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Date: Thu, 16 Sep 2010 16:15:12 -0700 From: john stultz <johnstul@...ibm.com> To: Alexander Shishkin <virtuoso@...nd.org> Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, "H. Peter Anvin" <hpa@...or.com>, Kay Sievers <kay.sievers@...y.org>, Greg KH <gregkh@...e.de>, Chris Friesen <chris.friesen@...band.com>, Linus Torvalds <torvalds@...ux-foundation.org>, "Kirill A. Shutemov" <kirill@...temov.name>, Thomas Gleixner <tglx@...utronix.de>, Martin Schwidefsky <schwidefsky@...ibm.com>, Jon Hunter <jon-hunter@...com>, Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, David Howells <dhowells@...hat.com>, Avi Kivity <avi@...hat.com>, John Kacur <jkacur@...hat.com> Subject: Re: [PATCH 1/7] notify userspace about time changes On Fri, 2010-09-17 at 01:58 +0300, Alexander Shishkin wrote: > On Thu, Sep 16, 2010 at 03:30:40 -0700, john stultz wrote: > > On Fri, 2010-09-17 at 01:10 +0300, Alexander Shishkin 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. > > > > > > 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. > > > After that, any calls to settimeofday()/stime()/adjtimex() made by other > > > processes will be signalled to this eventfd. Credits for suggesting the eventfd > > > mechanism for this purpose go to Kirill Shutemov. > > > > One thing I have thought of since the last time you posted this, maybe > > it would be worth adding a clockid field to the syscall? > > > > Basically, we're looking at extending the posix clocks interfaces to > > allow for additional clock hardware to be exposed (See the discussion on > > PTP and my CLOCK_RTC patch today for examples and details). > > > > So it seems possible that folks would want a similar interface to catch > > updates to non CLOCK_REALTIME clocks. > > > > Does this seem reasonable? > > The whole idea seems interesting, I'll try to add this in the next iteration > of this patchset. Very cool! > The first thing that comes it mind is -- are there going to be additional > events that the user might like to be notified of, like rtc_set_alarm()? > Doesn't seem too likely, though. Well, the posix interface patch is trying to abstract over the hardware details like rtc_set_alarm. So instead it would be timer_create/timer_settime/etc. These interfaces deal with timer structures that are per-process, so I don't think we need a notification hook for them. thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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