path: root/man2/fanotify_mark.2

.\" Copyright (C) 2013,  Heinrich Schuchardt <xypron.glpk@gmx.de>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.TH fanotify_mark 2 2023-03-30 "Linux man-pages 6.05.01"
.SH NAME
fanotify_mark \- add, remove, or modify an fanotify mark on a filesystem
object
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <sys/fanotify.h>
.PP
.BI "int fanotify_mark(int " fanotify_fd ", unsigned int " flags ,
.BI "                  uint64_t " mask ", int " dirfd ,
.BI "                  const char *_Nullable " pathname );
.fi
.SH DESCRIPTION
For an overview of the fanotify API, see
.BR fanotify (7).
.PP
.BR fanotify_mark ()
adds, removes, or modifies an fanotify mark on a filesystem object.
The caller must have read permission on the filesystem object that
is to be marked.
.PP
The
.I fanotify_fd
argument is a file descriptor returned by
.BR fanotify_init (2).
.PP
.I flags
is a bit mask describing the modification to perform.
It must include exactly one of the following values:
.TP
.B FAN_MARK_ADD
The events in
.I mask
will be added to the mark mask (or to the ignore mask).
.I mask
must be nonempty or the error
.B EINVAL
will occur.
.TP
.B FAN_MARK_REMOVE
The events in argument
.I mask
will be removed from the mark mask (or from the ignore mask).
.I mask
must be nonempty or the error
.B EINVAL
will occur.
.TP
.B FAN_MARK_FLUSH
Remove either all marks for filesystems, all marks for mounts, or all
marks for directories and files from the fanotify group.
If
.I flags
contains
.BR FAN_MARK_MOUNT ,
all marks for mounts are removed from the group.
If
.I flags
contains
.BR FAN_MARK_FILESYSTEM ,
all marks for filesystems are removed from the group.
Otherwise, all marks for directories and files are removed.
No flag other than, and at most one of, the flags
.B FAN_MARK_MOUNT
or
.B FAN_MARK_FILESYSTEM
can be used in conjunction with
.BR FAN_MARK_FLUSH .
.I mask
is ignored.
.PP
If none of the values above is specified, or more than one is specified,
the call fails with the error
.BR EINVAL .
.PP
In addition,
zero or more of the following values may be ORed into
.IR flags :
.TP
.B FAN_MARK_DONT_FOLLOW
If
.I pathname
is a symbolic link, mark the link itself, rather than the file to which it
refers.
(By default,
.BR fanotify_mark ()
dereferences
.I pathname
if it is a symbolic link.)
.TP
.B FAN_MARK_ONLYDIR
If the filesystem object to be marked is not a directory, the error
.B ENOTDIR
shall be raised.
.TP
.B FAN_MARK_MOUNT
Mark the mount specified by
.IR pathname .
If
.I pathname
is not itself a mount point, the mount containing
.I pathname
will be marked.
All directories, subdirectories, and the contained files of the mount
will be monitored.
The events which require that filesystem objects are identified by file handles,
such as
.BR FAN_CREATE ,
.BR FAN_ATTRIB ,
.BR FAN_MOVE ,
and
.BR FAN_DELETE_SELF ,
cannot be provided as a
.I mask
when
.I flags
contains
.BR FAN_MARK_MOUNT .
Attempting to do so will result in the error
.B EINVAL
being returned.
Use of this flag requires the
.B CAP_SYS_ADMIN
capability.
.TP
.BR FAN_MARK_FILESYSTEM " (since Linux 4.20)"
.\" commit d54f4fba889b205e9cd8239182ca5d27d0ac3bc2
Mark the filesystem specified by
.IR pathname .
The filesystem containing
.I pathname
will be marked.
All the contained files and directories of the filesystem from any mount
point will be monitored.
Use of this flag requires the
.B CAP_SYS_ADMIN
capability.
.TP
.B FAN_MARK_IGNORED_MASK
The events in
.I mask
shall be added to or removed from the ignore mask.
Note that the flags
.BR FAN_ONDIR ,
and
.B FAN_EVENT_ON_CHILD
have no effect when provided with this flag.
The effect of setting the flags
.BR FAN_ONDIR ,
and
.B FAN_EVENT_ON_CHILD
in the mark mask
on the events that are set in the ignore mask
is undefined and depends on the Linux kernel version.
Specifically, prior to Linux 5.9,
.\" commit 497b0c5a7c0688c1b100a9c2e267337f677c198e
setting a mark mask on a file
and a mark with ignore mask on its parent directory
would not result in ignoring events on the file,
regardless of the
.B FAN_EVENT_ON_CHILD
flag in the parent directory's mark mask.
When the ignore mask is updated with the
.B FAN_MARK_IGNORED_MASK
flag
on a mark that was previously updated with the
.B FAN_MARK_IGNORE
flag,
the update fails with
.B EEXIST
error.
.TP
.BR FAN_MARK_IGNORE " (since Linux 6.0)"
.\" commit e252f2ed1c8c6c3884ab5dd34e003ed21f1fe6e0
This flag has a similar effect as setting the
.B FAN_MARK_IGNORED_MASK
flag.
The events in
.I mask
shall be added to or removed from the ignore mask.
Unlike the
.B FAN_MARK_IGNORED_MASK
flag,
this flag also has the effect that the
.BR FAN_ONDIR ,
and
.B FAN_EVENT_ON_CHILD
flags take effect on the ignore mask.
Specifically, unless the
.B FAN_ONDIR
flag is set with
.BR FAN_MARK_IGNORE ,
events on directories will not be ignored.
If the flag
.B FAN_EVENT_ON_CHILD
is set with
.BR FAN_MARK_IGNORE ,
events on children will be ignored.
For example,
a mark on a directory with combination of
a mask with
.B FAN_CREATE
event
and
.B FAN_ONDIR
flag
and an ignore mask with
.B FAN_CREATE
event
and without
.B FAN_ONDIR
flag,
will result in getting only
the events for creation of sub-directories.
When using the
.B FAN_MARK_IGNORE
flag to add to an ignore mask
of a mount,
filesystem,
or directory inode mark,
the
.B FAN_MARK_IGNORED_SURV_MODIFY
flag must be specified.
Failure to do so will results with
.B EINVAL
or
.B EISDIR
error.
.TP
.B FAN_MARK_IGNORED_SURV_MODIFY
The ignore mask shall survive modify events.
If this flag is not set,
the ignore mask is cleared when a modify event occurs
on the marked object.
Omitting this flag is typically used to suppress events
(e.g.,
.BR FAN_OPEN )
for a specific file,
until that specific file's content has been modified.
It is far less useful to suppress events
on an entire filesystem,
or mount,
or on all files inside a directory,
until some file's content has been modified.
For this reason,
the
.B FAN_MARK_IGNORE
flag requires the
.B FAN_MARK_IGNORED_SURV_MODIFY
flag on a mount,
filesystem,
or directory inode mark.
This flag cannot be removed from a mark once set.
When the ignore mask is updated without this flag
on a mark that was previously updated with the
.B FAN_MARK_IGNORE
and
.B FAN_MARK_IGNORED_SURV_MODIFY
flags,
the update fails with
.B EEXIST
error.
.TP
.B FAN_MARK_IGNORE_SURV
This is a synonym for
.RB ( FAN_MARK_IGNORE | FAN_MARK_IGNORED_SURV_MODIFY ).
.TP
.BR FAN_MARK_EVICTABLE " (since Linux 5.19)"
.\" commit 5f9d3bd520261fd7a850818c71809fd580e0f30c
When an inode mark is created with this flag,
the inode object will not be pinned to the inode cache,
therefore,
allowing the inode object to be evicted from the inode cache
when the memory pressure on the system is high.
The eviction of the inode object
results in the evictable mark also being lost.
When the mask of an evictable inode mark is updated
without using the
.B FAN_MARK_EVICATBLE
flag,
the marked inode is pinned to inode cache
and the mark is no longer evictable.
When the mask of a non-evictable inode mark is updated
with the
.B FAN_MARK_EVICTABLE
flag,
the inode mark remains non-evictable
and the update fails with
.B EEXIST
error.
Mounts and filesystems are not evictable objects,
therefore,
an attempt to create a mount mark or a filesystem mark
with the
.B FAN_MARK_EVICTABLE
flag,
will result in the error
.BR EINVAL .
For example,
inode marks can be used in combination with mount marks
to reduce the amount of events from noninteresting paths.
The event listener reads events,
checks if the path reported in the event is of interest,
and if it is not,
the listener sets a mark with an ignore mask on the directory.
Evictable inode marks allow using this method for a large number of directories
without the concern of pinning all inodes and exhausting the system's memory.
.PP
.I mask
defines which events shall be listened for (or which shall be ignored).
It is a bit mask composed of the following values:
.TP
.B FAN_ACCESS
Create an event when a file or directory (but see BUGS) is accessed (read).
.TP
.B FAN_MODIFY
Create an event when a file is modified (write).
.TP
.B FAN_CLOSE_WRITE
Create an event when a writable file is closed.
.TP
.B FAN_CLOSE_NOWRITE
Create an event when a read-only file or directory is closed.
.TP
.B FAN_OPEN
Create an event when a file or directory is opened.
.TP
.BR FAN_OPEN_EXEC " (since Linux 5.0)"
.\" commit 9b076f1c0f4869b838a1b7aa0edb5664d47ec8aa
Create an event when a file is opened with the intent to be executed.
See NOTES for additional details.
.TP
.BR FAN_ATTRIB " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
Create an event when the metadata for a file or directory has changed.
An fanotify group that identifies filesystem objects by file handles
is required.
.TP
.BR FAN_CREATE " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
Create an event when a file or directory has been created in a marked
parent directory.
An fanotify group that identifies filesystem objects by file handles
is required.
.TP
.BR FAN_DELETE " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
Create an event when a file or directory has been deleted in a marked
parent directory.
An fanotify group that identifies filesystem objects by file handles
is required.
.TP
.BR FAN_DELETE_SELF " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
Create an event when a marked file or directory itself is deleted.
An fanotify group that identifies filesystem objects by file handles
is required.
.TP
.BR FAN_FS_ERROR " (since Linux 5.16)"
.\" commit 9709bd548f11a092d124698118013f66e1740f9b
Create an event when a filesystem error
leading to inconsistent filesystem metadata is detected.
An additional information record of type
.B FAN_EVENT_INFO_TYPE_ERROR
is returned for each event in the read buffer.
An fanotify group that identifies filesystem objects by file handles
is required.
.IP
Events of such type are dependent on support
from the underlying filesystem.
At the time of writing,
only the
.B ext4
filesystem reports
.B FAN_FS_ERROR
events.
.IP
See
.BR fanotify (7)
for additional details.
.TP
.BR FAN_MOVED_FROM " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
Create an event when a file or directory has been moved from a marked
parent directory.
An fanotify group that identifies filesystem objects by file handles
is required.
.TP
.BR FAN_MOVED_TO " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
Create an event when a file or directory has been moved to a marked parent
directory.
An fanotify group that identifies filesystem objects by file handles
is required.
.TP
.BR FAN_RENAME " (since Linux 5.17)"
.\" commit 8cc3b1ccd930fe6971e1527f0c4f1bdc8cb56026
This event contains the same information provided by events
.B FAN_MOVED_FROM
and
.BR FAN_MOVED_TO ,
however is represented by a single event with up to two information records.
An fanotify group that identifies filesystem objects by file handles
is required.
If the filesystem object to be marked is not a directory, the error
.B ENOTDIR
shall be raised.
.TP
.BR FAN_MOVE_SELF " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
Create an event when a marked file or directory itself has been moved.
An fanotify group that identifies filesystem objects by file handles
is required.
.TP
.B FAN_OPEN_PERM
Create an event when a permission to open a file or directory is requested.
An fanotify file descriptor created with
.B FAN_CLASS_PRE_CONTENT
or
.B FAN_CLASS_CONTENT
is required.
.TP
.BR FAN_OPEN_EXEC_PERM " (since Linux 5.0)"
.\" commit 66917a3130f218dcef9eeab4fd11a71cd00cd7c9
Create an event when a permission to open a file for execution is
requested.
An fanotify file descriptor created with
.B FAN_CLASS_PRE_CONTENT
or
.B FAN_CLASS_CONTENT
is required.
See NOTES for additional details.
.TP
.B FAN_ACCESS_PERM
Create an event when a permission to read a file or directory is requested.
An fanotify file descriptor created with
.B FAN_CLASS_PRE_CONTENT
or
.B FAN_CLASS_CONTENT
is required.
.TP
.B FAN_ONDIR
Create events for directories\[em]for example, when
.BR opendir (3),
.BR readdir (3)
(but see BUGS), and
.BR closedir (3)
are called.
Without this flag, events are created only for files.
In the context of directory entry events, such as
.BR FAN_CREATE ,
.BR FAN_DELETE ,
.BR FAN_MOVED_FROM ,
and
.BR FAN_MOVED_TO ,
specifying the flag
.B FAN_ONDIR
is required in order to create events when subdirectory entries are
modified (i.e.,
.BR mkdir (2)/
.BR rmdir (2)).
.TP
.B FAN_EVENT_ON_CHILD
Events for the immediate children of marked directories shall be created.
The flag has no effect when marking mounts and filesystems.
Note that events are not generated for children of the subdirectories
of marked directories.
More specifically, the directory entry modification events
.BR FAN_CREATE ,
.BR FAN_DELETE ,
.BR FAN_MOVED_FROM ,
and
.B FAN_MOVED_TO
are not generated for any entry modifications performed inside subdirectories
of marked directories.
Note that the events
.B FAN_DELETE_SELF
and
.B FAN_MOVE_SELF
are not generated for children of marked directories.
To monitor complete directory trees it is necessary to mark the relevant
mount or filesystem.
.PP
The following composed values are defined:
.TP
.B FAN_CLOSE
A file is closed
.RB ( FAN_CLOSE_WRITE | FAN_CLOSE_NOWRITE ).
.TP
.B FAN_MOVE
A file or directory has been moved
.RB ( FAN_MOVED_FROM | FAN_MOVED_TO ).
.PP
The filesystem object to be marked is determined by the file descriptor
.I dirfd
and the pathname specified in
.IR pathname :
.IP \[bu] 3
If
.I pathname
is NULL,
.I dirfd
defines the filesystem object to be marked.
.IP \[bu]
If
.I pathname
is NULL, and
.I dirfd
takes the special value
.BR AT_FDCWD ,
the current working directory is to be marked.
.IP \[bu]
If
.I pathname
is absolute, it defines the filesystem object to be marked, and
.I dirfd
is ignored.
.IP \[bu]
If
.I pathname
is relative, and
.I dirfd
does not have the value
.BR AT_FDCWD ,
then the filesystem object to be marked is determined by interpreting
.I pathname
relative the directory referred to by
.IR dirfd .
.IP \[bu]
If
.I pathname
is relative, and
.I dirfd
has the value
.BR AT_FDCWD ,
then the filesystem object to be marked is determined by interpreting
.I pathname
relative to the current working directory.
(See
.BR openat (2)
for an explanation of why the
.I dirfd
argument is useful.)
.SH RETURN VALUE
On success,
.BR fanotify_mark ()
returns 0.
On error, \-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EBADF
An invalid file descriptor was passed in
.IR fanotify_fd .
.TP
.B EBADF
.I pathname
is relative but
.I dirfd
is neither
.B AT_FDCWD
nor a valid file descriptor.
.TP
.B EEXIST
The filesystem object indicated by
.I dirfd
and
.I pathname
has a mark that was updated without the
.B FAN_MARK_EVICTABLE
flag,
and the user attempted to update the mark with
.B FAN_MARK_EVICTABLE
flag.
.TP
.B EEXIST
The filesystem object indicated by
.I dirfd
and
.I pathname
has a mark that was updated with the
.B FAN_MARK_IGNORE
flag,
and the user attempted to update the mark with
.B FAN_MARK_IGNORED_MASK
flag.
.TP
.B EEXIST
The filesystem object indicated by
.I dirfd
and
.I pathname
has a mark that was updated with the
.B FAN_MARK_IGNORE
and
.B FAN_MARK_IGNORED_SURV_MODIFY
flags,
and the user attempted to update the mark only with
.B FAN_MARK_IGNORE
flag.
.TP
.B EINVAL
An invalid value was passed in
.I flags
or
.IR mask ,
or
.I fanotify_fd
was not an fanotify file descriptor.
.TP
.B EINVAL
The fanotify file descriptor was opened with
.B FAN_CLASS_NOTIF
or the fanotify group identifies filesystem objects by file handles
and mask contains a flag for permission events
.RB ( FAN_OPEN_PERM
or
.BR FAN_ACCESS_PERM ).
.TP
.B EINVAL
The group was initialized without
.B FAN_REPORT_FID
but one or more event types specified in the
.I mask
require it.
.TP
.B EINVAL
.I flags
contains
.BR FAN_MARK_IGNORE ,
and either
.B FAN_MARK_MOUNT
or
.BR FAN_MARK_FILESYSTEM ,
but does not contain
.BR FAN_MARK_IGNORED_SURV_MODIFY .
.TP
.B EISDIR
.I flags
contains
.BR FAN_MARK_IGNORE ,
but does not contain
.BR FAN_MARK_IGNORED_SURV_MODIFY ,
and
.I dirfd
and
.I pathname
specify a directory.
.TP
.B ENODEV
The filesystem object indicated by
.I dirfd
and
.I pathname
is not associated with a filesystem that supports
.I fsid
(e.g.,
.BR fuse (4)).
.BR tmpfs (5)
did not support
.I fsid
prior to Linux 5.13.
.\" commit 59cda49ecf6c9a32fae4942420701b6e087204f6
This error can be returned only with an fanotify group that identifies
filesystem objects by file handles.
.TP
.B ENOENT
The filesystem object indicated by
.I dirfd
and
.I pathname
does not exist.
This error also occurs when trying to remove a mark from an object
which is not marked.
.TP
.B ENOMEM
The necessary memory could not be allocated.
.TP
.B ENOSPC
The number of marks for this user exceeds the limit and the
.B FAN_UNLIMITED_MARKS
flag was not specified when the fanotify file descriptor was created with
.BR fanotify_init (2).
See
.BR fanotify (7)
for details about this limit.
.TP
.B ENOSYS
This kernel does not implement
.BR fanotify_mark ().
The fanotify API is available only if the kernel was configured with
.BR CONFIG_FANOTIFY .
.TP
.B ENOTDIR
.I flags
contains
.BR FAN_MARK_ONLYDIR ,
and
.I dirfd
and
.I pathname
do not specify a directory.
.TP
.B ENOTDIR
.I mask
contains
.BR FAN_RENAME ,
and
.I dirfd
and
.I pathname
do not specify a directory.
.TP
.B ENOTDIR
.I flags
contains
.BR FAN_MARK_IGNORE ,
or the fanotify group was initialized with flag
.BR FAN_REPORT_TARGET_FID ,
and
.I mask
contains directory entry modification events
(e.g.,
.BR FAN_CREATE ,
.BR FAN_DELETE ),
or directory event flags
(e.g.,
.BR FAN_ONDIR ,
.BR FAN_EVENT_ON_CHILD ),
and
.I dirfd
and
.I pathname
do not specify a directory.
.TP
.B EOPNOTSUPP
The object indicated by
.I pathname
is associated with a filesystem that does not support the encoding of file
handles.
This error can be returned only with an fanotify group that identifies
filesystem objects by file handles.
.TP
.B EPERM
The operation is not permitted because the caller lacks a required capability.
.TP
.B EXDEV
The filesystem object indicated by
.I pathname
resides within a filesystem subvolume (e.g.,
.BR btrfs (5))
which uses a different
.I fsid
than its root superblock.
This error can be returned only with an fanotify group that identifies
filesystem objects by file handles.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 2.6.37.
.\" was introduced in Linux 2.6.36 and enabled in Linux 2.6.37.
.SH NOTES
.SS FAN_OPEN_EXEC and FAN_OPEN_EXEC_PERM
When using either
.B FAN_OPEN_EXEC
or
.B FAN_OPEN_EXEC_PERM
within the
.IR mask ,
events of these types will be returned only when the direct execution of a
program occurs.
More specifically, this means that events of these types will be generated
for files that are opened using
.BR execve (2),
.BR execveat (2),
or
.BR uselib (2).
Events of these types will not be raised in the situation where an
interpreter is passed (or reads) a file for interpretation.
.PP
Additionally, if a mark has also been placed on the Linux dynamic
linker, a user should also expect to receive an event for it when
an ELF object has been successfully opened using
.BR execve (2)
or
.BR execveat (2).
.PP
For example, if the following ELF binary were to be invoked and a
.B FAN_OPEN_EXEC
mark has been placed on /:
.PP
.in +4n
.EX
$ /bin/echo foo
.EE
.in
.PP
The listening application in this case would receive
.B FAN_OPEN_EXEC
events for both the ELF binary and interpreter, respectively:
.PP
.in +4n
.EX
/bin/echo
/lib64/ld\-linux\-x86\-64.so.2
.EE
.in
.SH BUGS
The following bugs were present in before Linux 3.16:
.IP \[bu] 3
.\" Fixed by commit 0a8dd2db579f7a0ac7033d6b857c3d5dbaa77563
If
.I flags
contains
.BR FAN_MARK_FLUSH ,
.IR dirfd ,
and
.I pathname
must specify a valid filesystem object, even though this object is not used.
.IP \[bu]
.\" Fixed by commit d4c7cf6cffb1bc711a833b5e304ba5bcfe76398b
.BR readdir (2)
does not generate a
.B FAN_ACCESS
event.
.IP \[bu]
.\" Fixed by commit cc299a98eb13a9853675a9cbb90b30b4011e1406
If
.BR fanotify_mark ()
is called with
.BR FAN_MARK_FLUSH ,
.I flags
is not checked for invalid values.
.SH SEE ALSO
.BR fanotify_init (2),
.BR fanotify (7)