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

#include <sys/fanotify.h>
int fanotify_mark(int fanotify_fd, unsigned int flags,
 uint64_t mask, int dirfd,
 const char *_Nullable pathname);

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.)

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

fanotify_init(2), fanotify(7)