Messages in this thread | | | Date | Fri, 17 Sep 2010 13:07:43 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH 1/7] notify userspace about time changes |
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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.
Thanks,
tglx
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