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

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Date:	Mon, 5 Jan 2009 09:51:30 -0800 (PST)
From:	david@...g.hm
To:	Linas Vepstas <linasvepstas@...il.com>
cc:	Nick Andrew <nick@...k-andrew.net>,
	David Newall <davidn@...idnewall.com>,
	Kyle Moffett <kyle@...fetthome.net>,
	Ben Goodger <goodgerster@...il.com>,
	Robert Hancock <hancockr@...w.ca>,
	linux-kernel@...r.kernel.org,
	"Jeffrey J. Kosowsky" <jeff@...owsky.org>,
	MentalMooMan <slashdot@...eshallam.info>,
	Travis Crump <pretzalz@...hhouse.org>, burdell@...ntheinter.net
Subject: Re: Bug: Status/Summary of slashdot leap-second crash on new years
 2008-2009

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?

David Lang

> If the kernel needs to track leap seconds, it could do
> so using a mechanism similar to the "random pool"
> that is saved across reboots.  Alternately, ntpd already
> stores slew rates &etc. in files, and could track leap
> seconds likewise.
>
>> Just so long as the
>> existing behaviour of time() which doesn't recognise leap seconds
>> is preserved.
>
> Well, 'man 2 time' is as clear as mud. It talks about leap seconds,
> but I can't figure out what its saying.  I rather
> doubt that time() is doing what POSIX.1 seems to want
> it to do (which is to ignore leap seconds?)
>
> The reason I'm guessing that time() is wrong, is because
> it seems that POSIX wants time() to use TAI time, and
> we don't have that handy anywhere (because we've lost
> track of those leap seconds)
>
> --linas
>
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