linux-kernel - Re: [RFC][PATCH -mm 1/3] PM: Hibernation and suspend notifiers

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Date:	Mon, 28 May 2007 19:26:59 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oliver@...kum.org>
Subject: Re: [RFC][PATCH -mm 1/3] PM: Hibernation and suspend notifiers

On Monday, 28 May 2007 15:12, Pavel Machek wrote:
> Hi!
> 
> > Make it possible to register hibernation and suspend notifiers, so that
> > subsystems can perform hibernation-related or suspend-related operations that
> > should not be carried out by device drivers' .suspend() and
> > .resume() routines.
> 
> I believe it adds _way_ too many notifiers.
> 
> > +PM_PRE_FREEZE		The system is going to hibernate or suspend, tasks will
> > +			be frozen immediately
> 
> 80 columns.

OK

> Anyway yes, this one is needed. 
> 
> > +PM_POST_THAW		Tasks have just been thawed after a resume or restore
> > +			from a hibernation image
> 
> Symetrical with the previous one, useful for freeing firmware images, ok.
> 
> > +PM_HIBERNATION_PREPARE	The system is preparing for hibernation.  Tasks have
> > +			been frozen, memory is going to be freed and devices
> > +			are going to be suspended.
> 
> What is this one good for?

Allocating memory before the hibernation, mainly.  Anything done after freezing
tasks.

> > +PM_SNAPSHOT_FAILED	The creation of hibernation image has failed.  Tasks
> > +			will be thawed immediately.
> 
> Does this one need to be different from POST_THAW?

Do you mean POST_RESTORE?  Well, maybe not.  Yesterday I thought it would be
for a specific reason, but now I can't recall what it was. :-(

> I do not see the need for the other chains. Notice that we do not
> _want_ to have too many of them, because changing anything in the
> hibernation will become impossible with 10 chains having intimate
> details of suspend sequence.

I think the two suspend-specific might be handy.

What about:

PM_PRE_FREEZE
PM_HIBERNATION_PREPARE
PM_POST_HIBERNATION (handling failed snapshots too)
PM_POST_THAW

plus PM_RESTORE_PREPARE for the restore and

PM_SUSPEND_PREPARE
PM_POST_SUSPEND (handling failed suspends too)

for the suspend code path?

Rafael
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