linux-kernel - Re: [PATCH v2 1/2] timekeeping: add EXPORT_SYMBOL_GPL for do

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Date:	Tue, 21 Oct 2014 10:13:55 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	Thomas Shao <huishao@...rosoft.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	KY Srinivasan <kys@...rosoft.com>,
	John Stultz <john.stultz@...aro.org>,
	Richard Cochran <rcochran@...utronix.de>
Subject: Re: [PATCH v2 1/2] timekeeping: add EXPORT_SYMBOL_GPL for
 do_adjtimex()

On Tue, Oct 21, 2014 at 03:18:58AM +0000, Thomas Shao wrote:
> 
> In some situation, the user is not able to enable guest VM to sync with external 
> time source, like NTP. But the host is still synced with a trusted time source. 

But the guest *is* networked, right?

(Otherwise syncing the guest's clock is pointless.)

> I've got some feedbacks from Richard and Mike, including reference NTP implementation
> and do the adjustment in the host side. I've already referenced some NTP design in
> my patch. I would consider my patch as a simplified implementation.

I really don't think we want a half baked servo in some random
driver. Instead, why not present the time difference using a standard
interface?

> I've also considered
> the host side implementation. But in host, we can only set time but not gradually slew/adjust
> time,

Why not implement adjustment in the host?

> which is not acceptable for the time sync solution.We still recommend user to configure
> NTP on the guest, which provides better accuracy. But if NTP is not applicable, this could be 
> another option. 

You did not really answer any of my objections, nor did you consider
the alternative ideas which I offered. Would you care to address
those?

Thanks,
Richard
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