linux-kernel - Re: [RFC][PATCH] PM / Hibernate / x86: Change RESTORE_MAGIC on x86

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Message-Id: <201009292205.45724.rjw@sisk.pl>
Date:	Wed, 29 Sep 2010 22:05:45 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Linux-pm mailing list" <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <nigel@...onice.net>
Subject: Re: [RFC][PATCH] PM / Hibernate / x86: Change RESTORE_MAGIC on x86_64

On Wednesday, September 29, 2010, Rafael J. Wysocki wrote:
> On Wednesday, September 29, 2010, H. Peter Anvin wrote:
> > On 09/28/2010 04:12 PM, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rjw@...k.pl>
> > > 
> > > On x86_64 the configuration and version of the kernel that
> > > hibernates and creates a system image may be different from the
> > > configuration and version of the boot kernel that loads the image.
> > > So long as both these kernels are built with the same value of
> > > RESTORE_MAGIC, the image created by one of them should be
> > > successfully loaded and restored by the other one.
> > > 
> > > It wasn't necessary to modify RESTORE_MAGIC in the past, but now
> > > that we are adding compression to the in-kernel hibernate code,
> > > change the value of RESTORE_MAGIC so that earlier kernels don't
> > > try to load compressed images they can't handle.
> > > 
> > > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> > > ---
> > >  arch/x86/power/hibernate_64.c |    2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > Index: linux-2.6/arch/x86/power/hibernate_64.c
> > > ===================================================================
> > > --- linux-2.6.orig/arch/x86/power/hibernate_64.c
> > > +++ linux-2.6/arch/x86/power/hibernate_64.c
> > > @@ -137,7 +137,7 @@ struct restore_data_record {
> > >  	unsigned long magic;
> > >  };
> > >  
> > > -#define RESTORE_MAGIC	0x0123456789ABCDEFUL
> > > +#define RESTORE_MAGIC	0x0123456789ABCDF0UL
> > >  
> > 
> > Two issues with this:
> > 
> > a) shouldn't we only set this when the image is actually compressed?
> 
> Well, in fact, this is a workaround, because the compression happens in a
> different layer.  However, that other layer doesn't have any compatibility
> checks (at least on x86-64), other than seeing that the image metadata
> don't make sense at one point.

Sorry, I was wrong.  This patch shouldn't be necessary, I'll send another one
that only touches things in kernel/power.

Thanks,
Rafael
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