fsnotify: use helpers to access data by data_type

Create helpers to access path and inode from different data types.

Link: https://lore.kernel.org/r/20200319151022.31456-5-amir73il@gmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

kernel/audit_watch.c

@@ -473,25 +473,13 @@ static int audit_watch_handle_event(struct fsnotify_group *group,
 				    struct fsnotify_iter_info *iter_info)
 {
 	struct fsnotify_mark *inode_mark = fsnotify_iter_inode_mark(iter_info);
-	const struct inode *inode;
+	const struct inode *inode = fsnotify_data_inode(data, data_type);
 	struct audit_parent *parent;
 
 	parent = container_of(inode_mark, struct audit_parent, mark);
 
 	BUG_ON(group != audit_watch_group);
-
-	switch (data_type) {
-	case (FSNOTIFY_EVENT_PATH):
-		inode = d_backing_inode(((const struct path *)data)->dentry);
-		break;
-	case (FSNOTIFY_EVENT_INODE):
-		inode = (const struct inode *)data;
-		break;
-	default:
-		BUG();
-		inode = NULL;
-		break;
-	}
+	WARN_ON(!inode);
 
 	if (mask & (FS_CREATE|FS_MOVED_TO) && inode)
 		audit_update_watch(parent, dname, inode->i_sb->s_dev, inode->i_ino, 0);