linux-kernel - Re: [PATCH v3 2/2] kbuild: Don't mess with the .cache.mk when root

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Message-ID: <CAD=FV=UvT-BrpZcz4RV=cRW4Nf9rBkYvc2JgcQr465NMYjAvJw@mail.gmail.com>
Date:   Tue, 13 Mar 2018 09:44:11 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Mathieu Malaterre <malat@...ian.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Yang Shi <yang.s@...baba-inc.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Matthias Kaehlcke <mka@...omium.org>,
        Cao jin <caoj.fnst@...fujitsu.com>,
        Arnd Bergmann <arnd@...db.de>,
        Mark Charlebois <charlebm@...il.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 2/2] kbuild: Don't mess with the .cache.mk when root

Hi,

On Tue, Mar 13, 2018 at 9:33 AM, Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
> On Mon, Mar 12, 2018 at 11:23 PM Doug Anderson <dianders@...omium.org>
> wrote:
>
>> Hi,
>
>> On Mon, Mar 12, 2018 at 11:16 PM, Ingo Molnar <mingo@...nel.org> wrote:
>> >
>> > * Douglas Anderson <dianders@...omium.org> wrote:
>> >
>> >> +# Don't create Makefile caches if running as root since they can't be
> deleted
>> >> +# easily; in the real world we might be root when doing "sudo make
> install"
>> >> +ifeq ($(shell id -u),0)
>> >> +export KBUILD_NOCACHE := 1
>> >> +endif
>> >
>> > Please don't do this - many prominent kernel developers build their
> kernels as
>> > root - this makes the build slower for them, and also bifurcates
> testing.
>
>> Ah, interesting.  I hadn't realized that!
>
>> I'm OK with dropping this patch myself.  It was mostly addressing a
>> potential problem pointed out by Masahiro Yamada when we were talking
>> about .cache.mk, but I don't think anyone has actually experienced the
>> problems listed in the CL description.
>
>>    /bin/sh: ./.cache.mk: Permission denied
>
> I feel like I've definitely seen that permission error before.

Hopefully the error message was obvious enough that it didn't take you
too long to think to type "sudo make clean"?  I know it's better for
people not to have to figure this out, but my hope is at least it's
not too arcane of an errror message.


> Is there any issue if I:
>
> $ make clean
> $ make
> $ sudo make install
> <hack around>
> $ make

I don't personally know of any problems with the above flow.


> Or it's only a problem if:
>
> $ make clean
> $ sudo make install
> <hack around>
> $ make

Yeah, just that one.

NOTE: as Masahiro noted in response to the cover letter [1], he's come
up with a better solution to the problem that was solved by the
.cache.mk and he's planning to remove it shortly.


[1] https://lkml.org/lkml/2018/3/13/100