[time-nuts] [LEAPSECS] Leap second to be introduced at midnight UTC December 31 this year

Bob Camp kb8tq at n1k.org
Mon Jul 25 13:36:32 EDT 2016


Hi


> On Jul 25, 2016, at 10:21 AM, Martin Burnicki <martin.burnicki at burnicki.net> wrote:
> 
> Bob,
> 
> Bob Camp wrote:
>> Hi
>> 
>> The practical problem with any change to leap seconds is transition from what we have
>> to the “new system”. Anything other than dropping them altogether involves a *lot* of 
>> coordination. You pretty much have to pick a date and bring everything onto the new
>> standard then. For testing purposes your time sources should “advertise” the new 
>> information ahead of that date. As a practical point, that means a new field in the data. 
>> In the case of GPS and other space based systems, that’s not going to happen. 
> 
> But if you
> 
> - stick with the leap seconds with UTC as-is
> - let the kernel alternatively run on TAI instead of UTC
> - keep existing API calls as they are, returning UTC
> - introduce new API calls which tell if the kernel runs UTC or TAI
>  and let you query the TAI time stamps
> 
> then both kernels and applications could make a change over to the new
> timekeeping seamlessly.
> 
> I agree this wouldn't fix all problems you may have with leap seconds,
> but it would at least avoid problems like "the kernel hangs when the
> system time is stepped back by 1 s to account for a leap second”.

Except that you still have the issue of “what time did this file get changed”. To most of us, that’s not 
really a big deal. A second either way … who cares. :) In some areas they care a *LOT* and a second
is a really big deal. Having two different time stamps running around in the same kernel with different 
people picking which one to use …. sounds like a recipe for trouble. 

Now, having the “new” calls ahead of the transition, yes, that’s pretty much mandatory. You do need to 
debug this stuff and it has to be done somehow. If we are talking about the original suggestion, it’s a one
second delta one way or the other. There is nothing going on below the second level. I suppose you *could*
have more than one second, but it seems unlikely. In that case, your call is pretty simple “give me the delta”. 
Seems fairly easy / safe. I’ve messed up things that are far simpler :) 

Bob

> 
> Martin
> 
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