[Xen-devel] Xen 3.4.1 and QCOW - sparse backing file support gone forever?

[Martin Troester <TroyMcClure@xxxxxx>]

Hi,

I'd like to get some hints on using or migrating QCOW images with sparse
backing files.

In February, I posted a question about this and got some hints by Ian
which generally state this support was removed/disabled due to a
possible security issue. For the full thread, please see the post at
http://lists.xensource.com/archives/html/xen-devel/2009-02/msg00150.html

So with Xen 3.4.1 being released already, it seems like I am stuck now
with my chosen approach of having a qcow file which points to another
(non-raw) qcow backing file. This does not boot, everything looks as in
the February Xen 3.3 posting.

Ian, these comments from your last response particularly are of interest
to me:
> So I `fixed' this by making all backing files of cow images always be
> treated as raw images.  (In upstream this is being fixed by adding
> more metadata to the data format but the exact syntax is still
> settling down and this change comes too late for Xen 3.3.)
Can you or some qemu developer reading this please explain if this code
actually made it into 3.4.1, and if yes, how I would migrate my existing
files to contain this "more metadata" to be working again?

If that's not in, is there any plan how to deal with scenarios like
mine? Especially, is there way to convert my images to some usable
format for not having to stick to Xen 3.2.1? Or is it just too exotic so
that I throw everything away and think of something else? (I am still
thinking that stacking qcow images is not the most stupid thing to do...)

Thanks for any support and hints on this topic!

Regards,
Martin

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