Btrfs: Add mount option to enforce a max extent size

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index b51b021..32b2446 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -322,6 +322,7 @@
 	u64 generation;
 	u64 last_trans_committed;
 	unsigned long mount_opt;
+	u64 max_extent;
 	struct btrfs_transaction *running_transaction;
 	struct btrfs_super_block super_copy;
 	struct extent_buffer *sb_buffer;