linux-kernel - Re: [PATCH net-next v3 11/11] wireguard: netlink: generate netlink code

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Message-ID: <CAHmME9oO0sGnHrZUeETmL+CCj1UZ+aQx_CPArXKpFuBhE9UYbw@mail.gmail.com>
Date: Thu, 20 Nov 2025 03:46:39 +0100
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Asbjørn Sloth Tønnesen <ast@...erby.net>, 
	Donald Hunter <donald.hunter@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Jacob Keller <jacob.e.keller@...el.com>, Andrew Lunn <andrew+netdev@...n.ch>, 
	wireguard@...ts.zx2c4.com, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Jordan Rife <jordan@...fe.io>
Subject: Re: [PATCH net-next v3 11/11] wireguard: netlink: generate netlink code

On Thu, Nov 20, 2025 at 3:44 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 20 Nov 2025 01:54:47 +0100 Jason A. Donenfeld wrote:
> > On Tue, Nov 18, 2025 at 05:00:45PM -0800, Jakub Kicinski wrote:
> > > On Tue, 18 Nov 2025 23:51:37 +0100 Jason A. Donenfeld wrote:
> > > > I mean, there is *tons* of generated code in the kernel. This is how it
> > > > works. And you *want the output to change when the tool changes*. That's
> > > > literally the point. It would be like if you wanted to check in all the
> > > > .o files, in case the compiler started generating different output, or
> > > > if you wanted the objtool output or anything else to be checked in. And
> > > > sheerly from a git perspective, it seems outrageous to touch a zillion
> > > > files every time the ynl code changes. Rather, the fact that it's
> > > > generated on the fly ensures that the ynl generator stays correctly
> > > > implemented. It's the best way to keep that code from rotting.
> > >
> > > CI checks validate that the files are up to date.
> > > There has been no churn to the kernel side of the generated code.
> > > Let's be practical.
> >
> > Okay, it sounds like neither of you want to do this. Darn. I really hate
> > having generated artifacts laying around that can be created efficiently
> > at compile time. But okay, so it goes. I guess we'll do that.
> >
> > I would like to ask two things, then, which may or may not be possible:
> >
> > 1) Can we put this in drivers/net/wireguard/generated/netlink.{c.h}
> >    And then in the Makefile, do `wireguard-y += netlink.o generated/netlink.o`
> >    on one line like that. I prefer this to keeping it in the same
> >    directory with the awkward -gen suffix.
>
> That should work, I think.
>
> > 2) In the header of each generated file, automatically write out the
> >    command that was used to generate it. Here's an example of this good
> >    habit from Go: https://github.com/golang/go/blob/master/src/syscall/zsyscall_linux_amd64.go
>
> You don't like the runes? :)
>
> /* Do not edit directly, auto-generated from: */
> /*      $YAML-path */
> /* YNL-GEN [kernel|user|uapi] [source|header] */
> /* YNL-ARG $extra-args */
>
> Do you care about the exact cmdline of the python tool, or can we just
> append:
>
> /* To regenerate run: tools/net/ynl/ynl-regen.sh */

The args are non-trivial, right? The idea is so that these files can
be regenerated in a few years when the ynl project has widely
succeeded and we've all paged this out of our minds and forgotten how
it all worked.