xfs_bmbt_key_t
(sizeof (xfs_bmbt_key_t) + sizeof (xfs_bmbt_ptr_t));
+ btroot_maxrecs ()*sizeof(xfs_bmbt_key_t));
(sizeof (xfs_bmbt_key_t) + sizeof (xfs_bmbt_ptr_t)))
* sizeof(xfs_bmbt_key_t) + sizeof(xfs_btree_block_t);