Re: [PATCH] [RFC] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for clock changes

[Artem Bityutskiy <dedekind1@gmail.com>]

On Tue, 2010-11-23 at 23:43 +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).

A "Tested-by: Lennart Poettering <mzxreary@0pointer.de>" would be
helpful, I think.

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

Hmm, and question about why exactly the timerfd interface is a bad way
to go was ignored.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)