From e52c654ee229f069ca2d720167cb753d60fac19b Mon Sep 17 00:00:00 2001
From: wollman <wollman@FreeBSD.org>
Date: Mon, 16 Oct 1995 18:21:26 +0000
Subject: [PATCH] The ability to administratively change the MTU of an
 interface presents a few new wrinkles for MTU discovery which tcp_output()
 had better be prepared to handle.  ip_output() is also modified to do
 something helpful in this case, since it has already calculated the
 information we need.

---
 sys/netinet/ip_output.c    | 16 +++++++++++++++-
 sys/netinet/tcp_output.c   | 14 +++++++++++++-
 sys/netinet/tcp_subr.c     |  8 ++------
 sys/netinet/tcp_timewait.c |  8 ++------
 sys/netinet/tcp_var.h      |  5 ++++-
 5 files changed, 36 insertions(+), 15 deletions(-)

diff --git a/sys/netinet/ip_output.c b/sys/netinet/ip_output.c
index 83e7382bc363..d536a8329023 100644
--- a/sys/netinet/ip_output.c
+++ b/sys/netinet/ip_output.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)ip_output.c	8.3 (Berkeley) 1/21/94
- * $Id: ip_output.c,v 1.22 1995/07/02 16:45:07 joerg Exp $
+ *	$Id: ip_output.c,v 1.23 1995/07/26 18:05:13 wollman Exp $
  */
 
 #include <sys/param.h>
@@ -331,6 +331,20 @@ sendit:
 	 */
 	if (ip->ip_off & IP_DF) {
 		error = EMSGSIZE;
+#ifdef MTUDISC
+		/*
+		 * This case can happen if the user changed the MTU
+		 * of an interface after enabling IP on it.  Because
+		 * most netifs don't keep track of routes pointing to
+		 * them, there is no way for one to update all its
+		 * routes when the MTU is changed.
+		 */
+		if ((ro->ro_rt->rt_flags & (RTF_UP | RTF_HOST))
+		    && !(ro->ro_rt->rt_rmx.rmx_locks & RTV_MTU)
+		    && (ro->ro_rt->rt_rmx.rmx_mtu > ifp->if_mtu)) {
+			ro->ro_rt->rt_rmx.rmx_mtu = ifp->if_mtu;
+		}
+#endif /* MTUDISC */
 		ipstat.ips_cantfrag++;
 		goto bad;
 	}
diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
index b14d645fbb18..9afaf97b6af6 100644
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)tcp_output.c	8.4 (Berkeley) 5/24/95
- *	$Id: tcp_output.c,v 1.13 1995/09/20 21:00:58 wollman Exp $
+ *	$Id: tcp_output.c,v 1.14 1995/09/22 20:05:58 wollman Exp $
  */
 
 #include <sys/param.h>
@@ -689,6 +689,18 @@ out:
 			tcp_quench(tp->t_inpcb, 0);
 			return (0);
 		}
+#ifdef MTUDISC
+		if (error == EMSGSIZE) {
+			/*
+			 * ip_output() will have already fixed the route
+			 * for us.  tcp_mtudisc() will, as its last action,
+			 * initiate retransmission, so it is important to
+			 * not do so here.
+			 */
+			tcp_mtudisc(tp->t_inpcb, 0);
+			return 0;
+		}
+#endif /* MTUDISC */.
 		if ((error == EHOSTUNREACH || error == ENETDOWN)
 		    && TCPS_HAVERCVDSYN(tp->t_state)) {
 			tp->t_softerror = error;
diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
index 404208399745..b0b75b8ee696 100644
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)tcp_subr.c	8.2 (Berkeley) 5/24/95
- *	$Id: tcp_subr.c,v 1.18 1995/10/10 17:45:40 wollman Exp $
+ *	$Id: tcp_subr.c,v 1.19 1995/10/12 17:37:24 wollman Exp $
  */
 
 #include <sys/param.h>
@@ -429,10 +429,6 @@ tcp_notify(inp, error)
 	sowwakeup(so);
 }
 
-#ifdef MTUDISC
-static void tcp_mtudisc __P((struct inpcb *, int));
-#endif /* MTUDISC */
-
 void
 tcp_ctlinput(cmd, sa, ip)
 	int cmd;
@@ -481,7 +477,7 @@ tcp_quench(inp, errno)
  * since we know the packet we just sent was dropped.
  * This duplicates some code in the tcp_mss() function in tcp_input.c.
  */
-static void
+void
 tcp_mtudisc(inp, errno)
 	struct inpcb *inp;
 	int errno;
diff --git a/sys/netinet/tcp_timewait.c b/sys/netinet/tcp_timewait.c
index 404208399745..b0b75b8ee696 100644
--- a/sys/netinet/tcp_timewait.c
+++ b/sys/netinet/tcp_timewait.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)tcp_subr.c	8.2 (Berkeley) 5/24/95
- *	$Id: tcp_subr.c,v 1.18 1995/10/10 17:45:40 wollman Exp $
+ *	$Id: tcp_subr.c,v 1.19 1995/10/12 17:37:24 wollman Exp $
  */
 
 #include <sys/param.h>
@@ -429,10 +429,6 @@ tcp_notify(inp, error)
 	sowwakeup(so);
 }
 
-#ifdef MTUDISC
-static void tcp_mtudisc __P((struct inpcb *, int));
-#endif /* MTUDISC */
-
 void
 tcp_ctlinput(cmd, sa, ip)
 	int cmd;
@@ -481,7 +477,7 @@ tcp_quench(inp, errno)
  * since we know the packet we just sent was dropped.
  * This duplicates some code in the tcp_mss() function in tcp_input.c.
  */
-static void
+void
 tcp_mtudisc(inp, errno)
 	struct inpcb *inp;
 	int errno;
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
index b2703ae2c955..0a1ce277ac60 100644
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)tcp_var.h	8.4 (Berkeley) 5/24/95
- * 	$Id: tcp_var.h,v 1.19 1995/10/10 17:45:43 wollman Exp $
+ * 	$Id: tcp_var.h,v 1.20 1995/10/12 17:37:25 wollman Exp $
  */
 
 #ifndef _NETINET_TCP_VAR_H_
@@ -349,6 +349,9 @@ void	 tcp_init __P((void));
 void	 tcp_input __P((struct mbuf *, int));
 void	 tcp_mss __P((struct tcpcb *, int));
 int	 tcp_mssopt __P((struct tcpcb *));
+#ifdef MTUDISC
+void tcp_mtudisc __P((struct inpcb *, int));
+#endif /* MTUDISC */
 struct tcpcb *
 	 tcp_newtcpcb __P((struct inpcb *));
 void	 tcp_notify __P((struct inpcb *, int));