linux-kernel - Re: Hibernation considerations

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Message-Id: <200707160038.12943.rjw@sisk.pl>
Date:	Mon, 16 Jul 2007 00:38:11 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Dr. David Alan Gilbert" <linux@...blig.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	Jeremy Maitin-Shepard <jbms@....edu>,
	Kyle Moffett <mrmacman_g4@....com>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.linux-foundation.org>, david@...g.hm,
	Al Boldi <a1426z@...ab.com>
Subject: Re: Hibernation considerations

On Sunday, 15 July 2007 14:58, Dr. David Alan Gilbert wrote:
> * Rafael J. Wysocki (rjw@...k.pl) wrote:
> 
> > (5) Hibernation should be transparent from the applications' point of view
> > 
> >     Generally, applications should not notice that hibernation took place.
> >     [Note that I don't regard all processes as applications and I think that
> >     there may be processes which need to handle the hibernation in a special
> >     way.]  Ideally, for example, if some audio is being played when a
> >     hibernation starts, the audio player should be able to continue playing the
> >     same audio after the restore from the point in which it has been
> >     interrupted by the hibernation.  Also, the CPU affinities and similar
> 
> That would be _so_ embarrassing in a library; I'd rather the audio
> player had the opportunity to consider whether restarting was a good idea.
> 
> > (6) State of devices from before hibernation should be restored, if possible
> > 
> >     If possible, during a restore devices should be brought back to the same
> >     state in which they were before the corresponding hibernation.  Of course
> >     in some situations it might be impossible to do that (eg. the user
> >     connected the hibernated system to a different IP subnet and then
> >     restored), but as a general rule, we should do our best to restore the
> >     state of devices, which is directly related to point (5) above.
> 
> Or the user unplugs their flash drive after hibernation rather than before.
> 
> Two things which I think would be nice to consider are:
>    1) Encryption - I'd actually prefer if my luks device did not
>        remember the key accross a hibernation; I want to be forced to
>        reenter the phrase.  However I don't know what the best thing
>        to do to partitions/applications using the luks device is.

Encryption is possible with both the userland hibernation (aka uswsusp) and
TuxOnIce (formerly known as suspend2).  Still, I don't consider it as a "must
have" feature for a framework to be generally useful (many users don't use it
anyway).

>    2) Some level of debugging needs to be available so that users can
>       provide something so you can see why something hasn't hibernated
>       or why (as in the case of this tosh laptop) it still takes power
>       during hibernation.

I agree.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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