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

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Message-ID: <v6p7dcbtka6juf2ibero7ivimuhfbxs37uf5qihjbq4un4bdm6@ofdo34scswqq>
Date: Tue, 22 Apr 2025 11:14:36 +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

Sat, Apr 19, 2025 at 02:08:03AM +0200, kuba@...nel.org wrote:
>On Fri, 18 Apr 2025 12:26:50 +0200 Jiri Pirko wrote:
>> 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.
>
>Ugh, I thought enum netlink_attribute_type matches the values :|
>And user space uses MNL_ types.
>
>Please don't invent _DYN_ATTR at least. Why not PARAM_TYPE ?

Because it is used for both params and health reporters (fmsg).