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Date:   Fri, 3 Nov 2023 14:08:14 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     David Hildenbrand <david@redhat.com>
Cc:     John Hubbard <jhubbard@nvidia.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Xu <peterx@redhat.com>, Shuah Khan <shuah@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>, linux-mm@kvack.org,
        linux-kselftest@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Muhammad Usama Anjum <usama.anjum@collabora.com>,
        Jonathan Corbet <corbet@lwn.net>, linux-doc@vger.kernel.org
Subject: Re: [PATCH v3 11/11] selftests: error out if kernel header files are
 not yet built
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On Fri, Nov 03, 2023 at 01:59:28PM +0100, David Hildenbrand wrote:

> Okay. the question is if your workflow can be easily adjusted, or if we can
> improve that header handling as a whole.

So on IRC the following was suggested:

  make O=defconfig-build headers ; make O=defconfig-build -C tools/testing/selftests/x86

But that makes absolutely no sense to me; because the headers and
selftests are not .config dependent. Furthermore I don't want them in a
kernel build dir.

> The problem I had with this recently: just because we did a "make headers"
> once in a git tree doesn't mean that it is still up-to-date.
> 
> So once some selftest changes showed up that require newer headers, building
> the selftests again fails without a hint that another round of "make
> headers" would be required.

Yeah, so I've been adding #ifndef guards all over the place for decades
and that just works. You need it in normal userspace too.

This super reliance on the very latestesetst headers is just a total
pain.