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    SubjectRe: [PATCH] [RFC] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for clock changes
    On Tue, 2010-11-23 at 23:43 +0100, Lennart Poettering wrote:
    > On Tue, 23.11.10 19:22, Alexander Shishkin ( 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 <>" 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)

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