Re: [Xen-devel] Preventing corruption if filesystem is modified between 'save' and 'restore'

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

FWIW, I quite like your idea of checking a magic number.  The managed domains 
functionality *should* help prevent users shooting themselves in the foot on 
this but it's not necessarily completely bullet proof in the case where users 
might be extracting the save images, backing them up somewhere, etc.

Have you looked anymore at doing this?  I wouldn't say it's essential but it 
is quite a neat idea.

Cheers,
Mark

On Sunday 29 June 2008, James Harper wrote:
> Is there currently a way of preventing filesystem corruption if the
> following sequence of events occurs:
>
> 1. 'xm save domain domain.chk'
> 2. 'xm create domain'
> 3. 'xm shutdown domain'
> 4. 'xm restore domain.chk'
>
> ?
>
> If not, I'm thinking of trying to implement into the windows gplpv
> xenvbd driver something along the lines of writing a magic hash of the
> date, time, and whatever else we can fit in 512 bytes to a certain
> sector, inside a file that the (usermode) service reserves for such a
> purpose, on 'save'. On resume, before we let xenvbd accept commands from
> the operating system we would confirm that the magic number is still
> correct.
>
> The usermode service would blank those sectors if a normal boot
> occurred, thus xenvbd would deliberately cause a crash before the
> filesystem got corrupted by the os.
>
> Any comments? I haven't really thought it all the way through so there
> may yet be some problems that cannot be resolved...
>
> Thanks
>
> James
>
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