fsnotify: allow fsnotify_{peek,remove}_first_event with empty queue

Current code has an assumtion that fsnotify_notify_queue_is_empty() is
called to verify that queue is not empty before trying to peek or remove
an event from queue.

Remove this assumption by moving the fsnotify_notify_queue_is_empty()
into the functions, allow them to return NULL value and check return
value by all callers.

This is a prep patch for multi event queues.

Link: https://lore.kernel.org/r/20210304104826.3993892-2-amir73il@gmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 19 insertions, 23 deletions

diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index 75d79d6d3ef0..001cfe7d2e4e 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -47,13 +47,6 @@ u32 fsnotify_get_cookie(void)
 }
 EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
 
-/* return true if the notify queue is empty, false otherwise */
-bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
-{
-	assert_spin_locked(&group->notification_lock);
-	return list_empty(&group->notification_list) ? true : false;
-}
-
 void fsnotify_destroy_event(struct fsnotify_group *group,
 			    struct fsnotify_event *event)
 {
@@ -141,33 +134,36 @@ void fsnotify_remove_queued_event(struct fsnotify_group *group,
 }
 
 /*
- * Remove and return the first event from the notification list.  It is the
- * responsibility of the caller to destroy the obtained event
+ * Return the first event on the notification list without removing it.
+ * Returns NULL if the list is empty.
  */
-struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
+struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
 {
-	struct fsnotify_event *event;
-
 	assert_spin_locked(&group->notification_lock);
 
-	pr_debug("%s: group=%p\n", __func__, group);
+	if (fsnotify_notify_queue_is_empty(group))
+		return NULL;
 
-	event = list_first_entry(&group->notification_list,
-				 struct fsnotify_event, list);
-	fsnotify_remove_queued_event(group, event);
-	return event;
+	return list_first_entry(&group->notification_list,
+				struct fsnotify_event, list);
 }
 
 /*
- * This will not remove the event, that must be done with
- * fsnotify_remove_first_event()
+ * Remove and return the first event from the notification list.  It is the
+ * responsibility of the caller to destroy the obtained event
  */
-struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
+struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
 {
-	assert_spin_locked(&group->notification_lock);
+	struct fsnotify_event *event = fsnotify_peek_first_event(group);
 
-	return list_first_entry(&group->notification_list,
-				struct fsnotify_event, list);
+	if (!event)
+		return NULL;
+
+	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
+
+	fsnotify_remove_queued_event(group, event);
+
+	return event;
 }
 
 /*