Ubuntu Manpage: fanotify_mark - add, remove, or modify an fanotify mark on a filesystem object

NAME

       fanotify_mark - add, remove, or modify an fanotify mark on a filesystem object

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sys/fanotify.h>

       int fanotify_mark(int fanotify_fd, unsigned int flags,
                         uint64_t mask, int dirfd,
                         const char *_Nullable pathname);

DESCRIPTION

For an overview of the fanotify API, see fanotify(7).

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.

The fanotify_fd argument is a file descriptor returned by fanotify_init(2).

flags is a bit mask describing the modification to perform. It must include exactly one
of the following values:

FAN_MARK_ADD
The events in mask will be added to the mark mask (or to the ignore mask). mask
must be nonempty or the error EINVAL will occur.

FAN_MARK_REMOVE
The events in argument mask will be removed from the mark mask (or from the ignore
mask). mask must be nonempty or the error EINVAL will occur.

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 flags contains FAN_MARK_MOUNT,
all marks for mounts are removed from the group. If flags contains
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 FAN_MARK_MOUNT or FAN_MARK_FILESYSTEM can be used in
conjunction with FAN_MARK_FLUSH. mask is ignored.

If none of the values above is specified, or more than one is specified, the call fails
with the error EINVAL.

In addition, zero or more of the following values may be ORed into flags:

FAN_MARK_DONT_FOLLOW
If pathname is a symbolic link, mark the link itself, rather than the file to which
it refers. (By default, fanotify_mark() dereferences pathname if it is a symbolic
link.)

FAN_MARK_ONLYDIR
If the filesystem object to be marked is not a directory, the error ENOTDIR shall
be raised.

FAN_MARK_MOUNT
Mark the mount specified by pathname. If pathname is not itself a mount point, the
mount containing 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 FAN_CREATE, FAN_ATTRIB,
FAN_MOVE, and FAN_DELETE_SELF, cannot be provided as a mask when flags contains
FAN_MARK_MOUNT. Attempting to do so will result in the error EINVAL being
returned. Use of this flag requires the CAP_SYS_ADMIN capability.

FAN_MARK_FILESYSTEM (since Linux 4.20)
Mark the filesystem specified by pathname. The filesystem containing 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 CAP_SYS_ADMIN
capability.

FAN_MARK_IGNORED_MASK
The events in mask shall be added to or removed from the ignore mask. Note that
the flags FAN_ONDIR, and FAN_EVENT_ON_CHILD have no effect when provided with this
flag. The effect of setting the flags FAN_ONDIR, and 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, 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 FAN_EVENT_ON_CHILD flag in the
parent directory's mark mask. When the ignore mask is updated with the
FAN_MARK_IGNORED_MASK flag on a mark that was previously updated with the
FAN_MARK_IGNORE flag, the update fails with EEXIST error.

FAN_MARK_IGNORE (since Linux 6.0)
This flag has a similar effect as setting the FAN_MARK_IGNORED_MASK flag. The
events in mask shall be added to or removed from the ignore mask. Unlike the
FAN_MARK_IGNORED_MASK flag, this flag also has the effect that the FAN_ONDIR, and
FAN_EVENT_ON_CHILD flags take effect on the ignore mask. Specifically, unless the
FAN_ONDIR flag is set with FAN_MARK_IGNORE, events on directories will not be
ignored. If the flag FAN_EVENT_ON_CHILD is set with FAN_MARK_IGNORE, events on
children will be ignored. For example, a mark on a directory with combination of a
mask with FAN_CREATE event and FAN_ONDIR flag and an ignore mask with FAN_CREATE
event and without FAN_ONDIR flag, will result in getting only the events for
creation of sub-directories. When using the FAN_MARK_IGNORE flag to add to an
ignore mask of a mount, filesystem, or directory inode mark, the
FAN_MARK_IGNORED_SURV_MODIFY flag must be specified. Failure to do so will results
with EINVAL or EISDIR error.

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., 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
FAN_MARK_IGNORE flag requires the 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 FAN_MARK_IGNORE and FAN_MARK_IGNORED_SURV_MODIFY flags,
the update fails with EEXIST error.

FAN_MARK_IGNORE_SURV
This is a synonym for (FAN_MARK_IGNORE|FAN_MARK_IGNORED_SURV_MODIFY).

FAN_MARK_EVICTABLE (since Linux 5.19)
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 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 FAN_MARK_EVICTABLE flag,
the inode mark remains non-evictable and the update fails with EEXIST error.
Mounts and filesystems are not evictable objects, therefore, an attempt to create a
mount mark or a filesystem mark with the FAN_MARK_EVICTABLE flag, will result in
the error 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.

mask defines which events shall be listened for (or which shall be ignored). It is a bit
mask composed of the following values:

FAN_ACCESS
Create an event when a file or directory (but see BUGS) is accessed (read).

FAN_MODIFY
Create an event when a file is modified (write).

FAN_CLOSE_WRITE
Create an event when a writable file is closed.

FAN_CLOSE_NOWRITE
Create an event when a read-only file or directory is closed.

FAN_OPEN
Create an event when a file or directory is opened.

FAN_OPEN_EXEC (since Linux 5.0)
Create an event when a file is opened with the intent to be executed. See NOTES
for additional details.

FAN_ATTRIB (since Linux 5.1)
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.

FAN_CREATE (since Linux 5.1)
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.

FAN_DELETE (since Linux 5.1)
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.

FAN_DELETE_SELF (since Linux 5.1)
Create an event when a marked file or directory itself is deleted. An fanotify
group that identifies filesystem objects by file handles is required.

FAN_FS_ERROR (since Linux 5.16)
Create an event when a filesystem error leading to inconsistent filesystem metadata
is detected. An additional information record of type 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.

Events of such type are dependent on support from the underlying filesystem. At
the time of writing, only the ext4 filesystem reports FAN_FS_ERROR events.

See fanotify(7) for additional details.

FAN_MOVED_FROM (since Linux 5.1)
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.

FAN_MOVED_TO (since Linux 5.1)
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.

FAN_RENAME (since Linux 5.17)
This event contains the same information provided by events FAN_MOVED_FROM and
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
ENOTDIR shall be raised.

FAN_MOVE_SELF (since Linux 5.1)
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.

FAN_OPEN_PERM
Create an event when a permission to open a file or directory is requested. An
fanotify file descriptor created with FAN_CLASS_PRE_CONTENT or FAN_CLASS_CONTENT is
required.

FAN_OPEN_EXEC_PERM (since Linux 5.0)
Create an event when a permission to open a file for execution is requested. An
fanotify file descriptor created with FAN_CLASS_PRE_CONTENT or FAN_CLASS_CONTENT is
required. See NOTES for additional details.

FAN_ACCESS_PERM
Create an event when a permission to read a file or directory is requested. An
fanotify file descriptor created with FAN_CLASS_PRE_CONTENT or FAN_CLASS_CONTENT is
required.

FAN_ONDIR
Create events for directories—for example, when opendir(3), readdir(3) (but see
BUGS), and closedir(3) are called. Without this flag, events are created only for
files. In the context of directory entry events, such as FAN_CREATE, FAN_DELETE,
FAN_MOVED_FROM, and FAN_MOVED_TO, specifying the flag FAN_ONDIR is required in
order to create events when subdirectory entries are modified (i.e., mkdir(2)/
rmdir(2)).

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 FAN_CREATE, FAN_DELETE,
FAN_MOVED_FROM, and FAN_MOVED_TO are not generated for any entry modifications
performed inside subdirectories of marked directories. Note that the events
FAN_DELETE_SELF and 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.

The following composed values are defined:

FAN_CLOSE
A file is closed (FAN_CLOSE_WRITE|FAN_CLOSE_NOWRITE).

FAN_MOVE
A file or directory has been moved (FAN_MOVED_FROM|FAN_MOVED_TO).

The filesystem object to be marked is determined by the file descriptor dirfd and the
pathname specified in pathname:

• If pathname is NULL, dirfd defines the filesystem object to be marked.

• If pathname is NULL, and dirfd takes the special value AT_FDCWD, the current working
directory is to be marked.

• If pathname is absolute, it defines the filesystem object to be marked, and dirfd is
ignored.

• If pathname is relative, and dirfd does not have the value AT_FDCWD, then the
filesystem object to be marked is determined by interpreting pathname relative the
directory referred to by dirfd.

• If pathname is relative, and dirfd has the value AT_FDCWD, then the filesystem object
to be marked is determined by interpreting pathname relative to the current working
directory. (See openat(2) for an explanation of why the dirfd argument is useful.)

RETURN VALUE

       On  success,  fanotify_mark()  returns  0.   On error, -1 is returned, and errno is set to
       indicate the error.

ERRORS

EBADF An invalid file descriptor was passed in fanotify_fd.

EBADF pathname is relative but dirfd is neither AT_FDCWD nor a valid file descriptor.

EEXIST The filesystem object indicated by dirfd and pathname has a mark that was updated
without the FAN_MARK_EVICTABLE flag, and the user attempted to update the mark with
FAN_MARK_EVICTABLE flag.

EEXIST The filesystem object indicated by dirfd and pathname has a mark that was updated
with the FAN_MARK_IGNORE flag, and the user attempted to update the mark with
FAN_MARK_IGNORED_MASK flag.

EEXIST The filesystem object indicated by dirfd and pathname has a mark that was updated
with the FAN_MARK_IGNORE and FAN_MARK_IGNORED_SURV_MODIFY flags, and the user
attempted to update the mark only with FAN_MARK_IGNORE flag.

EINVAL An invalid value was passed in flags or mask, or fanotify_fd was not an fanotify
file descriptor.

EINVAL The fanotify file descriptor was opened with FAN_CLASS_NOTIF or the fanotify group
identifies filesystem objects by file handles and mask contains a flag for
permission events (FAN_OPEN_PERM or FAN_ACCESS_PERM).

EINVAL The group was initialized without FAN_REPORT_FID but one or more event types
specified in the mask require it.

EINVAL flags contains FAN_MARK_IGNORE, and either FAN_MARK_MOUNT or FAN_MARK_FILESYSTEM,
but does not contain FAN_MARK_IGNORED_SURV_MODIFY.

EISDIR flags contains FAN_MARK_IGNORE, but does not contain FAN_MARK_IGNORED_SURV_MODIFY,
and dirfd and pathname specify a directory.

ENODEV The filesystem object indicated by dirfd and pathname is not associated with a
filesystem that supports fsid (e.g., fuse(4)). tmpfs(5) did not support fsid prior
to Linux 5.13. This error can be returned only with an fanotify group that
identifies filesystem objects by file handles.

ENOENT The filesystem object indicated by dirfd and pathname does not exist. This error
also occurs when trying to remove a mark from an object which is not marked.

ENOMEM The necessary memory could not be allocated.

ENOSPC The number of marks for this user exceeds the limit and the FAN_UNLIMITED_MARKS
flag was not specified when the fanotify file descriptor was created with
fanotify_init(2). See fanotify(7) for details about this limit.

ENOSYS This kernel does not implement fanotify_mark(). The fanotify API is available only
if the kernel was configured with CONFIG_FANOTIFY.

ENOTDIR
flags contains FAN_MARK_ONLYDIR, and dirfd and pathname do not specify a directory.

ENOTDIR
mask contains FAN_RENAME, and dirfd and pathname do not specify a directory.

ENOTDIR
flags contains FAN_MARK_IGNORE, or the fanotify group was initialized with flag
FAN_REPORT_TARGET_FID, and mask contains directory entry modification events (e.g.,
FAN_CREATE, FAN_DELETE), or directory event flags (e.g., FAN_ONDIR,
FAN_EVENT_ON_CHILD), and dirfd and pathname do not specify a directory.

EOPNOTSUPP
The object indicated by 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. Calling
name_to_handle_at(2) with the flag AT_HANDLE_FID (since Linux 6.5) can be used as a
test to check if a filesystem supports reporting events with file handles.

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

EXDEV The filesystem object indicated by pathname resides within a filesystem subvolume
(e.g., btrfs(5)) which uses a different fsid than its root superblock. This error
can be returned only with an fanotify group that identifies filesystem objects by
file handles.

STANDARDS

       Linux.

HISTORY

       Linux 2.6.37.

NOTES

   FAN_OPEN_EXEC and FAN_OPEN_EXEC_PERM
       When  using  either  FAN_OPEN_EXEC  or FAN_OPEN_EXEC_PERM within the 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 execve(2), execveat(2), or uselib(2).  Events of  these  types  will  not  be
       raised   in  the  situation  where  an  interpreter  is  passed  (or  reads)  a  file  for
       interpretation.

       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 execve(2) or execveat(2).

       For example, if the following ELF binary were to be invoked and a FAN_OPEN_EXEC  mark  has
       been placed on /:

           $ /bin/echo foo

       The listening application in this case would receive FAN_OPEN_EXEC events for both the ELF
       binary and interpreter, respectively:

           /bin/echo
           /lib64/ld-linux-x86-64.so.2

BUGS

       The following bugs were present in before Linux 3.16:

       •  If flags contains FAN_MARK_FLUSH, dirfd, and pathname must specify a  valid  filesystem
          object, even though this object is not used.

       •  readdir(2) does not generate a FAN_ACCESS event.

       •  If  fanotify_mark()  is  called  with  FAN_MARK_FLUSH, flags is not checked for invalid
          values.