Btrfs: Rev the disk format for compression and root pointer generation fields

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 0621ab9..abb2733 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -39,7 +39,7 @@
 extern struct kmem_cache *btrfs_path_cachep;
 struct btrfs_ordered_sum;
 
-#define BTRFS_MAGIC "_BBRfS_M"
+#define BTRFS_MAGIC "_BCRfS_M"
 
 #define BTRFS_ACL_NOT_CACHED    ((void *)-1)