linux-kernel - Re: [PATCH v3] selftests/mm: add process

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Message-ID: <aHDMnogm_EOx4oMU@finisterre.sirena.org.uk>
Date: Fri, 11 Jul 2025 09:34:38 +0100
From: Mark Brown <broonie@...nel.org>
To: Zi Yan <ziy@...dia.com>
Cc: wang lian <lianux.mm@...il.com>, Liam.Howlett@...cle.com,
	akpm@...ux-foundation.org, brauner@...nel.org, david@...hat.com,
	gkwang@...x-info.com, jannh@...gle.com,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
	linux-mm@...ck.org, lorenzo.stoakes@...cle.com,
	p1ucky0923@...il.com, ryncsn@...il.com, shuah@...nel.org,
	sj@...nel.org, vbabka@...e.cz, zijing.zhang@...ton.me
Subject: Re: [PATCH v3] selftests/mm: add process_madvise() tests

On Thu, Jul 10, 2025 at 12:28:13PM -0400, Zi Yan wrote:
> On 10 Jul 2025, at 4:42, Mark Brown wrote:
> > On Wed, Jul 09, 2025 at 10:46:07AM -0400, Zi Yan wrote:

> >> Right. My /usr/include/sys does not have pidfd.h. IMHO selftests
> >> should not rely on userspace headers, otherwise we cannot test
> >> latest kernel changes.

> > That's not realistic, we need to be able to use things like libc and for
> > many areas you'd just end up copying or reimplmenenting the userspace
> > libraries.  There's some concerns for sure, for example we used to have

> Sure. For libraries like libc, it is unrealistic to not rely on it.
> But for header files, are we expecting to install any kernel headers
> to the running system to get selftests compiled? If we are testing
> RC versions and header files might change before the actual release,
> that would pollute the system header files, right?

Right, for the kernel's headers there's two things - we use a
combination of tools/include and 'make headers_install' which populates
usr/include in the kernel tree (apparently mm rejects the latter but it
is widely used in the selftests, especially for architecture specifics).
These install locally and used before the system headers.

> > OTOH in a case like this where we can just refer directly to a kernel
> > header for some constants or structs then it does make sense to use the
> > kernel headers, or in other cases where we're testing things that are

> That is exactly my point above.

What was said was a bit stronger though, and might lead people down a
wheel reinvention path.

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