[LEAPSECS] Leap seconds have a larger context than POSIX

[Warner Losh]

On Thu, Feb 6, 2020, 3:22 AM Tom Van Baak <tvb at leapsecond.com> wrote:

> Hi Hal,
>
> It's 2020. How on earth can NTP still not implement UTC correctly, in all
> cases? Or is it a fundamental NTP design flaw?
>

Design flaw. NTP time stamps can't encode a leap second. It can therefore
never really work in all cases. We are left with what hack do you want to
do today.

> The Z3801A issue doesn't sound like an NTP problem. This is a known legacy
> Z3801A f/w or Motorola Oncore problem, yes? Maybe also affected by one or
> even two GPS WNRO problems buy now?
>
Known past issues are likely future problems. 40 years in software has
taught me that we do not always learn and apply the lessons of the past.
Every 5-10 years we swap out the coders that learned them for newer,
cheaper labor. Or there are new players in a niche that have more hubris
than tribal knowledge. This guarantees bugs will repeat.

Warner


/tvb
>
> On 2/6/2020 1:41 AM, Hal Murray wrote:
>
> tvb said:
>
> There's no ambiguity. Those are just bugs. No software should depend on  more
> than 1 month notice of a leap second and no software should be  fooled if the
> notice is months or even years in advance.
>
> There are plenty of quirks in ntp code along that line.  The APIs don't have
> an explicit when.  The NTP-Kernal API for leap-pending is leap-tonight.  You
> have most of the next day to turn it off.  The leap-pending on the wire is
> leap-at-the-end-of-this-month.
>
> I fixed a bug in the Z3801 driver by ignoring a leap pending unless it was
> June or December.  It's a hack, but it gets the job done and the code wasn't
> setup to ask it when the leap would happen.
>
>
> tvb said:
>
> If you're writing a FAQ or best practices guide stay in touch. I have a
> semi-technical leap second report in the works. UTC is actually very  simple;
> but it's been complicated by untold levels of bad assumptions,  bad
> execution, and bad prose.
>
> Are you going to say anything about POSIX?
>
>
>
>
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