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 4.15 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)
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