netdev - Re: [PATCH net-next] net: ethtool: Don't check if RSS context exists in case of context 0

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Message-ID: <cd0b748b-fe7d-86ac-098b-0d6ec78a04a2@gmail.com>
Date: Thu, 27 Feb 2025 19:54:17 +0000
From: Edward Cree <ecree.xilinx@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Gal Pressman <gal@...dia.com>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, netdev@...r.kernel.org,
 Andrew Lunn <andrew@...n.ch>, Simon Horman <horms@...nel.org>,
 Joe Damato <jdamato@...tly.com>, Tariq Toukan <tariqt@...dia.com>
Subject: Re: [PATCH net-next] net: ethtool: Don't check if RSS context exists
 in case of context 0

On 27/02/2025 16:56, Jakub Kicinski wrote:
> On Thu, 27 Feb 2025 16:24:52 +0000 Edward Cree wrote:
>>> I never uttered the thought that lead me to opposing. 
>>> ctx 0 is a poor man's pass / accept. If someone needs a pass we should
>>> add an explicit "action pass".  
>>
>> To me 'pass' is just a shorthand for whatever specific behaviour
>>  happens to match the default.  I.e. if you can already express
>>  that behaviour directly, then 'pass' is a strictly nonorthogonal
>>  addition and therefore bad interface design.
> 
> I presume sfc matches only one rule. For devices which terminate on
> first hit and rules are ordered by ntuple ID, the following rules*:
> 
>  src-ip 192.168.0.2                 context 0
>  src-ip 192.0.0.0   m 0.255.255.255 action -1
> 
> implement allowing only 192.168.0.2 out of the 192.0.0.0/8 subnet. 

Ah, so the point is that "pass" wasn't expressible before RSS contexts
 came along, and may therefore be surprising and new.  I get you now.

> The device may not even support RSS contexts.

I think in that case the driver will reject the first filter because it
 doesn't recognise flow_type == FLOW_RSS | WHATEVER_FLOW.  Unless the
 driver writer has deliberately added support for RSS filters despite
 only having context 0, which seems like a signal they know it means
 'pass' and explicitly wanted that.