linux-kernel - Re: [PATCH, v3] shmat: introduce flag SHM_MAP_NOT

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Date:	Wed, 8 Oct 2008 01:20:59 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Andi Kleen <andi@...stfloor.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Hugh Dickins <hugh@...itas.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH, v3] shmat: introduce flag SHM_MAP_NOT_FIXED

On Wed, Oct 08, 2008 at 12:05:18AM +0100, Alan Cox wrote:
> On Tue, 7 Oct 2008 23:10:38 +0200
> Andi Kleen <andi@...stfloor.org> wrote:
> 
> > > Sorry, no.
> > > This description still doesn't explain why this interface is needed.
> > > 
> > > The one of the points is this interface is used by another person or not.
> > > You should explain how large this interface benefit has.
> > > 
> > > Andi kleen explained this interface _can_  be used another one.
> > > but nobody explain who use it actually.
> > 
> > Anyone who doesn't want to use fixed addresses. 
> 
> Can use shm_open and mmap to get POSIX standard shm behaviour via a sane

I don't think shm_open can attach to SYSV shared segments. Or are you
proposing to add "sysvshmfs" to make that possible? 

> interface without adding more crap to the sys3 shm madness. 
> 
> Sorry this patch is completely bogus - introduce the user programs
> involved to 1990s technology. 

As already listed in an earlier email, but here again:

- There are legacy interfaces that cannot be really changed who use sysv shm
(e.g. X shm and others -- just do a ipcs on your system) 
- An system call emulation as in qemu obviously has to implement the
existing system call semantics.

-Andi

-- 
ak@...ux.intel.com
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