linux-kernel - Re: [RFC][PATCH] kconfig: introduce listunknownconfig

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Date:   Thu, 24 Aug 2023 10:00:11 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Ying Sun <sunying@...iscas.ac.cn>,
        Jesse T <mr.bossman075@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Jonathan Corbet <corbet@....net>,
        Tomasz Figa <tfiga@...omium.org>, linux-kbuild@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] kconfig: introduce listunknownconfig

On Tue, Aug 22, 2023 at 4:30 PM Sergey Senozhatsky
<senozhatsky@...omium.org> wrote:
>
> On (23/08/21 21:27), Masahiro Yamada wrote:
> >
> > My (original) hope was to add a single switch, KCONFIG_VERBOSE, to address both:
> >
> >   - A CONFIG option is hidden by unmet dependency (Ying Sun's case)
> >   - A CONFIG option no longer exists  (your case)
> >   - Anything else we need to be careful
>
> A quick question: is it too late to suggest an alternative name?
> Could KCONFIG_SANITY_CHECKS be a little cleaner? Because we basically
> run sanity checks on the config.

Ying's is not applied yet. So, it is not too late.

But, I started to be a little worried
because it is unpredictable how many KCONFIG_* env
variables will increase until people are satisfied.

>
> And one more question: those sanity checks seem very reasonable.
> Is there any reason we would not want to keep them ON by default?
> And those brave souls, that do not wish for the tool to very that
> the .config is sane and nothing will get downgraded/disabled, can
> always set KCONFIG_SANITY_CHECKS to 0.

Kconfig is meant to resolve the dependency without causing an error.
If a feature is not available, it is automatically, silently hidden,
and that works well.

When a compiler does not support a particular feature,
'depends on $(cc-option )' hides that CONFIG option.
Kconfig is meant to work like that.

For your case, it is case-by-case.

Let's say a stale code is removed from upstream.

After "obj-$(CONFIG_FOO) += foo.o" is removed
from upstream, CONFIG_FOO in the .config is a "don't care".

If it were an error, all arch/*/configs/*_defconfig
must be cleaned up at the same time.

So, sometimes it is helpful, but sometimes noisy.

For the MFD_RK808 case particularly,
I believe Kconfig showed MFD_RK8XX_I2C
as a new option.

Or, when you bumped to a new kernel version,
you could run 'make listnewconfig'.
(See 17baab68d337a0bf4654091e2b4cd67c3fdb44d8.
Redhat says they review every new config option.)

If you had done a per-config review
you would have noticed
c20e8c5b1203af3726561ee5649b147194e0618e
before spending time on run-time debugging.

-- 
Best Regards
Masahiro Yamada