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Date: Mon, 6 Apr 2009 18:24:10 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: David Woodhouse <dwmw2@infradead.org>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, rostedt@goodmis.org
Subject: Re: intel-iommu: Add for_each_iommu() and for_each_active_iommu()
 macros
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On Mon, 06 Apr 2009 18:19:06 -0700
David Woodhouse <dwmw2@infradead.org> wrote:

> On Mon, 2009-04-06 at 18:09 -0700, David Woodhouse wrote:
> > 
> > I'm unconvinced by the fix -- can we find a way to fix the if() macro so
> > that normal (if fugly) C code like this doesn't doesn't need this kind
> > of workaround?
> 
> Something like this perhaps? I'd reformat it but dinner calls...
> 
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 6faa7e5..1da2e72 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -114,7 +114,7 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
>   * "Define 'is'", Bill Clinton
>   * "Define 'if'", Steven Rostedt
>   */
> -#define if(cond) if (__builtin_constant_p((cond)) ? !!(cond) :		\
> +#define if(cond, ...) if (__builtin_constant_p((cond, ## __VA_ARGS__)) ? !!(cond, ## __VA_ARGS__) : \
>  	({								\
>  		int ______r;						\
>  		static struct ftrace_branch_data			\
> @@ -125,7 +125,7 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
>  				.file = __FILE__,			\
>  				.line = __LINE__,			\
>  			};						\
> -		______r = !!(cond);					\
> +		______r = !!(cond, ## __VA_ARGS__);					\
>  		______f.miss_hit[______r]++;					\
>  		______r;						\
>  	}))

That would be better.  If it works, please send something Linuswards?