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

From: Bastien ROUCARIES
Date: Fri Aug 06 2010 - 03:43:53 EST

On Fri, Aug 6, 2010 at 12:22 AM, Kay Sievers <kay.sievers@xxxxxxxx> wrote:
> On Thu, Aug 5, 2010 at 23:38, Greg KH <gregkh@xxxxxxx> 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@xxxxxxxxxx> 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. :)
See and it is plan9 compatible

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