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