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       fanotify_init - create and initialize fanotify group


       #include <fcntl.h>
       #include <sys/fanotify.h>

       int fanotify_init(unsigned int flags, unsigned int event_f_flags);


       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
       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
       another  application  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

       The flags argument contains a multi-bit field defining the notification
       class  of  the  listening  application  and  further  single bit fields
       specifying 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

              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
              managers, for example.

              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
              programs, for example.

              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 of notification for listeners in the same notification  class
       is undefined.

       The following bits can additionally be set in flags:

              Set   the  close-on-exec  flag  (FD_CLOEXEC)  on  the  new  file
              descriptor.  See  the  description  of  the  O_CLOEXEC  flag  in

              Enable   the   nonblocking   flag   (O_NONBLOCK)  for  the  file
              descriptor.  Reading from the file descriptor  will  not  block.
              Instead,  if  no  data  is available, read(2) will fail with the
              error EAGAIN.

              Remove the limit of 16384 events for the event  queue.   Use  of
              this flag requires the CAP_SYS_ADMIN capability.

              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:

              This value allows only read access.

              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

              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

              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_NONBLOCK,  and  O_SYNC.   Specifying  any other flag in event_f_flags
       yields the error EINVAL (but see BUGS).


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


       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.

       The per-process limit on the number of open file descriptors  has  been

       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

       EPERM  The  operation  is  not  permitted  because the caller lacks the
              CAP_SYS_ADMIN capability.


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


       This system call is Linux-specific.


       As of Linux 3.17, the following bug exists:

       *  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.


       fanotify_mark(2), fanotify(7)


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