This sl enhancement helps to keep serial line (modem) connection alive.

It is common case when modem hangs with carier on but don't
receive anything from another side.
This thing commonly healed with hangup and redialing.
Enhancements below allows to determine when such action
is needed and inform attach program with SIGURG signal.
There two ioctls set: outfill and keepalive, used from both
sides of connection. Outfill repeatedly sends FRAME_END with
specified timeout (i.e. 40 seconds). It is needed to get input on
other side even if no user activity on slip line currently.
Keepalive checks FRAME_ENDs from other side, and if no one
got in specified timeout (i.e. 60 seconds, max modem retrain time),
send SIGURG to attach program.
I plan to add code to slattach to handle this thing too.

Reviewed by: wollman

3 files changed, 100 insertions, 5 deletions

diff --git a/sys/net/if_sl.c b/sys/net/if_sl.c
index 77dfa05..fc407cd 100644
--- a/sys/net/if_sl.c
+++ b/sys/net/if_sl.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)if_sl.c	8.6 (Berkeley) 2/1/94
- * $Id: if_sl.c,v 1.13 1995/03/16 18:14:27 bde Exp $
+ * $Id: if_sl.c,v 1.14 1995/03/20 19:20:43 wollman Exp $
  */
 
 /*
@@ -182,6 +182,8 @@ struct sl_softc sl_softc[NSL];
 
 static int slinit __P((struct sl_softc *));
 static struct mbuf *sl_btom __P((struct sl_softc *, int));
+static void sl_keepalive __P((struct sl_softc *));
+static void sl_outfill __P((struct sl_softc *));
 
 
 #define ttyerrio ((int (*) __P((struct tty *, struct uio *, int)))enodev)
@@ -320,7 +322,16 @@ slclose(tp,flag)
 	tp->t_line = 0;
 	sc = (struct sl_softc *)tp->t_sc;
 	if (sc != NULL) {
+		if (sc->sc_outfill) {
+			sc->sc_outfill = 0;
+			untimeout((timeout_func_t) sl_outfill, (caddr_t) sc);
+		}
+		if (sc->sc_keepalive) {
+			sc->sc_keepalive = 0;
+			untimeout((timeout_func_t) sl_keepalive, (caddr_t) sc);
+		}
 		if_down(&sc->sc_if);
+		sc->sc_flags = 0;
 		sc->sc_ttyp = NULL;
 		tp->t_sc = NULL;
 		MCLFREE((caddr_t)(sc->sc_ep - SLBUFSIZE));
@@ -346,15 +357,49 @@ sltioctl(tp, cmd, data, flag, p)
 	struct proc *p;
 {
 	struct sl_softc *sc = (struct sl_softc *)tp->t_sc;
+	int s;
 
+	s = splimp();
 	switch (cmd) {
 	case SLIOCGUNIT:
 		*(int *)data = sc->sc_if.if_unit;
 		break;
 
+	case SLIOCSKEEPAL:
+		sc->sc_keepalive = *(u_int *)data * hz;
+		if (sc->sc_keepalive) {
+			sc->sc_flags |= SC_KEEPALIVE;
+			timeout((timeout_func_t) sl_keepalive, (caddr_t) sc, sc->sc_keepalive);
+		} else {
+			sc->sc_flags &= ~SC_KEEPALIVE;
+			untimeout((timeout_func_t) sl_keepalive, (caddr_t) sc);
+		}
+		break;
+
+	case SLIOCGKEEPAL:
+		*(int *)data = sc->sc_keepalive / hz;
+		break;
+
+	case SLIOCSOUTFILL:
+		sc->sc_outfill = *(u_int *)data * hz;
+		if (sc->sc_outfill) {
+			sc->sc_flags |= SC_OUTWAIT;
+			timeout((timeout_func_t) sl_outfill, (caddr_t) sc, sc->sc_outfill);
+		} else {
+			sc->sc_flags &= ~SC_OUTWAIT;
+			untimeout((timeout_func_t) sl_outfill, (caddr_t) sc);
+		}
+		break;
+
+	case SLIOCGOUTFILL:
+		*(int *)data = sc->sc_outfill / hz;
+		break;
+
 	default:
-		return (-1);
+		splx(s);
+		return (ENOTTY);
 	}
+	splx(s);
 	return (0);
 }
 
@@ -448,6 +493,8 @@ slstart(tp)
 		 * it would.
 		 */
 		if (tp->t_outq.c_cc != 0) {
+			if (sc != NULL)
+				sc->sc_flags &= ~SC_OUTWAIT;
 			(*tp->t_oproc)(tp);
 			if (tp->t_outq.c_cc > SLIP_HIWAT)
 				return 0;
@@ -470,6 +517,7 @@ slstart(tp)
 		splx(s);
 		if (m == NULL)
 			return 0;
+		sc->sc_flags &= ~SC_OUTWAIT;
 
 		/*
 		 * We do the header compression here rather than in sloutput
@@ -728,6 +776,7 @@ slinput(c, tp)
 		return 0;
 
 	case FRAME_END:
+		sc->sc_flags &= ~SC_KEEPALIVE;
 		if(sc->sc_flags & SC_ERROR) {
 			sc->sc_flags &= ~SC_ERROR;
 			goto newpack;
@@ -901,4 +950,42 @@ slioctl(ifp, cmd, data)
 	splx(s);
 	return (error);
 }
+
+static void sl_keepalive (sc)
+	struct sl_softc *sc;
+{
+	if (sc->sc_keepalive) {
+		if (sc->sc_flags & SC_KEEPALIVE)
+			pgsignal (sc->sc_ttyp->t_pgrp, SIGURG, 1);
+		else
+			sc->sc_flags |= SC_KEEPALIVE;
+		timeout ((timeout_func_t) sl_keepalive, (caddr_t) sc, sc->sc_keepalive);
+	} else {
+		sc->sc_flags &= ~SC_KEEPALIVE;
+		untimeout ((timeout_func_t) sl_keepalive, (caddr_t) sc);
+	}
+}
+
+static void sl_outfill (sc)
+	struct sl_softc *sc;
+{
+	register struct tty *tp = sc->sc_ttyp;
+	int s;
+
+	if (sc->sc_outfill && tp != NULL) {
+		if (sc->sc_flags & SC_OUTWAIT) {
+			s = splimp ();
+			++sc->sc_if.if_obytes;
+			putc(FRAME_END, tp->t_out);
+			(*tp->t_oproc)(tp);
+			splx (s);
+		} else
+			sc->sc_flags |= SC_OUTWAIT;
+		timeout ((timeout_func_t) sl_outfill, (caddr_t) sc, sc->sc_outfill);
+	} else {
+		sc->sc_flags &= ~SC_OUTWAIT;
+		untimeout ((timeout_func_t) sl_outfill, (caddr_t) sc);
+	}
+}
+
 #endif
diff --git a/sys/net/if_slvar.h b/sys/net/if_slvar.h
index f94ec40..2fb3f9f 100644
--- a/sys/net/if_slvar.h
+++ b/sys/net/if_slvar.h
@@ -32,7 +32,7 @@
  *
  *	@(#)if_slvar.h	8.3 (Berkeley) 2/1/94
  *
- * $Id: if_slvar.h,v 1.3 1994/08/21 05:11:43 paul Exp $
+ * $Id: if_slvar.h,v 1.4 1994/10/08 01:40:23 phk Exp $
  */
 
 #ifndef _NET_IF_SLVAR_H_
@@ -56,6 +56,8 @@ struct sl_softc {
 	long	sc_lasttime;		/* last time a char arrived */
 	long	sc_abortcount;		/* number of abort esacpe chars */
 	long	sc_starttime;		/* time of first abort in window */
+	u_int	sc_keepalive;		/* time	to decide link hang */
+	u_int	sc_outfill;		/* time	to send	FRAME_END when output idle */
 #ifdef INET				/* XXX */
 	struct	slcompress sc_comp;	/* tcp compression data */
 #endif
@@ -64,6 +66,8 @@ struct sl_softc {
 
 /* internal flags */
 #define	SC_ERROR	0x0001		/* had an input error */
+#define	SC_OUTWAIT	0x0002		/* waiting for output fill */
+#define	SC_KEEPALIVE	0x0004		/* input keepalive */
 
 /* visible flags */
 #define	SC_COMPRESS	IFF_LINK0	/* compress TCP traffic */
diff --git a/sys/net/slip.h b/sys/net/slip.h
index 1c9ffca..a9730b5 100644
--- a/sys/net/slip.h
+++ b/sys/net/slip.h
@@ -31,14 +31,18 @@
  * SUCH DAMAGE.
  *
  *	@(#)slip.h	8.1 (Berkeley) 2/12/94
- * $Id: slip.h,v 1.2 1994/08/02 07:46:50 davidg Exp $
+ * $Id: slip.h,v 1.3 1994/08/21 05:11:48 paul Exp $
  */
 
 #ifndef _NET_SLIP_H_
 #define _NET_SLIP_H_
 
 /* Ioctls operating on SLIP ttys. */
-#define	SLIOCGUNIT	_IOR('t', 88, int)	/* get slip unit number */
+#define	SLIOCGUNIT	_IOR('t', 88, int)	/* get slip unit number	*/
+#define	SLIOCSKEEPAL	_IOW('t', 84, int)	/* set keepalive */
+#define	SLIOCSOUTFILL	_IOW('t', 83, int)	/* set out fill	time */
+#define	SLIOCGKEEPAL	_IOR('t', 82, int)	/* get keepalive time */
+#define	SLIOCGOUTFILL	_IOR('t', 81, int)	/* get out fill	time */
 
 /*
  * Definitions of the pseudo-link-level header attached to slip