net: bridge: add support for IGMP/MLD stats and export them via netlink

This patch adds stats support for the currently used IGMP/MLD types by the
bridge. The stats are per-port (plus one stat per-bridge) and per-direction
(RX/TX). The stats are exported via netlink via the new linkxstats API
(RTM_GETSTATS). In order to minimize the performance impact, a new option
is used to enable/disable the stats - multicast_stats_enabled, similar to
the recent vlan stats. Also in order to avoid multiple IGMP/MLD type
lookups and checks, we make use of the current "igmp" member of the bridge
private skb->cb region to record the type on Rx (both host-generated and
external packets pass by multicast_rcv()). We can do that since the igmp
member was used as a boolean and all the valid IGMP/MLD types are positive
values. The normal bridge fast-path is not affected at all, the only
affected paths are the flooding ones and since we make use of the IGMP/MLD
type, we can quickly determine if the packet should be counted using
cache-hot data (cb's igmp member). We add counters for:
* IGMP Queries
* IGMP Leaves
* IGMP v1/v2/v3 reports

* MLD Queries
* MLD Leaves
* MLD v1/v2 reports

These are invaluable when monitoring or debugging complex multicast setups
with bridges.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_input.c

@@ -60,6 +60,9 @@ static int br_pass_frame_up(struct sk_buff *skb)
 	skb = br_handle_vlan(br, vg, skb);
 	if (!skb)
 		return NET_RX_DROP;
+	/* update the multicast stats if the packet is IGMP/MLD */
+	br_multicast_count(br, NULL, skb->protocol, br_multicast_igmp_type(skb),
+			   BR_MCAST_DIR_TX);
 
 	return NF_HOOK(NFPROTO_BRIDGE, NF_BR_LOCAL_IN,
 		       dev_net(indev), NULL, skb, indev, NULL,