bridge: add export of multicast database adjacent to net_dev

With this new, exported function br_multicast_list_adjacent(net_dev) a
list of IPv4/6 addresses is returned. This list contains all multicast
addresses sensed by the bridge multicast snooping feature on all bridge
ports of the bridge interface of net_dev, excluding addresses from the
specified net_device itself.

Adding bridge support to the batman-adv multicast optimization requires
batman-adv knowing about the existence of bridged-in multicast
listeners to be able to reliably serve them with multicast packets.
Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/if_bridge.h

@@ -16,9 +16,27 @@
 #include <linux/netdevice.h>
 #include <uapi/linux/if_bridge.h>
 
+struct br_ip {
+	union {
+		__be32	ip4;
+#if IS_ENABLED(CONFIG_IPV6)
+		struct in6_addr ip6;
+#endif
+	} u;
+	__be16		proto;
+	__u16           vid;
+};
+
+struct br_ip_list {
+	struct list_head list;
+	struct br_ip addr;
+};
+
 extern void brioctl_set(int (*ioctl_hook)(struct net *, unsigned int, void __user *));
 
 typedef int br_should_route_hook_t(struct sk_buff *skb);
 extern br_should_route_hook_t __rcu *br_should_route_hook;
+int br_multicast_list_adjacent(struct net_device *dev,
+			       struct list_head *br_ip_list);
 
 #endif

net/bridge/br_multicast.c

@@ -11,6 +11,7 @@
  */
 
 #include <linux/err.h>
+#include <linux/export.h>
 #include <linux/if_ether.h>
 #include <linux/igmp.h>
 #include <linux/jhash.h>
@@ -2141,3 +2142,60 @@ int br_multicast_set_hash_max(struct net_bridge *br, unsigned long val)
 
 	return err;
 }
+
+/**
+ * br_multicast_list_adjacent - Returns snooped multicast addresses
+ * @dev:	The bridge port adjacent to which to retrieve addresses
+ * @br_ip_list:	The list to store found, snooped multicast IP addresses in
+ *
+ * Creates a list of IP addresses (struct br_ip_list) sensed by the multicast
+ * snooping feature on all bridge ports of dev's bridge device, excluding
+ * the addresses from dev itself.
+ *
+ * Returns the number of items added to br_ip_list.
+ *
+ * Notes:
+ * - br_ip_list needs to be initialized by caller
+ * - br_ip_list might contain duplicates in the end
+ *   (needs to be taken care of by caller)
+ * - br_ip_list needs to be freed by caller
+ */
+int br_multicast_list_adjacent(struct net_device *dev,
+			       struct list_head *br_ip_list)
+{
+	struct net_bridge *br;
+	struct net_bridge_port *port;
+	struct net_bridge_port_group *group;
+	struct br_ip_list *entry;
+	int count = 0;
+
+	rcu_read_lock();
+	if (!br_ip_list || !br_port_exists(dev))
+		goto unlock;
+
+	port = br_port_get_rcu(dev);
+	if (!port || !port->br)
+		goto unlock;
+
+	br = port->br;
+
+	list_for_each_entry_rcu(port, &br->port_list, list) {
+		if (!port->dev || port->dev == dev)
+			continue;
+
+		hlist_for_each_entry_rcu(group, &port->mglist, mglist) {
+			entry = kmalloc(sizeof(*entry), GFP_ATOMIC);
+			if (!entry)
+				goto unlock;
+
+			entry->addr = group->addr;
+			list_add(&entry->list, br_ip_list);
+			count++;
+		}
+	}
+
+unlock:
+	rcu_read_unlock();
+	return count;
+}
+EXPORT_SYMBOL_GPL(br_multicast_list_adjacent);

net/bridge/br_private.h

@@ -54,18 +54,6 @@ struct mac_addr
 	unsigned char	addr[ETH_ALEN];
 };
 
-struct br_ip
-{
-	union {
-		__be32	ip4;
-#if IS_ENABLED(CONFIG_IPV6)
-		struct in6_addr ip6;
-#endif
-	} u;
-	__be16		proto;
-	__u16		vid;
-};
-
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
 /* our own querier */
 struct bridge_mcast_own_query {