linux-kernel - Re: kernel coding style for if ... else which cross #ifdef

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Date:	Sat, 24 May 2008 13:27:04 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Steve French <smfrench@...il.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: kernel coding style for if ... else which cross #ifdef

On Sat, May 24, 2008 at 11:06:21AM +0100, Jeremy Fitzhardinge wrote:
> Sam Ravnborg wrote:
> >On Fri, May 23, 2008 at 10:42:58PM -0700, H. Peter Anvin wrote:
> >  
> >>Sam Ravnborg wrote:
> >>    
> >>>>*However*, the best would really be if we changed Kconfig to emit 
> >>>>configuration constants what were 0/1 instead of undefined/defined. 
> >>>>That way we could do:
> >>>>
> >>>>	if (CONFIG_SOMETHING && foo) {
> >>>>		/* ... something ... */
> >>>>	} else if ((mode & S_IWUGO) == 0) {
> >>>>		/* ... */
> >>>>        
> >>>We could do that - but then it would need another
> >>>name not to clash with all the places where we rely
> >>>on CONFIG_FOO='n' => CONFIG_FOO is not defined.
> >>>
> >>>We could teach kconfig to emit something like:
> >>>#define KFOO 0   (for the 'n' value)
> >>>And 1 or 2 for the y and m values.
> >>>
> >>>      
> >>I don't think we want to use "1 or 2"... I suspect we want to use the 
> >>same booleans we currently have.
> >>    
> >I'm a bit dense (or I need more coffe - it's morning here).
> >What "same booleans"?
> >  
> 
> They should be plain 0/1 booleans.  For a bool/tristate option FOO, it 
> would define:
> 
> Enabled y:
> 
>    #define CONFIG_FOO
>    #define CFG_FOO   1
>    #undef CONFIG_FOO_MODULE
>    #define CFG_FOO_MODULE 0
Agreed

> 
> Enabled m:
> 
>    #define CONFIG_FOO
>    #define CFG_FOO   1
>    #define CONFIG_FOO_MODULE
>    #define CFG_FOO_MODULE 1

I assume you wanted to say:
>    #undef  CONFIG_FOO
>    #define CFG_FOO   1
>    #define CONFIG_FOO_MODULE
>    #define CFG_FOO_MODULE 1
Because then the CONFIG_* is not changed
and we do not want to change that.

I'm not fully convinced about:
>    #define CFG_FOO   1
But on the other hand it is only in odd
cases we distingush between built-in and module.
So it makes most sense.

> Disabled n:
> 
>    #undef CONFIG_FOO
>    #define CFG_FOO   0
>    #undef CONFIG_FOO_MODULE
>    #define CFG_FOO_MODULE 0
Agree.

> 
> Not sure what CFG_* should be for string/numeric options.  Probably "1" 
> if the value is defined, "0" if not, with CONFIG_* being the actual 
> value (so a CONFIG_ value of 0 is distinguishable from not defined).
For non-boolean/tristate values we simply skip CFG_ values - thats
the most simple approach.

	Sam
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