From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753793Ab0IPXPY (ORCPT ); Thu, 16 Sep 2010 19:15:24 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:55344 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750826Ab0IPXPX (ORCPT ); Thu, 16 Sep 2010 19:15:23 -0400 Subject: Re: [PATCH 1/7] notify userspace about time changes From: john stultz To: Alexander Shishkin 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 In-Reply-To: <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> <20100916225843.GB10463@shisha.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" Date: Thu, 16 Sep 2010 16:15:12 -0700 Message-ID: <1284678912.2669.92.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2010-09-17 at 01:58 +0300, Alexander Shishkin wrote: > 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. Very cool! > 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. Well, the posix interface patch is trying to abstract over the hardware details like rtc_set_alarm. So instead it would be timer_create/timer_settime/etc. These interfaces deal with timer structures that are per-process, so I don't think we need a notification hook for them. thanks -john