linux-kernel - Re: [PATCH 2.6.20-rc4 4/4][RFC] sys

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Message-ID: <20070111221446.GF29911@devserv.devel.redhat.com>
Date:	Thu, 11 Jan 2007 17:14:46 -0500
From:	Jakub Jelinek <jakub@...hat.com>
To:	Pierre Peiffer <pierre.peiffer@...l.net>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Dinakar Guniguntala <dino@...ibm.com>,
	Jean-Pierre Dion <jean-pierre.dion@...l.net>,
	Ingo Molnar <mingo@...e.hu>,
	Ulrich Drepper <drepper@...hat.com>,
	Darren Hart <dvhltc@...ibm.com>
Subject: Re: [PATCH 2.6.20-rc4 4/4][RFC] sys_futex64 : allows 64bit futexes

On Tue, Jan 09, 2007 at 05:25:26PM +0100, Pierre Peiffer wrote:
> This latest patch is an adaptation of the sys_futex64 syscall provided in 
> -rt
> patch (originally written by Ingo). It allows the use of 64bit futex.
> 
> I have re-worked most of the code to avoid the duplication of the code.
> 
> It does not provide the functionality for all architectures, and thus, it 
> can
> not be applied "as is".
> But, again, feedbacks and comments are welcome.

Why do you support all operations for 64-bit futexes?
IMHO PI futexes don't make sense for 64-bit futexes, PI futexes have
hardcoded bit layout of the 32-bit word.  Similarly, FUTEX_WAKE
is not really necessary for 64-bit futexes, 32-bit futex's FUTEX_WAKE
can wake it equally well (it never reads anything, all it cares
is about the futex's address).  Similarly, I don't see a need for
FUTEX_WAKE_OP (and this could simplify the patch quite a lot, no
need to change asm*/futex.h headers at all).
All that's needed is 64-bit FUTEX_WAIT and perhaps FUTEX_CMP_REQUEUE.

	Jakub
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