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

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Date:	Wed, 14 May 2014 23:12:53 -0400
From:	"Carlos O'Donell" <carlos@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	mtk.manpages@...il.com, Darren Hart <dvhart@...ux.intel.com>,
	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 05/14/2014 07:34 PM, Thomas Gleixner wrote:
> On Wed, 14 May 2014, Carlos O'Donell 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.
> 
> Nonsense. 

What is nonsense?

I do not want to be responsible for the futex API by having glibc provide
wrappers. That can't be nonsense since it's a glibc community decision to
make.

Perhaps the point at which we disagree is that I said "writers of core runtimes"
and you would rather I have said "any application wishing to use raw syscalls."
That's fine, I concede that point, I have no right to restrict raw syscall
usage.
 
> If we change that interface (aside of adding functionality or some new
> error return) it would break the world and some more, simply because
> out of the blue glibc-2.xx would stop to work on linux-3.yy.

No disagreement from me.

> Aside of that the futex syscall is used as a bare interface without
> any glibc interaction:
> 
>  - It's handy to implement user space wait queues
> 
>  - It's (ab)used in very interesting ways by data base apps
> 
>  - It's (ab)used by some Java monstrosities.
> 
> Nothing you care about and you really don't want to see the gory
> details, but you have to accept that there is an universe which is
> happy to deal with the raw syscalls instead of going through some ill
> defined posix interfaces.

Sure :-)

Cheers,
Carlos.

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