Re: [linux-pm] Re: [patch] hibernation: utilize ACPI hardware signature

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Wednesday, 2 of January 2008, Nigel Cunningham wrote:
> Hi.
> 
> Rafael J. Wysocki wrote:
> > On Wednesday, 2 of January 2008, Erik Andrén wrote:
> >> Hi,
> >>
> >> 2008/1/2, Shaohua Li <shaohua.li@intel.com>:
> >>> ACPI defines a hardware signature. BIOS calculates the signature
> >>> according to hardware configure, if hardware changes, the signature will
> >>> change, in this case, S4 resume should fail.
> >>>
> >>> Signed-off-by: Shaohua Li <shaohua.li@intel.com>
> >>> ---
> >>
> >> Would it be possible to extend this mechanism to prevent the following
> >> scenario:
> >>
> >> 1. Linux image A is suspended to disk
> >> 2. Linux image B is booted and various changes to the system are done.
> >> 3. Linux image B is shut down
> >> 4. Linux image A is booted, restoring the suspend to disk image.
> >> 5. Chaos is ensured as the file system state is changed in regard to how
> >> linux image A expects it.
> >>
> >> Correct behaviour would naturally be that image A detects that changes have
> >> been made under its feet and proceed to perform a normal boot instead of
> >> resuming the stored suspend-to-disk image.
> > 
> > It should be possible in theory.
> > 
> >> Is there another mechanism preventing this?
> > 
> > Not at the kernel level, but you can prevent this from happening by running
> > mkswap on all swap spaces that refuse to come up after a fresh boot.
> 
> We really should do something about this. It should be possible to
> handle this properly if something along the following lines was implemented:
> 
> 1) Each filesystem implements a function taking a pointer to a struct
> block_device and returns a mount count for that filesystem without
> making any modifications to the filesystem.
> 2) Hibernation implementations store the major & minor numbers and mount
> counts for each mounted filesystem in the image header when hibernating,
> and recheck those values at resume time. If the mount count on any
> filesystem has changes, we warn the user, invalidate the image and boot
> normally.

That may quickly become complicated.

For example, boot kernel need not contain all drivers used by the hibernated
ones, so some filesystems may be physically inaccessible to them.

Greetings,
Rafael
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