linux-kernel - Re: [suspend/resume] Re: userspace notification from module

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Date:	Sun, 17 Jan 2010 13:26:18 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Pavel Machek <pavel@....cz>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Andy Walls <awalls@...ix.net>,
	Eric Miao <eric.y.miao@...il.com>, omegamoon@...il.com,
	dbaryshkov@...il.com, Cyril Hrubis <metan@....cz>,
	arminlitzel@....de, linux-kernel@...r.kernel.org,
	Dirk@...er-online.de, Stanislav Brabec <utx@...guin.cz>,
	lenz@...wisc.edu, rpurdie@...ys.net,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Bart?omiej Zimo? <uzi18@...pl>,
	zaurus-devel@...ts.linuxtogo.org,
	Daniel Borkmann <danborkmann@...glemail.com>,
	thommycheck@...il.com
Subject: Re: [suspend/resume] Re: userspace notification from module

On Sun, Jan 17, 2010 at 02:07:39PM +0100, Pavel Machek wrote:
> AFAICT following message would be nice.
> 
> 1) battery is critical, userspace please do something
> 
> On zaurus and similar, you could add
> 
> 2) oh and btw we had power failure so we suspended (or maybe -- so
> hardware suspended itself -- rmk's examples and old apm systems); we
> are now back and running
> 
> notification... but... ideally those power failures should never
> happen anyway, so... having this notification is in no way neccessary.

There's another consideration here: the more complex the emergency
procedure, the higher the chance of _something_ causing it to fail,
and if it does fail, the result is data loss.

In a properly running system, this isn't something that's going to
get a lot of testing, so there's a higher chance that there will be
bugs, so the simpler the solution, the better.

It's a bit like the kernel shutdown paths - because they don't get a
lot of use, they don't get tested enough, and having discussed it with
Arjan van de Ven, it's a known weakness.  So we know that they're not
that well tested - and the result is eg, 33-rc3 on shutdown results
in an oops for me on x86.

You really don't want to oops or deadlock on "battery critically low".
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