linux-kernel - Re: [PATCH] kconfig: always use user input symbols

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Date:   Fri, 19 May 2017 12:09:23 -0600
From:   Tycho Andersen <tycho@...ker.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "Yann E . MORIN" <yann.morin.1998@...e.fr>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Roman Zippel <zippel@...ux-m68k.org>
Subject: Re: [PATCH] kconfig: always use user input symbols

Hi Geert,

On Fri, May 19, 2017 at 07:29:05PM +0200, Geert Uytterhoeven wrote:
> Hi Tycho,
> 
> On Fri, May 19, 2017 at 5:08 PM, Tycho Andersen <tycho@...ker.com> wrote:
> > ...regardless of visibility.
> >
> > When a symbol that is not visible by default (e.g. PNFS_FLEXFILE_LAYOUT)
> > has a default value, it is impossible to set the value to something not the
> > default:
> >
> > ~/packages/linux render-symbol-inputs grep FLEXFILE .config
> > CONFIG_PNFS_FLEXFILE_LAYOUT=y
> > ~/packages/linux render-symbol-inputs make oldconfig
> > scripts/kconfig/conf  --oldconfig Kconfig
> > ~/packages/linux render-symbol-inputs grep FLEXFILE .config
> > CONFIG_PNFS_FLEXFILE_LAYOUT=m
> >
> > There are two reasons for this: the symbol's user input value is only
> > considered when it is visible (hunks 2 and 3), and the user values are
> > explicitly ignored (hunk 1) if the symbols are not visible.
> >
> > It's not clear to me why hunk 1 exists. I'm sure it solve some problem, but
> > I'm not sure why we would ever want to discard user input values, and
> > causes a problem exactly as the comment describes.
> 
> This is intentional.  If a symbol is not visible, it's not meant to be changed
> by the user, as doing so may break things (at build or runtime).
> 
> E.g. running "make oldconfig" after a kernel upgrade may retain the old
> state of a variable, which is now invalid.  Ignoring invisible symbols
> avoids this.

Makes sense. Thanks!

Tycho