fsnotify: Add helper to detect overflow_event

Similarly to fanotify_is_perm_event and friends, provide a helper
predicate to say whether a mask is of an overflow event.

Link: https://lore.kernel.org/r/20211025192746.66445-9-krisman@collabora.comSuggested-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/notify/fanotify/fanotify.h

@@ -315,7 +315,8 @@ static inline struct path *fanotify_event_path(struct fanotify_event *event)
  */
 static inline bool fanotify_is_hashed_event(u32 mask)
 {
-	return !fanotify_is_perm_event(mask) && !(mask & FS_Q_OVERFLOW);
+	return !(fanotify_is_perm_event(mask) ||
+		 fsnotify_is_overflow_event(mask));
 }
 
 static inline unsigned int fanotify_event_hash_bucket(

include/linux/fsnotify_backend.h

@@ -510,6 +510,11 @@ static inline void fsnotify_queue_overflow(struct fsnotify_group *group)
 	fsnotify_add_event(group, group->overflow_event, NULL, NULL);
 }
 
+static inline bool fsnotify_is_overflow_event(u32 mask)
+{
+	return mask & FS_Q_OVERFLOW;
+}
+
 static inline bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
 {
 	assert_spin_locked(&group->notification_lock);