netdev - Re: [PATCH net-next V2 01/14] devlink: define enum for attr types of dynamic attributes

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Message-ID: <bctzge47tevxcbbawe7kvbzlygimyxstqiqpptfc63o67g4slc@jenow3ls7fgz>
Date: Fri, 18 Apr 2025 12:26:50 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Saeed Mahameed <saeed@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, 
	Eric Dumazet <edumazet@...gle.com>, Saeed Mahameed <saeedm@...dia.com>, netdev@...r.kernel.org, 
	Tariq Toukan <tariqt@...dia.com>, Gal Pressman <gal@...dia.com>, 
	Leon Romanovsky <leonro@...dia.com>, Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH net-next V2 01/14] devlink: define enum for attr types of
 dynamic attributes

Thu, Apr 17, 2025 at 03:08:26AM +0200, kuba@...nel.org wrote:
>On Mon, 14 Apr 2025 12:59:46 -0700 Saeed Mahameed wrote:
>> From: Jiri Pirko <jiri@...dia.com>
>> 
>> Devlink param and health reporter fmsg use attributes with dynamic type
>> which is determined according to a different type. Currently used values
>> are NLA_*. The problem is, they are not part of UAPI. They may change
>> which would cause a break.
>> 
>> To make this future safe, introduce a enum that shadows NLA_* values in
>> it and is part of UAPI.
>> 
>> Also, this allows to possibly carry types that are unrelated to NLA_*
>> values.
>
>I don't think you need to expose this in C. I had to solve this
>problem for rtnl because we nested dpll attrs in link info. Please see:
>
>https://github.com/kuba-moo/linux/commit/6faf7a638d0a5ded688a22a1337f56470dca85a3
>
>and look at the change for dpll here (sorry IDK how to link to a line :S)
>
>https://github.com/kuba-moo/linux/commit/00c8764ebb12f925b6f1daedd5e08e6fac478bfd
>
>With that you can add the decode info to the YAML spec for Python et al.
>but there's no need do duplicate the values. Right now this patch
>generates a bunch of "missing kdoc" warnings.
>
>Ima start sending those changes after the net -> net-next merge,
>some of the prep had to go to net :(

I may be missing something, I don't see how your work is related to
mine. The problem I'm trying to solve is that kernel sends NLA_* values
to userspace, without NLA_* being part of UAPI. At any time (even unlikely),
NLA_* values in kernel may change and that would break the userspace
suddenly getting different values.

Therefore, I introduce an enum for this. This is how it should have been
done from day 1, it's a bug in certain sense. Possibility to carry
non-NLA_* type in this enum is a plus we benefit from later in this
patchset.
>