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

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Message-ID: <7b9198260805240940v46db928ak9bcacf9363c46d41@mail.gmail.com>
Date:	Sat, 24 May 2008 17:40:37 +0100
From:	"Tom Spink" <tspink@...il.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
Cc:	"Vegard Nossum" <vegard.nossum@...il.com>,
	"Sam Ravnborg" <sam@...nborg.org>,
	"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

2008/5/24 Jeremy Fitzhardinge <jeremy@...p.org>:
> Vegard Nossum wrote:
>>
>> Why not use all-lowercase config_* names? It seems elegant, and fits
>> in with the notion that these are to be used not as macros, but as
>> ordinary constants.
>>
>
> We tend to use all caps for symbolic constants, even if they're enums.
>
>> (The only disadvantage I can see is that they will stand out less. But
>> I don't know how great the disadvantage is.)
>>
>> You could even go further and make them real constants, something
>> along the lines of:
>>
>> enum config_value { no, yes, mod };
>>
>> static const enum config_value config_lockdep_support = yes;
>>
>
> Well, you could use "enum { config_foo = 0/1 }"  to define a proper C
> constant.
>
> But it means you could only use them in C, not in CPP or asm expressions.
>
>   J

Hi,

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.");
}

Thoughts?

-- 
Tom Spink
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