linux-kernel - Re: [PATCH] timerfd: add TFD_NOTIFY_CLOCK

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Date:	Wed, 01 Dec 2010 16:14:27 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Alexander Shishkin <virtuoso@...nd.org>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Feng Tang <feng.tang@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michael Tokarev <mjt@....msk.ru>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Chris Friesen <chris.friesen@...band.com>,
	Kay Sievers <kay.sievers@...y.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Artem Bityutskiy <dedekind1@...il.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Lennart Poettering <mzxreary@...inter.de>,
	linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for clock
 changes

On Wed, 2010-12-01 at 03:39 +0200, Alexander Shishkin wrote:
> To use this notification functionality, user has to call timerfd_settime()
> with TFD_NOTIFY_CLOCK_SET flag. After this CLOCK_REALTIME timers will
> read as the number of times the wall clock has been set since last read
> and poll every time the wall clock is set; CLOCK_MONOTONIC timers will
> behave likewise, but in the event of the clock being updated upon resuming
> from suspend. For both CLOCK_REALTIME and CLOCK_MONOTONIC timers with
> TFD_NOTIFY_CLOCK_SET flag set, a call to timerfd_gettime() will return
> current wall clock in it_value.

The CLOCK_MONOTONIC flag on resume worries me a bit (since
CLOCK_MONOTONIC isn't adjusted on resume).

What is the use case there?

thanks
-john


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