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

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Date:	Mon, 21 Sep 2009 11:30:26 +0200
From:	Arnd Bergmann <arnd@...db.de>
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
Subject: Re: [PATCH] remove duplicate asm/mman.h files

On Monday 21 September 2009, David Rientjes wrote:
> > 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.

It's more a matter of principle of my patches. I try to strictly separate
patches that move code around (like the one I sent) from those that
change contents (like yours, or the one before that adds MAP_STACK and
MAP_HUGETLB).

Removing a definition from an exported header file either requires
specific knowledge about why it is there to start with, or more
research on the topic than I wanted to do. For instance, a theoretical
program might have a helper function correctly doing

void *xmmap(void *addr, size_t length, int prot, int flags,
                  int fd, off_t offset)
{
	if (flags & MAP_GROWSUP) { /* MAP_GROWSUP is not supported */
		errno = -EINVAL;
		return MAP_FAILED;
	}

	return mmap(addr, length, prot, flags, fd, offset);
}

Of course, such a program would only work on ia64 currently, so
it should be safe to make ia64 behave like the other architectures
in this regard.

> ia64: remove definition for MAP_GROWSUP
> 
> MAP_GROWSUP is unused.
>
> Signed-off-by: David Rientjes <rientjes@...gle.com>

Acked-by: Arnd Bergmann <arnd@...db.de>
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