XFS_RTREFCOUNT_BLOCK_LEN
blocklen -= XFS_RTREFCOUNT_BLOCK_LEN;
size_t sz = XFS_RTREFCOUNT_BLOCK_LEN;
((char *)block + XFS_RTREFCOUNT_BLOCK_LEN +
((char *)block + XFS_RTREFCOUNT_BLOCK_LEN +
((char *)block + XFS_RTREFCOUNT_BLOCK_LEN +