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

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Message-ID: <4837E89D.9040008@goop.org>
Date:	Sat, 24 May 2008 11:06:21 +0100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Sam Ravnborg <sam@...nborg.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

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


Enabled m:

    #define CONFIG_FOO
    #define CFG_FOO   1
    #define CONFIG_FOO_MODULE
    #define CFG_FOO_MODULE 1


Disabled n:

    #undef CONFIG_FOO
    #define CFG_FOO   0
    #undef CONFIG_FOO_MODULE
    #define CFG_FOO_MODULE 0

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).

    J
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