netdev - Re: [PATCH net-next] bridge: Propagate NETDEV_NOTIFY

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Date:   Thu, 28 Jan 2021 11:27:26 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Nikolay Aleksandrov <nikolay@...dia.com>
Cc:     netdev@...r.kernel.org, Roopa Prabhu <roopa@...dia.com>,
        "David S . Miller" <davem@...emloft.net>,
        bridge@...ts.linux-foundation.org, Jarod Wilson <jarod@...hat.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Ido Schimmel <idosch@...sch.org>
Subject: Re: [PATCH net-next] bridge: Propagate NETDEV_NOTIFY_PEERS notifier

On Wed, Jan 27, 2021 at 11:43:30AM +0200, Nikolay Aleksandrov wrote:
> > For IGMP, although you said they are different. In my understanding, when
> > bridge mac changed, we need to re-join multicast group, while a gratuitous
> > ARP is also needed. I couldn't find a reason why IGMP message is OK but GARP
> > is not.
> > 
> 
> I think that's needed more because of port changing rather than mac changing.
> Switches need to be updated if the port has changed, all of that is already handled
> correctly by the bond. And I also meant that mcast is handled very differently in
> the bridge, usually you'd have snooping enabled.
> 
> The patch below isn't correct and will actually break some cases when bonding
> flaps ports and propagates NETDEV_RESEND_IGMP with a bridge on top.

Hi Nikolay,

I'm little curious. bond/team device will resend IGMP as their MAC address changed.

- bond_resend_igmp_join_requests_delayed()
  - call_netdevice_notifiers(NETDEV_RESEND_IGMP, bond->dev);
- team_mcast_rejoin_work()
  - call_netdevice_notifiers(NETDEV_RESEND_IGMP, team->dev);

What's the purpose that bridge resend IGMP if it's mac address not changed?

I mean, when there is a bridge on top of bond/team, when bond/team flap ports,
bond/team will re-send IGMP and bridge just need to forward it. bridge doesn't
need to re-send the IGMP itself if it's MAC address not changed.

Thanks
Hangbin