Function tty_watermarks

freebsd/kern/tty.c:124–150

* Allocate buffer space if necessary, and set low watermarks, based on speed. * Note that the ttyxxxq_setsize() functions may drop and then reacquire the tty * lock during memory allocation. They will return ENXIO if the tty disappears * while unlocked. */

 * while unlocked.
 */
static int
tty_watermarks(struct tty *tp)
{
	size_t bs = 0;
	int error;

	/* Provide an input buffer for 2 seconds of data. */
	if (tp->t_termios.c_cflag & CREAD)
		bs = MIN(tp->t_termios.c_ispeed / 5, TTYBUF_MAX);
	error = ttyinq_setsize(&tp->t_inq, tp, bs);
	if (error != 0)
		return (error);

	/* Set low watermark at 10% (when 90% is available). */
	tp->t_inlow = (ttyinq_getallocatedsize(&tp->t_inq) * 9) / 10;

	/* Provide an output buffer for 2 seconds of data. */
	bs = MIN(tp->t_termios.c_ospeed / 5, TTYBUF_MAX);
	error = ttyoutq_setsize(&tp->t_outq, tp, bs);
	if (error != 0)
		return (error);

	/* Set low watermark at 10% (when 90% is available). */
	tp->t_outlow = (ttyoutq_getallocatedsize(&tp->t_outq) * 9) / 10;

	return (0);
}

static int
tty_drain(struct tty *tp, int leaving)