fsnotify: fsnotify_add_notify_event should return an event

Rather than the horrific void ** argument and such just to pass the
fanotify_merge event back to the caller of fsnotify_add_notify_event() have
those things return an event if it was different than the event suggusted to
be added.
Signed-off-by: Eric Paris <eparis@redhat.com>

fs/notify/fanotify/fanotify.c

@@ -30,65 +30,58 @@ static bool should_merge(struct fsnotify_event *old, struct fsnotify_event *new)
 	return false;
 }
 
-/* Note, if we return an event in *arg that a reference is being held... */
-static int fanotify_merge(struct list_head *list,
-			  struct fsnotify_event *event,
-			  void **arg)
+/* and the list better be locked by something too! */
+static struct fsnotify_event *fanotify_merge(struct list_head *list,
+					     struct fsnotify_event *event)
 {
 	struct fsnotify_event_holder *test_holder;
-	struct fsnotify_event *test_event;
+	struct fsnotify_event *test_event = NULL;
 	struct fsnotify_event *new_event;
-	struct fsnotify_event **return_event = (struct fsnotify_event **)arg;
-	int ret = 0;
 
 	pr_debug("%s: list=%p event=%p\n", __func__, list, event);
 
-	*return_event = NULL;
-
-	/* and the list better be locked by something too! */
 
 	list_for_each_entry_reverse(test_holder, list, event_list) {
+		if (should_merge(test_holder->event, event)) {
 			test_event = test_holder->event;
-		if (should_merge(test_event, event)) {
+			break;
+		}
+	}
+
+	if (!test_event)
+		return NULL;
+
 	fsnotify_get_event(test_event);
-			*return_event = test_event;
 
-			ret = -EEXIST;
 	/* if they are exactly the same we are done */
 	if (test_event->mask == event->mask)
-				goto out;
+		return test_event;
 
 	/*
-			 * if the refcnt == 1 this is the only queue
+	 * if the refcnt == 2 this is the only queue
 	 * for this event and so we can update the mask
 	 * in place.
 	 */
-			if (atomic_read(&test_event->refcnt) == 1) {
+	if (atomic_read(&test_event->refcnt) == 2) {
 		test_event->mask |= event->mask;
-				goto out;
+		return test_event;
 	}
 
-			/* can't allocate memory, merge was no possible */
 	new_event = fsnotify_clone_event(test_event);
-			if (unlikely(!new_event)) {
-				ret = 0;
-				goto out;
-			}
 
-			/* we didn't return the test_event, so drop that ref */
+	/* done with test_event */
 	fsnotify_put_event(test_event);
-			/* the reference we return on new_event is from clone */
-			*return_event = new_event;
+
+	/* couldn't allocate memory, merge was not possible */
+	if (unlikely(!new_event))
+		return ERR_PTR(-ENOMEM);
 
 	/* build new event and replace it on the list */
 	new_event->mask = (test_event->mask | event->mask);
 	fsnotify_replace_event(test_holder, new_event);
 
-			break;
-		}
-	}
-out:
-	return ret;
+	/* we hold a reference on new_event from clone_event */
+	return new_event;
 }
 
 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
@@ -123,7 +116,7 @@ static int fanotify_get_response_from_access(struct fsnotify_group *group,
 
 static int fanotify_handle_event(struct fsnotify_group *group, struct fsnotify_event *event)
 {
-	int ret;
+	int ret = 0;
 	struct fsnotify_event *notify_event = NULL;
 
 	BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
@@ -138,13 +131,9 @@ static int fanotify_handle_event(struct fsnotify_group *group, struct fsnotify_e
 
 	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
-	ret = fsnotify_add_notify_event(group, event, NULL, fanotify_merge,
-					(void **)&notify_event);
-	/* -EEXIST means this event was merged with another, not that it was an error */
-	if (ret == -EEXIST)
-		ret = 0;
-	if (ret)
-		goto out;
+	notify_event = fsnotify_add_notify_event(group, event, NULL, fanotify_merge);
+	if (IS_ERR(notify_event))
+		return PTR_ERR(notify_event);
 
 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 	if (event->mask & FAN_ALL_PERM_EVENTS) {
@@ -155,9 +144,9 @@ static int fanotify_handle_event(struct fsnotify_group *group, struct fsnotify_e
 	}
 #endif
 
-out:
 	if (notify_event)
 		fsnotify_put_event(notify_event);
+
 	return ret;
 }
 

fs/notify/inotify/inotify_fsnotify.c

@@ -68,13 +68,11 @@ static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new
 	return false;
 }
 
-static int inotify_merge(struct list_head *list,
-			 struct fsnotify_event *event,
-			 void **arg)
+static struct fsnotify_event *inotify_merge(struct list_head *list,
+					    struct fsnotify_event *event)
 {
 	struct fsnotify_event_holder *last_holder;
 	struct fsnotify_event *last_event;
-	int ret = 0;
 
 	/* and the list better be locked by something too */
 	spin_lock(&event->lock);
@@ -82,11 +80,13 @@ static int inotify_merge(struct list_head *list,
 	last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list);
 	last_event = last_holder->event;
 	if (event_compare(last_event, event))
-		ret = -EEXIST;
+		fsnotify_get_event(last_event);
+	else
+		last_event = NULL;
 
 	spin_unlock(&event->lock);
 
-	return ret;
+	return last_event;
 }
 
 static int inotify_handle_event(struct fsnotify_group *group, struct fsnotify_event *event)
@@ -96,7 +96,8 @@ static int inotify_handle_event(struct fsnotify_group *group, struct fsnotify_ev
 	struct inode *to_tell;
 	struct inotify_event_private_data *event_priv;
 	struct fsnotify_event_private_data *fsn_event_priv;
-	int wd, ret;
+	struct fsnotify_event *added_event;
+	int wd, ret = 0;
 
 	pr_debug("%s: group=%p event=%p to_tell=%p mask=%x\n", __func__, group,
 		 event, event->to_tell, event->mask);
@@ -120,14 +121,13 @@ static int inotify_handle_event(struct fsnotify_group *group, struct fsnotify_ev
 	fsn_event_priv->group = group;
 	event_priv->wd = wd;
 
-	ret = fsnotify_add_notify_event(group, event, fsn_event_priv, inotify_merge, NULL);
-	if (ret) {
+	added_event = fsnotify_add_notify_event(group, event, fsn_event_priv, inotify_merge);
+	if (added_event) {
 		inotify_free_event_priv(fsn_event_priv);
-		/* EEXIST says we tail matched, EOVERFLOW isn't something
-		 * to report up the stack. */
-		if ((ret == -EEXIST) ||
-		    (ret == -EOVERFLOW))
-			ret = 0;
+		if (!IS_ERR(added_event))
+			fsnotify_put_event(added_event);
+		else
+			ret = PTR_ERR(added_event);
 	}
 
 	if (fsn_mark->mask & IN_ONESHOT)

fs/notify/inotify/inotify_user.c

@@ -516,7 +516,7 @@ void inotify_ignored_and_remove_idr(struct fsnotify_mark *fsn_mark,
 				    struct fsnotify_group *group)
 {
 	struct inotify_inode_mark *i_mark;
-	struct fsnotify_event *ignored_event;
+	struct fsnotify_event *ignored_event, *notify_event;
 	struct inotify_event_private_data *event_priv;
 	struct fsnotify_event_private_data *fsn_event_priv;
 	int ret;
@@ -538,9 +538,14 @@ void inotify_ignored_and_remove_idr(struct fsnotify_mark *fsn_mark,
 	fsn_event_priv->group = group;
 	event_priv->wd = i_mark->wd;
 
-	ret = fsnotify_add_notify_event(group, ignored_event, fsn_event_priv, NULL, NULL);
-	if (ret)
+	notify_event = fsnotify_add_notify_event(group, ignored_event, fsn_event_priv, NULL);
+	if (notify_event) {
+		if (IS_ERR(notify_event))
+			ret = PTR_ERR(notify_event);
+		else
+			fsnotify_put_event(notify_event);
 		inotify_free_event_priv(fsn_event_priv);
+	}
 
 skip_send_ignore:
 

fs/notify/notification.c

@@ -137,16 +137,14 @@ struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnot
  * event off the queue to deal with.  If the event is successfully added to the
  * group's notification queue, a reference is taken on event.
  */
-int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
+struct fsnotify_event *fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
 						 struct fsnotify_event_private_data *priv,
-			      int (*merge)(struct list_head *,
-					   struct fsnotify_event *,
-					   void **arg),
-			      void **arg)
+						 struct fsnotify_event *(*merge)(struct list_head *,
+										 struct fsnotify_event *))
 {
+	struct fsnotify_event *return_event = NULL;
 	struct fsnotify_event_holder *holder = NULL;
 	struct list_head *list = &group->notification_list;
-	int rc = 0;
 
 	pr_debug("%s: group=%p event=%p priv=%p\n", __func__, group, event, priv);
 
@@ -162,27 +160,37 @@ int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_even
 alloc_holder:
 		holder = fsnotify_alloc_event_holder();
 		if (!holder)
-			return -ENOMEM;
+			return ERR_PTR(-ENOMEM);
 	}
 
 	mutex_lock(&group->notification_mutex);
 
 	if (group->q_len >= group->max_events) {
 		event = q_overflow_event;
-		rc = -EOVERFLOW;
+
+		/*
+		 * we need to return the overflow event
+		 * which means we need a ref
+		 */
+		fsnotify_get_event(event);
+		return_event = event;
+
 		/* sorry, no private data on the overflow event */
 		priv = NULL;
 	}
 
 	if (!list_empty(list) && merge) {
-		int ret;
+		struct fsnotify_event *tmp;
 
-		ret = merge(list, event, arg);
-		if (ret) {
+		tmp = merge(list, event);
+		if (tmp) {
 			mutex_unlock(&group->notification_mutex);
+
+			if (return_event)
+				fsnotify_put_event(return_event);
 			if (holder != &event->holder)
 				fsnotify_destroy_event_holder(holder);
-			return ret;
+			return tmp;
 		}
 	}
 
@@ -197,6 +205,12 @@ int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_even
 		 * event holder was used, go back and get a new one */
 		spin_unlock(&event->lock);
 		mutex_unlock(&group->notification_mutex);
+
+		if (return_event) {
+			fsnotify_put_event(return_event);
+			return_event = NULL;
+		}
+
 		goto alloc_holder;
 	}
 
@@ -211,7 +225,7 @@ int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_even
 	mutex_unlock(&group->notification_mutex);
 
 	wake_up(&group->notification_waitq);
-	return rc;
+	return return_event;
 }
 
 /*

include/linux/fsnotify_backend.h

@@ -379,13 +379,11 @@ extern struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struc
 									   struct fsnotify_event *event);
 
 /* attach the event to the group notification queue */
-extern int fsnotify_add_notify_event(struct fsnotify_group *group,
+extern struct fsnotify_event *fsnotify_add_notify_event(struct fsnotify_group *group,
 							struct fsnotify_event *event,
 							struct fsnotify_event_private_data *priv,
-				     int (*merge)(struct list_head *,
-						  struct fsnotify_event *,
-						  void **),
-				     void **arg);
+							struct fsnotify_event *(*merge)(struct list_head *,
+											struct fsnotify_event *));
 /* true if the group notification queue is empty */
 extern bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group);
 /* return, but do not dequeue the first event on the notification queue */