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From: Martin Walch <walch.martin@web.de>
Subject: Re: [PATCH 1/4] kconfig: add short explanation to SYMBOL_WRITE
Date: Thu, 03 Oct 2013 01:39:13 +0200
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Cc: Michal Marek <mmarek@suse.cz>, Jiri Kosina <trivial@kernel.org>, "Yann E. MORIN" <yann.morin.1998@free.fr>, Arve =?ISO-8859-1?Q?Hj=F8nnev=E5g?= <arve@android.com>, Benjamin Poirier <bpoirier@suse.de>, Dirk Gouders <dirk@gouders.net>, Wang YanQing <udknight@gmail.com>, Andrew Morton <akpm@linux-foundation.org>, Jean Delvare <jdelvare@suse.de>, Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org

> > diff --git a/scripts/kconfig/expr.h b/scripts/kconfig/expr.h
> > index df198a5..ba663e1 100644
> > --- a/scripts/kconfig/expr.h
> > +++ b/scripts/kconfig/expr.h
> > @@ -93,7 +93,7 @@ struct symbol {
> >  #define SYMBOL_CHOICEVAL  0x0020  /* used as a value in a choice block */
> >  #define SYMBOL_VALID      0x0080  /* set when symbol.curr is calculated */
> >  #define SYMBOL_OPTIONAL   0x0100  /* choice is optional - values can be 'n' */
> > -#define SYMBOL_WRITE      0x0200  /* ? */
> > +#define SYMBOL_WRITE      0x0200  /* write symbol to file (KCONFIG_CONFIG) */
> >  #define SYMBOL_CHANGED    0x0400  /* ? */
> >  #define SYMBOL_AUTO       0x1000  /* value from environment variable */
> >  #define SYMBOL_CHECKED    0x2000  /* used during dependency checking */
> 
> Perhaps stating that the choice is writable by the user?

As far as I understand SYMBOL_WRITE, its main purpose is in the function
conf_write in confdata.c:

>if (!(sym->flags & SYMBOL_WRITE))
>	goto next;
>sym->flags &= ~SYMBOL_WRITE;
>
>conf_write_symbol(out, sym, &kconfig_printer_cb, NULL);

So, if I have not missed anything, SYMBOL_WRITE decides whether to write a symbol
to .config or not. This does not necessarily mean that the user can change the value.
SYMBOL_WRITE may be set and the symbol may be written to .config while the user
does not even see the corresponding prompt.