From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754101Ab0IPXEH (ORCPT ); Thu, 16 Sep 2010 19:04:07 -0400 Received: from filtteri1.pp.htv.fi ([213.243.153.184]:57321 "EHLO filtteri1.pp.htv.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753145Ab0IPXEE (ORCPT ); Thu, 16 Sep 2010 19:04:04 -0400 Date: Fri, 17 Sep 2010 01:58:43 +0300 From: Alexander Shishkin To: john stultz Cc: linux-kernel@vger.kernel.org, Andrew Morton , "H. Peter Anvin" , Kay Sievers , Greg KH , Chris Friesen , Linus Torvalds , "Kirill A. Shutemov" , Thomas Gleixner , Martin Schwidefsky , Jon Hunter , Ingo Molnar , Peter Zijlstra , "Paul E. McKenney" , David Howells , Avi Kivity , John Kacur Subject: Re: [PATCH 1/7] notify userspace about time changes Message-ID: <20100916225843.GB10463@shisha.kicks-ass.net> References: <1284675049-23479-1-git-send-email-virtuoso@slind.org> <1284675049-23479-2-git-send-email-virtuoso@slind.org> <1284676240.2669.41.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1284676240.2669.41.camel@localhost.localdomain> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 16, 2010 at 03:30:40 -0700, john stultz wrote: > On Fri, 2010-09-17 at 01:10 +0300, Alexander Shishkin wrote: > > Certain userspace applications (like "clock" desktop applets or cron) 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. > > > > This patch implements a notification interface via eventfd mechanism. Proccess > > wishing to be notified about time changes should create an eventfd and pass it > > to time_change_notify() syscall along with notification options. > > After that, any calls to settimeofday()/stime()/adjtimex() made by other > > processes will be signalled to this eventfd. Credits for suggesting the eventfd > > mechanism for this purpose go to Kirill Shutemov. > > One thing I have thought of since the last time you posted this, maybe > it would be worth adding a clockid field to the syscall? > > Basically, we're looking at extending the posix clocks interfaces to > allow for additional clock hardware to be exposed (See the discussion on > PTP and my CLOCK_RTC patch today for examples and details). > > So it seems possible that folks would want a similar interface to catch > updates to non CLOCK_REALTIME clocks. > > Does this seem reasonable? The whole idea seems interesting, I'll try to add this in the next iteration of this patchset. The first thing that comes it mind is -- are there going to be additional events that the user might like to be notified of, like rtc_set_alarm()? Doesn't seem too likely, though. Regards, -- Alex