Message-ID: <1400101522.6897.1.camel@buesod1.americas.hpqcorp.net>
Date:	Wed, 14 May 2014 14:05:22 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	Darren Hart <dvhart@...ux.intel.com>
Cc:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	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 Wed, 2014-05-14 at 09:18 -0700, Darren Hart 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.
> 
> However, unless I'm sorely mistaken, the larger problem is that glibc
> removed the futex() call entirely, so these man pages don't describe
> 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/inclu
> 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)

Yeah, and I actually stole that from you for perf :)

> 
> 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, ...) ?

+1, is there anything preventing adding a futex wrapper... glibc folks?

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