From: Chris Friesen on
On 08/04/2010 06:52 PM, john stultz wrote:
> On Wed, 2010-08-04 at 12:48 -0600, Chris Friesen wrote:
>> On 08/04/2010 09:58 AM, john stultz 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.
>>
>> We actually added a time-change-notification mechanism internally a long
>> time ago but never saw demand for it and so never bothered trying to
>> push it upstream. Ours is signal-based.
>>
>> Among other things we use it to pass on time-change notifications to an
>> emulator running a proprietary OS that really cares about having an
>> accurate time-of-day but can't afford a syscall to retrieve it every time.
>
> So the eventfd based method (and the filtering) proposed would work for
> you?

The eventfd based method would work. The filtering is unnecessary for
us and seems somewhat fragile as currently implemented.

Chris

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Chris Friesen
Software Developer
GENBAND
chris.friesen(a)genband.com
www.genband.com
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From: john stultz on
On Thu, 2010-08-05 at 15:33 +0300, Alexander Shishkin wrote:
> On 4 August 2010 18:58, john stultz <johnstul(a)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?

thanks
-john


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From: Greg KH on
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(a)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 :)

thanks,

greg k-h
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From: Kay Sievers on
On Thu, Aug 5, 2010 at 23:11, john stultz <johnstul(a)us.ibm.com> wrote:
> On Thu, 2010-08-05 at 15:33 +0300, Alexander Shishkin wrote:
>> On 4 August 2010 18:58, john stultz <johnstul(a)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.

Basically everything that schedules an action based on an absolute
time specification, like at 3pm today, and not in 3 hours from now,
needs to track such system time changes. Otherwise it has to do
nonsense like cron does, to wake up every minute to check the current
time.

Kay
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From: Kay Sievers on
On Thu, Aug 5, 2010 at 23:38, Greg KH <gregkh(a)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(a)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.

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. :)

Kay
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