linux-kernel - Re: [PATCH V7 1/8] ntp: add ADJ

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Message-ID: <1292968784.2618.51.camel@work-vm>
Date:	Tue, 21 Dec 2010 13:59:44 -0800
From:	john stultz <johnstul@...ibm.com>
To:	"Kuwahara,T." <6vvetjsrt26xsrzlh1z0zn4d2grdah@...il.com>,
	Alexander Gordeev <lasaine@....cs.msu.su>,
	Rodolfo Giometti <giometti@...eenne.com>
Cc:	Richard Cochran <richardcochran@...il.com>,
	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>,
	Krzysztof Halasa <khc@...waw.pl>,
	Peter Zijlstra <peterz@...radead.org>,
	Rodolfo Giometti <giometti@...ux.it>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH V7 1/8] ntp: add ADJ_SETOFFSET mode bit

On Wed, 2010-12-22 at 06:13 +0900, Kuwahara,T. wrote:
> On Wed, Dec 22, 2010 at 4:37 AM, john stultz <johnstul@...ibm.com> wrote:
> > adjtimex is a linux specific interface, which is compatible but not
> > identical to the ntp specified interfaces. The ntp client code already
> > has Linux specific modifications, so I don't think we have to worry
> > about 0x40 specifically being reserved by the NTP client.
> 
> But struct timex is not linux-specific...

It is if you're compiling against linux's timex.h file. 

We already have a number of differences compared with BSD's timex mode
definitions:
We have ADJ_TICK: 0x4000, which is MOD_CLKB in FreeBSD.
We also have ADJ_OFFSET_SINGLESHOT and ADJ_OFFSET_SS_READ which allow
adjtimex act like the original ntp_adjtime.

The key bit is that we map the shared MOD_* definitions that the NTP
client uses to the linux specific ADJ_* values in the linux timex.h

However, your concern does bring up a good point: 0x40 is MOD_PPSMAX in
BSD, and we should at-least check to make sure that the PPS code that is
currently floating around on the lists and is in akpm's tree hasn't
already reserved that bit.

Rodolfo, Alexander: Any comments here?

thanks
-john


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