STALE
       NFS4ERR_WRONGSEC

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.
 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

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    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

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;
    };
 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 file system on the server.  On success, the current
    filehandle will continue to be the target directory.
    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.

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    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 comments under RENAME regarding object and target residing on
    the same file system apply here as well. The comments regarding
    the target name applies as well.
    Note that symbolic links are created with the CREATE operation.
 ERRORS
    NFS4ERR_ACCES NFS4ERR_BADHANDLE NFS4ERR_DELAY NFS4ERR_DQUOT
    NFS4ERR_EXIST NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_IO
    NFS4ERR_ISDIR NFS4ERR_MLINK NFS4ERR_MOVED NFS4ERR_NAMETOOLONG
    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) type, seqid, reclaim, stateid, offset, length -> stateid,
    access
 ARGUMENT
    enum nfs4_lock_type {
            READ_LT         = 1,
            WRITE_LT        = 2,
            READW_LT        = 3,    /* blocking read */
            WRITEW_LT       = 4     /* blocking write */ };
    struct LOCK4args {
            /* CURRENT_FH: file */
            nfs_lock_type4  locktype;
            seqid4          seqid;
            bool            reclaim;
            stateid4        stateid;
            offset4         offset;

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            length4         length; };
 RESULT
    struct LOCK4denied {
            nfs_lockowner4  owner;
            offset4         offset;
            length4         length; };
    union LOCK4res switch (nfsstat4 status) {
     case NFS4_OK:
             stateid4       stateid;
     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 nfs4_lock_types.  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).  To
    lock the entire file, use an offset of 0 (zero) and a length with
    all bits set to 1.  A length of 0 is reserved and should not be
    used.
    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.
 ERRORS
    NFS4ERR_ACCES NFS4ERR_BADHANDLE NFS4ERR_BAD_SEQID

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    NFS4ERR_BAD_STATEID NFS4ERR_DELAY NFS4ERR_DENIED 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_CLIENTID
    NFS4ERR_STALE_STATEID NFS4ERR_WRONGSEC

14.2.11. Operation 13: LOCKT - Test For Lock

 SYNOPSIS
    (cfh) type, owner, offset, length -> {void, NFS4ERR_DENIED ->
    owner}
 ARGUMENT
    struct LOCKT4args {
            /* CURRENT_FH: file */
            nfs_lock_type4  locktype;
            nfs_lockowner4  owner;
            offset4         offset;
            length4         length; };
 RESULT
    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, and length of the
    conflicting lock are returned; if no lock is held, nothing other
    than NFS4_OK is 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

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    results.  The File Locking section contains further discussion of
    the file locking mechanisms.
    LOCKT uses nfs_lockowner4 instead of a stateid4, as LOCK does, to
    identify the owner so that the client does not have to open the
    file to test for the existence of a lock.
 ERRORS
    NFS4ERR_ACCES
    NFS4ERR_BADHANDLE
    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
    NFS4ERR_WRONGSEC

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:

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             stateid4       stateid;
     default:
             void;
    };
 DESCRIPTION
    The LOCKU operation unlocks the record lock specified by the
    parameters.
    On success, the current filehandle retains its value.
 IMPLEMENTATION
    The File Locking section contains a full description of this and
    the other file locking procedures.
 ERRORS
    NFS4ERR_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_SEQID
    NFS4ERR_BAD_STATEID
    NFS4ERR_EXPIRED
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_INVAL
    NFS4ERR_LOCK_RANGE
    NFS4ERR_LEASE_MOVED
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_OLD_STATEID
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_CLIENTID
    NFS4ERR_STALE_STATEID

14.2.13. Operation 15: LOOKUP - Lookup Filename

 SYNOPSIS
    (cfh), filenames -> (cfh)
 ARGUMENT
    struct LOOKUP4args {
            /* CURRENT_FH: directory */

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            pathname4       path;
    };
 RESULT
    struct LOOKUP4res {
            /* CURRENT_FH: object */
            nfsstat4        status;
    };
 DESCRIPTION
    This operation LOOKUPs or finds a file system object starting from
    the directory specified by the current filehandle.  LOOKUP
    evaluates the pathname contained in the array of names and obtains
    a new current filehandle from the final name.  All but the final
    name in the list must be the names of directories.
    If the pathname cannot be evaluated either because a component
    does not exist or because the client does not have permission to
    evaluate a component of the path, then an error will be returned
    and the current filehandle will be unchanged.
    If the path is a zero length array, if any component does not obey
    the UTF-8 definition, or if any component in the path is of zero
    length, the error NFS4ERR_INVAL will be returned.
 IMPLEMENTATION
    If the client prefers a partial evaluation of the path then a
    sequence of LOOKUP operations can be substituted e.g.
             PUTFH  (directory filehandle)
             LOOKUP "pub" "foo" "bar"
             GETFH
    or, if the client wishes to obtain the intermediate filehandles
             PUTFH  (directory filehandle)
             LOOKUP "pub"
             GETFH
             LOOKUP "foo"
             GETFH
             LOOKUP "bar"
             GETFH

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    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.
    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 procedure 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 file handle 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_ACCES
    NFS4ERR_BADHANDLE
    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

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14.2.14. Operation 16: LOOKUPP - Lookup Parent Directory

 SYNOPSIS
    (cfh) -> (cfh)
 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_ENOENT error must be returned.
    Therefore, NFS4ERR_ENOENT 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_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTDIR
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT

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    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

14.2.15. Operation 17: NVERIFY - Verify Difference in Attributes

 SYNOPSIS
    (cfh), fattr -> -
 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 "pub" "foo" "bar"
             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 file system object, the error NFS4ERR_NOTSUPP is returned
    to the client.

Shepler, et al. Standards Track [Page 127] RFC 3010 NFS version 4 Protocol December 2000

 ERRORS
    NFS4ERR_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTSUPP
    NFS4ERR_RESOURCE
    NFS4ERR_SAME
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

14.2.16. Operation 18: OPEN - Open a Regular File

 SYNOPSIS
(cfh), claim, openhow, owner, seqid, access, deny -> (cfh),
stateid, cinfo, rflags, open_confirm, delegation
 ARGUMENT
struct OPEN4args {
        open_claim4     claim;
        openflag4       openhow;
        nfs_lockowner4  owner;
        seqid4          seqid;
        uint32_t        share_access;
        uint32_t        share_deny;
};
enum createmode4 {
        UNCHECKED4      = 0,
        GUARDED4        = 1,
        EXCLUSIVE4      = 2
};
union createhow4 switch (createmode4 mode) {
 case UNCHECKED4:
 case GUARDED4:
         fattr4         createattrs;
 case EXCLUSIVE4:
         verifier4      createverf;
};

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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
};
struct open_claim_delegate_cur4 {
        pathname4       file;

Shepler, et al. Standards Track [Page 129] RFC 3010 NFS version 4 Protocol December 2000

        stateid4        delegate_stateid;
};
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 */
         pathname4      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 */
         uint32_t        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 */
         pathname4      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
                                           open for read */
};

Shepler, et al. Standards Track [Page 130] RFC 3010 NFS version 4 Protocol December 2000

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_MLOCK        = 0x00000001;
const OPEN4_RESULT_CONFIRM= 0x00000002;
struct OPEN4resok {
        stateid4        stateid;        /* Stateid for open */
        change_info4    cinfo;          /* Directory Change Info */
        uint32_t        rflags;         /* Result flags */
        verifier4       open_confirm;   /* OPEN_CONFIRM verifier */
        open_delegation4 delegation;    /* Info on any open
                                           delegation */
};
union OPEN4res switch (nfsstat4 status) {
 case NFS4_OK:
        /* CURRENT_FH: opened file */
        OPEN4resok      resok4;
 default:
        void;
};

Shepler, et al. Standards Track [Page 131] RFC 3010 NFS version 4 Protocol December 2000

 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.
    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 includes any writable attribute valid for regular
    files.  When an UNCHECKED create encounters an existing file, the
    attributes specified by createattrs is not used, except that when
    an object_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.
    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,

Shepler, et al. Standards Track [Page 132] RFC 3010 NFS version 4 Protocol December 2000

    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.
    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 procedure provides for DOS SHARE capability with the use
    of the access and deny fields of the OPEN arguments.  The client
    specifies at OPEN the required access and 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_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 reclaim 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:
    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 file
                          handles; the client may not have the
                          file name to reclaim the OPEN.

Shepler, et al. Standards Track [Page 133] RFC 3010 NFS version 4 Protocol December 2000

    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.
    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.
    OPEN4_RESULT_MLOCK indicates to the caller that mandatory locking
    is in effect for this file and the client should act appropriately
    with regard to data cached on the client.  OPEN4_RESULT_CONFIRM
    indicates that the client MUST execute an OPEN_CONFIRM operation
    before using the open file.
    If the file is a zero length array, if any component does not obey
    the UTF-8 definition, or if any component in the path is of zero
    length, the error NFS4ERR_INVAL will be returned.
    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
    OPEN's were completed.

Shepler, et al. Standards Track [Page 134] RFC 3010 NFS version 4 Protocol December 2000

 IMPLEMENTATION
    The OPEN procedure 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
    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 file systems 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 file system 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,

Shepler, et al. Standards Track [Page 135] RFC 3010 NFS version 4 Protocol December 2000

    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 procedure can
    fail with NFS4ERR_EXIST, even though the create was performed
    successfully.
    For SHARE reservations, the client must specify a value for access
    that is one of READ, WRITE, or BOTH.  For 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.
    If the final component provided to OPEN is a symbolic link, the
    error NFS4ERR_SYMLINK will be returned to the client.  If an
    intermediate component of the pathname provided to OPEN is a
    symbolic link, the error NFS4ERR_NOTDIR will be returned to the
    client.
 ERRORS
    NFS4ERR_ACCES
    NFS4ERR_BAD_SEQID
    NFS4ERR_DELAY
    NFS4ERR_DQUOT
    NFS4ERR_EXIST
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_IO
    NFS4ERR_ISDIR
    NFS4ERR_LEASE_MOVED
    NFS4ERR_MOVED
    NFS4ERR_NAMETOOLONG
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOSPC
    NFS4ERR_NOTDIR
    NFS4ERR_NOTSUPP
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_SHARE_DENIED
    NFS4ERR_STALE_CLIENTID
    NFS4ERR_SYMLINK

Shepler, et al. Standards Track [Page 136] RFC 3010 NFS version 4 Protocol December 2000

14.2.17. Operation 19: OPENATTR - Open Named Attribute Directory

 SYNOPSIS
 (cfh) -> (cfh)
 ARGUMENT
 /* CURRENT_FH: file or directory */
 void;
 RESULT
 struct OPENATTR4res {
         /* CURRENT_FH: name attr directory*/
         nfsstat4        status;
 };
 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
    procedures can be used to obtain filehandles for the various named
    attributes associated with the original file system object.
    Filehandles returned within the named attribute directory will
    have a type of NF4NAMEDATTR.
 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_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTSUPP
    NFS4ERR_RESOURCE

Shepler, et al. Standards Track [Page 137] RFC 3010 NFS version 4 Protocol December 2000

    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

14.2.18. Operation 20: OPEN_CONFIRM - Confirm Open

 SYNOPSIS
 (cfh), seqid, open_confirm-> stateid
 ARGUMENT
 struct OPEN_CONFIRM4args {
         /* CURRENT_FH: opened file */
         seqid4          seqid;
         verifier4       open_confirm;   /* OPEN_CONFIRM verifier */
 };
 RESULT
 struct OPEN_CONFIRM4resok {
         stateid4        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 nfs_lockowner is used by a client.  The OPEN
    operation returns a opaque confirmation verifier that is then
    passed to this operation along with the next sequence id for the
    nfs_lockowner.  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.

Shepler, et al. Standards Track [Page 138] RFC 3010 NFS version 4 Protocol December 2000

 IMPLEMENTATION
    A given client might generate many nfs_lockowner data structures
    for a given clientid.  The client will periodically either dispose
    of its nfs_lockowners or stop using them for indefinite periods of
    time.  The latter situation is why the NFS version 4 protocol does
    not have a an explicit operation to exit an nfs_lockowner: 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 nfs_lockowners 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
    nfs_lockowners 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 nfs_lockowner data structures.
    In the case that a client issues an OPEN operation and the server
    no longer has a record of the nfs_lockowner, the server needs
    ensure that this is a new OPEN and not a replay or retransmission.
    A lazy server implementation might require confirmation for every
    nfs_lockowner for which it has no record.  However, this is not
    necessary until the server records the fact that it has disposed
    of one nfs_lockowner for the given clientid.
    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 confirmation verifier within
    the lease period.  In this case, the OPEN state on the server goes
    to confirmed, and the nfs_lockowner on the server is fully
    established.
    Second, the client sends another OPEN request with a sequence id
    that is incorrect for the nfs_lockowner (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.

Shepler, et al. Standards Track [Page 139] RFC 3010 NFS version 4 Protocol December 2000

    What if the server is in the unconfirmed OPEN state for a given
    nfs_lockowner, and it receives an operation on the nfs_lockowner
    that has a stateid but the operation is not OPEN, or it is
    OPEN_CONFIRM but with the wrong confirmation verifier?  Then, even
    if the seqid is correct, the 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
    nfs_lockowner within the lease period.  In this case, the OPEN
    state is cancelled and disposal of the nfs_lockowner can occur.
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_SEQID
    NFS4ERR_EXPIRED
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_INVAL
    NFS4ERR_MOVED
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTSUPP
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

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        stateid;
         seqid4          seqid;
         uint32_t        share_access;
         uint32_t        share_deny;
 };
 RESULT

Shepler, et al. Standards Track [Page 140] RFC 3010 NFS version 4 Protocol December 2000

 struct OPEN_DOWNGRADE4resok {
         stateid4        stateid;
 };
 union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
  case NFS4_OK:
         OPEN_DOWNGRADE4resok    resok4;
  default:
         void;
 };
 This operation is used to adjust the access and deny bits for a given
 open.  This is necessary when a given lockowner opens the same file
 multiple times with different access and deny flags.  In this
 situation, a close of one of the open's may change the appropriate
 access and deny flags to remove bits associated with open's no longer
 in effect.
 The access and deny bits specified in this operation replace the
 current ones for the specified open file.  If either the access or
 the deny mode specified includes bits not in effect for the open, the
 error NFS4ERR_INVAL should be returned.  Since access and 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_BADHANDLE NFS4ERR_BAD_SEQID NFS4ERR_BAD_STATEID
    NFS4ERR_EXPIRED NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE NFS4ERR_OLD_STATEID NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_STALE_STATEID

14.2.20. Operation 22: PUTFH - Set Current Filehandle

 SYNOPSIS
    filehandle -> (cfh)
 ARGUMENT
    struct PUTFH4args {
            nfs4_fh         object; };
 RESULT
    struct PUTFH4res {

Shepler, et al. Standards Track [Page 141] RFC 3010 NFS version 4 Protocol December 2000

            /* CURRENT_FH: */
            nfsstat4        status; };
 DESCRIPTION
    Replaces the current filehandle with the filehandle provided as an
    argument.
 IMPLEMENTATION
    Commonly used as the first operator in an NFS request to set the
    context for following operations.
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_FHEXPIRED
    NFS4ERR_MOVED
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

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.

Shepler, et al. Standards Track [Page 142] RFC 3010 NFS version 4 Protocol December 2000

 IMPLEMENTATION
    Used as the first operator in an NFS request to set the context
    for following operations.
 ERRORS
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_WRONGSEC

14.2.22. Operation 24: PUTROOTFH - Set Root Filehandle

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

Shepler, et al. Standards Track [Page 143] RFC 3010 NFS version 4 Protocol December 2000

14.2.23. Operation 25: READ - Read from File

 SYNOPSIS
    (cfh), offset, count, stateid -> 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;
    };
 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.

Shepler, et al. Standards Track [Page 144] RFC 3010 NFS version 4 Protocol December 2000

    The stateid value for a READ request represents a value returned
    from a previous record lock or share reservation request.  Used by
    the server to verify that the associated lock is 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.
    On success, the current filehandle retains its value.
 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
    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 the file is locked the server will return an NFS4ERR_LOCKED
    error.  Since the lock may be of short duration, the client may
    choose to retransmit the READ request (with exponential backoff)
    until the operation succeeds.
 ERRORS
    NFS4ERR_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_STATEID
    NFS4ERR_DELAY
    NFS4ERR_DENIED
    NFS4ERR_EXPIRED
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_LOCKED
    NFS4ERR_LEASE_MOVED
    NFS4ERR_MOVED

Shepler, et al. Standards Track [Page 145] RFC 3010 NFS version 4 Protocol December 2000

    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NXIO
    NFS4ERR_OLD_STATEID
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_STATEID
    NFS4ERR_WRONGSEC

14.2.24. Operation 26: READDIR - Read Directory

 SYNOPSIS
    (cfh), cookie, cookieverf, dircount, maxcount, attrbits ->
    cookieverf { cookie, filename, attrbits, attributes }
 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) {

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     case NFS4_OK:
             READDIR4resok  resok4;
     default:
             void;
    };
 DESCRIPTION
    The READDIR operation retrieves a variable number of entries from
    a file system 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.
    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 server may
    return less data.
    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 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_READDIR_NOSPC will be returned to the client.
    Finally, attrbits 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.

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    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 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 file system 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
    returned.
    On success, the current filehandle retains its value.
 IMPLEMENTATION
    The server's file system 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

Shepler, et al. Standards Track [Page 148] RFC 3010 NFS version 4 Protocol December 2000

    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.
    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_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_COOKIE
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTDIR
    NFS4ERR_NOTSUPP
    NFS4ERR_READDIR_NOSPC
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_TOOSMALL
    NFS4ERR_WRONGSEC

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14.2.25. Operation 27: READLINK - Read Symbolic Link

 SYNOPSIS
    (cfh) -> linktext
 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.

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 ERRORS
    NFS4ERR_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTSUPP
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

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

Shepler, et al. Standards Track [Page 151] RFC 3010 NFS version 4 Protocol December 2000

    to the corresponding file system object, the object may be
    destroyed.
    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.  NFS version 4 REMOVE can be used to delete any
    directory entry independent of its file type.
    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 file handle. 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.
 ERRORS
    NFS4ERR_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NAMETOOLONG
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTDIR
    NFS4ERR_NOTEMPTY
    NFS4ERR_NOTSUPP
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT

Shepler, et al. Standards Track [Page 152] RFC 3010 NFS version 4 Protocol December 2000

    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

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;
    };
 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 file system 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

Shepler, et al. Standards Track [Page 153] RFC 3010 NFS version 4 Protocol December 2000

    removed before the rename occurs.  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 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 file system
    on the server" means that the fsid fields in the attributes for
    the directories are the same. If they reside on different file
    systems, the error, NFS4ERR_XDEV, is returned.
    A filehandle may or may not become stale or expire on a rename.
    However, server implementors are strongly encouraged to attempt to
    keep file handles from becoming stale or expiring in this fashion.
    On some servers, the filenames, "." and "..", are illegal as
    either oldname or newname.  In addition, neither oldname nor
    newname can be an alias for the source directory.  These servers
    will return the error, NFS4ERR_INVAL, in these cases.
 ERRORS
    NFS4ERR_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_DELAY
    NFS4ERR_DQUOT
    NFS4ERR_EXIST
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_ISDIR
    NFS4ERR_MOVED
    NFS4ERR_NAMETOOLONG

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    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOSPC
    NFS4ERR_NOTDIR
    NFS4ERR_NOTEMPTY
    NFS4ERR_NOTSUPP
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC
    NFS4ERR_XDEV

14.2.28. Operation 30: RENEW - Renew a Lease

 SYNOPSIS
    stateid -> ()
 ARGUMENT
    struct RENEW4args {
            stateid4        stateid;
    };
 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 client id provided via the
    SETCLIENTID procedure.
    The stateid for RENEW may not be one of the special stateids
    consisting of all bits 0 (zero) or all bits 1.
 IMPLEMENTATION
 ERRORS
    NFS4ERR_BAD_STATEID
    NFS4ERR_EXPIRED

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    NFS4ERR_GRACE
    NFS4ERR_INVAL
    NFS4ERR_LEASE_MOVED
    NFS4ERR_MOVED
    NFS4ERR_OLD_STATEID
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE_STATEID
    NFS4ERR_WRONGSEC

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;
    };
 DESCRIPTION
    Set the current filehandle to the value in the saved filehandle.
    If there is no saved filehandle then return an error
    NFS4ERR_NOFILEHANDLE.
 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)

Shepler, et al. Standards Track [Page 156] RFC 3010 NFS version 4 Protocol December 2000

             RESTOREFH
             GETATTR attrbits     (post-op dir attrs)
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_FHEXPIRED
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

14.2.30. Operation 32: SAVEFH - Save Current Filehandle

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

Shepler, et al. Standards Track [Page 157] RFC 3010 NFS version 4 Protocol December 2000

    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

14.2.31. Operation 33: SECINFO - Obtain Available Security

 SYNOPSIS
    (cfh), name -> { secinfo }
 ARGUMENT
    struct SECINFO4args {
            /* CURRENT_FH: */
            component4     name;
    };
 RESULT
    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;
    };
    struct secinfo4 {
            uint32_t flavor;
            opaque flavor_info<>;   /* null for AUTH_SYS, AUTH_NONE;
                                       contains rpcsec_gss_info for
                                       RPCSEC_GSS. */
    };
    typedef secinfo4 SECINFO4resok<>;
    union SECINFO4res switch (nfsstat4 status) {
     case NFS4_OK:
             SECINFO4resok resok4;
     default:
             void;
    };

Shepler, et al. Standards Track [Page 158] RFC 3010 NFS version 4 Protocol December 2000

 DESCRIPTION
    The SECINFO operation is used by the client to obtain a list of
    valid RPC authentication flavors for a specific file handle, file
    name pair.  The result will contain an array which represents the
    security mechanisms available.  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 [RFC2078]), the quality of protection (as defined
    in [RFC2078]) 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.
    On success, the current filehandle retains its value.
 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.
    It is recommended that the client issue the SECINFO call protected
    by a security triple that uses either rpc_gss_svc_integrity or
    rpc_gss_svc_privacy service. The use of rpc_gss_svc_none would
    allow an attacker in the middle to modify the SECINFO 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.
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_FHEXPIRED
    NFS4ERR_MOVED
    NFS4ERR_NAMETOOLONG
    NFS4ERR_NOENT
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTDIR
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT

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    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

14.2.32. Operation 34: SETATTR - Set Attributes

 SYNOPSIS
    (cfh), attrbits, attrvals -> -
 ARGUMENT
    struct SETATTR4args {
            /* CURRENT_FH: target object */
            stateid4        stateid;
            fattr4          obj_attributes;
    };
 RESULT
    struct SETATTR4res {
            nfsstat4        status;
            bitmap4         attrsset;
    };
 DESCRIPTION
    The SETATTR operation changes one or more of the attributes of a
    file system object.  The new attributes are specified with a
    bitmap and the attributes that follow the bitmap in bit order.
    The stateid is necessary for SETATTRs that change the size of a
    file (modify the attribute object_size).  This stateid represents
    a record lock, share reservation, or delegation which must be
    valid for the SETATTR to modify the file data.  A valid stateid
    would always be specified.  When the file size is not changed, the
    special stateid consisting of all bits 0 (zero) should be used.
    On either success or failure of the operation, the server will
    return the attrsset bitmask to represent what (if any) attributes
    were successfully set.
    On success, the current filehandle retains its value.
 IMPLEMENTATION
    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

Shepler, et al. Standards Track [Page 160] RFC 3010 NFS version 4 Protocol December 2000

    size to 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.
    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.
    If the server cannot successfully set all the attributes it must
    return an NFS4ERR_INVAL error.  If the server can only support 32
    bit offsets and sizes, a SETATTR request to set the size of a file
    to larger than can be represented in 32 bits will be rejected with
    this same error.
 ERRORS
    NFS4ERR_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_STATEID
    NFS4ERR_DELAY
    NFS4ERR_DENIED
    NFS4ERR_DQUOT
    NFS4ERR_EXPIRED
    NFS4ERR_FBIG
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE
    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOSPC
    NFS4ERR_NOTSUPP
    NFS4ERR_OLD_STATEID
    NFS4ERR_PERM
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS

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    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_STATEID
    NFS4ERR_WRONGSEC

14.2.33. Operation 35: SETCLIENTID - Negotiate Clientid

 SYNOPSIS
    client, callback -> clientid, setclientid_confirm
 ARGUMENT
    struct SETCLIENTID4args {
            nfs_client_id4  client;
            cb_client4      callback;
    };
 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 SETCLIENTID operation introduces the ability of the client to
    notify the server of its intention to use a particular client
    identifier and verifier pair.  Upon successful completion the
    server will return a clientid which is used in subsequent file
    locking requests and a confirmation verifier.  The client will use
    the SETCLIENTID_CONFIRM operation to return the verifier to the
    server.  At that point, the client may use the clientid in
    subsequent operations that require an nfs_lockowner.

Shepler, et al. Standards Track [Page 162] RFC 3010 NFS version 4 Protocol December 2000

    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.
 IMPLEMENTATION
    The server takes the verifier and client identification supplied
    in the nfs_client_id4 and searches for a match of the client
    identification.  If no match is found the server saves the
    principal/uid information along with the verifier and client
    identification and returns a unique clientid that is used as a
    shorthand reference to the supplied information.
    If the server finds matching client identification and a
    corresponding match in principal/uid, the server releases all
    locking state for the client and returns a new clientid.
    The principal, or principal to user-identifier mapping is taken
    from the credential presented in the RPC.  As mentioned, the
    server will use the credential and associated principal for the
    matching with existing clientids.  If the client is a traditional
    host-based client like a Unix NFS client, then the credential
    presented may be the host credential.  If the client is a user
    level client or lightweight client, the credential used may be the
    end user's credential.  The client should take care in choosing an
    appropriate credential since denial of service attacks could be
    attempted by a rogue client that has access to the credential.
 ERRORS
    NFS4ERR_CLID_INUSE
    NFS4ERR_INVAL
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT

14.2.34. Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid

 SYNOPSIS
    setclientid_confirm -> -
 ARGUMENT
    struct SETCLIENTID_CONFIRM4args {
            verifier4       setclientid_confirm;
    };

Shepler, et al. Standards Track [Page 163] RFC 3010 NFS version 4 Protocol December 2000

 RESULT
    struct SETCLIENTID_CONFIRM4res {
            nfsstat4        status;
    };
 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) opaque confirmation
    verifier.  The server responds with a simple status of success or
    failure.
 IMPLEMENTATION
    The client must use the SETCLIENTID_CONFIRM operation to confirm
    its use of client identifier.  If the server is holding state for
    a client which has presented a new verifier via SETCLIENTID, then
    the state will not be released, as described in the section
    "Client Failure and Recovery", until a valid SETCLIENTID_CONFIRM
    is received.  Upon successful confirmation the server will release
    the previous state held on behalf of the client.  The server
    should choose a confirmation cookie value that is reasonably
    unique for the client.
 ERRORS
    NFS4ERR_CLID_INUSE
    NFS4ERR_INVAL
    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;
    };

Shepler, et al. Standards Track [Page 164] RFC 3010 NFS version 4 Protocol December 2000

 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)
    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 file system object, the error NFS4ERR_NOTSUPP is returned
    to the client.
 ERRORS
    NFS4ERR_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_DELAY
    NFS4ERR_FHEXPIRED
    NFS4ERR_INVAL
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOTSUPP

Shepler, et al. Standards Track [Page 165] RFC 3010 NFS version 4 Protocol December 2000

    NFS4ERR_NOT_SAME
    NFS4ERR_RESOURCE
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_WRONGSEC

14.2.36. Operation 38: WRITE - Write to File

 SYNOPSIS
    (cfh), offset, count, stability, stateid, data -> count, committed,
    verifier
 ARGUMENT
    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<>;
    };
 RESULT
    struct WRITE4resok {
            count4          count;
            stable_how4     committed;
            verifier4       writeverf;
    };
    union WRITE4res switch (nfsstat4 status) {
     case NFS4_OK:
             WRITE4resok    resok4;
     default:
             void;
    };

Shepler, et al. Standards Track [Page 166] RFC 3010 NFS version 4 Protocol December 2000

 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 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 file system 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 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 returned from a previous record lock or share
    reservation request is provided as part of the argument.  The
    stateid is used by the server to verify that the associated lock
    is 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

Shepler, et al. Standards Track [Page 167] RFC 3010 NFS version 4 Protocol December 2000

    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, verf.  The
    write verifier is a cookie that the client can use to determine
    whether the server has changed 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.
    On success, the current filehandle retains its value.
 IMPLEMENTATION
    It is possible for the server to write fewer than count bytes of
    data.  In this case, the server should not return an error unless
    no data was written at all.  If the server writes less than count
    bytes, 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:

Shepler, et al. Standards Track [Page 168] RFC 3010 NFS version 4 Protocol December 2000

             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).
    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.
 ERRORS
    NFS4ERR_ACCES
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_STATEID
    NFS4ERR_DELAY
    NFS4ERR_DENIED
    NFS4ERR_DQUOT
    NFS4ERR_EXPIRED
    NFS4ERR_FBIG
    NFS4ERR_FHEXPIRED
    NFS4ERR_GRACE

Shepler, et al. Standards Track [Page 169] RFC 3010 NFS version 4 Protocol December 2000

    NFS4ERR_INVAL
    NFS4ERR_IO
    NFS4ERR_LEASE_MOVED
    NFS4ERR_LOCKED
    NFS4ERR_MOVED
    NFS4ERR_NOFILEHANDLE
    NFS4ERR_NOSPC
    NFS4ERR_OLD_STATEID
    NFS4ERR_RESOURCE
    NFS4ERR_ROFS
    NFS4ERR_SERVERFAULT
    NFS4ERR_STALE
    NFS4ERR_STALE_STATEID
    NFS4ERR_WRONGSEC

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 170] RFC 3010 NFS version 4 Protocol December 2000

15.2. Procedure 1: CB_COMPOUND - Compound Operations

 SYNOPSIS
    compoundargs -> compoundres
 ARGUMENT
    enum nfs_cb_opnum4 {
            OP_CB_GETATTR           = 3,
            OP_CB_RECALL            = 4 };
    union nfs_cb_argop4 switch (unsigned argop) {
     case OP_CB_GETATTR:    CB_GETATTR4args opcbgetattr;
     case OP_CB_RECALL:     CB_RECALL4args  opcbrecall; };
    struct CB_COMPOUND4args {
            utf8string      tag;
            uint32_t        minorversion;
            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;
            utf8string      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.
    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.

Shepler, et al. Standards Track [Page 171] RFC 3010 NFS version 4 Protocol December 2000

    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.
 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_RESOURCE

15.2.1. Operation 3: CB_GETATTR - Get Attributes

 SYNOPSIS
    fh, attrbits -> attrbits, attrvals
 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;
    };

Shepler, et al. Standards Track [Page 172] RFC 3010 NFS version 4 Protocol December 2000

 DESCRIPTION
    The CB_GETATTR operation is used to obtain the attributes modified
    by an open delegate to allow the server to respond to GETATTR
    requests for a file which is the subject of an open delegation.
    If the handle specified is not one for which the client holds a
    write open delegation, an NFS4ERR_BADHANDLE error is returned.
 IMPLEMENTATION
    The client returns attrbits and the associated attribute values
    only for attributes that it may change (change, time_modify,
    object_size).
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_RESOURCE

15.2.2. Operation 4: CB_RECALL - Recall an Open Delegation

 SYNOPSIS
    stateid, truncate, fh -> status
 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.

Shepler, et al. Standards Track [Page 173] RFC 3010 NFS version 4 Protocol December 2000

    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.
 IMPLEMENTATION
    The client should reply to the callback immediately.  Replying
    does not complete the recall.  The recall is not complete until
    the delegation is returned using a DELEGRETURN.
 ERRORS
    NFS4ERR_BADHANDLE
    NFS4ERR_BAD_STATEID
    NFS4ERR_RESOURCE

16. Security Considerations

 The major security feature to consider is the authentication of the
 user making the request of NFS service.  Consideration should also be
 given to the integrity and privacy of this NFS request.  These
 specific issues are discussed as part of the section on "RPC and
 Security Flavor".

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; the
 application developer or system vendor is allowed to define the
 attribute, its semantics, and the associated name.  Even though this
 name space will not be specifically controlled to prevent collisions,
 the application developer or system vendor is strongly encouraged to
 provide the name assignment and associated semantics for attributes
 via an Informational RFC.  This will provide for interoperability
 where common interests exist.

Shepler, et al. Standards Track [Page 174] RFC 3010 NFS version 4 Protocol December 2000

18. RPC definition file

 /*
  *  Copyright (C) The Internet Society (1998,1999,2000).
  *  All Rights Reserved.
  */
 /*
  *      nfs4_prot.x
  *
  */
 %#pragma ident  "@(#)nfs4_prot.x        1.97    00/06/12"
 /*
  * 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;
 /*
  * File types
  */
 enum nfs_ftype4 {
         NF4REG          = 1,    /* Regular File */
         NF4DIR          = 2,    /* Directory */
         NF4BLK          = 3,    /* Special File - block device */
         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,

Shepler, et al. Standards Track [Page 175] RFC 3010 NFS version 4 Protocol December 2000

         NFS4ERR_PERM            = 1,
         NFS4ERR_NOENT           = 2,
         NFS4ERR_IO              = 5,
         NFS4ERR_NXIO            = 6,
         NFS4ERR_ACCES           = 13,
         NFS4ERR_EXIST           = 17,
         NFS4ERR_XDEV            = 18,
         NFS4ERR_NODEV           = 19,
         NFS4ERR_NOTDIR          = 20,
         NFS4ERR_ISDIR           = 21,
         NFS4ERR_INVAL           = 22,
         NFS4ERR_FBIG            = 27,
         NFS4ERR_NOSPC           = 28,
         NFS4ERR_ROFS            = 30,
         NFS4ERR_MLINK           = 31,
         NFS4ERR_NAMETOOLONG     = 63,
         NFS4ERR_NOTEMPTY        = 66,
         NFS4ERR_DQUOT           = 69,
         NFS4ERR_STALE           = 70,
         NFS4ERR_BADHANDLE       = 10001,
         NFS4ERR_BAD_COOKIE      = 10003,
         NFS4ERR_NOTSUPP         = 10004,
         NFS4ERR_TOOSMALL        = 10005,
         NFS4ERR_SERVERFAULT     = 10006,
         NFS4ERR_BADTYPE         = 10007,
         NFS4ERR_DELAY           = 10008,
         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,/* file handle expired     */
         NFS4ERR_SHARE_DENIED    = 10015,/* share reserve denied    */
         NFS4ERR_WRONGSEC        = 10016,/* wrong security flavor   */
         NFS4ERR_CLID_INUSE      = 10017,/* clientid in use         */
         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,
         NFS4ERR_STALE_STATEID   = 10023,
         NFS4ERR_OLD_STATEID     = 10024,
         NFS4ERR_BAD_STATEID     = 10025,
         NFS4ERR_BAD_SEQID       = 10026,
         NFS4ERR_NOT_SAME        = 10027,/* verify - attrs not same */
         NFS4ERR_LOCK_RANGE      = 10028,
         NFS4ERR_SYMLINK         = 10029,
         NFS4ERR_READDIR_NOSPC   = 10030,

Shepler, et al. Standards Track [Page 176] RFC 3010 NFS version 4 Protocol December 2000

         NFS4ERR_LEASE_MOVED     = 10031
 };
 /*
  * Basic data types
  */
 typedef uint32_t        bitmap4<>;
 typedef uint64_t        offset4;
 typedef uint32_t        count4;
 typedef uint64_t        length4;
 typedef uint64_t        clientid4;
 typedef uint64_t        stateid4;
 typedef uint32_t        seqid4;
 typedef opaque          utf8string<>;
 typedef utf8string      component4;
 typedef component4      pathname4<>;
 typedef uint64_t        nfs_lockid4;
 typedef uint64_t        nfs_cookie4;
 typedef utf8string      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
  */

Shepler, et al. Standards Track [Page 177] RFC 3010 NFS version 4 Protocol December 2000

 typedef opaque  nfs_fh4<NFS4_FHSIZE>;
 /*
  * File attribute definitions
  */
 /*
  * FSID structure for major/minor
  */
 struct fsid4 {
         uint64_t        major;
         uint64_t        minor;
 };
 /*
  * Filesystem locations attribute for relocation/migration
  */
 struct fs_location4 {
         utf8string      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;

Shepler, et al. Standards Track [Page 178] RFC 3010 NFS version 4 Protocol December 2000

 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;
 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;

Shepler, et al. Standards Track [Page 179] RFC 3010 NFS version 4 Protocol December 2000

 /*
  * 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 |
  *      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;
         utf8string      who;
 };
 /*
  * Special data/attribute associated with
  * file types NF4BLK and NF4CHR.
  */
 struct specdata4 {

Shepler, et al. Standards Track [Page 180] RFC 3010 NFS version 4 Protocol December 2000

         uint32_t        specdata1;
         uint32_t        specdata2;
 };
 /*
  * 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 utf8string      fattr4_mimetype;

Shepler, et al. Standards Track [Page 181] RFC 3010 NFS version 4 Protocol December 2000

 typedef mode4           fattr4_mode;
 typedef bool            fattr4_no_trunc;
 typedef uint32_t        fattr4_numlinks;
 typedef utf8string      fattr4_owner;
 typedef utf8string      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;
 /*
  * Recommended Attributes
  */
 const FATTR4_ACL                = 12;
 const FATTR4_ACLSUPPORT         = 13;
 const FATTR4_ARCHIVE            = 14;
 const FATTR4_CANSETTIME         = 15;
 const FATTR4_CASE_INSENSITIVE   = 16;

Shepler, et al. Standards Track [Page 182] RFC 3010 NFS version 4 Protocol December 2000

 const FATTR4_CASE_PRESERVING    = 17;
 const FATTR4_CHOWN_RESTRICTED   = 18;
 const FATTR4_FILEHANDLE         = 19;
 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;
 typedef opaque  attrlist4<>;
 /*
  * File attribute container
  */
 struct fattr4 {
         bitmap4         attrmask;
         attrlist4       attr_vals;

Shepler, et al. Standards Track [Page 183] RFC 3010 NFS version 4 Protocol December 2000

 };
 /*
  * 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 {
         unsigned int    cb_program;
         clientaddr4     cb_location;
 };
 /*
  * Client ID
  */
 struct nfs_client_id4 {
         verifier4       verifier;
         opaque          id<>;
 };
 struct nfs_lockowner4 {
         clientid4       clientid;
         opaque          owner<>;
 };
 enum nfs_lock_type4 {
         READ_LT         = 1,
         WRITE_LT        = 2,
         READW_LT        = 3,    /* blocking read */
         WRITEW_LT       = 4     /* blocking write */
 };
 /*
  * ACCESS: Check access permission
  */

Shepler, et al. Standards Track [Page 184] RFC 3010 NFS version 4 Protocol December 2000

 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 locks
  */
 struct CLOSE4args {
         /* CURRENT_FH: object */
         seqid4          seqid;
         stateid4        stateid;
 };
 union CLOSE4res switch (nfsstat4 status) {
  case NFS4_OK:
          stateid4       stateid;
  default:
          void;
 };
 /*
  * COMMIT: Commit cached data on server to stable storage
  */
 struct COMMIT4args {
         /* CURRENT_FH: file */
         offset4         offset;
         count4          count;
 };

Shepler, et al. Standards Track [Page 185] RFC 3010 NFS version 4 Protocol December 2000

 struct COMMIT4resok {
         verifier4       writeverf;
 };
 union COMMIT4res switch (nfsstat4 status) {
  case NFS4_OK:
          COMMIT4resok   resok4;
  default:
          void;
 };
 /*
  * CREATE: Create a file
  */
 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 */
         component4      objname;
         createtype4     objtype;
 };
 struct CREATE4resok {
         change_info4     cinfo;
 };
 union CREATE4res switch (nfsstat4 status) {
  case NFS4_OK:
          CREATE4resok resok4;
  default:
          void;
 };
 /*
  * DELEGPURGE: Purge Delegations Awaiting Recovery
  */
 struct DELEGPURGE4args {

Shepler, et al. Standards Track [Page 186] RFC 3010 NFS version 4 Protocol December 2000

         clientid4       clientid;
 };
 struct DELEGPURGE4res {
         nfsstat4        status;
 };
 /*
  * DELEGRETURN: Return a delegation
  */
 struct DELEGRETURN4args {
         stateid4        stateid;
 };
 struct DELEGRETURN4res {
         nfsstat4        status;
 };
 /*
  * GETATTR: Get file attributes
  */
 struct GETATTR4args {
         /* CURRENT_FH: directory or file */
         bitmap4         attr_request;
 };
 struct GETATTR4resok {
         fattr4          obj_attributes;
 };
 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:

Shepler, et al. Standards Track [Page 187] RFC 3010 NFS version 4 Protocol December 2000

         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;
 };
 /*
  * LOCK/LOCKT/LOCKU: Record lock management
  */
 struct LOCK4args {
         /* CURRENT_FH: file */
         nfs_lock_type4  locktype;
         seqid4          seqid;
         bool            reclaim;
         stateid4        stateid;
         offset4         offset;
         length4         length;
 };
 struct LOCK4denied {
         nfs_lockowner4  owner;
         offset4         offset;
         length4         length;
 };
 union LOCK4res switch (nfsstat4 status) {
  case NFS4_OK:
          stateid4       stateid;
  case NFS4ERR_DENIED:
          LOCK4denied    denied;
  default:

Shepler, et al. Standards Track [Page 188] RFC 3010 NFS version 4 Protocol December 2000

          void;
 };
 struct LOCKT4args {
         /* CURRENT_FH: file */
         nfs_lock_type4  locktype;
         nfs_lockowner4  owner;
         offset4         offset;
         length4         length;
 };
 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        stateid;
         offset4         offset;
         length4         length;
 };
 union LOCKU4res switch (nfsstat4 status) {
  case   NFS4_OK:
          stateid4       stateid;
  default:
          void;
 };
 /*
  * LOOKUP: Lookup filename
  */
 struct LOOKUP4args {
         /* CURRENT_FH: directory */
         pathname4       path;
 };
 struct LOOKUP4res {
         /* CURRENT_FH: object */
         nfsstat4        status;
 };

Shepler, et al. Standards Track [Page 189] RFC 3010 NFS version 4 Protocol December 2000

 /*
  * 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 190] RFC 3010 NFS version 4 Protocol December 2000

 /* 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 {
         pathname4       file;

Shepler, et al. Standards Track [Page 191] RFC 3010 NFS version 4 Protocol December 2000

         stateid4        delegate_stateid;
 };
 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 */
         pathname4       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 */
         uint32_t        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 */
         pathname4       file_delegate_prev;
 };
 /*
  * OPEN: Open a file, potentially receiving an open delegation
  */
 struct OPEN4args {
         open_claim4     claim;
         openflag4       openhow;
         nfs_lockowner4  owner;
         seqid4          seqid;
         uint32_t        share_access;
         uint32_t        share_deny;
 };

Shepler, et al. Standards Track [Page 192] RFC 3010 NFS version 4 Protocol December 2000

 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
  */
 /* Mandatory locking is in effect for this file. */
 const OPEN4_RESULT_MLOCK        = 0x00000001;
 /* Client must confirm open */
 const OPEN4_RESULT_CONFIRM      = 0x00000002;
 struct OPEN4resok {

Shepler, et al. Standards Track [Page 193] RFC 3010 NFS version 4 Protocol December 2000

         stateid4        stateid;        /* Stateid for open */
         change_info4    cinfo;          /* Directory Change Info */
         uint32_t        rflags;         /* Result flags */
         verifier4       open_confirm;   /* OPEN_CONFIRM verifier */
         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 OPENATTR4res {
         /* CURRENT_FH: name attr directory*/
         nfsstat4        status;
 };
 /*
  * OPEN_CONFIRM: confirm the open
  */
 struct OPEN_CONFIRM4args {
         /* CURRENT_FH: opened file */
         seqid4          seqid;
         verifier4       open_confirm;   /* OPEN_CONFIRM verifier */
 };
 struct OPEN_CONFIRM4resok {
         stateid4        stateid;
 };
 union OPEN_CONFIRM4res switch (nfsstat4 status) {
  case NFS4_OK:
          OPEN_CONFIRM4resok     resok4;
  default:
          void;
 };
 /*
  * OPEN_DOWNGRADE: downgrade the access/deny for a file
  */
 struct OPEN_DOWNGRADE4args {

Shepler, et al. Standards Track [Page 194] RFC 3010 NFS version 4 Protocol December 2000

         /* CURRENT_FH: opened file */
         stateid4        stateid;
         seqid4          seqid;
         uint32_t        share_access;
         uint32_t        share_deny;
 };
 struct OPEN_DOWNGRADE4resok {
            stateid4        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 */
         nfsstat4        status;
 };
 /*
  * READ: Read from file

Shepler, et al. Standards Track [Page 195] RFC 3010 NFS version 4 Protocol December 2000

  • /

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;
 };
 struct READDIR4resok {
         verifier4       cookieverf;
         dirlist4        reply;
 };

Shepler, et al. Standards Track [Page 196] RFC 3010 NFS version 4 Protocol December 2000

 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;
 };
 /*
  * RENAME: Rename directory entry
  */
 struct RENAME4args {
         /* SAVED_FH: source directory */
         component4      oldname;
         /* CURRENT_FH: target directory */

Shepler, et al. Standards Track [Page 197] RFC 3010 NFS version 4 Protocol December 2000

         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 {
         stateid4        stateid;
 };
 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;
 };
 /*
  * SECINFO: Obtain Available Security Mechanisms
  */
 struct SECINFO4args {

Shepler, et al. Standards Track [Page 198] RFC 3010 NFS version 4 Protocol December 2000

         /* CURRENT_FH: */
         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;
 };
 struct secinfo4 {
         uint32_t        flavor;
         /* null for AUTH_SYS, AUTH_NONE;
            contains rpcsec_gss_info for
            RPCSEC_GSS. */
         opaque          flavor_info<>;
 };
 typedef secinfo4 SECINFO4resok<>;
 union SECINFO4res switch (nfsstat4 status) {
  case NFS4_OK:
          SECINFO4resok resok4;
  default:
          void;
 };
 /*
  * SETATTR: Set attributes
  */
 struct SETATTR4args {
         /* CURRENT_FH: target object */
         stateid4        stateid;
         fattr4          obj_attributes;
 };
 struct SETATTR4res {
         nfsstat4        status;

Shepler, et al. Standards Track [Page 199] RFC 3010 NFS version 4 Protocol December 2000

         bitmap4         attrsset;
 };
 /*
  * SETCLIENTID
  */
 struct SETCLIENTID4args {
         nfs_client_id4  client;
         cb_client4      callback;
 };
 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 {
         verifier4       setclientid_confirm;
 };
 struct SETCLIENTID_CONFIRM4res {
         nfsstat4        status;
 };
 /*
  * VERIFY: Verify attributes same
  */
 struct VERIFY4args {
         /* CURRENT_FH: object */
         fattr4          obj_attributes;
 };
 struct VERIFY4res {
         nfsstat4        status;
 };
 /*
  * WRITE: Write to file
  */

Shepler, et al. Standards Track [Page 200] RFC 3010 NFS version 4 Protocol December 2000

 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;
 };
 /*
  * 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,

Shepler, et al. Standards Track [Page 201] RFC 3010 NFS version 4 Protocol December 2000

         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
 };
 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:      void;
  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;

Shepler, et al. Standards Track [Page 202] RFC 3010 NFS version 4 Protocol December 2000

  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;
 };
 union nfs_resop4 switch (nfs_opnum4 resop){
  case OP_ACCESS:        ACCESS4res opaccess;
  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;

Shepler, et al. Standards Track [Page 203] RFC 3010 NFS version 4 Protocol December 2000

  case OP_SETCLIENTID_CONFIRM:   SETCLIENTID_CONFIRM4res
                                         opsetclientid_confirm;
  case OP_VERIFY:        VERIFY4res opverify;
  case OP_WRITE:         WRITE4res opwrite;
 };
 struct COMPOUND4args {
         utf8string      tag;
         uint32_t        minorversion;
         nfs_argop4      argarray<>;
 };
 struct COMPOUND4res {
         nfsstat4 status;
         utf8string      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;

Shepler, et al. Standards Track [Page 204] RFC 3010 NFS version 4 Protocol December 2000

 };
 union CB_GETATTR4res switch (nfsstat4 status) {
  case NFS4_OK:
          CB_GETATTR4resok       resok4;
  default:
          void;
 };
 /*
  * CB_RECALL: Recall an Open Delegation
  */
 struct CB_RECALL4args {
         stateid4        stateid;
         bool            truncate;
         nfs_fh4         fh;
 };
 struct CB_RECALL4res {
         nfsstat4        status;
 };
 /*
  * Various definitions for CB_COMPOUND
  */
 enum nfs_cb_opnum4 {
         OP_CB_GETATTR           = 3,
         OP_CB_RECALL            = 4
 };
 union nfs_cb_argop4 switch (unsigned argop) {
  case OP_CB_GETATTR:    CB_GETATTR4args opcbgetattr;
  case OP_CB_RECALL:     CB_RECALL4args  opcbrecall;
 };
 union nfs_cb_resop4 switch (unsigned resop){
  case OP_CB_GETATTR:    CB_GETATTR4res  opcbgetattr;
  case OP_CB_RECALL:     CB_RECALL4res   opcbrecall;
 };
 struct CB_COMPOUND4args {
         utf8string      tag;
         uint32_t        minorversion;
         nfs_cb_argop4   argarray<>;
 };
 struct CB_COMPOUND4res {
         nfsstat4 status;

Shepler, et al. Standards Track [Page 205] RFC 3010 NFS version 4 Protocol December 2000

         utf8string      tag;
         nfs_cb_resop4   resarray<>;
 };
 /*
  * 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;
 } = 40000000;

19. Bibliography

 [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.
 [ISO10646]   "ISO/IEC 10646-1:1993. International Standard --
              Information technology -- Universal Multiple-Octet Coded
              Character Set (UCS) -- Part 1: Architecture and Basic
              Multilingual Plane."
 [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 206] RFC 3010 NFS version 4 Protocol December 2000

 [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.
 [RFC1700]    Reynolds, J. and J. Postel, "Assigned Numbers", STD 2,
              RFC 1700, October 1994.
 [RFC1813]    Callaghan, B., Pawlowski, B. and P. Staubach, "NFS
              Version 3 Protocol Specification", RFC 1813, June 1995.
 [RFC1831]    Srinivasan, R., "RPC: Remote Procedure Call Protocol
              Specification Version 2", RFC 1831, August 1995.

Shepler, et al. Standards Track [Page 207] RFC 3010 NFS version 4 Protocol December 2000

 [RFC1832]    Srinivasan, R., "XDR: External Data Representation
              Standard", RFC 1832, August 1995.
 [RFC1833]    Srinivasan, R., "Binding Protocols for ONC RPC Version
              2", RFC 1833, August 1995.
 [RFC2025]    Adams, C., "The Simple Public-Key GSS-API Mechanism
              (SPKM)", RFC 2025, October 1996.
 [RFC2054]    Callaghan, B., "WebNFS Client Specification", RFC 2054,
              October 1996.
 [RFC2055]    Callaghan, B., "WebNFS Server Specification", RFC 2055,
              October 1996.
 [RFC2078]    Linn, J., "Generic Security Service Application Program
              Interface, Version 2", RFC 2078, January 1997.
 [RFC2152]    Goldsmith, D., "UTF-7 A Mail-Safe Transformation Format
              of Unicode", RFC 2152, May 1997.
 [RFC2203]    Eisler, M., Chiu, A. and L. Ling, "RPCSEC_GSS Protocol
              Specification", RFC 2203, August 1995.
 [RFC2277]    Alvestrand, H., "IETF Policy on Character Sets and
              Languages", BCP 18, 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.
 [RFC2624]    Shepler, S., "NFS Version 4 Design Considerations", RFC
              2624, June 1999.
 [RFC2847]    Eisler, M., "LIPKEY - A Low Infrastructure Public Key
              Mechanism Using SPKM", RFC 2847, 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 208] RFC 3010 NFS version 4 Protocol December 2000

 [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].
 [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
 [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

Shepler, et al. Standards Track [Page 209] RFC 3010 NFS version 4 Protocol December 2000

20. Authors

20.1. Editor's Address

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

20.2. Authors' Addresses

 Carl Beame
 Hummingbird Ltd.
 EMail: beame@bws.com
 Brent Callaghan
 Sun Microsystems, Inc.
 901 San Antonio Road
 Palo Alto, CA 94303
 Phone: +1 650-786-5067
 EMail: brent.callaghan@sun.com
 Mike Eisler
 5565 Wilson Road
 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: +1 781-895-4949
 E-mail: dnoveck@netapp.com

Shepler, et al. Standards Track [Page 210] RFC 3010 NFS version 4 Protocol December 2000

 David Robinson
 Sun Microsystems, Inc.
 901 San Antonio Road
 Palo Alto, CA 94303
 Phone: +1 650-786-5088
 EMail: david.robinson@sun.com
 Robert Thurlow
 Sun Microsystems, Inc.
 901 San Antonio Road
 Palo Alto, CA 94303
 Phone: +1 650-786-5096
 EMail: robert.thurlow@sun.com

20.3. Acknowledgements

 The author thanks and acknowledges:
 Neil Brown for his extensive review and comments of various drafts.

Shepler, et al. Standards Track [Page 211] RFC 3010 NFS version 4 Protocol December 2000

21. Full Copyright Statement

 Copyright (C) The Internet Society (2000).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

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

Shepler, et al. Standards Track [Page 212]

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