fsnotify: introduce fsnotify_get_group()

Introduce fsnotify_get_group() which increments the reference counter of a group.
Signed-off-by: NLino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: NEric Paris <eparis@redhat.com>

fs/notify/group.c

@@ -62,6 +62,14 @@ void fsnotify_destroy_group(struct fsnotify_group *group)
 		fsnotify_final_destroy_group(group);
 }
 
+/*
+ * Get reference to a group.
+ */
+void fsnotify_get_group(struct fsnotify_group *group)
+{
+	atomic_inc(&group->refcnt);
+}
+
 /*
  * Drop a reference to a group.  Free it if it's through.
  */

include/linux/fsnotify_backend.h

@@ -360,8 +360,10 @@ static inline void __fsnotify_d_instantiate(struct dentry *dentry, struct inode
 
 /* called from fsnotify listeners, such as fanotify or dnotify */
 
-/* get a reference to an existing or create a new group */
+/* create a new group */
 extern struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops);
+/* get reference to a group */
+extern void fsnotify_get_group(struct fsnotify_group *group);
 /* drop reference on a group from fsnotify_alloc_group */
 extern void fsnotify_put_group(struct fsnotify_group *group);
 /* destroy group */