[libvirt] Domain XML isn't dumping full backing chain

Kashyap Chamarthy kchamart at redhat.com
Wed Mar 18 14:52:46 UTC 2015


On Wed, Mar 18, 2015 at 07:21:22AM -0600, Eric Blake wrote:
> On 03/18/2015 07:03 AM, Deepak Shetty wrote:
> 
> [please don't top-post on technical lists]
> 
> > Hmm interesting, so without adding backing_fmt, if i enable the below in
> > /etc/libvirt/qemu.conf, will it work ?
> > 
> > # If allow_disk_format_probing is enabled, libvirt will probe disk
> > # images to attempt to identify their format, when not otherwise
> > # specified in the XML. This is disabled by default.
> > #
> > # WARNING: Enabling probing is a security hole in almost all
> > # deployments. It is strongly recommended that users update their
> > # guest XML <disk> elements to include  <driver type='XXXX'/>
> > # elements instead of enabling this option.
> > #
> > #allow_disk_format_probing = 1

Along with what Eric says, here's some detailed description of issues
(that are fixed) from Daniel Berrange:

    https://www.redhat.com/archives/libvir-list/2010-July/msg00221.html
 
> It _might_ work in that libvirt will then probe the backing chain as
> qcow2, rather than treating it as raw; on the other hand, the upcoming
> qemu 2.3 is trying to deprecate probing altogether because of the
> security problems it represented, and so you may reach a point where
> even if you tell libvirt it is okay to probe, that qemu will refuse to
> open your image if you didn't specify backing format.

-- 
/kashyap




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