Commit 318652e0 authored by Amir Goldstein's avatar Amir Goldstein Committed by Jan Kara
Browse files

fsnotify: check if file is actually being watched for pre-content events on open 



So far, we set FMODE_NONOTIFY_ flags at open time if we know that there
are no permission event watchers at all on the filesystem, but lack of
FMODE_NONOTIFY_ flags does not mean that the file is actually watched.

For pre-content events, it is possible to optimize things so that we
don't bother trying to send pre-content events if file was not watched
(through sb, mnt, parent or inode itself) on open. Set FMODE_NONOTIFY_
flags according to that.

Signed-off-by: default avatarAmir Goldstein <amir73il@gmail.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Link: https://patch.msgid.link/2ddcc9f8d1fde48d085318a6b5a889289d8871d8.1731684329.git.josef@toxicpanda.com
parent a94204f4

fs/notify/fsnotify.c

+26 −3
Original line number Diff line number Diff line
@@ -193,7 +193,7 @@ static bool fsnotify_event_needs_parent(struct inode *inode, __u32 mnt_mask, 
	return mask & marks_mask;

}



/* Are there any inode/mount/sb objects that are interested in this event? */

/* Are there any inode/mount/sb objects that watch for these events? */

static inline bool fsnotify_object_watched(struct inode *inode, __u32 mnt_mask,

					   __u32 mask)

{
@@ -632,7 +632,9 @@ EXPORT_SYMBOL_GPL(fsnotify); 
 */

void file_set_fsnotify_mode(struct file *file)

{

	struct super_block *sb = file->f_path.dentry->d_sb;

	struct dentry *dentry = file->f_path.dentry, *parent;

	struct super_block *sb = dentry->d_sb;

	__u32 mnt_mask, p_mask;



	/* Is it a file opened by fanotify? */

	if (FMODE_FSNOTIFY_NONE(file->f_mode))
@@ -653,11 +655,32 @@ void file_set_fsnotify_mode(struct file *file) 
	 * If there are permission event watchers but no pre-content event

	 * watchers, set FMODE_NONOTIFY | FMODE_NONOTIFY_PERM to indicate that.

	 */

	if (likely(!fsnotify_sb_has_priority_watchers(sb,

	if ((!d_is_dir(dentry) && !d_is_reg(dentry)) ||

	    likely(!fsnotify_sb_has_priority_watchers(sb,

						FSNOTIFY_PRIO_PRE_CONTENT))) {

		file->f_mode |= FMODE_NONOTIFY | FMODE_NONOTIFY_PERM;

		return;

	}



	/*

	 * OK, there are some pre-content watchers. Check if anybody is

	 * watching for pre-content events on *this* file.

	 */

	mnt_mask = READ_ONCE(real_mount(file->f_path.mnt)->mnt_fsnotify_mask);

	if (unlikely(fsnotify_object_watched(d_inode(dentry), mnt_mask,

				     FSNOTIFY_PRE_CONTENT_EVENTS)))

		return;



	/* Is parent watching for pre-content events on this file? */

	if (dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED) {

		parent = dget_parent(dentry);

		p_mask = fsnotify_inode_watches_children(d_inode(parent));

		dput(parent);

		if (p_mask & FSNOTIFY_PRE_CONTENT_EVENTS)

			return;

	}

	/* Nobody watching for pre-content events from this file */

	file->f_mode |= FMODE_NONOTIFY | FMODE_NONOTIFY_PERM;

}

#endif

include/linux/fsnotify_backend.h

+3 −0
Original line number Diff line number Diff line
@@ -77,6 +77,9 @@ 
 */

#define ALL_FSNOTIFY_DIRENT_EVENTS (FS_CREATE | FS_DELETE | FS_MOVE | FS_RENAME)



/* Pre-content events can be used to fill file content */

#define FSNOTIFY_PRE_CONTENT_EVENTS 0



#define ALL_FSNOTIFY_PERM_EVENTS (FS_OPEN_PERM | FS_ACCESS_PERM | \

				  FS_OPEN_EXEC_PERM)