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

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Date:	Wed, 14 May 2014 13:44:46 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"Carlos O'Donell" <carlos@...hat.com>
Cc:	Michael Kerrisk-manpages <mtk.manpages@...il.com>,
	Darren Hart <dvhart@...ux.intel.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>
Subject: Re: futex(2) man page update help request

On Wed, May 14, 2014 at 1:23 PM, Carlos O'Donell <carlos@...hat.com> wrote:
> On 05/14/2014 03:03 PM, Michael Kerrisk (man-pages) wrote:
>>> 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*".)
>
> I fully agree with Michael here.
>
> The futex() syscall was never exposed to userspace specifically because
> it was an interface we did not want to support forever with a stable ABI.
> The futex() syscall is an implementation detail that is shared between
> the kernel and the writers of core runtimes for Linux.
>
> The fact that the futex() syscall is out of date is my fault, is the fault
> of Linux kernel developers, etc. etc., we should all have reached out to
> Michael with patches to keep this developer-centric documentation updated.

I realize that this is out of scope for linux-abi, but I *stongly*
disagree with this notion.  futex() needs to be just as stable as
anything else: old glibc versions must continue to work.  I just
jumped through a bunch of hoops to keep a single glibc patch release
in OpenSUSE 9 working in a maintainable way; breaking futex will break
far more than that.

Additionally, at least the FUTEX_WAIT and FUTEX_WAKE operations are
extremely useful, and they can do things that are tedious at best
using mutexes and condvars.  It's a simple API to use.  I use it, and
I've seen plenty of other open-source apps using the futex API
directly.

I think the best way forward might be to try to convince the glibc
maintainers to add the wrapper.

--Andy
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