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Date: Fri, 1 Feb 2008 11:24:09 -0800 (PST)
From: Trent Piepho <xyzzy@speakeasy.org>
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To: Jan Engelhardt <jengelh@computergmbh.de>
cc: Adrian Bunk <bunk@kernel.org>,
       Mauro Carvalho Chehab <mchehab@infradead.org>,
       Hans Verkuil <hverkuil@xs4all.nl>, v4l-dvb-maintainer@linuxtv.org,
       Marcin Slusarz <marcin.slusarz@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: [v4l-dvb-maintainer] 2.6.25 regression: VIDEO_DEV=y/m, I2C=n
 compile error
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On Mon, 28 Jan 2008, Jan Engelhardt wrote:
> On Jan 28 2008 01:05, Trent Piepho wrote:
>
> >Maybe the kernel headers should provide a couple macros for testing
> >configs, since people get it wrong over and over again?
> >
> >#define CONFIG_ON(x) (defined(CONFIG_##x) || defined(CONFIG_##x##_MODULE))
> >#define CONFIG_AVAIABLE(x) (defined(CONFIG_##x) || (defined(MODULE) && defined(CONFIG_##x##_MODULE)))
>                ^AVAILABLE(x)
>
> What's the difference between these two?
>
> CONFIG_x_MODULE will never be defined if MODULE is not, so defined(MODULE)
> seems redundant.

You're probably thinking of CONFIG_MODULES, which indicates the kernel
supports module loading.  MODULE indicates the current code is being
compiled as a module.  The idea is that code compiled in the kernel can't
call modules.  Generally what you would see is:

#if CONFIG_ON(x)
code that will be _used by_ x
probably want x to depend on us in Kconfig
#endif
#if CONFIG_AVAILABLE(x)
code that wants _to use_ x
#endif