linux-kernel - Re: [ntpwg] Bug: Status/Summary of slashdot leap-second crash on new years 2008-2009

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Message-Id: <20090106.124055.143671472.imp@bsdimp.com>
Date:	Tue, 06 Jan 2009 12:40:55 -0700 (MST)
From:	"M. Warner Losh" <imp@...imp.com>
To:	linasvepstas@...il.com
Cc:	johnstul.lkml@...il.com, david@...g.hm, goodgerster@...il.com,
	kyle@...fetthome.net, slashdot@...eshallam.info,
	zippel@...ux-m68k.org, davidn@...idnewall.com,
	linux-kernel@...r.kernel.org, hancockr@...w.ca,
	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: <3ae3aa420901052053m5a410671u13ecccfb7e29260c@...l.gmail.com>
            "Linas Vepstas" <linasvepstas@...il.com> writes:
: 2009/1/5 john stultz-lkml <johnstul.lkml@...il.com>:
: > On Mon, Jan 5, 2009 at 9:42 AM, Linas Vepstas <linasvepstas@...il.com> wrote:
: > [snip]
: >> 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 believe Roman has already added this ability:
: > http://git.kernel.org/gitweb.cgi?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=153b5d054ac2d98ea0d86504884326b6777f683d;hp=9f14f669d18477fe3df071e2fa4da36c00acee8e
: 
: Well, you're answering a different statment than what
: I was talking about -- I wanted to make sure that TAI
: information was available via NTP -- this has nothing
: to do with the kernel, and would be something available
: to all operating systems.
: 
: Anyway -- I'm looking at the patch you reference, and
: maybe I'm being dumb -- but -- I think I see a bug.
: 
: case TIME_DEL decrements TAI, but TIME_INS does
: not increment it. Instead, there's a lonely increment in
: TIME_OOP which seems wrong.  ??

No.  That's right.  The increment doesn't happen until the leap second
has happened.  The TIME_OOP exists to increment the TAI offset at the
right time.  The decrement would happen right away, since the second
is deleted at the end of :58.

I had to draw lots of pictures when I was working this code out in
FreeBSD.

Warner
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