Re: [Qemu-devel] [PATCH] Make default invocation of block drivers safer

[Daniel P. Berrange]

On Wed, Jul 14, 2010 at 01:50:02PM -0500, Anthony Liguori wrote:
> On 07/14/2010 01:43 PM, Christoph Hellwig wrote:
> >Err, strong NACK.  Please don't start messing with the contents of the
> >data plane, we're getting into real trouble there.  It's perfectly
> >valid for a guest to create an image inside an image, and with hardware
> >support for nested virtualization I guess this use case will become
> >rather common, just as it already is on S/390 with VM.
> >   
> 
> Then we have to remove block format probing.
> 
> The two things are fundamentally incompatible.

FWIW, the latest libvirt code will now always set a fmt=XXX arg even
for raw, so probing will never be performed. We also always set a backing
store format when creating qcow2 files.

The main remaining unsolved issues are backing stores with non-qcow2 
files for which QEMU will always probe, and pre-existing qcow2 files
which have been created without backing store formats.  It would be 
nice to have an explicit arg to disable all backing store probing, 
forcing backing format to either be raw, or match the parent image 
format.

Regards,
Daniel
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