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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: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/2ddcc9f8d1fde48d085318a6b5a889289d8871d8.1731684329.git.josef@toxicpanda.com
This commit is contained in:
Amir Goldstein 2024-11-15 10:30:16 -05:00 committed by Jan Kara
parent a94204f4d4
commit 318652e07f
2 changed files with 29 additions and 3 deletions
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29
fs/notify/fsnotify.c
View File

@ -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

3
include/linux/fsnotify_backend.h
View File

@ -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)