linux-kernel - Re: [PATCH] kconfig: change .config format to use =n instead of "is not set"

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Date:   Sun, 27 Feb 2022 08:54:54 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kconfig: change .config format to use =n instead of "is
 not set"

On Sun, Feb 27, 2022 at 5:24 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> On Sun, Feb 27, 2022 at 6:38 AM Sedat Dilek <sedat.dilek@...il.com> wrote:
> >
> > On Sat, Feb 26, 2022 at 2:34 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> > >
> > > The .config file uses "# CONFIG_FOO is not set" form to represent
> > > disabled options. In the old days, it was useful because the .config
> > > was directly included from Makefiles. For example, you can use
> > > "ifdef CONFIG_FOO" in Makefiles to check if the option is enabled.
> > >
> > > Commit c955ccafc38e ("kconfig: fix .config dependencies") introduced
> > > include/config/auto.conf, which mirrors the .config, but trims down
> > > all disabled options.
> > >
> > > Since then, include/config/auto.conf defines CONFIG options during the
> > > build. The .config is used just for storing the user's configuration.
> > > I do not see a strong reason to use a particular pattern of comment
> > > for disabled options.
> > >
> > > With this commit, Kconfig will output disable options in a more natural
> > > form, "CONFIG_FOO=n".
> > >
> > > Kconfig accepts both "# CONFIG_FOO is not set" and "CONFIG_FOO=n" as a
> > > valid input. You do not need to update arch/*/configs/*_defconfig files
> > > for now. "git bisect" should be able to cross the commit in both ways
> > > without any issue.
> > >
> >
> > Good.
> >
> > Lot of people use/used the notation CONFIG_FOO=n, so did I.
> >
> > Thanks for keeping the "compatibility" with old usage "# CONFIG_FOO is not set".
> >
> > Normally, I use git diff (or scripts/diffconfig in Git tree) to
> > compare two kernel-configs, so seeing
> >
> > -CONFIG_FOO=y
> > +CONFIG_FOO=n
> >
> > ...might be at first view unfamiliar/unusual.
> > With the old notation it was easier to see that Kconfig is unset.
>
> I agree on this point.
>
> "is not set" stands out much better than "=n",
> and our eyes are accustomed to this notation for 20 years.
>
> However, real comments do not stand out since
> we already (ab)use comments for disabled options.
>
> This is related thread
> https://patchwork.kernel.org/project/linux-kbuild/patch/20211213100043.45645-3-arielmarcovitch@gmail.com/
>

Thanks for the link.

> >
> > Is this patch on top of kbuild-next Git?
> >
>
> Yes.

Let me see if I will try kbuild-next with this patch on top of
upcoming Linux v5.17-rc6.

- Sedat -