linux-kernel - Re: [PATCH v3] ipv6: add `force_forwarding` sysctl to enable per-interface forwarding

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Message-ID: <bes2ehifwb25xwbxg6dog27hi63vzn2phnhtiibed3wgazjpms@cwcrjo3ky7xq>
Date: Thu, 3 Jul 2025 13:05:11 +0200
From: Gabriel Goller <g.goller@...xmox.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Nicolas Dichtel <nicolas.dichtel@...nd.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Jonathan Corbet <corbet@....net>, David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] ipv6: add `force_forwarding` sysctl to enable
 per-interface forwarding

On 02.07.2025 09:10, Jakub Kicinski wrote:
>On Wed, 2 Jul 2025 17:14:42 +0200 Nicolas Dichtel wrote:
>> > Should we invert the polarity? It appears that the condition below only
>> > let's this setting _disable_ forwarding. IMO calling it "force" suggests
>> > to the user that it will force it to be enabled.
>> Not sure to follow you. When force_forwarding is set to 1 the forwarding is
>> always enabled.
>>
>> sysctl | all.forwarding | iface.force_forwarding | packet processing from iface
>>        |      0         |           0            |        no forward
>>        |      0         |           1            |         forward
>>        |      1         |           0            |         forward
>>        |      1         |           1            |         forward
>
>Ugh, I can't read comparisons to zero.
>Let's switch to more sane logic:
>
>	if (idev && !READ_ONCE(idev->cnf.force_forwarding) &&
>	    !READ_ONCE(net->ipv6.devconf_all->forwarding))

Agree!

Thanks for the review.