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Date: Sat, 24 May 2008 21:51:51 +0100
From: Jeremy Fitzhardinge <jeremy@goop.org>
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To: "H. Peter Anvin" <hpa@zytor.com>
CC: Tom Spink <tspink@gmail.com>, Vegard Nossum <vegard.nossum@gmail.com>,
       Sam Ravnborg <sam@ravnborg.org>, Steve French <smfrench@gmail.com>,
       lkml <linux-kernel@vger.kernel.org>
Subject: Re: kernel coding style for if ... else which cross #ifdef
References: <524f69650805231211r315be4e4u5890aa0f914bcb4f@mail.gmail.com>	 <4837AAE2.9090102@zytor.com>	 <20080524064201.GA4133@uranus.ravnborg.org>	 <4837E89D.9040008@goop.org>	 <20080524112704.GA7292@uranus.ravnborg.org>	 <483827CE.9080200@goop.org>	 <20080524153611.GA13890@uranus.ravnborg.org>	 <48383830.6060504@goop.org>	 <19f34abd0805240857l57e667fdicb240baf898f6296@mail.gmail.com>	 <48383C26.5040106@goop.org> <7b9198260805240940v46db928ak9bcacf9363c46d41@mail.gmail.com> <48387CCB.1030801@goop.org> <48387DF0.7000600@zytor.com>
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H. Peter Anvin wrote:
> 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. 

Yes, I'd agree if we were starting from scratch.  But given that we 
can't get rid of CONFIG_* and their dubious semantics, we just have to 
make do.

But typo-detection *would* be very nice: I can never remember if its 
CONFIG_MEMORY_HOTPLUG or CONFIG_HOTPLUG_MEMORY.

    J