Fix line discipline switching issues: If opening a new ldisc fails,

we have to revert to TTYDISC which we know will successfully open
rather than try the previous ldisc which might also fail to open.

Do not let ldisc implementations muck about with ->t_line, and remove
code which checks for reopens, it should never happen.

Move ldisc->l_hotchar to tty->t_hotchar and have ldisc implementation
initialize it in their open routines.  Reset to zero when we enter
TTYDISC.  ("no" should really be -1 since zero could be a valid
hotchar for certain old european mainframe protocols.)

7 files changed, 29 insertions, 49 deletions

diff --git a/sys/kern/tty.c b/sys/kern/tty.c
index fced5d7..5520b82 100644
--- a/sys/kern/tty.c
+++ b/sys/kern/tty.c
@@ -236,6 +236,7 @@ ttyopen(struct cdev *device, struct tty *tp)
 
 	s = spltty();
 	tp->t_dev = device;
+	tp->t_hotchar = 0;
 	if (!ISSET(tp->t_state, TS_ISOPEN)) {
 		ttyref(tp);
 		SET(tp->t_state, TS_ISOPEN);
@@ -276,6 +277,7 @@ ttyclose(struct tty *tp)
 
 	tp->t_gen++;
 	tp->t_line = TTYDISC;
+	tp->t_hotchar = 0;
 	tp->t_pgrp = NULL;
 	tp->t_session = NULL;
 	tp->t_state = 0;
@@ -1072,18 +1074,25 @@ ttioctl(struct tty *tp, u_long cmd, void *data, int flag)
 
 		if ((u_int)t >= nlinesw)
 			return (ENXIO);
-		if (t != tp->t_line) {
-			s = spltty();
-			ttyld_close(tp, flag);
-			error = (*linesw[t]->l_open)(device, tp);
-			if (error) {
-				(void)ttyld_open(tp, device);
-				splx(s);
-				return (error);
-			}
-			tp->t_line = t;
-			splx(s);
+		if (t == tp->t_line)
+			return (0);
+		s = spltty();
+		ttyld_close(tp, flag);
+		tp->t_line = t;
+		error = ttyld_open(tp, device);
+		if (error) {
+			/*
+			 * If we fail to switch line discipline we cannot
+			 * fall back to the previous, because we can not
+			 * trust that ldisc to open successfully either.
+			 * Fall back to the default ldisc which we know 
+			 * will allways succeed.
+			 */
+			tp->t_line = TTYDISC;
+			(void)ttyld_open(tp, device);
 		}
+		splx(s);
+		return (error);
 		break;
 	}
 	case TIOCSTART:			/* start output, like ^Q */
@@ -2905,7 +2914,7 @@ ttyldoptim(struct tty *tp)
 		tp->t_state |= TS_CAN_BYPASS_L_RINT;
 	else
 		tp->t_state &= ~TS_CAN_BYPASS_L_RINT;
-	return (linesw[tp->t_line]->l_hotchar);
+	return (tp->t_hotchar);
 }
 
 
diff --git a/sys/net/if_sl.c b/sys/net/if_sl.c
index c05ecd0..3595b77 100644
--- a/sys/net/if_sl.c
+++ b/sys/net/if_sl.c
@@ -186,8 +186,7 @@ static int	slstart(struct tty *);
 
 static struct linesw slipdisc = {
 	slopen,		slclose,	l_noread,	l_nowrite,
-	sltioctl,	slinput,	slstart,	ttymodem,
-	FRAME_END
+	sltioctl,	slinput,	slstart,	ttymodem
 };
 
 /*
@@ -350,17 +349,14 @@ slopen(dev, tp)
 	if (error)
 		return (error);
 
-	if (tp->t_line == SLIPDISC)
-		return (0);
-
 	if ((sc = slcreate()) == NULL)
 		return (ENOBUFS);
 
+	tp->t_hotchar = FRAME_END;
 	tp->t_sc = (caddr_t)sc;
 	sc->sc_ttyp = tp;
 	sc->sc_if.if_baudrate = tp->t_ospeed;
 	ttyflush(tp, FREAD | FWRITE);
-	tp->t_line = SLIPDISC;
 
 	/*
 	 * We don't use t_canq or t_rawq, so reduce their
@@ -417,7 +413,6 @@ slclose(tp,flag)
 	 */
 	s = splimp();		/* actually, max(spltty, splnet) */
 	clist_free_cblocks(&tp->t_outq);
-	tp->t_line = 0;
 	sc = (struct sl_softc *)tp->t_sc;
 	if (sc != NULL) {
 		if (sc->sc_outfill) {
diff --git a/sys/net/ppp_tty.c b/sys/net/ppp_tty.c
index 0270acb..05ffb16 100644
--- a/sys/net/ppp_tty.c
+++ b/sys/net/ppp_tty.c
@@ -148,8 +148,7 @@ void		pppasyncdetach(void);
 
 static struct linesw pppdisc = {
 	pppopen,	pppclose,	pppread,	pppwrite,
-	ppptioctl,	pppinput,	pppstart,	ttymodem,
-	PPP_FLAG
+	ppptioctl,	pppinput,	pppstart,	ttymodem
 };
 
 void
@@ -185,13 +184,7 @@ pppopen(dev, tp)
 
     s = spltty();
 
-    if (tp->t_line == PPPDISC) {
-	sc = (struct ppp_softc *) tp->t_sc;
-	if (sc != NULL && sc->sc_devp == (void *) tp) {
-	    splx(s);
-	    return (0);
-	}
-    }
+    tp->t_hotchar = PPP_FLAG;
 
     if ((sc = pppalloc(td->td_proc->p_pid)) == NULL) {
 	splx(s);
@@ -254,7 +247,6 @@ pppclose(tp, flag)
     ttyflush(tp, FREAD | FWRITE);
     clist_free_cblocks(&tp->t_canq);
     clist_free_cblocks(&tp->t_outq);
-    tp->t_line = 0;
     sc = (struct ppp_softc *) tp->t_sc;
     if (sc != NULL) {
 	tp->t_sc = NULL;
diff --git a/sys/netgraph/bluetooth/drivers/h4/ng_h4.c b/sys/netgraph/bluetooth/drivers/h4/ng_h4.c
index 27b6641..1710a4c 100644
--- a/sys/netgraph/bluetooth/drivers/h4/ng_h4.c
+++ b/sys/netgraph/bluetooth/drivers/h4/ng_h4.c
@@ -97,8 +97,7 @@ static struct linesw		ng_h4_disc = {
 	ng_h4_ioctl,		/* ioctl */
 	ng_h4_input,		/* input */
 	ng_h4_start,		/* start */
-	ttymodem,		/* modem */
-	0 			/* hotchar (don't really care which one) */
+	ttymodem		/* modem */
 };
 
 /* Netgraph methods */
@@ -161,13 +160,6 @@ ng_h4_open(struct cdev *dev, struct tty *tp)
 	s = splnet(); /* XXX */
 	spltty(); /* XXX */
 
-	/* Already installed? */
-	if (tp->t_line == H4DISC) {
-		sc = (ng_h4_info_p) tp->t_sc;
-		if (sc != NULL && sc->tp == tp)
-			goto out;
-	}
-
 	/* Initialize private struct */
 	MALLOC(sc, ng_h4_info_p, sizeof(*sc), M_NETGRAPH_H4, M_NOWAIT|M_ZERO);
 	if (sc == NULL) {
@@ -243,7 +235,6 @@ ng_h4_close(struct tty *tp, int flag)
 
 	ttyflush(tp, FREAD | FWRITE);
 	clist_free_cblocks(&tp->t_outq);
-	tp->t_line = 0;
 	if (sc != NULL) {
 		tp->t_sc = NULL;
 
diff --git a/sys/netgraph/ng_tty.c b/sys/netgraph/ng_tty.c
index 0ce67a5..9e4ecc3 100644
--- a/sys/netgraph/ng_tty.c
+++ b/sys/netgraph/ng_tty.c
@@ -148,8 +148,7 @@ static struct linesw ngt_disc = {
 	ngt_tioctl,
 	ngt_input,
 	ngt_start,
-	ttymodem,
-	NG_TTY_DFL_HOTCHAR	/* XXX can't change this in serial driver */
+	ttymodem
 };
 
 /* Netgraph node type descriptor */
@@ -193,12 +192,7 @@ ngt_open(struct cdev *dev, struct tty *tp)
 	s = splnet();
 	(void) spltty();	/* XXX is this necessary? */
 
-	/* Already installed? */
-	if (tp->t_line == NETGRAPHDISC) {
-		sc = (sc_p) tp->t_sc;
-		if (sc != NULL && sc->tp == tp)
-			goto done;
-	}
+	tp->t_hotchar = NG_TTY_DFL_HOTCHAR;
 
 	/* Initialize private struct */
 	MALLOC(sc, sc_p, sizeof(*sc), M_NETGRAPH, M_WAITOK | M_ZERO);
@@ -265,7 +259,6 @@ ngt_close(struct tty *tp, int flag)
 	s = spltty();
 	ttyflush(tp, FREAD | FWRITE);
 	clist_free_cblocks(&tp->t_outq);
-	tp->t_line = 0;
 	if (sc != NULL) {
 		if (sc->flags & FLG_TIMEOUT) {
 			untimeout(ngt_timeout, sc, sc->chand);
diff --git a/sys/sys/linedisc.h b/sys/sys/linedisc.h
index 5c378f7..659aa4b 100644
--- a/sys/sys/linedisc.h
+++ b/sys/sys/linedisc.h
@@ -66,7 +66,6 @@ struct linesw {
 	l_rint_t	*l_rint;
 	l_start_t	*l_start;
 	l_modem_t	*l_modem;
-	u_char		l_hotchar;
 };
 
 extern struct linesw *linesw[];
diff --git a/sys/sys/tty.h b/sys/sys/tty.h
index 8c96dde..853b5f3 100644
--- a/sys/sys/tty.h
+++ b/sys/sys/tty.h
@@ -116,6 +116,7 @@ struct tty {
 
 	struct mtx t_mtx;
 	int	t_refcnt;
+	int	t_hotchar;		/* linedisc preferred hot char */
 };
 
 #define	t_cc		t_termios.c_cc