net: ipv6: Clear joined flag on all mcast address when operational down

When the network inteface goes operational DOWN (for example cable
unplugged), clear "joined" flag on all registered multicast addresses,
so that MLD report is sent for them when the interface goes back up.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>

subsys/net/ip/net_if.c

@@ -1667,6 +1667,7 @@ static void rejoin_ipv6_mcast_groups(struct net_if *iface)
 		goto out;
 	}
 
+	/* Rejoin solicited node multicasts. */
 	ARRAY_FOR_EACH(ipv6->unicast, i) {
 		if (!ipv6->unicast[i].is_used) {
 			continue;
@@ -1675,6 +1676,52 @@ static void rejoin_ipv6_mcast_groups(struct net_if *iface)
 		join_mcast_nodes(iface, &ipv6->unicast[i].address.in6_addr);
 	}
 
+	/* Rejoin any mcast address present on the interface, but marked as not joined. */
+	ARRAY_FOR_EACH(ipv6->mcast, i) {
+		int ret;
+
+		if (!ipv6->mcast[i].is_used ||
+		    net_if_ipv4_maddr_is_joined(&ipv6->mcast[i])) {
+			continue;
+		}
+
+		ret = net_ipv6_mld_join(iface, &ipv6->mcast[i].address.in6_addr);
+		if (ret < 0) {
+			NET_ERR("Cannot join mcast address %s for %d (%d)",
+				net_sprint_ipv6_addr(&ipv6->mcast[i].address.in6_addr),
+				net_if_get_by_iface(iface), ret);
+		}
+	}
+
+out:
+	net_if_unlock(iface);
+}
+
+/* To be called when interface comes operational down so that multicast
+ * groups are rejoined when back up.
+ */
+static void clear_joined_ipv6_mcast_groups(struct net_if *iface)
+{
+	struct net_if_ipv6 *ipv6;
+
+	net_if_lock(iface);
+
+	if (!net_if_flag_is_set(iface, NET_IF_IPV6)) {
+		goto out;
+	}
+
+	if (net_if_config_ipv6_get(iface, &ipv6) < 0) {
+		goto out;
+	}
+
+	ARRAY_FOR_EACH(ipv6->mcast, i) {
+		if (!ipv6->mcast[i].is_used) {
+			continue;
+		}
+
+		net_if_ipv6_maddr_leave(iface, &ipv6->mcast[i]);
+	}
+
 out:
 	net_if_unlock(iface);
 }
@@ -5033,6 +5080,7 @@ static void notify_iface_down(struct net_if *iface)
 
 	if (!net_if_is_offloaded(iface) &&
 	    !(l2_flags_get(iface) & NET_L2_POINT_TO_POINT)) {
+		clear_joined_ipv6_mcast_groups(iface);
 		iface_ipv6_stop(iface);
 		net_ipv4_autoconf_reset(iface);
 	}