WBUF_MASK
if (sz > (WBUF_SIZE - WBUF_MASK(cons->wc)))
sz = WBUF_SIZE - WBUF_MASK(cons->wc);
sent = cons->ops->write(cons, &cons->wbuf[WBUF_MASK(cons->wc)],
cons->wbuf[WBUF_MASK(cons->wp++)] = c;