vdev_label_offset
off = vdev_label_offset(vd->v_psize, l, offset);
off = vdev_label_offset(vd->v_psize, l, o_phys);
if (vdev_label_offset(vd->v_psize, l, offset) + VDEV_PAD_SIZE != off)
off = vdev_label_offset(vd->v_psize, l, offset);