Message-ID: <1414420084.30379.53.camel@hadess.net>
Subject: Re: A desktop environment[1] kernel wishlist
From: Bastien Nocera <hadess@hadess.net>
To: Zygo Blaxell <zblaxell@furryterror.org>
Cc: John Stultz <john.stultz@linaro.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Date: Mon, 27 Oct 2014 15:28:04 +0100
In-Reply-To: <20141022170433.GA10186@hungrycats.org>
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On Wed, 2014-10-22 at 13:04 -0400, Zygo Blaxell wrote:
> On Tue, Oct 21, 2014 at 08:09:38PM +0200, Bastien Nocera wrote:
> > On Tue, 2014-10-21 at 11:00 -0700, John Stultz wrote:
> > > On Tue, Oct 21, 2014 at 10:14 AM, Bastien Nocera <hadess@hadess.net> wrote:
> > > >> As for: 'Export of "wake reason" when the system wakes up (rtc alarm,
> > > >> lid open, etc.) and wakealarm (/sys/class/rtc/foo/wakealarm)
> > > >> documentation'
> > > >>
> > > >> Can you expand more on the rational for the need here? Is this for UI
> > > >> for power debugging, or something else?
> > > >
> > > > No, it would be used for automating backups, or implementing
> > > > suspend->hibernation transitions. For example, right before the machine
> > > > suspends, I would schedule it to wake up in a hour. If I get woken up by
> > > > the rtc alarm (and not by the user through a lid open), I might:
> > > > - check that I'm plugged into the AC, it's night, and in the vicinity of
> > > > the server that handles my backups and so backup the system.
> > > > - check whether the battery is low, and hibernate the machine (if it
> > > > supports it, obviously).
> > > >
> > > > We cannot do that if we can't make out whether the wake-up came from a
> > > > user action, or the alarm we set.
> > > 
> > > I suspect wakeup type reporting is maybe not the best way to go about
> > > this, since there may be a number of causes for wakeups and they can
> > > arrive closely together in different orders, which can result in
> > > races.
> > > 
> > > For instance, if the machine suspends, and sets an alarm to be woken
> > > up at midnight to do a backup, if the user resumes their laptop at
> > > 11:59:59, should the backup still proceed at midnight?
> > 
> > No. And I would expect that we would get a wake up type of "power
> > button" or "lid open" in this case.
> 
> I have been using something like this for the last 7 years or so.
> The relevant inputs are:
> 
> 	1. is the user present (is there recent input on HID devices,
> 	keyboard/mouse, but ignore devices like light sensors, 3D
> 	accelerometers, and ACPI virtual keys)?

If the user woke the machine up through the power button, you wouldn't
see that from user-space. You could detect that the lid was opened,
because you have state.

> 	2. which network connection(s) are available to reach the
> 	backup server?
> 
> 	3. how much power is available (if on battery, how much run
> 	time left?)
> 
> 	4. what is the policy (do backups happen at a specific time
> 	of day, or whenever they can?)
> 
> 	5. was a backup completed successfully in the last N hours?
> 
> Note the absence of any information about the cause of recent
> suspend/resume activity, or any input from suspend/resume at all.

How do I tell my environment not to wake the screen up when the machine
was woken up by an alarm I scheduled to launch a backup? Or not to
resume audio playback when I get woken up to handle network events
(through connected suspend, or Wake-On-(Wireless-)LAN)?

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