linux-kernel - [PATCH -mm] 64bit-futex - provide new commands instead of new syscall

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Date:	Mon, 23 Apr 2007 16:35:53 +0200
From:	Pierre Peiffer <pierre.peiffer@...l.net>
To:	Jakub Jelinek <jakub@...hat.com>
Cc:	akpm@...ux-foundation.org, mingo@...e.hu, drepper@...hat.com,
	linux-kernel@...r.kernel.org, jean-pierre.dion@...l.net
Subject: [PATCH -mm] 64bit-futex - provide new commands instead of new syscall

Hi,

Jakub Jelinek a écrit :
> 
> I don't think you should blindly add all operations to sys_futex64 without
> thinking what they really do.
> E.g. FUTEX_{{,UN,TRY}LOCK,CMP_REQUEUE}_PI doesn't really make any sense for 64-bit
> futexes, the format of PI futexes is hardcoded in the kernel and is always
> 32-bit, see FUTEX_TID_MASK, FUTEX_WAITERS, FUTEX_OWNER_DIED definitions.
> exit_robust_list/handle_futex_death will handle 32-bit PI futexes anyway.
> Similarly, sys_futex64 shouldn't support the obsolete operations that
> are there solely for compatibility (e.g. FUTEX_REQUEUE or FUTEX_FD).
> 
> When you just -ENOSYS on the PI ops, there is no need to implement
> futex_atomic_cmpxchg_inatomic64.
> 
> FUTEX_WAKE_OP is questionable for 64-bit, IMHO it is better to just
> -ENOSYS on it and only if anyone ever finds actual uses for it, add it.
> 
> For 64-bit futexes the only needed operations are actually
> FUTEX_WAIT and perhaps FUTEX_CMP_REQUEUE, so I wonder if it isn't
> better to just add FUTEX_WAIT64 and FUTEX_CMP_REQUEUE64 ops to sys_futex
> instead of adding a new syscall.
> 
> But the FUTEX_{{,UN,TRY}LOCK,CMP_REQUEUE}_PI removal for 64-bit futexes
> is IMHO the most important part of my complain.
> 

Following this mail sent few weeks ago, here is a patch which should meet your 
requirements.
I've quickly done it on top of the latest -mm (2.6.21-rc6-mm2) and a little bit 
tested.
To be honest, as I'm not really aware of your exact needs and as I don't know 
the exact usage which will be done with 64bit futexes, I can't really maintain 
it. So I'll let you take/modify/adapt this patch following your needs.

Thanks,

Signed-off-by: Pierre Peiffer <pierre.peiffer@...l.net>



-- 
Pierre

View attachment "futex-64bits-command.patch" of type "text/x-patch" (24428 bytes)