linux-kernel - Re: nanosleep() uses CLOCK_MONOTONIC, should be CLOCK

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Date:	Mon, 23 Jun 2008 10:34:05 +0200
From:	"Bart Van Assche" <bart.vanassche@...il.com>
To:	"Michael Kerrisk" <mtk.manpages@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"john stultz" <johnstul@...ibm.com>, "Ingo Molnar" <mingo@...e.hu>,
	"Roman Zippel" <zippel@...ux-m68k.org>
Subject: Re: nanosleep() uses CLOCK_MONOTONIC, should be CLOCK_REALTIME?

On Sun, Jun 22, 2008 at 9:35 AM, Michael Kerrisk <mtk.manpages@...il.com> wrote:
> Thomas,
>
> (I gues you are the right target for this?)
>
> The POSIX.1 specification of nanosleep() says:
>
>       But, except for the case of being interrupted by a signal, the
>       suspension time shall not be less than the time  specified  by
>       rqtp, as measured by the system clock CLOCK_REALTIME.
>
>
> However, reading kernel/hrtimer.c:sys_nanosleep(), it appears that
> CLOCK_MONOTONIC is used.
>
>    return hrtimer_nanosleep(&tu, rmtp, HRTIMER_MODE_REL, CLOCK_MONOTONIC);
>
> Is there a reason to use CLOCK_MONOTONIC, instead of CLOCK_REALTIME?  Is it
> intentional?  If yes, then I should document this in the man-pages.  If not,
> then it should be fixed.

CLOCK_MONOTONIC works fine even if ntpd steps the clock forward or
backward, CLOCK_REALTIME not. So the man page should be fixed.

Strange to find such phrases in the POSIX specs ...

Bart.
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