linux-kernel - Re: [PATCH V9 02/13] ntp: add ADJ

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Message-ID: <AANLkTimHP1OsWauj6O566WgnxVTjMbNg2PK644QcT9Lq@mail.gmail.com>
Date:	Fri, 14 Jan 2011 05:39:31 +0900
From:	"Kuwahara,T." <6vvetjsrt26xsrzlh1z0zn4d2grdah@...il.com>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	netdev@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Christoph Lameter <cl@...ux.com>,
	David Miller <davem@...emloft.net>,
	John Stultz <johnstul@...ibm.com>,
	Krzysztof Halasa <khc@...waw.pl>,
	Peter Zijlstra <peterz@...radead.org>,
	Rodolfo Giometti <giometti@...ux.it>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH V9 02/13] ntp: add ADJ_SETOFFSET mode bit

On Thu, Jan 13, 2011 at 8:32 PM, Richard Cochran
<richardcochran@...il.com> wrote:
> This patch adds a new mode bit into the timex structure. When set, the bit
> instructs the kernel to add the given time value to the current time.

The unix time is a nonlinear timescale and there's no way to predict
how many leap seconds will be inserted/deleted during the given time
interval.  So it is impossible to convert relative time to absolute
time and thus your patch is broken. (More specifically, the
timekeeping_inject_offset function is broken.)

My proposal: Limit the adjustable range of the offset so that leap
seconds will never occur more than once. (2147.5 seconds would be the
best choice. :-)
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