RQLEN
struct mbuf *xq[XQLEN], *rq[RQLEN];
while (sc->tail_rq != ((sc->head_rq - 1) & (RQLEN - 1))) {
sc->tail_rq &= (RQLEN - 1);
sc->head_rq &= (RQLEN - 1);
sc->head_rq &= (RQLEN - 1);