btrfs_create_tree
struct btrfs_root *btrfs_create_tree(struct btrfs_trans_handle *trans,
free_space_root = btrfs_create_tree(trans,
quota_root = btrfs_create_tree(trans, BTRFS_QUOTA_TREE_OBJECTID);
uuid_root = btrfs_create_tree(trans, BTRFS_UUID_TREE_OBJECTID);