netdev - Re: [RFC PATCH v2 net-next 05/17] net: bridge: implement unicast filtering for the bridge device

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Date:   Mon, 1 Mar 2021 17:22:48 +0200
From:   Ido Schimmel <idosch@...sch.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        DENG Qingfang <dqfext@...il.com>,
        Tobias Waldekranz <tobias@...dekranz.com>,
        George McCollister <george.mccollister@...il.com>,
        Vlad Yasevich <vyasevich@...il.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>
Subject: Re: [RFC PATCH v2 net-next 05/17] net: bridge: implement unicast
 filtering for the bridge device

On Wed, Feb 24, 2021 at 01:43:38PM +0200, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> The bridge device currently goes into promiscuous mode when it has an
> upper with a different MAC address than itself. But it could do better:
> it could sync the MAC addresses of its uppers to the software FDB, as
> local entries pointing to the bridge itself. This is compatible with
> switchdev, since drivers are now instructed to trap these MAC addresses
> to the CPU.
> 
> Note that the dev_uc_add API does not propagate VLAN ID, so this only
> works for VLAN-unaware bridges.

IOW, it breaks VLAN-aware bridges...

I understand that you do not want to track bridge uppers, but once you
look beyond L2 you will need to do it anyway.

Currently, you only care about getting packets with specific DMACs to
the CPU. With L3 offload you will need to send these packets to your
router block instead and track other attributes of these uppers such as
their MTU so that the hardware will know to generate MTU exceptions. In
addition, the hardware needs to know the MAC addresses of these uppers
so that it will rewrite the SMAC of forwarded packets.