xfs_rbmblock_wordptr
first = (void *)xfs_rbmblock_wordptr(args, from) - bp->b_addr;
last = ((void *)xfs_rbmblock_wordptr(args, next) - 1) - bp->b_addr;
union xfs_rtword_raw *word = xfs_rbmblock_wordptr(args, index);
union xfs_rtword_raw *word = xfs_rbmblock_wordptr(args, index);
ondisk = xfs_rbmblock_wordptr(&rtb->args, 0);