netdev - Re: [PATCH v3 2/2] netconsole: allow selection of egress interface via MAC address

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Message-ID: <20250207162844.43b20256@kernel.org>
Date: Fri, 7 Feb 2025 16:28:44 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Uday Shankar <ushankar@...estorage.com>
Cc: Breno Leitao <leitao@...ian.org>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Srinivas Kandagatla
 <srinivas.kandagatla@...aro.org>, Rafał Miłecki
 <rafal@...ecki.pl>, Simon Horman <horms@...nel.org>, Andrew Morton
 <akpm@...ux-foundation.org>, Johannes Berg <johannes@...solutions.net>,
 Jonathan Corbet <corbet@....net>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
 linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 2/2] netconsole: allow selection of egress interface
 via MAC address

On Wed, 05 Feb 2025 22:21:31 -0700 Uday Shankar wrote:
> Currently, netconsole has two methods of configuration - module
> parameter and configfs. The former interface allows for netconsole
> activation earlier during boot (by specifying the module parameter on
> the kernel command line), so it is preferred for debugging issues which
> arise before userspace is up/the configfs interface can be used. The
> module parameter syntax requires specifying the egress interface name.
> This requirement makes it hard to use for a couple reasons:
> - The egress interface name can be hard or impossible to predict. For
>   example, installing a new network card in a system can change the
>   interface names assigned by the kernel.
> - When constructing the module parameter, one may have trouble
>   determining the original (kernel-assigned) name of the interface
>   (which is the name that should be given to netconsole) if some stable
>   interface naming scheme is in effect. A human can usually look at
>   kernel logs to determine the original name, but this is very painful
>   if automation is constructing the parameter.
> 
> For these reasons, allow selection of the egress interface via MAC
> address when configuring netconsole using the module parameter. Update
> the netconsole documentation with an example of the new syntax.
> Selection of egress interface by MAC address via configfs is far less
> interesting (since when this interface can be used, one should be able
> to easily convert between MAC address and interface name), so it is left
> unimplemented.

Sounds like dev_getbyhwaddr_rcu() will warn here. Either wrap it 
in  RCU temporarily or combine the series with Breno's patch to 
add a new helper?
-- 
pw-bot: cr