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man:fanotify_init

FANOTIFY_INIT(2) Linux Programmer's Manual FANOTIFY_INIT(2)

NAME

     fanotify_init - create and initialize fanotify group

SYNOPSIS

     #include <fcntl.h>
     #include <sys/fanotify.h>
     int fanotify_init(unsigned int flags, unsigned int event_f_flags);

DESCRIPTION

     For an overview of the fanotify API, see fanotify(7).
     fanotify_init()  initializes  a  new  fanotify group and returns a file
     descriptor for the event queue associated with the group.
     The file descriptor is used in calls to fanotify_mark(2) to specify the
     files,  directories, and mounts for which fanotify events shall be cre-
     ated.  These events are received by reading from the  file  descriptor.
     Some  events  are  only  informative,  indicating  that a file has been
     accessed.  Other events can be used to determine whether another appli-
     cation  is  permitted  to  access  a  file or directory.  Permission to
     access filesystem objects is granted by writing to the file descriptor.
     Multiple  programs may be using the fanotify interface at the same time
     to monitor the same files.
     In the current implementation, the number of fanotify groups  per  user
     is limited to 128.  This limit cannot be overridden.
     Calling  fanotify_init()  requires  the CAP_SYS_ADMIN capability.  This
     constraint might be relaxed in future versions of the API.   Therefore,
     certain additional capability checks have been implemented as indicated
     below.
     The flags argument contains a multi-bit field defining the notification
     class of the listening application and further single bit fields speci-
     fying the behavior of the file descriptor.
     If multiple listeners for permission  events  exist,  the  notification
     class  is used to establish the sequence in which the listeners receive
     the events.
     Only one of the following notification  classes  may  be  specified  in
     flags:
     FAN_CLASS_PRE_CONTENT
            This  value  allows  the receipt of events notifying that a file
            has been accessed and events for permission decisions if a  file
            may  be  accessed.  It is intended for event listeners that need
            to access files before they  contain  their  final  data.   This
            notification  class  might  be used by hierarchical storage man-
            agers, for example.
     FAN_CLASS_CONTENT
            This value allows the receipt of events notifying  that  a  file
            has  been accessed and events for permission decisions if a file
            may be accessed.  It is intended for event listeners  that  need
            to  access  files when they already contain their final content.
            This notification class might be used by malware detection  pro-
            grams, for example.
     FAN_CLASS_NOTIF
            This  is  the  default value.  It does not need to be specified.
            This value only allows the receipt of events  notifying  that  a
            file has been accessed.  Permission decisions before the file is
            accessed are not possible.
     Listeners with different notification classes will  receive  events  in
     the  order  FAN_CLASS_PRE_CONTENT,  FAN_CLASS_CONTENT, FAN_CLASS_NOTIF.
     The order of notification for listeners in the same notification  class
     is undefined.
     The following bits can additionally be set in flags:
     FAN_CLOEXEC
            Set the close-on-exec flag (FD_CLOEXEC) on the new file descrip-
            tor.  See the description of the O_CLOEXEC flag in open(2).
     FAN_NONBLOCK
            Enable the nonblocking flag (O_NONBLOCK) for the  file  descrip-
            tor.  Reading from the file descriptor will not block.  Instead,
            if no data is available, read(2) fails with the error EAGAIN.
     FAN_UNLIMITED_QUEUE
            Remove the limit of 16384 events for the event  queue.   Use  of
            this flag requires the CAP_SYS_ADMIN capability.
     FAN_UNLIMITED_MARKS
            Remove  the  limit of 8192 marks.  Use of this flag requires the
            CAP_SYS_ADMIN capability.
     The event_f_flags argument defines the file status flags that  will  be
     set on the open file descriptions that are created for fanotify events.
     For details of these flags, see the description of the flags values  in
     open(2).  event_f_flags includes a multi-bit field for the access mode.
     This field can take the following values:
     O_RDONLY
            This value allows only read access.
     O_WRONLY
            This value allows only write access.
     O_RDWR This value allows read and write access.
     Additional bits can be set in event_f_flags.  The  most  useful  values
     are:
     O_LARGEFILE
            Enable  support  for  files exceeding 2 GB.  Failing to set this
            flag will result in an EOVERFLOW error when  trying  to  open  a
            large  file  which is monitored by an fanotify group on a 32-bit
            system.
     O_CLOEXEC (since Linux 3.18)
            Enable the close-on-exec flag for the file descriptor.  See  the
            description  of  the  O_CLOEXEC  flag in open(2) for reasons why
            this may be useful.
     The following are also allowable: O_APPEND, O_DSYNC, O_NOATIME,  O_NON-
     BLOCK,  and  O_SYNC.  Specifying any other flag in event_f_flags yields
     the error EINVAL (but see BUGS).

RETURN VALUE

     On success, fanotify_init() returns a new file descriptor.   On  error,
     -1 is returned, and errno is set to indicate the error.

ERRORS

     EINVAL An   invalid   value  was  passed  in  flags  or  event_f_flags.
            FAN_ALL_INIT_FLAGS defines all allowable bits for flags.
     EMFILE The number of fanotify groups for this user exceeds 128.
     EMFILE The per-process limit on the number of open file descriptors has
            been reached.
     ENOMEM The allocation of memory for the notification group failed.
     ENOSYS This  kernel  does  not implement fanotify_init().  The fanotify
            API is available only if the kernel  was  configured  with  CON-
            FIG_FANOTIFY.
     EPERM  The  operation  is  not  permitted  because the caller lacks the
            CAP_SYS_ADMIN capability.

VERSIONS

     fanotify_init() was introduced in version 2.6.36 of  the  Linux  kernel
     and enabled in version 2.6.37.

CONFORMING TO

     This system call is Linux-specific.

BUGS

     The following bug was present in Linux kernels before version 3.18:
  • The O_CLOEXEC is ignored when passed in event_f_flags.
     The following bug was present in Linux kernels before version 3.14:
  • The event_f_flags argument is not checked for invalid flags. Flags

that are intended only for internal use, such as FMODE_EXEC, can be

        set,  and will consequently be set for the file descriptors returned
        when reading from the fanotify file descriptor.

SEE ALSO

     fanotify_mark(2), fanotify(7)

COLOPHON

     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at
     https://www.kernel.org/doc/man-pages/.

Linux 2017-09-15 FANOTIFY_INIT(2)

/data/webs/external/dokuwiki/data/pages/man/fanotify_init.txt · Last modified: 2019/05/17 09:32 by 127.0.0.1

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