RING_INIT
#define RING_INIT(ap) ((ap)->async_rput = (ap)->async_rget = 0)
#define RING_INIT(zap) ((zap)->za_rput = (zap)->za_rget = 0)
#define RING_INIT(ap) ((ap)->async_rput = (ap)->async_rget = 0)
#define RING_INIT(qsp) ((qsp)->qcn_rput = (qsp)->qcn_rget = 0)