==== //depot/user/bms/netdev/sys/netinet/in.c#11 - /home/bms/p4/netdev/sys/netinet/in.c ====
--- /tmp/tmp.1127.0	Tue Mar 27 16:43:56 2007
+++ /home/bms/p4/netdev/sys/netinet/in.c	Tue Mar 27 16:40:04 2007
@@ -212,6 +212,11 @@
 /*
  * Generic internet control operations (ioctl's).
  * Ifp is 0 if not an interface-specific ioctl.
+ *
+ * XXX: This code has some nice big juicy bugs related to interface
+ * attach and detach. Specifically, the 224.0.0.1 group is now only
+ * joined on the first IPv4 address configured on an interface, and
+ * only left when all IPv4 state is torn down for an interface.
  */
 /* ARGSUSED */
 int
@@ -230,7 +235,9 @@
 	struct in_aliasreq *ifra = (struct in_aliasreq *)data;
 	struct sockaddr_in oldaddr;
 	int error, hostIsNew, iaIsNew, maskIsNew, s;
+	int iaIsFirst;
 
+	iaIsFirst = 0;
 	iaIsNew = 0;
 
 	switch (cmd) {
@@ -282,6 +289,8 @@
 					break;
 				}
 			}
+		if (ia == NULL)
+			iaIsFirst = 1;
 	}
 
 	switch (cmd) {
@@ -423,8 +432,20 @@
 		    (struct sockaddr_in *) &ifr->ifr_addr, 1);
 		if (error != 0 && iaIsNew)
 			break;
-		if (error == 0)
+		if (error == 0) {
+			/*
+			 * Only join 224.0.0.1 if this is the very first
+			 * IPv4 unicast address which has been configured
+			 * on this ifnet.
+			 */
+			if (iaIsFirst && (ifp->if_flags & IFF_MULTICAST) != 0) {
+				struct in_addr addr;
+
+				addr.s_addr = htonl(INADDR_ALLHOSTS_GROUP);
+				in_addmulti(&addr, ifp);
+			}
 			EVENTHANDLER_INVOKE(ifaddr_event, ifp);
+		}
 		return (0);
 
 	case SIOCSIFNETMASK:
@@ -467,8 +488,20 @@
 		if ((ifp->if_flags & IFF_BROADCAST) &&
 		    (ifra->ifra_broadaddr.sin_family == AF_INET))
 			ia->ia_broadaddr = ifra->ifra_broadaddr;
-		if (error == 0)
+		if (error == 0) {
+			/*
+			 * Only join 224.0.0.1 if this is the very first
+			 * IPv4 unicast address which has been configured
+			 * on this ifnet.
+			 */
+			if (iaIsFirst && (ifp->if_flags & IFF_MULTICAST) != 0) {
+				struct in_addr addr;
+
+				addr.s_addr = htonl(INADDR_ALLHOSTS_GROUP);
+				in_addmulti(&addr, ifp);
+			}
 			EVENTHANDLER_INVOKE(ifaddr_event, ifp);
+		}
 		return (error);
 
 	case SIOCDIFADDR:
@@ -503,8 +536,33 @@
 	s = splnet();
 	TAILQ_REMOVE(&ifp->if_addrhead, &ia->ia_ifa, ifa_link);
 	TAILQ_REMOVE(&in_ifaddrhead, ia, ia_link);
-	if (ia->ia_addr.sin_family == AF_INET)
+	if (ia->ia_addr.sin_family == AF_INET) {
+		struct in_ifaddr *pia;
+
 		LIST_REMOVE(ia, ia_hash);
+		/*
+		 * Only purge the 224.0.0.1 membership if the last IPv4
+		 * unicast address configured on this ifnet is removed.
+		 *
+		 * XXX: This currently involves trawling through the
+		 * in_ifaddrhead list looking for a match, which is
+		 * inefficient, though this is only done when an interface
+		 * address goes away. This could be done much more elegantly.
+		 */
+		pia = NULL;
+		IFP_TO_IA(ifp, pia);
+		if (pia == NULL) {
+			struct in_multi *inm;
+			struct in_addr addr;
+
+			addr.s_addr = htonl(INADDR_ALLHOSTS_GROUP);
+			IN_MULTI_LOCK();
+			IN_LOOKUP_MULTI(addr, ifp, inm);
+			if (inm != NULL)
+				in_delmulti(inm);
+			IN_MULTI_UNLOCK();
+		}
+	}
 	IFAFREE(&ia->ia_ifa);
 	splx(s);
 
@@ -793,16 +851,6 @@
 	if ((error = in_addprefix(ia, flags)) != 0)
 		return (error);
 
-	/*
-	 * If the interface supports multicast, join the "all hosts"
-	 * multicast group on that interface.
-	 */
-	if (ifp->if_flags & IFF_MULTICAST) {
-		struct in_addr addr;
-
-		addr.s_addr = htonl(INADDR_ALLHOSTS_GROUP);
-		in_addmulti(&addr, ifp);
-	}
 	return (error);
 }
 
@@ -1114,6 +1162,9 @@
 		igmp_leavegroup(inm);
 
 		ifma = inm->inm_ifma;
+#ifdef DIAGNOSTIC
+		printf("%s: purging ifma %p\n", __func__, ifma);
+#endif
 		KASSERT(ifma->ifma_protospec == inm,
 		    ("%s: ifma_protospec != inm", __func__));
 		ifma->ifma_protospec = NULL;
@@ -1135,6 +1186,9 @@
 	struct in_multi *inm;
 	struct in_multi *oinm;
 
+#ifdef DIAGNOSTIC
+	printf("%s: purging ifp %p\n", __func__, ifp);
+#endif
 	IFF_LOCKGIANT(ifp);
 	IN_MULTI_LOCK();
 	LIST_FOREACH_SAFE(inm, &in_multihead, inm_link, oinm) {