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

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Message-ID: <20250702091055.3d70a5ee@kernel.org>
Date: Wed, 2 Jul 2025 09:10:55 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc: Gabriel Goller <g.goller@...xmox.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 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))