Function ttydisc_getc_uio

freebsd/kern/tty_ttydisc.c:1217–1260

}

int
ttydisc_getc_uio(struct tty *tp, struct uio *uio)
{
	int error = 0;
	ssize_t obytes = uio->uio_resid;
	size_t len;
	char buf[TTY_STACKBUF];

	tty_assert_locked(tp);

	if (tp->t_flags & TF_STOPPED)
		return (0);

	/*
	 * When a TTY hook is attached, we cannot perform unbuffered
	 * copying to userspace. Just call ttydisc_getc() and
	 * temporarily store data in a shadow buffer.
	 */
	if (ttyhook_hashook(tp, getc_capture) ||
	    ttyhook_hashook(tp, getc_inject)) {
		while (uio->uio_resid > 0) {
			/* Read to shadow buffer. */
			len = ttydisc_getc(tp, buf,
			    MIN(uio->uio_resid, sizeof buf));
			if (len == 0)
				break;

			/* Copy to userspace. */
			tty_unlock(tp);
			error = uiomove(buf, len, uio);
			tty_lock(tp);

			if (error != 0)
				break;
		}
	} else {
		error = ttyoutq_read_uio(&tp->t_outq, tp, uio);

		ttydisc_wakeup_watermark(tp);
		atomic_add_long(&tty_nout, obytes - uio->uio_resid);
	}

	return (error);
}

size_t
ttydisc_getc_poll(struct tty *tp)