linux-kernel - Re: implementing Futex

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Message-ID: <4A9BFA92.2030300@us.ibm.com>
Date:	Mon, 31 Aug 2009 09:30:10 -0700
From:	Darren Hart <dvhltc@...ibm.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Michael Schnell <mschnell@...ino.de>, linux-kernel@...r.kernel.org,
	Mike Frysinger <vapier.adi@...il.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Jakub Jelinek <jakub@...hat.com>,
	Thomas Chou <thomas@...ron.com.tw>
Subject: Re: implementing Futex

Arnd Bergmann wrote:
> On Friday 14 August 2009, Michael Schnell wrote:
>> Arnd Bergmann wrote:
>>> The man page says that the last parameter is ignored for op=FUTEX_WAKE,
>>> which is correct. The code that you were looking at however is for
>>> of=FUTEX_WAKE_OP, which is not documented as of manpages-3.22.
>>>
>>> It was added by Jakub back in 2005, but if he wrote a documentation
>>> for it, it never went into the man pages package. On a similar
>>> note, Ingo also added other futex operations that are not documented
>>> yet.
>>>
>> Thus in any documented software, the quite complex stuff in
>> "futex_atomic_op_inuser", which is provided in several different
>> "futex.h" files for all those architectures never is used ?
> 
> No, my point was that futex_atomic_op_inuser is indeed used
> correctly, it's just not documented.
> See http://lwn.net/Articles/148830/ for the initial posting
> 
>> Is there any viable use for this ?
> 
> glibc heavily uses it for the pthreads implementation.
> 
>> Would it not be appropriate either to do a documentation or to remove it ?
> 
> Adding documentation, yes.

I also recently added two futex op codes which need to be added to the 
man page, but they are documented in Documentation/futex-requeue-pi.txt. 
   Documentation/pi-futex.txt documents the FUTEX_(UN)LOCK_PI opcodes 
which aren't in the man pages either.

-- 
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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