RING_CNT
#define RING_CNT(ap) (((ap)->async_rput >= (ap)->async_rget) ? \
#define RING_CNT(zap) (((zap)->za_rput - (zap)->za_rget) & RINGMASK)
#define RING_CNT(ap) (((ap)->async_rput - (ap)->async_rget) & RINGMASK)
#define RING_CNT(qsp) (((qsp)->qcn_rput - (qsp)->qcn_rget) & RINGMASK)