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

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Date:	Wed, 14 May 2014 17:28:32 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Davidlohr Bueso <davidlohr@...com>, mtk.manpages@...il.com
CC:	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>,
	"Carlos O'Donell" <carlos@...hat.com>
Subject: Re: futex(2) man page update help request

On 05/14/2014 01:56 PM, Davidlohr Bueso 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(). 
> 
> That's actually not quite true. There are plenty of software efforts out
> there that use futex calls directly to implement userspace serialization
> mechanisms as an alternative to the bulky sysv semaphores. I worked
> closely with an in-memory DB project that makes heavy use of them. Not
> everyone can simply rely on pthreads.
> 

More fundamentally, futex(2), like clone(2), are things that can be
legitimately by user space without automatically breaking all of glibc.
 There are some other things where that is *not* true, because glibc
relies on being able to mediate all accesses to a kernel facility, but
not here.

	-hpa

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