netdev - MDB offloading of local ipv4 multicast groups

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Date:   Thu, 15 Sep 2016 20:58:50 +0200
From:   John Crispin <john@...ozen.org>
To:     Elad Raz <eladr@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:     Ido Schimmel <idosch@...lanox.com>, Jiri Pirko <jiri@...lanox.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: MDB offloading of local ipv4 multicast groups

Hi,

While adding MDB support to the qca8k dsa driver I found that ipv4 mcast
groups don't always get propagated to the dsa driver. In my setup there
are 2 clients connected to the switch, both running a mdns client. The
.port_mdb_add() callback is properly called for 33:33:00:00:00:FB but
01:00:5E:00:00:FB never got propagated to the dsa driver.

The reason is that the call to ipv4_is_local_multicast() here [1] will
return true and the notifier is never called. Is this intentional or is
there something missing in the code ?

	John

[1]
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/net/bridge/br_multicast.c?id=refs/tags/v4.8-rc6#n737