netdev - Re: [PATCH net-next 02/17] net: switchdev: Add a helper to replay objects on a bridge port

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Date: Wed, 31 Jan 2024 17:47:28 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: Petr Machata <petrm@...dia.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, Ido Schimmel <idosch@...dia.com>,
	Danielle Ratson <danieller@...dia.com>, mlxsw@...dia.com,
	Jiri Pirko <jiri@...nulli.us>, Ivan Vecera <ivecera@...hat.com>,
	Roopa Prabhu <roopa@...dia.com>,
	Nikolay Aleksandrov <razor@...ckwall.org>,
	bridge@...ts.linux-foundation.org
Subject: Re: [PATCH net-next 02/17] net: switchdev: Add a helper to replay
 objects on a bridge port

Hi Petr,

On Wed, Jul 19, 2023 at 01:01:17PM +0200, Petr Machata wrote:
> When a front panel joins a bridge via another netdevice (typically a LAG),
> the driver needs to learn about the objects configured on the bridge port.
> When the bridge port is offloaded by the driver for the first time, this
> can be achieved by passing a notifier to switchdev_bridge_port_offload().
> The notifier is then invoked for the individual objects (such as VLANs)
> configured on the bridge, and can look for the interesting ones.
> 
> Calling switchdev_bridge_port_offload() when the second port joins the
> bridge lower is unnecessary, but the replay is still needed. To that end,
> add a new function, switchdev_bridge_port_replay(), which does only the
> replay part of the _offload() function in exactly the same way as that
> function.
> 
> Cc: Jiri Pirko <jiri@...nulli.us>
> Cc: Ivan Vecera <ivecera@...hat.com>
> Cc: Roopa Prabhu <roopa@...dia.com>
> Cc: Nikolay Aleksandrov <razor@...ckwall.org>
> Cc: bridge@...ts.linux-foundation.org
> Signed-off-by: Petr Machata <petrm@...dia.com>
> Reviewed-by: Danielle Ratson <danieller@...dia.com>
> ---

I just noticed this commit in the kernel, and the commit message did not
really convince me.

As unnecessary as the second switchdev_bridge_port_offload() call may be,
it does not hurt either, because it just bumps p->offload_count in the bridge.
And with just this justification, adding a new function to the switchdev API
is equally unnecessary.

Even worse, switchdev_bridge_port_replay() is a partial misnomer, and
will become a complete misnomer soon. Out of 3 object classes (FDB, MDB
and VLAN), FDB and VLAN are not actually replayed just for the given
bridge port given as argument, but for all ports of the bridge. And Tobias
wants to change things so that the same will happen for MDB too.
https://lore.kernel.org/netdev/87bk927bxl.fsf@waldekranz.com/

Can mlxsw not use the same replay code path as DSA, through the _offload()
and _unoffload() entry points?