linux-kernel - Re: [mingo@...e.hu: [git pull] headers

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Date:	Tue, 27 Jan 2009 15:22:40 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sam Ravnborg <sam@...nborg.org>,
	Jaswinder Singh Rajput <jaswinderrajput@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [mingo@...e.hu: [git pull] headers_check fixes]

Linus Torvalds wrote:
> 
> So I think it makes our headers worse. Code like
> 
> 	> +#ifdef __KERNEL__
> 	> +# ifdef CONFIG_X86_BSWAP
> 	> +# define __X86_BSWAP  
> 	> +# endif /* CONFIG_X86_BSWAP */
> 	> +#endif /* __KERNEL__ */
> 
> just doesn't make sense. It doesn't make sense _inside_ the kernel, and it 
> doesn't make sense _outside_ it either.
> 
> As far as I can tell, the header install script could literally just do 
> something like run 'sed' over the headers as it installs them, and do 
> something like
> 
> 	sed 's/\<CONFIG_[A-Z0-9_]*\>/__kernel_only__/g'
> 
> which I realize is not really the complete/correct solution (ie you could 
> write a nicer thing that does a better job), but my point here is that 
> rather than have scripts that _whine_ about these kinds of trivial things 
> and cause people to write less readable header files, we should just make 
> sure that if we can recognize them so easily, we can just fix them 
> instead.
> 

We already run the headers through unifdef, so this should be trivial to 
add.

The intent of headers_check is to try to catch people who put things 
that depend on CONFIG_* stuff in exported headers (which, as we have 
seen, have been too sadly common.)  If we declare that the export 
process will treat all CONFIG_* as undefined, we do lose some coverage 
but potentially end up with cleaner code.  Not sure which is worse...

	-hpa
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