linux-kernel - Re: [v4l-dvb-maintainer] 2.6.25 regression: VIDEO

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Date:	Fri, 1 Feb 2008 11:24:09 -0800 (PST)
From:	Trent Piepho <xyzzy@...akeasy.org>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
cc:	Adrian Bunk <bunk@...nel.org>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	v4l-dvb-maintainer@...uxtv.org,
	Marcin Slusarz <marcin.slusarz@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [v4l-dvb-maintainer] 2.6.25 regression: VIDEO_DEV=y/m, I2C=n
 compile error

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
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