ZSKBD_RING_SIZE
#ifndef ZSKBD_RING_SIZE
u_int zskbd_rbuf_size = ZSKBD_RING_SIZE;
u_int zskbd_rbuf_hiwat = (ZSKBD_RING_SIZE * 1) / 4;
u_int zskbd_rbuf_lowat = (ZSKBD_RING_SIZE * 3) / 4;
u_char zst_tbuf[ZSKBD_RING_SIZE];
zst->zst_tend = zst->zst_tbeg + ZSKBD_RING_SIZE;
if (zst->zst_tbc + len > ZSKBD_RING_SIZE) {