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 de-
       scriptor for the event queue associated with the group.

       The file descriptor is used in calls to fanotify_mark(2) to specify the
       files,  directories,  mounts  or  filesystems for which fanotify events
       shall be created.  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  an-
       other  application is permitted to access a file or directory.  Permis-
       sion to access filesystem objects is granted by writing to the file de-
       scriptor.

       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  no-
              tification class might be used by hierarchical storage managers,
              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_REPORT_FID (since Linux 5.1)
              This value allows the receipt of events which contain additional
              information about the underlying filesystem object correlated to
              an  event.  An additional structure encapsulates the information
              about the object and is included  alongside  the  generic  event
              metadata  structure.  The file descriptor that is used to repre-
              sent the object correlated to an event  is  instead  substituted
              with  a  file  handle.  It is intended for applications that may
              find the use of a file handle to identify an object  more  suit-
              able  than  a file descriptor.  Additionally, it may be used for
              applications that are interested in directory entry events, such
              as FAN_CREATE, FAN_ATTRIB, FAN_MOVE, and FAN_DELETE for example.
              Note that the use of directory modification events are not  sup-
              ported when monitoring a mount point.  The use of FAN_CLASS_CON-
              TENT or FAN_CLASS_PRE_CONTENT is not permitted  with  this  flag
              and  will result in the error EINVAL.  See fanotify(7) for addi-
              tional information.

       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.

       FAN_REPORT_TID (since Linux 4.20)
              Report  thread  ID  (TID) instead of process ID (PID) in the pid
              field of the struct fanotify_event_metadata supplied to  read(2)
              (see fanotify(7)).

       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  (deprecated since Linux kernel version 4.20)
              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 5.05 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                             2019-08-02                  FANOTIFY_INIT(2)