MGB_NEXT_RING_IDX
rdata->last_head = MGB_NEXT_RING_IDX(rdata->last_head);
for (; idx != *(rdata->head_wb); idx = MGB_NEXT_RING_IDX(idx)) {
rdata->last_head = MGB_NEXT_RING_IDX(rdata->last_head);
pidx = MGB_NEXT_RING_IDX(pidx);