Messages in this thread | | | Date | Wed, 18 Aug 2010 16:53:03 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] [RFCv2] notify userspace about time changes |
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On Wed, 18 Aug 2010 16:43:48 -0700 "H. Peter Anvin" <hpa@zytor.com> wrote:
> On 08/18/2010 03:57 PM, Andrew Morton wrote: > > On Wed, 18 Aug 2010 16:55:39 +0300 > > Alexander Shishkin <virtuoso@slind.org> wrote: > > > >> Certain userspace applications (like "clock" desktop applets or cron) might > >> want to be notified when some other application changes the system time. > > > > The requirements sound a bit fluffy to me. > > > > Any time-displaying application will find out the new time next time > > it reads the time. So afaict this is only really useful for clock > > applets which display once per minute, so they will show the new time > > promptly after the time was altered, yes? Is that really worth adding > > new code for? > > > > Actually a much more significant use case was given for the "civil > periodic" type events: something that wants to happen "every day at > noon", for example. The logical thing of sleeping until the next noon > breaks if the walltime clock is changed. As such, things like cron have > to resort to wake up once a minute just to assure themselves that they > have nothing to do. This is inefficient, especially for battery-powered > devices.
OK.
Such applications might be better served via a wake-me-at-this-time syscall instead of a sleep-me-for-this-long syscall. Although such a thing is less general.
Is sysfs the right interface for this thing? Bear in mind that CONFIG_SYSFS does exist.
> + fd = open("/sys/kernel/time_notify", O_WRONLY); > + fdprintf(fd, "%d 1 0 1 1", efd);
why not
sys_time_notify(efd, 1, 0, 1, 1);
?
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