linux-kernel - Re: [PATCH 4/4] timers: posix interface for alarm-timers

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Date:	Thu, 21 Apr 2011 11:19:45 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Arve Hjønnevåg <arve@...roid.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [PATCH 4/4] timers: posix interface for alarm-timers

On Wed, 2011-04-20 at 08:34 +0200, Richard Cochran wrote:
> On Tue, Apr 19, 2011 at 04:58:30PM -0700, John Stultz wrote:
> > This patch exposes alarm-timers to userland via the posix clock
> > and timers interface, using two new clockids: CLOCK_REALTIME_ALARM
> > and CLOCK_BOOTTIME_ALARM. Both clockids behave identically to
> > CLOCK_REALTIME and CLOCK_BOOTTIME, respectively, but timers
> > set against the _ALARM suffixed clockids will wake the system if
> > it is suspended.
> 
> So, is there reason these cannot or should not be using the dynamic
> posix clock interface?

So in this case, since the clockids are not directly linked to specific
dynamic hardware, I'm not sure if that's the best route.

> > The semantics of the Android alarm driver are different from what
> > this posix interface provides.
> ...
> > One potential way to implement similar semantics may be via
> > the timerfd infrastructure, but this needs more research.
> > 
> > There may also need to be some sort of sysfs system level policy
> > hooks that allow alarm timers to be disabled to keep them
> > from firing at inappropriate times (ie: laptop in a well insulated
> > bag, mid-flight).
> 
> I have not put hardly any thought into these issues, but the dynamic
> interface gives you a character device at no extra charge.

True, but I'd like to first try to extend the existing interface
(timerfd) before we look at adding new ones.

thanks
-john


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