[Ntp] Antw: Re: Leap second draft

"Ulrich Windl" <Ulrich.Windl@rz.uni-regensburg.de> Mon, 27 January 2020 07:07 UTC

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Date: Mon, 27 Jan 2020 08:07:43 +0100
From: Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de>
To: watsonbladd@gmail.com
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Subject: [Ntp] Antw: Re: Leap second draft
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>>> Watson Ladd <watsonbladd@gmail.com> schrieb am 24.01.2020 um 16:04 in
Nachricht
<CACsn0ckf91GH7tSr6d2KEz7T6N7z0t7LyF6JSr66dn0OA5m2Tg@mail.gmail.com>:
> On Thu, Jan 23, 2020, 10:51 PM Patrik Fältström <paf@frobbit.se> wrote:
> 
>> On 24 Jan 2020, at 0:36, Warner Losh wrote:
>>
>> >> POSIX doesn't specify, and so systems choose a number of different ways
>> of coping (repeat the last second of the day, repeat the first second of
>> the next day, freeze time during leap second, do some crazy smear to
>> pretend reality matches the POSIX spec, kernel panic, etc).
>> >
>> >
>> >
>> > This part is true. It's the biggest flaw with time_t: It doesn't
>> acknowledge that leap seconds exist, so what to do during that thing which
>> the standard says doesn't exist is up for grabs :(
>>
>> As the POSIX definition of "number of seconds since the epoch" is "number
>> of days since the epoch plus number of seconds within the current day" the
>> last second of one day and the first on the next have the same number.
>>
>> The fix is of course to be made at POSIX and if it was done, tons of
>> issues would just go poof as time then always did increase.
>>
> 
> Why does POSIX matter for NTP timestamps? We can always clarify the
> language independently.

I guess ist because operating systems keep time as POSIX time, and after
starting NTP, it's the only local time it has to start with.  Any additional
time scale could be maintained within NTP only (i.e. is lost when NTP stops).

> 
> 
>> There would still be an issue with "what time is it a gazillion seconds
>> from now" as one do not know the number of leap seconds to be added in the
>> future.
>>
>> But lets not mix up the issues.
>>
>> Anyway, I have seen proposals in POSIX on fixing this which have not been
>> moved forward. Anyone being involved in POSIX that knows anything about
>> that status?
>>
>>    Patrik
>>