Re: [PATCH] [RFC] notify userspace about time changes

[Greg KH <gregkh@suse.de>]

On Fri, Aug 06, 2010 at 12:22:27AM +0200, Kay Sievers wrote:
> On Thu, Aug 5, 2010 at 23:38, Greg KH <gregkh@suse.de> wrote:
> > On Thu, Aug 05, 2010 at 02:11:05PM -0700, john stultz wrote:
> >> On Thu, 2010-08-05 at 15:33 +0300, Alexander Shishkin wrote:
> >> > On 4 August 2010 18:58, john stultz <johnstul@us.ibm.com> wrote:
> >> > > Is there a actual use case that you need this for?  I don't really have
> >> > > an issue with the code I just really want to make sure the feature would
> >> > > be useful enough to justify the API and code maintenance going forward.
> >> >
> >> > Yes. What we have here is an application which takes care of different means
> >> > of time synchronization (trusted time servers, different GSM operators, etc)
> >> > and also different kinds of time-based events/notifications (like "dentist
> >> > appointment next thursday"). When it encounters a time change that is
> >> > made by some other application, it basically wants to disable automatic
> >> > time adjustment and trigger the events/notifications which are due at this
> >> > (new) time.
> >>
> >> Ok. Something specific is always more helpful then theoretical uses.
> >>
> >> I think the filtering is still a bit controversial, so you might want to
> >> respin it without that. But otherwise I'm ok with it as long as no one
> >> else objects to any of the minor details of the interface
> >>
> >> GregKH: Does /sys/kernel/time_notify seem ok by you?
> >
> > Um, it depends, what is that file going to do?  I don't see a
> > Documentation/ABI/ entry here that describes it fully :)
> 
> I think that's really awkward interface, to pass file descriptor
> numbers around and write them to magic sysfs files.

Ick, really?  That's not ok for sysfs.

> I would very much prefer a file that contains the current time, and
> wakes up possible users with a POLL_ERR on changes caused by some
> other process. That works very well for things like /proc/mounts, is
> easy to get, and does not need a full page of weird instructions to
> get stuff done. :)

That sounds more reasonable.

thanks,

greg k-h