linux-kernel - Re: [PATCH] kbuild: deb-pkg: support DEB_BUILD

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Message-ID: <CAK7LNARk52-MvsPSjgQV3vDXpv2RXpeg0vkzMJAsLR1yQwr7Qw@mail.gmail.com>
Date:   Mon, 21 Aug 2023 06:05:30 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Bastian Germann <bage@...utronix.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>
Subject: Re: [PATCH] kbuild: deb-pkg: support DEB_BUILD_OPTIONS=parallel=N in debian/rules

On Mon, Aug 21, 2023 at 1:20 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> 'make srcdeb-pkg' generates a source package, which you can build
> later by using dpkg-buildpackage.
>
> In older dpkg versions, 'dpkg-buildpackage -j N' sets not only
> DEB_BUILD_OPTIONS but also MAKEFLAGS. Hence, passing -j (--jobs)
> to dpkg-buildpackage was enough to run parallel building.
>
> The behavior was changed by commit 1d0ea9b2ba3f ("dpkg-buildpackage:
> Change -j, --jobs semantics to non-force mode") of dpkg project. [1]
>
> Since then, 'dpkg-buildpackage -j N' sets only DEB_BUILD_OPTIONS,
> which is not parsed by the current debian/rules. You cannot build it
> in parallel unless you pass --jobs-force instead or set the MAKEFLAGS
> environment variable.
>
> Debian policy [2] suggests the following code snippet for debian/rules.
>
>   ifneq (,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))
>       NUMJOBS = $(patsubst parallel=%,%,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))
>       MAKEFLAGS += -j$(NUMJOBS)
>   endif
>
> I added slightly different code to debian/rules so 'make -j N deb-pkg'
> works as before. In this case, the '-j N' should not be specified in
> debian/rules again. 'make deb-pkg' without the -j option must explicitly
> pass -j1 to dpkb-buildpackage because otherwise DEB_BUILD_OPTIONS
> contains parallel=<nproc> by default.
>
> This should work with almost all Make versions Kbuild supports.
>
> Only the corner case I found not working is 'make-3.82 -j deb-pkg',
> which results in single thread building. It is not a big deal because
> -j without an argument, which does not limit the number of jobs, is
> rarely used.
>
> As far as I tested, the MAKEFLAGS format varies by Make versions.
>
>                  command line option         $(MAKEFLAGS) in recipe
>  Make 3.82            -j                            j
>                       -j1                         <none>
>                       -j2                          -j
>  Make 4.0/4.1         -j                           -j
>                       -j1                         <none>
>                       -j2                          -j
>  Make 4.2+            -j                           -j
>                       -j1                          -j1
>                       -j2                          -j2



On second thought, this is not a good idea.

I will send v2 with a different solution.





-- 
Best Regards
Masahiro Yamada