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    SubjectRe: [PATCH 1/7] notify userspace about time changes
    On Fri, 17 Sep 2010, Alan Cox wrote:

    > > Certain userspace applications (like "clock" desktop applets or cron) might
    > > want to be notified when some other application changes the system time. It
    > > might also be important for an application to be able to distinguish between
    > > its own and somebody else's time changes.
    > A program that cannot work out if it or someone else changed the time is
    > very very broken indeed !
    > > This patch implements a notification interface via eventfd mechanism. Proccess
    > > wishing to be notified about time changes should create an eventfd and pass it
    > > to time_change_notify() syscall along with notification options.
    > This seems complete overkill and it doesn't really help applications much
    > that I can see because of suspend/resume.
    > What are your actual use cases ?
    > Clocks apps don't care because they check the actual time so notice it
    > shfited. Cron and anacron appear to contain the needed internal handling.
    > Anything sleeping until a time occurs maybe ? In which case its a lot
    > simpler and cleaner than events to provide a new itimer which wakes the
    > process when the wall time hits the time specified in the timer.

    We already have that. posix timers provide this.

    The only case I can imagine where a notification might be interesting
    is when something armed an absolute timer on CLOCK_REALTIME and time
    is set backwards.



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