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Date: Wed, 8 Oct 2008 00:40:30 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Andi Kleen <andi@firstfloor.org>
Cc: Andi Kleen <andi@firstfloor.org>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
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       Hugh Dickins <hugh@veritas.com>, Ulrich Drepper <drepper@redhat.com>,
       Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH, v3] shmat: introduce flag SHM_MAP_NOT_FIXED
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> > 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? 

Actually you can do so. As it stands today the SYS3 SHM interface code
does the following

	create a char array in the form SYS%08ld, key
	open it on shmfs

> - 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) 

They can be changed and nobody is wanting to map those at fixed addresses.

> - An system call emulation as in qemu obviously has to implement the
> existing system call semantics.

Which it can do perfectly well using shm_open to create its SYS3
SHM objects. In fact theoertically we could bin the whole of SYS3 shm and
push it into glibc emulation if we wanted.

Alan