Btrfs: Change the super to point to a tree of trees to enable persistent snapshots

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/TODO b/fs/btrfs/TODO
index ad29267..ff90e5e 100644
--- a/fs/btrfs/TODO
+++ b/fs/btrfs/TODO
@@ -5,6 +5,7 @@
 * make a real mkfs and superblock
 * Do checksumming
 * Define FS objects in terms of different item types
+* add inode tree
 * Add block mapping tree (simple dm layer)
 * Add simple tree locking (semaphore per tree)
 * Make allocator smarter