xfs_refc_next
if (rcext.rc_startblock == agbno || xfs_refc_next(&rcext) <= agbno)
if (xfs_refc_next(&tmp) != agbno)
if (xfs_refc_next(&tmp) == agbno + aglen)
cright->rc_startblock = max(agbno, xfs_refc_next(&tmp));