linux-kernel - Re: Why does timerfd() only support CLOCK_REALTIME and CLOCK

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Date:	Sun, 8 Feb 2009 11:29:33 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Michael Kerrisk <mtk.manpages@...il.com>
cc:	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Why does timerfd() only support CLOCK_REALTIME and
 CLOCK_MONOTONIC?

On Mon, 9 Feb 2009, Michael Kerrisk wrote:

> Hi Davide,
> 
> At the moment I'm looking into writing man pages for timer_create(2)
> and friends.  (Somewhat bizarrely, these pages do not yet exist.)  As
> I looked into the source code of timer_create(), etc., and did some
> tests, I saw that timer_create() supports the following clocks:
> 
> TIMER_REALTIME
> TIMER_MONOTONIC
> TIMER_PROCESS_CPUTIME_ID
> TIMER_THREAD_CPUTIME_ID
> clockid obtained from clock_getcpuclockid(3)
> clockid obtained from pthread_getcpuclockid(3)
> 
> On the other hand, timerfd() only permits the first two of these.
> What's the reason for that limitation of timerfd()?  (It may be worth
> adding something to the man page on this point.)

No particular reason I can think of. If Thomas makes invalid_clockid() 
available, we could allow timerfd() to support all time timers 
timer_create() supports.
Do you see any reason why this won't work Thomas?



- Davide


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