Re: [PATCH] [RFC] notify userspace about time changes
From: Kirill A. Shutemov
Date: Thu Aug 05 2010 - 06:05:42 EST
On Wed, Aug 04, 2010 at 06:46:38PM +0300, Alexander Shishkin wrote:
> On Wed, Aug 04, 2010 at 06:32:21 +0300, Kirill A. Shutemov wrote:
> > On Wed, Aug 04, 2010 at 03:48:28PM +0300, Alexander Shishkin wrote:
> > > Certain userspace applications (like "clock" desktop applets or ntpd) 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 echo
> > > its file descriptor to /sys/kernel/time_notify. 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 te Kirill Shutemov.
> > >
> > > So far, this implementation can only filter out notifications caused by
> > > time change calls made by the process that wrote the eventfd descriptor to
> > > sysfs, but not its children which (might) have inherited the eventfd. It
> > > is so far not clear to me whether this is bad and more confusing than
> > > excluding such children as well.
> > I think it's a bad idea to filter notifications. Let's leave it for
Someone might want to recieve notifications about its own activity.
It's a policy. Kernel should provide mechanism, not policy.
Kirill A. Shutemov
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