Implement pts(4) packet mode.

As reported by several users on the mailing lists, applications like
screen(1) fail to properly handle ^S and ^Q characters. This was because
MPSAFE TTY didn't implement packet mode (TIOCPKT) yet. Add basic packet
mode support to make these applications work again.

Obtained from:	//depot/projects/mpsafetty/...

share/man/man4/pts.4

@@ -173,9 +173,3 @@ In
 it was replaced with the
 .Nm
 driver.
-.Sh BUGS
-Packet mode has not been properly implemented in this version of
-.Fx .
-When enabled, it will always prepend
-.Dv TIOCPKT_DATA ,
-even if other events have been triggered.

sys/kern/tty.c

@@ -815,6 +815,11 @@ ttydevsw_defmmap(struct tty *tp, vm_offset_t offset, vm_paddr_t *paddr,
 	return (-1);
 }
 
+static void
+ttydevsw_defpktnotify(struct tty *tp, char event)
+{
+}
+
 static void
 ttydevsw_deffree(void *softc)
 {
@@ -846,6 +851,7 @@ tty_alloc(struct ttydevsw *tsw, void *sc, struct mtx *mutex)
 	PATCH_FUNC(param);
 	PATCH_FUNC(modem);
 	PATCH_FUNC(mmap);
+	PATCH_FUNC(pktnotify);
 	PATCH_FUNC(free);
 #undef PATCH_FUNC
 
@@ -1226,11 +1232,13 @@ tty_flush(struct tty *tp, int flags)
 		tp->t_flags &= ~TF_HIWAT_OUT;
 		ttyoutq_flush(&tp->t_outq);
 		tty_wakeup(tp, FWRITE);
+		ttydevsw_pktnotify(tp, TIOCPKT_FLUSHWRITE);
 	}
 	if (flags & FREAD) {
 		tty_hiwat_in_unblock(tp);
 		ttyinq_flush(&tp->t_inq);
 		ttydevsw_inwakeup(tp);
+		ttydevsw_pktnotify(tp, TIOCPKT_FLUSHREAD);
 	}
 }
 
@@ -1372,6 +1380,17 @@ tty_generic_ioctl(struct tty *tp, u_long cmd, void *data, struct thread *td)
 			ttyinq_canonicalize(&tp->t_inq);
 			tty_wakeup(tp, FREAD);
 		}
+
+		/*
+		 * For packet mode: notify the PTY consumer that VSTOP
+		 * and VSTART may have been changed.
+		 */
+		if (tp->t_termios.c_iflag & IXON &&
+		    tp->t_termios.c_cc[VSTOP] == CTRL('S') &&
+		    tp->t_termios.c_cc[VSTART] == CTRL('Q'))
+			ttydevsw_pktnotify(tp, TIOCPKT_DOSTOP);
+		else
+			ttydevsw_pktnotify(tp, TIOCPKT_NOSTOP);
 		return (0);
 	}
 	case TIOCGETD:
@@ -1562,10 +1581,12 @@ tty_generic_ioctl(struct tty *tp, u_long cmd, void *data, struct thread *td)
 		return (0);
 	case TIOCSTOP:
 		tp->t_flags |= TF_STOPPED;
+		ttydevsw_pktnotify(tp, TIOCPKT_STOP);
 		return (0);
 	case TIOCSTART:
 		tp->t_flags &= ~TF_STOPPED;
 		ttydevsw_outwakeup(tp);
+		ttydevsw_pktnotify(tp, TIOCPKT_START);
 		return (0);
 	case TIOCSTAT:
 		tty_info(tp);

sys/kern/tty_pts.c

@@ -82,6 +82,7 @@ struct pts_softc {
 	int		pts_unit;	/* (c) Device unit number. */
 	unsigned int	pts_flags;	/* (t) Device flags. */
 #define PTS_PKT		0x1	/* Packet mode. */
+	char		pts_pkt;	/* (t) Unread packet mode data. */
 
 	struct cv	pts_inwait;	/* (t) Blocking write() on master. */
 	struct selinfo	pts_inpoll;	/* (t) Select queue for write(). */
@@ -105,34 +106,54 @@ ptsdev_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
 {
 	struct tty *tp = fp->f_data;
 	struct pts_softc *psc = tty_softc(tp);
-	int error, oresid;
+	int error = 0;
+	char pkt;
 
 	if (uio->uio_resid == 0)
 		return (0);
-	
-	/*
-	 * Implement packet mode. When packet mode is turned on, the
-	 * first byte contains a bitmask of events that occured (start,
-	 * stop, flush, window size, etc).
-	 */
-
-	if (psc->pts_flags & PTS_PKT) {
-		/* XXX: return proper bits. */
-		error = ureadc(0, uio);
-		if (error != 0)
-			return (error);
-		if (uio->uio_resid == 0)
-			return (0);
-	}
-
-	oresid = uio->uio_resid;
 
 	tty_lock(tp);
+
 	for (;;) {
-		error = ttydisc_getc_uio(tp, uio);
-		/* We've got data (or an error). */
-		if (error != 0 || uio->uio_resid != oresid)
+		/*
+		 * Implement packet mode. When packet mode is turned on,
+		 * the first byte contains a bitmask of events that
+		 * occured (start, stop, flush, window size, etc).
+		 */
+		if (psc->pts_flags & PTS_PKT && psc->pts_pkt) {
+			pkt = psc->pts_pkt;
+			psc->pts_pkt = 0;
+			tty_unlock(tp);
+
+			error = ureadc(pkt, uio);
+			return (error);
+		}
+
+		/*
+		 * Transmit regular data.
+		 *
+		 * XXX: We shouldn't use ttydisc_getc_poll()! Even
+		 * though in this implementation, there is likely going
+		 * to be data, we should just call ttydisc_getc_uio()
+		 * and use its return value to sleep.
+		 */
+		if (ttydisc_getc_poll(tp)) {
+			if (psc->pts_flags & PTS_PKT) {
+				/*
+				 * XXX: Small race. Fortunately PTY
+				 * consumers aren't multithreaded.
+				 */
+
+				tty_unlock(tp);
+				error = ureadc(TIOCPKT_DATA, uio);
+				if (error)
+					return (error);
+				tty_lock(tp);
+			}
+
+			error = ttydisc_getc_uio(tp, uio);
 			break;
+		}
 
 		/* Maybe the device isn't used anyway. */
 		if (tty_opened(tp) == 0)
@@ -147,6 +168,7 @@ ptsdev_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
 		if (error != 0)
 			break;
 	}
+
 	tty_unlock(tp);
 
 	return (error);
@@ -162,14 +184,14 @@ ptsdev_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
 	size_t iblen, rintlen;
 	int error = 0;
 
-	tty_lock(tp);
+	if (uio->uio_resid == 0)
+		return (0);
 
-	while (uio->uio_resid > 0) {
-		/* Temporarily unlock to buffer new characters. */
-		tty_unlock(tp);
+	for (;;) {
 		ibstart = ib;
 		iblen = MIN(uio->uio_resid, sizeof ib);
 		error = uiomove(ib, iblen, uio);
+
 		tty_lock(tp);
 		if (error != 0)
 			goto done;
@@ -178,7 +200,8 @@ ptsdev_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
 		 * When possible, avoid the slow path. rint_bypass()
 		 * copies all input to the input queue at once.
 		 */
-		while (iblen > 0) {
+		MPASS(iblen > 0);
+		do {
 			if (ttydisc_can_bypass(tp)) {
 				/* Store data at once. */
 				rintlen = ttydisc_rint_bypass(tp,
@@ -188,7 +211,7 @@ ptsdev_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
 
 				if (iblen == 0) {
 					/* All data written. */
-					continue;
+					break;
 				}
 			} else {
 				error = ttydisc_rint(tp, *ibstart, 0);
@@ -217,7 +240,11 @@ ptsdev_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
 			error = cv_wait_sig(&psc->pts_inwait, tp->t_mtx);
 			if (error != 0)
 				goto done;
-		}
+		} while (iblen > 0);
+
+		if (uio->uio_resid == 0)
+			break;
+		tty_unlock(tp);
 	}
 
 done:	ttydisc_rint_done(tp);
@@ -362,7 +389,8 @@ ptsdev_poll(struct file *fp, int events, struct ucred *active_cred,
 
 	if (events & (POLLIN|POLLRDNORM)) {
 		/* See if we can getc something. */
-		if (ttydisc_getc_poll(tp))
+		if (ttydisc_getc_poll(tp) ||
+		    (psc->pts_flags & PTS_PKT && psc->pts_pkt))
 			revents |= events & (POLLIN|POLLRDNORM);
 	}
 	if (events & (POLLOUT|POLLWRNORM)) {
@@ -480,6 +508,34 @@ ptsdrv_close(struct tty *tp)
 	ptsdrv_inwakeup(tp);
 }
 
+static void
+ptsdrv_pktnotify(struct tty *tp, char event)
+{
+	struct pts_softc *psc = tty_softc(tp);
+
+	/*
+	 * Clear conflicting flags.
+	 */
+
+	switch (event) {
+	case TIOCPKT_STOP:
+		psc->pts_pkt &= ~TIOCPKT_START;
+		break;
+	case TIOCPKT_START:
+		psc->pts_pkt &= ~TIOCPKT_STOP;
+		break;
+	case TIOCPKT_NOSTOP:
+		psc->pts_pkt &= ~TIOCPKT_DOSTOP;
+		break;
+	case TIOCPKT_DOSTOP:
+		psc->pts_pkt &= ~TIOCPKT_NOSTOP;
+		break;
+	}
+
+	psc->pts_pkt |= event;
+	ptsdrv_outwakeup(tp);
+}
+
 static void
 ptsdrv_free(void *softc)
 {
@@ -506,6 +562,7 @@ static struct ttydevsw pts_class = {
 	.tsw_outwakeup	= ptsdrv_outwakeup,
 	.tsw_inwakeup	= ptsdrv_inwakeup,
 	.tsw_close	= ptsdrv_close,
+	.tsw_pktnotify	= ptsdrv_pktnotify,
 	.tsw_free	= ptsdrv_free,
 };
 

sys/sys/ttydevsw.h

@@ -48,6 +48,7 @@ typedef int tsw_ioctl_t(struct tty *, u_long, caddr_t, struct thread *);
 typedef int tsw_param_t(struct tty *, struct termios *);
 typedef int tsw_modem_t(struct tty *, int, int);
 typedef int tsw_mmap_t(struct tty *, vm_offset_t, vm_paddr_t *, int);
+typedef void tsw_pktnotify_t(struct tty *, char);
 typedef void tsw_free_t(void *);
 
 struct ttydevsw {
@@ -64,6 +65,7 @@ struct ttydevsw {
 	tsw_modem_t	*tsw_modem;	/* Modem sigon/sigoff. */
 
 	tsw_mmap_t	*tsw_mmap;	/* mmap() hooks. */
+	tsw_pktnotify_t	*tsw_pktnotify;	/* TIOCPKT events. */
 
 	tsw_free_t	*tsw_free;	/* Destructor. */
 };
@@ -147,6 +149,15 @@ ttydevsw_mmap(struct tty *tp, vm_offset_t offset, vm_paddr_t *paddr, int nprot)
 	return tp->t_devsw->tsw_mmap(tp, offset, paddr, nprot);
 }
 
+static __inline void
+ttydevsw_pktnotify(struct tty *tp, char event)
+{
+	tty_lock_assert(tp, MA_OWNED);
+	MPASS(!tty_gone(tp));
+
+	tp->t_devsw->tsw_pktnotify(tp, event);
+}
+
 static __inline void
 ttydevsw_free(struct tty *tp)
 {