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

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Date:	Sat, 24 May 2008 13:43:28 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Tom Spink <tspink@...il.com>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Sam Ravnborg <sam@...nborg.org>,
	Steve French <smfrench@...il.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: kernel coding style for if ... else which cross #ifdef

Jeremy Fitzhardinge wrote:
> Tom Spink wrote:
>> A thought occurred to me that we may be able to used some preprocessor
>> magic and do this:
>>
>> #define config_defined(x) CFGVAL_## x
>>
>> Which means that, if we get Kconfig to produce:
>>
>> #define CFGVAL_CONFIG_FOO 0
>> #define CFGVAL_CONFIG_VALUE_BAR 1
>> #define CFGVAL_CONFIG_VALUE_BAZ_MODULE 1
>>
>> We can use this:
>>
>> if (config_defined(CONFIG_FOO) && some_expr) {
>>    panic("Oh no.");
>> }
> 
> Well, in that case you could use Willy's magic hack:
> 
> #define config_defined(x)      (x - 0)
> 
> Which isn't a bad alternative to defining a whole pile of new symbols...
> 

That can *strongly* be argued with.

In particular, the use of #ifdef is crap to begin with.  Using #if even 
for the preprocessor makes it possible to trap misspellings.

	-hpa
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