From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexander Shishkin <virtuoso@slind.org>
Subject: Re: [PATCH] [RFC] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for
 clock changes
Date: Wed, 1 Dec 2010 02:33:58 +0200
Message-ID: <20101201003358.GJ26184@shisha.kicks-ass.net>
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 <20101123224346.GA19350@tango.0pointer.de>
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Cc: linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@suse.de>,
	Feng Tang <feng.tang@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Michael Tokarev <mjt@tls.msk.ru>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	John Stultz <johnstul@us.ibm.com>,
	Chris Friesen <chris.friesen@genband.com>,
	Kay Sievers <kay.sievers@vrfy.org>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Artem Bityutskiy <dedekind1@gmail.com>,
	Davide Libenzi <davidel@xmailserver.org>,
	linux-fsdevel@vger.kernel.org,
	Alexander Shishkin <virtuoso@slind.org>
To: Lennart Poettering <mzxreary@0pointer.de>
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On Tue, Nov 23, 2010 at 11:43:46PM +0100, Lennart Poettering wrote:
> On Tue, 23.11.10 19:22, Alexander Shishkin (virtuoso@slind.org) wrote:
> 
> > Certain userspace applications (like "clock" desktop applets or cron or
> > systemd) might want to be notified when some other application changes
> > the system time. There are several known to me reasons for this:
> >  - avoiding periodic wakeups to poll time changes;
> >  - rearming CLOCK_REALTIME timers when said changes happen;
> >  - changing system timekeeping policy for system-wide time management
> >    programs;
> >  - keeping guest applications/operating systems running in emulators
> >    up to date.
> > 
> > This is another attempt to approach notifying userspace about system
> > clock changes. The other one is using an eventfd and a syscall [1]. In
> > the course of discussing the necessity of a syscall for this kind of
> > notifications, it was suggested that this functionality can be achieved
> > via timers [2] (and timerfd in particular [3]). This idea got quite
> > some support [4], [5], [6] and some vague criticism [7], so I decided
> > to try and go a bit further with it.
> 
> I agree with Kay, this is pretty much exactly what we want for
> systemd. (Assuming that the time jump due to system suspend is
> propagated to userspace like any other time jump with this path).

Good point, I'll add the notification to the resume point.

> So yeah, I'd be very happy if this could be merged.

Good to hear.

Regards,
--
Alex