xfs_rgbno_to_rtx
startrtx = xfs_rgbno_to_rtx(mp, rgbno);
endrtx = xfs_rgbno_to_rtx(mp, rgbno + len - 1);
startrtx = xfs_rgbno_to_rtx(mp, rtb->next_rgbno);
nextrtx = xfs_rgbno_to_rtx(mp, rgbno - 1) + 1;
*resrtx = xfs_rgbno_to_rtx(mp, aligned_rgbno);
*resrtx = xfs_rgbno_to_rtx(mp, rgbno);