linux-kernel - Re: [PATCH v2 0/4] kbuild: resurrect generic header check facility

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Message-ID: <20250408160127.GD1778492@nvidia.com>
Date: Tue, 8 Apr 2025 13:01:27 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Jani Nikula <jani.nikula@...el.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, David Airlie <airlied@...il.com>,
	Simona Vetter <simona.vetter@...ll.ch>,
	linux-kbuild@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	intel-xe@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org
Subject: Re: [PATCH v2 0/4] kbuild: resurrect generic header check facility

On Tue, Apr 08, 2025 at 11:27:58AM +0300, Jani Nikula wrote:
> On Mon, 07 Apr 2025, Jason Gunthorpe <jgg@...dia.com> wrote:
> > On Mon, Apr 07, 2025 at 10:17:40AM +0300, Jani Nikula wrote:
> >
> >> Even with Jason's idea [1], you *still* have to start small and opt-in
> >> (i.e. the patch series at hand). You can't just start off by testing
> >> every header in one go, because it's a flag day switch. 
> >
> > You'd add something like 'make header_check' that does not run
> > automatically. Making it run automatically after everything is fixed
> > to keep it fixed would be the flag day change. It is how we have
> > managed to introduce other warning levels in the past.
> 
> That approach does not help *me* or drm, i915 and xe in the least. They
> are already fixed, and we want a way to keep them fixed. This is how all
> of this got started.

I imagine you'd include a way to have the 'make header_check' run on
some subset of files only, then use that in your CI for the interm.

> Your goal may be to make everything self-contained, but AFAICS there is
> no agreement on that goal. As long as there's no buy-in to this, it's
> not possible fix everything, it's an unreachable goal.

I didn't see that. I saw technical problems with the implementation
that was presented. I'd be shocked if there was broad opposition to
adding missing includes and forward declaration to most headers. It is
a pretty basic C thing. :\ 

Until someone sends a series trying to add missing includes and
forward declarations we can't really know..

> Arguably the situation is similar to W=1 builds. We can't run W=1 in our
> CI, because of failures outside of the drivers we maintain. 

You can run W=1 using a subdirectory build just for your drivers.

> Even if I put in the effort to generalize this the way you prefer, I
> guess a few kernel releases from now, it still would not do what we have
> already in place in i915 and xe. And, no offense, but I think your
> proposal is technically vague to start with. I really don't know where
> the goal posts are.

Well, I spent a little bit and wrote a mock up and did some looking at
how much work is here. Focusing on allnoconfig as a starting point,
293 out of 1858 headers failed to build, and with some fiddling I got
it down to 150, a couple of hours would get patches made for the vast
majority of it.

https://github.com/jgunthorpe/linux/commits/hdrcheck/

I don't see the same dire view as you do, it seems reasonable and doable.

Jason