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

From: Doug Anderson <dianders@chromium.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Mathieu Malaterre <malat@debian.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Yang Shi <yang.s@alibaba-inc.com>,
	Guenter Roeck <linux@roeck-us.net>,
	Matthias Kaehlcke <mka@chromium.org>,
	Cao jin <caoj.fnst@cn.fujitsu.com>, Arnd Bergmann <arnd@arndb.de>,
	Mark Charlebois <charlebm@gmail.com>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Michal Marek <michal.lkml@markovi.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v3 2/2] kbuild: Don't mess with the .cache.mk when root
Date: Tue, 13 Mar 2018 09:44:11 -0700	[thread overview]
Message-ID: <CAD=FV=UvT-BrpZcz4RV=cRW4Nf9rBkYvc2JgcQr465NMYjAvJw@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdnPSMSOenPiPqBpDf=hf5q5uQ5MF0pOLAea5T5_VPhmaA@mail.gmail.com>

Hi,

On Tue, Mar 13, 2018 at 9:33 AM, Nick Desaulniers
<ndesaulniers@google.com> wrote:
> On Mon, Mar 12, 2018 at 11:23 PM Doug Anderson <dianders@chromium.org>
> wrote:
>
>> Hi,
>
>> On Mon, Mar 12, 2018 at 11:16 PM, Ingo Molnar <mingo@kernel.org> wrote:
>> >
>> > * Douglas Anderson <dianders@chromium.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