linux-kernel - Re: [PATCH] kbuild: compile-test global headers to ensure they are self-contained

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Date:   Sat, 22 Jun 2019 21:30:24 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] kbuild: compile-test global headers to ensure they are self-contained

Hi Sam,

On Sat, Jun 22, 2019 at 2:51 AM Sam Ravnborg <sam@...nborg.org> wrote:
>
> Hi Masahiro.
>
> On Sat, Jun 22, 2019 at 01:39:31AM +0900, Masahiro Yamada wrote:
> > Make as many headers self-contained as possible so that they can be
> > included without relying on a specific include order.
> It is very nice finally to get some infrastructure to validate header
> files.
>
> But to avoid too many conflicts while including more and more headers
> that are selfcontained we really need something that is more
> distributed.
> So for example all header files in include/drm/* could be in one
> Makefile, incl. sub-directories, but the same Makefile would not include
> the files in include/soc/
>
> If you just show how ot do it, others can follow-up with the
> relevant directories.

At first, I tried to split Makefile per directory,
and add header-test-y one by one.

I think you expect they look like this:

include/Makefile:

subdir-y += drm
subdir-y += linux
subdir-y += media

include/drm/Makefile:

header-test-y += drm_cache.h
header-test-y += drm_file.h
header-test-y += drm_util.h
...

include/linux/Makefile:

header-test-y += io.h
header-test-y += list.h
header-test-y += kernel.h
header-test-y += types.h
...

This is a straightforward way,
but I see some disadvantages.

Currently, there are more than 4000 headers
under include/.

So, to cover (almost) all of them, we must
list out 4000 entries.

When somebody adds a new header,
he will be very likely to forget to add
header-test-y for it.
So, newly added headers will always
fall off the coverage.

So, I am trying to take an opposite approach.

Add all headers in include/ by wildcard, then
filter-out one that cannot be self-contained.

In my analysis, 70% of headers are already conf-contained.
After some fixups, 95% of headers can become self-contained.

At this moment, the wildcard only covers some directories
or patterns, but my plan is to extend the wildcard gradually.

Please feel free to suggest alternative ideas.

-- 
Best Regards
Masahiro Yamada