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Date: Tue, 21 Dec 2010 08:56:12 +0100
From: Richard Cochran <richardcochran@gmail.com>
To: "Kuwahara,T." <6vvetjsrt26xsrzlh1z0zn4d2grdah@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        netdev@vger.kernel.org, Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Arnd Bergmann <arnd@arndb.de>, Christoph Lameter <cl@linux.com>,
        David Miller <davem@davemloft.net>, John Stultz <johnstul@us.ibm.com>,
        Krzysztof Halasa <khc@pm.waw.pl>,
        Peter Zijlstra <peterz@infradead.org>,
        Rodolfo Giometti <giometti@linux.it>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH V7 1/8] ntp: add ADJ_SETOFFSET mode bit
Message-ID: <20101221075612.GA13626@riccoc20.at.omicron.at>
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On Sat, Dec 18, 2010 at 05:16:52AM +0900, Kuwahara,T. wrote:
> On 12/17/10, Richard Cochran <richardcochran@gmail.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 proposed new control mode, ADJ_SETOFFSET, is logically the same as
> ADJ_OFFSET with timex.constant == -INFINITY.  So it is possible to do
> the same thing without risking forward compatibility.  (I mean by "risking
> forward compatibility" that the mode bit 0x0040 may be defined differently
> by the upstream maintainer anytime in the future.)

Can you please elaborate?

I don't see any way to use timex.constant with ADJ_OFFSET in order to
correct a time offset. The 'time_constant' in kernel/time/ntp.c is
restricted to the interval [0..MAXTC], and MAXTC is 10 in timex.h.

Richard
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