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Cc: aoliva@redhat.com, linux-kernel@vger.kernel.org, matthew@wil.cx,
       dwmw2@infradead.org, torvalds@osdl.org, libc-hacker@sources.redhat.com,
       hch@infradead.org
From: Kyle Moffett <mrmacman_g4@mac.com>
Subject: Re: [RFC] Splitting kernel headers and deprecating __KERNEL__
Date: Fri, 26 Nov 2004 22:07:18 -0500
To: David Howells <dhowells@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
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On Nov 25, 2004, at 10:13, David Howells wrote:
> We've been discussing splitting the kernel headers into userspace API 
> headers
> and kernel internal headers and deprecating the __KERNEL__ macro. This 
> will
> permit a cleaner interface between the kernel and userspace; and one 
> that's
> easier to keep up to date.

Yay!!! Finally!!!

> 	NEW DIRECTORY		DIRECTORY SHADOWED
> 	=============		==================
> 	include/user/		include/linux/
> 	include/user-*/		include/asm-*/

How about include/abi for the platform-independent headers and 
include/arch-*
for the platform-specific headers?  Then include/arch would be 
symlinked to the
correct arch-* directory.

>      Note that this doesn't take account of the other directories under
>      include/, but I don't think they're relevant.

Perhaps such directories should either be broken out into 
abi/foo<->linux/foo
pieces, or put into their own top-level directories.

>  (2) Take each file from the shadowed directory. If it has any 
> userspace
>      relevant stuff, then:
[...snip...]

Something like this would warn about incorrect uses of the linux/ 
headers, yet
still allow for a period of backwards compatibility.  Once such period 
has passed,
then linux/* would not even be installed, only abi/* and arch/*

include/linux/foo.h:
#ifndef _LINUX_FOO_H
#define _LINUX_FOO_H 1

#ifndef __KERNEL__
# warning "Directly including <kernel/foo.h> is deprecated!!!"
# warning "Please change your program to include <abi/foo.h> instead!!!"
#endif

#include <abi/foo.h>

#ifdef __KERNEL__
/* Old __KERNEL__ contents of include/linux/foo.h */
#endif

#endif /* not _LINUX_FOO_H */


include/abi/foo.h:
#ifndef _ABI_FOO_H
#define_ABI_FOO_H 1

#include <abi/bar.h>
#include <arch/baz.h>

/* Old non-__KERNEL__ contents of include/linux/foo.h */

#endif /* not _ABI_FOO_H */

Cheers,
Kyle Moffett

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