linux-kernel - Re: [PATCH] [RFC] notify userspace about time changes

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Date:	Wed, 04 Aug 2010 08:58:46 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Alexander Shishkin <virtuoso@...nd.org>, gregkh@...e.de
Cc:	lkml@...r.kernel.org, "Kirill A. Shutemov" <kirill@...temov.name>,
	Thomas Gleixner <tglx@...utronix.de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jon Hunter <jon-hunter@...com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Avi Kivity <avi@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	John Kacur <jkacur@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFC] notify userspace about time changes

On Wed, 2010-08-04 at 15:48 +0300, Alexander Shishkin wrote:
> Certain userspace applications (like "clock" desktop applets or ntpd) might
> want to be notified when some other application changes the system time. It
> might also be important for an application to be able to distinguish between
> its own and somebody else's time changes.

So NTP doesn't actually care, as it will notice the STA_UNSYNC flag is
set the next time it checks adjtimex.

The clock apps example seems reasonable, but maybe isn't the most
compelling argument for adding a new kernel api.

Is there a actual use case that you need this for?  I don't really have
an issue with the code I just really want to make sure the feature would
be useful enough to justify the API and code maintenance going forward.

Doing some of my own googling, I see Apple added such a notification
method, which suggests there are apps that want this. 
http://stackoverflow.com/questions/690326/how-can-i-get-notified-of-a-system-time-change-in-my-cocoa-application

But it doesn't give any specific examples either.

thanks
-john

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