netdev - Re: [PATCH net-next v2 0/8] net: Shift responsibility for FDB notifications to drivers

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Message-ID: <7426480f-6443-497f-8d37-b11f8f22069e@redhat.com>
Date: Tue, 5 Nov 2024 10:11:58 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Petr Machata <petrm@...dia.com>, Jakub Kicinski <kuba@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
 Ido Schimmel <idosch@...dia.com>, Amit Cohen <amcohen@...dia.com>,
 Vladimir Oltean <vladimir.oltean@....com>, Andy Roulin <aroulin@...dia.com>,
 mlxsw@...dia.com
Subject: Re: [PATCH net-next v2 0/8] net: Shift responsibility for FDB
 notifications to drivers

On 11/4/24 12:43, Petr Machata wrote:
> Jakub Kicinski <kuba@...nel.org> writes:
>> On Thu, 24 Oct 2024 18:57:35 +0200 Petr Machata wrote:
>>> Besides this approach, we considered just passing a boolean back from the
>>> driver, which would indicate whether the notification was done. But the
>>> approach presented here seems cleaner.
>>
>> Oops, I missed the v2, same question:
>>
>>   What about adding a bit to the ops struct to indicate that 
>>   the driver will generate the notification? Seems smaller in 
>>   terms of LoC and shifts the responsibility of doing extra
>>   work towards more complex users.
>>
>> https://lore.kernel.org/all/20241029121619.1a710601@kernel.org/
> 
> Sorry for only responding now, I was out of office last week.
> 
> The reason I went with outright responsibility shift is that the
> alternatives are more complex.
> 
> For the flag in particular, first there's no place to set the flag
> currently, we'd need a field in struct net_device_ops. But mainly, then
> you have a code that needs to corrently handle both states of the flag,
> and new-style drivers need to remember to set the flag, which is done in
> a different place from the fdb_add/del themselves. It might be fewer
> LOCs, but it's a harder to understand system.
> 
> Responsibility shift is easy. "Thou shalt notify." Done, easy to
> understand, easy to document. When cut'n'pasting, you won't miss it.
> 
> Let me know what you think.

I think that keeping as much action/responsibilities as possible in the
core code is in general a better option - at very least to avoid
duplicate code.

I don't think that the C&P is a very good argument, as I would argue
against C&P without understanding of the underlying code. Still I agree
that keeping all the relevant info together is better, and a separate
flag would be not so straight-forward.

What about using the return value of fbd_add/fdb_del to tell the core
that the driver did the notification? a positive value means 'already
notified', a negative one error, zero 'please notify.

Cheers,

Paolo