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From: "Alexander V. Chernikov" <melifaro@FreeBSD.org>
Date: Sun, 15 Jul 2012 17:44:28 +0000 (UTC)
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Subject: svn commit: r238492 - head/sys/net
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Author: melifaro
Date: Sun Jul 15 17:44:27 2012
New Revision: 238492
URL: http://svn.freebsd.org/changeset/base/238492

Log:
  Permit changing MTU in 6to4 relay.
  
  This behavior is recommended by RFC 4213 clause 3.2.
  
  Sometimes fragmentation is the least evil.
  For example, some Linux IPVS kernels forwards
  ICMPv6 checksums to real servers incorrectly.
  
  Reviewed by:      hrs(previous version)
  Approved by:      kib(mentor)
  MFC after:        1 week

Modified:
  head/sys/net/if_stf.c

Modified: head/sys/net/if_stf.c
==============================================================================
--- head/sys/net/if_stf.c	Sun Jul 15 15:50:12 2012	(r238491)
+++ head/sys/net/if_stf.c	Sun Jul 15 17:44:27 2012	(r238492)
@@ -793,7 +793,7 @@ stf_rtrequest(cmd, rt, info)
 	struct rt_addrinfo *info;
 {
 	RT_LOCK_ASSERT(rt);
-	rt->rt_rmx.rmx_mtu = IPV6_MMTU;
+	rt->rt_rmx.rmx_mtu = rt->rt_ifp->if_mtu;
 }
 
 static int
@@ -806,7 +806,7 @@ stf_ioctl(ifp, cmd, data)
 	struct ifreq *ifr;
 	struct sockaddr_in6 *sin6;
 	struct in_addr addr;
-	int error;
+	int error, mtu;
 
 	error = 0;
 	switch (cmd) {
@@ -840,6 +840,18 @@ stf_ioctl(ifp, cmd, data)
 			error = EAFNOSUPPORT;
 		break;
 
+	case SIOCGIFMTU:
+		break;
+
+	case SIOCSIFMTU:
+		ifr = (struct ifreq *)data;
+		mtu = ifr->ifr_mtu;
+		/* RFC 4213 3.2 ideal world MTU */
+		if (mtu < IPV6_MINMTU || mtu > IF_MAXMTU - 20)
+			return (EINVAL);
+		ifp->if_mtu = mtu;
+		break;
+
 	default:
 		error = EINVAL;
 		break;