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From: David Howells <dhowells@redhat.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: dhowells@redhat.com, tj@kernel.org, mingo@elte.hu,
       akpm@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] FRV: Fix the section attribute on UP DECLARE_PER_CPU()
Date: Wed, 15 Apr 2009 12:40:32 +0100
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Linus Torvalds <torvalds@linux-foundation.org> wrote:

> But yeah, I didn't look at all the details. It _looked_ pretty
> straightforward to just move the DEFINE/DECLARE stuff up, but there may well
> be something subtle I'm missing.

The problem is mainly one of #include recursion.  There's way too much of it.

I wonder if we should replace the standard headerfile boilerplate:

	#ifndef _THIS_HEADER_H
	#define _THIS_HEADER_H
	...
	#endif /* _THIS_HEADER_H */

with something a bit nastier:

	#ifndef _THIS_HEADER_H
	#define _THIS_HEADER_H 1
	...
	#undef _THIS_HEADER_H
	#define _THIS_HEADER_H 2
	#elif  _THIS_HEADER_H == 1
	#error Recursive inclusion is not permitted
	#endif /* _THIS_HEADER_H */

and make people break up their header files to avoid getting this error.

There are a number of problems with doing this, of course; the least of which
is that cpp has special code for handling the first case efficiently, IIRC.

David