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

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Message-Id: <201001162305.56972.rjw@sisk.pl>
Date:	Sat, 16 Jan 2010 23:05:56 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Stanislav Brabec <utx@...guin.cz>,
	Eric Miao <eric.y.miao@...il.com>,
	"Bart?omiej Zimo?" <uzi18@...pl>, Andy Walls <awalls@...ix.net>,
	Daniel Borkmann <danborkmann@...glemail.com>,
	linux-kernel@...r.kernel.org, rpurdie@...ys.net, lenz@...wisc.edu,
	Dirk@...er-online.de, arminlitzel@....de,
	Cyril Hrubis <metan@....cz>, thommycheck@...il.com,
	"linux-arm-kernel" <linux-arm-kernel@...ts.infradead.org>,
	dbaryshkov@...il.com, omegamoon@...il.com,
	zaurus-devel@...ts.linuxtogo.org
Subject: Re: [suspend/resume] Re: userspace notification from module

On Saturday 16 January 2010, Pavel Machek wrote:
> On Sat 2010-01-16 18:00:58, Stanislav Brabec wrote:
> > Eric Miao wrote:
> > 
> > > And the other way we may need to look into what API the current userland
> > > apps on zaurus is depending on this 2.4 compatibility and make changes
> > > slowly to those apps.
> > 
> > I guess that 2.4 compatibility is not an issue. Most modern Zaurus
> > distributions are even unable to run Sharp ROM compatible binaries.
> > 
> > Distributions either stay on 2.4 kernel or use modern systems based on
> > modern kernel 2.6 API.
> > 
> > Distributions that decided to migrate to kernel 2.6 are far from
> > finished state. Any change that allows to use modern applications using
> > standard kernel API is welcome.
> 
> There is no API involved. It is just ... if you leave zaurus in
>  init=/bin/bash mode, it must not kill the battery. Smart and
>  currently implemented way to do that is to suspend.

IMHO it should just plain shutdown in that case.  Suspending doesn't really
solve the problem, because the battery is going to drain still.  Unless you
mean suspend=hibernate, but I guess you don't.

> That's counterexample to rjw, but it does not matter -- reasonable
> userland should never ever hit that, in a same way PCs should not hit
> emergency power cut...

I don't really understand what you mean.  The user space doesn't know the
battery state if the kernel doesn't tell it, AFAICS, so how exactly can it
predict the critical battery condition without the kernel notifying it?

Rafael
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