linux-kernel - Re: [PATCH] Make asm-generic/ioctl.h more generic using conditionals.

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Date:	Thu, 12 Jul 2007 20:51:35 -0400 (EDT)
From:	"Robert P. J. Day" <rpjday@...dspring.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>, matthew@....cx
Subject: Re: [PATCH] Make asm-generic/ioctl.h more generic using conditionals.


On Thu, 12 Jul 2007, Andrew Morton wrote:

> On Tue, 10 Jul 2007 06:33:26 -0400 (EDT)
> "Robert P. J. Day" <rpjday@...dspring.com> wrote:
>
> >
> > Allow individual architectures to override a small set of macros
> > before including asm-generic/ioctl.h, in order to greatly simplify a
> > number of existing ioctl.h files.
> >
> > The overrideable macros would be:
> >
> > 	_IOC_SIZEBITS
> > 	_IOC_DIRBITS
> > 	_IOC_NONE
> > 	_IOC_WRITE
> > 	_IOC_READ
> >
> > ---
> >
> >   i've submitted this once before, and it didn't seem to garner a
> > lot of attention one way or the other.  this patch can be applied
> > standalone and shouldn't affect anything, but it would
> > subsequently allow at least a few ioctl.h files to be shortened
> > considerably.
>
> It would be good if we could see one of these followon patches.  If
> such an example patch (cc'ed to the arch maintainer, please) looks
> OK then we can go ahead with this base patch.

as a trivial example, i can demonstrate on include/asm-mips/ioctl.h.
once the generic ioctl.h file is enhanced, then the entire mips
ioctl.h file is reduced from 94 lines to:

===================================
#define _IOC_SIZEBITS	13
#define _IOC_DIRBITS	3

#define _IOC_NONE	1U
#define _IOC_READ	2U
#define _IOC_WRITE	4U

#include <asm-generic/ioctl.h>

/*
 * The following are included for compatibility
 */

#define _IOC_VOID	0x20000000
#define _IOC_OUT	0x40000000
#define _IOC_IN		0x80000000
#define _IOC_INOUT	(IOC_IN|IOC_OUT)
=================================

and the last part of that is purely MIPS-specific content.

  there are at least a couple other ioctl.h files that could be
reduced even further.  asm-parisc/ioctl.h would subsequently become
all of four lines:

=================================
#define _IOC_NONE	0U   (this line isn't even necessary)
#define _IOC_WRITE	2U
#define _IOC_READ	1U

#include <asm-generic/ioctl.h>
=================================

etc, etc.

rday
-- 
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA

http://fsdev.net/wiki/index.php?title=Main_Page
========================================================================
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