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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | BUGS | SEE ALSO | COLOPHON |
FANOTIFY_INIT(2) Linux Programmer's Manual FANOTIFY_INIT(2)
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 below.
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
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
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 programs, 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
descriptor. See the description of the O_CLOEXEC flag in
open(2).
FAN_NONBLOCK
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.
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_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
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
CONFIG_FANOTIFY.
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.
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.
fanotify_mark(2), fanotify(7)
This page is part of release 4.12 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 2016-10-08 FANOTIFY_INIT(2)
Pages that refer to this page: fanotify_mark(2), syscalls(2), proc(5), fanotify(7)