linux-kernel - Re: futex(2) man page update help request

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Date:	Wed, 14 May 2014 12:59:16 -0700
From:	Darren Hart <dvhart@...ux.intel.com>
To:	<mtk.manpages@...il.com>
CC:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	Jakub Jelinek <jakub@...hat.com>,
	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Arnd Bergmann <arnd@...db.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux API <linux-api@...r.kernel.org>,
	Carlos O'Donell <carlos@...hat.com>
Subject: Re: futex(2) man page update help request

On 5/14/14, 12:03, "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
wrote:

>Hi Darren,
>
>On Wed, May 14, 2014 at 6:18 PM, Darren Hart <dvhart@...ux.intel.com>
>wrote:
>> On 5/14/14, 3:35, "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
>> wrote:
>>
>>>[So, some futex recent discussions remind me I should make this request]
>>>
>>>Hello all (especially those in the To:, namely Thomas, Darren, Ingo,
>>>Jakub),
>>>
>>>The futex man pages:
>>>http://man7.org/linux/man-pages/man2/futex.2.html
>>>http://man7.org/linux/man-pages/man7/futex.7.html
>>>are currently in a sorry state. I'm by no means convinced that all of
>>>the
>>>futex operations described there are explained fully and correctly. And
>>>probably not all error cases for each operation are properly documented.
>>>I'd be very happy if some folk could review those pages and send me
>>>corrections (Git:
>>>http://git.kernel.org/pub/scm/docs/man-pages/man-pages).
>>>
>>>But worse, a number of futex operations remain undocumented in futex(2)
>>>(see the list below).
>>>
>>>I am aware of Documentation/pi-futex.txt and
>>>Documentation/futex-requeue-pi.txt. However, both of those documents
>>>are rather thin on details / explain what certain FUTEX_* operations are
>>>used for rather than what they do / focus on the implementation, rather
>>>than the semantics.
>>>
>>>What I would like is that the futex(2) page documenta each one of
>>>these operations with a focus on the semantics in a way that might be
>>>useful to writers of library functions or those who simply wish to
>>>better understand (from a user-space perspective) what futexes are
>>>and how they are used. However, I don't have the knowledge to do
>>>this well in any reasonable time.
>>>
>>>Would the folk in the To: list (or anyone else who is knowledgeable)
>>>be willing to write patches
>>>(Git: http://git.kernel.org/pub/scm/docs/man-pages/man-pages )
>>>or just supply me with some raw text that documents these currently
>>>undocumented futex operations, in the manner suggested?
>>
>> Yes, I'll be glad to help.
>
>Thanks!
>
>> However, unless I'm sorely mistaken, the larger problem is that glibc
>> removed the futex() call entirely, so these man pages don't describe
>
>I don't think futex() ever was in glibc--that's by design, and
>completely understandable: no user-space application would want to
>directly use futex(). (BTW, I mispoke in my earlier mail when I said I
>wanted documentation suitable for "writers of library functions" -- I
>meant suitable for "writers of *C library*".)
>
>> something users even have access to anymore. I had to revert to calling
>> the syscalls directly in the futextest test suite because of this:
>>
>> 
>>http://git.kernel.org/cgit/linux/kernel/git/dvhart/futextest.git/tree/inc
>>lu
>> de/futextest.h#n67
>>
>>
>> Which basically defines:
>>
>> #define futex(uaddr, op, val, timeout, uaddr2, val3, opflags) \
>>         syscall(SYS_futex, uaddr, op | opflags, val, timeout, uaddr2,
>>val3)
>>
>>
>> Adding Carlos for his perspective.
>>
>> If I'm wrong, or we can restore the futex() call, great. If not...
>>Should
>> we keep the man-pages and document it as syscall(SYS_futex, ..., op,
>>...) ?
>
>We should keep the man page ;-). I just need to add some words to
>point out the use of syscall(). Mostly though, I'm interested in
>getting documentation of the operations listed below :-).

OK, yes - because the following doesn't work:

#include <linux/futex.h>
       #include <sys/time.h>

       int futex(int *uaddr, int op, int val, const struct timespec
*timeout,
          int *uaddr2, int val3);


It's going to be difficult for me to make the time to do this - but I do
want it done, so please don't hesitate to nag me.

Thanks,

>>>    commit 4732efbeb997189d9f9b04708dc26bf8613ed721
>>>    Author: Jakub Jelinek <jakub@...hat.com>
>>>    Date:   Tue Sep 6 15:16:25 2005 -0700
>>>    See also https://bugzilla.kernel.org/show_bug.cgi?id=14303
>>>
>>>2.6.18 adds priority inheritance support:
>>>FUTEX_LOCK_PI, FUTEX_UNLOCK_PI, and FUTEX_TRYLOCK_PI.
>>>    commit c87e2837be82df479a6bae9f155c43516d2feebc
>>>    Author: Ingo Molnar <mingo@...e.hu>
>>>    Date:   Tue Jun 27 02:54:58 2006 -0700
>>>
>>>    commit e2970f2fb6950183a34e8545faa093eb49d186e1
>>>    Author: Ingo Molnar <mingo@...e.hu>
>>>    Date:   Tue Jun 27 02:54:47 2006 -0700
>>>
>>>    See Documentation/pi-futex.txt
>>>
>>>2.6.25 adds FUTEX_WAKE_BITSET, FUTEX_WAIT_BITSET
>>>    commit cd689985cf49f6ff5c8eddc48d98b9d581d9475d
>>>    Author: Thomas Gleixner <tglx@...utronix.de>
>>>    Date:   Fri Feb 1 17:45:14 2008 +0100
>>>
>>>2.6.31 adds FUTEX_WAIT_REQUEUE_PI, FUTEX_CMP_REQUEUE_PI
>>>    commit 52400ba946759af28442dee6265c5c0180ac7122
>>>    Author: Darren Hart <dvhltc@...ibm.com>
>>>    Date:   Fri Apr 3 13:40:49 2009 -0700
>>>
>>>    commit ba9c22f2c01cf5c88beed5a6b9e07d42e10bd358
>>>    Author: Darren Hart <dvhltc@...ibm.com>
>>>    Date:   Mon Apr 20 22:22:22 2009 -0700
>>>
>>>    See Documentation/futex-requeue-pi.txt
>>>
>>>Thanks,
>>>
>>>Michael
>>>
>>>
>>>--
>>>Michael Kerrisk
>>>Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
>>>Linux/UNIX System Programming Training: http://man7.org/training/
>>>
>>
>>
>> --
>> Darren Hart                                     Open Source Technology
>>Center
>> darren.hart@...el.com                                       Intel
>>Corporation
>>
>>
>>
>
>
>
>-- 
>Michael Kerrisk
>Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
>Linux/UNIX System Programming Training: http://man7.org/training/
>


-- 
Darren Hart					Open Source Technology Center
darren.hart@...el.com				            Intel Corporation



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