linux-kernel - Re: [PATCH] remove duplicate asm/mman.h files

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Date:	Mon, 21 Sep 2009 13:02:44 +0100 (BST)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	David Rientjes <rientjes@...gle.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Tony Luck <tony.luck@...el.com>, ebmunson@...ibm.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-man@...r.kernel.org, mtk.manpages@...il.com,
	randy.dunlap@...cle.com, rth@...ddle.net, ink@...assic.park.msu.ru,
	linux-ia64@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] remove duplicate asm/mman.h files

On Mon, 21 Sep 2009, David Rientjes wrote:
> On Mon, 21 Sep 2009, Arnd Bergmann wrote:
> 
> > > > -#define MCL_CURRENT	1		/* lock all current mappings */
> > > > -#define MCL_FUTURE	2		/* lock all future mappings */
> > > > +#define MAP_GROWSUP	0x0200		/* register stack-like segment */
> > > >  
> > > >  #ifdef __KERNEL__
> > > >  #ifndef __ASSEMBLY__
> > > 
> > > ia64 doesn't use MAP_GROWSUP, so it's probably not necessary to carry it 
> > > along with your cleanup.
> > 
> > ia64 is the only architecture defining it, nobody uses it in the kernel.
> > If the ia64 maintainers want to remove it in a separate patch, that
> > would probably be a good idea.
> > 
> 
> I'll do it then.
> 
> > I tried not to change the ABI in any way in my patch, and there is
> > a theoretical possibility that some user space program on ia64 currently
> > depends on that definition.
> > 
> 
> I don't buy that as justification, if some userspace program uses it based 
> on the false belief that it actually does what it says, it's probably 
> better to break their build than perpetuating the lie that it's different 
> than ~MAP_GROWSDOWN.
> 
> 
> ia64: remove definition for MAP_GROWSUP
> 
> MAP_GROWSUP is unused.

Is it perhaps the case that some UNIX on ia64 does implement MAP_GROWSUP,
and these numbers in the Linux ia64 mman.h have been chosen to match that
reference implementation?  Tony will know.  But I wonder if you'd do
better at least to leave a MAP_GROWSUP comment on that line, so that
somebody doesn't go and reuse the empty slot later on.

Hugh

> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
> diff --git a/arch/ia64/include/asm/mman.h b/arch/ia64/include/asm/mman.h
> --- a/arch/ia64/include/asm/mman.h
> +++ b/arch/ia64/include/asm/mman.h
> @@ -11,7 +11,6 @@
>  #include <asm-generic/mman-common.h>
>  
>  #define MAP_GROWSDOWN	0x00100		/* stack-like segment */
> -#define MAP_GROWSUP	0x00200		/* register stack-like segment */
>  #define MAP_DENYWRITE	0x00800		/* ETXTBSY */
>  #define MAP_EXECUTABLE	0x01000		/* mark it as an executable */
>  #define MAP_LOCKED	0x02000		/* pages are locked */
--
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