Date:	Tue, 06 Jan 2009 12:50:34 -0700 (MST)
From:	"M. Warner Losh" <imp@...imp.com>
To:	linasvepstas@...il.com
Cc:	david@...g.hm, hancockr@...w.ca, goodgerster@...il.com,
	kyle@...fetthome.net, slashdot@...eshallam.info,
	davidn@...idnewall.com, linux-kernel@...r.kernel.org,
	ntpwg@...ts.ntp.isc.org, pretzalz@...hhouse.org,
	burdell@...ntheinter.net, nick@...k-andrew.net, jeff@...owsky.org
Subject: Re: [ntpwg] Bug: Status/Summary of slashdot leap-second crash on
 new years 2008-2009

In message: <3ae3aa420901050942y56f0ecdei39c091a73e49c1fd@...l.gmail.com>
            "Linas Vepstas" <linasvepstas@...il.com> writes:
: 2009/1/5  <david@...g.hm>:
: > On Mon, 5 Jan 2009, Linas Vepstas wrote:
: >
: >>> Arguably the kernel's responsibility should be to keep track of the
: >>> most fundamental representation of time possible for a machine (that's
: >>> probably TAI) and it is a userspace responsibility to map from that
: >>> value to other time standards including UTC,
: >>
: >> Yes, this really does seem like the right solution.
: >>
: >>> using control files
: >>> which are updated as leap seconds are declared.
: >>
: >> Lets be clear on what "control files" means.  This does
: >> *NOT* mean some config file shipped by some distro
: >> for some package. That would be a horrid solution.
: >> People don't install updates, patches, etc.  Distros
: >> ship them late, or never, if the distro is old enough.
: >>
: >> A more appropriate solution would be to have
: >> either the kernel or ntpd track the leap seconds
: >> automatically.  First, the ntp protocol already provides
: >> the needed notification of a leap second to anyone
: >> who cares about it (i.e. there is no point in getting a
: >> Linux distro involved in this -- a distribution mechanism
: >> already exists, and works *better* than having a distro
: >> do it).
: >
: > I disagree with this. NTP will only know about leap seconds if it was
: > running and connected to a server that advertised the leap seconds during
: > that month.
: >
: > for example, if you installed a new server today, how would it ever know
: > that there was a leap second a couple of days ago?
: 
: OK, good point.  Unless your distro was less
: than a few days old (unlikely), you are faced with the
: same problem.  Sure, eventually, the distro will publish
: an update (which will add to the existing list of 36 leap

List of 24 leap seconds.  Although the delta is 34 right now, the
first 10 leap seconds were done as tiny steps (~50-100ms) plus
frequency offsets.  Well, the first 'leap' was 1.4228180s on Jan 1,
1961.  Everybody assumes that those seconds don't exist to simplify
things (or that there was simply a 10s step between TAI and UTC on
1-Jan-1972).  The leapsecond file from NIST doesn't even have them.

: seconds -- which is needed in any case, since no one
: has a server that's been up since 1958),  but this is
: unlikely to happen during this install window.
: 
: The long term solution would be write an RFC to extend
: NTP to also provide TAI information -- e.g. to add a
: message that indicates the current leap-second offset
: between UTC and TAI.

I'd love that.  There's likely going to be some resistance to that
because the leapfile is available via the crypto-authenticated means.
However, there's no real-time information available...  Also, there
are many reference clocks that would need this information plugged
into it somehow (IRIG doesn't report leap seconds in any meaningful[*]
way, let alone UTC-TAI offset).

[*] Some IRIG extensions do support reporting leap seconds at the end
of the hour, but that's too late...

Warner
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