external snapshot create error

[Peter Krempa]

On Mon, Apr 19, 2021 at 20:19:31 -0500, Eyüp Hakan Duran wrote:
> Dear all,
> 
> I have been creating external snapshots of my KVM/QEMU VMs for more than a
> year on a host machine that runs Manjaro Linux. The current version of
> libvirt I am using is 1:7.1.0-3. I just noticed that the script I am using
> for this purpose has been failing. More specifically the command below
> returns with the error message indicated underneath the command:
> 
> sudo virsh snapshot-create-as --no-metadata --domain myVM myVM-state
> --diskspec hda,file=overlay.qcow2 --disk-only --atomic
> error: XML document failed to validate against schema: Unable to validate
> doc against /usr/share/libvirt/schemas/domainsnapshot.rng

The problem is that file=overlay.qcow2 points to a relative path (not
starting with a leading '/'). Libvirt enforces that the path must be a
full path.

> Extra element disks in interleave
> Element domainsnapshot failed to validate content

I've recently pushed a commit which removes the XML validation in this
case as it's counter-productive and the XML parser provides a more
understandable error:

https://gitlab.com/libvirt/libvirt/-/commit/f1c9fed2ca8f2509495f46b355dab019604f7475

(note that this commit will be in the upcomming libvirt-7.3 release)

> I also tried different versions of the command above with similar results,
> such as:
> sudo virsh snapshot-create-as mvVM --no-metadata myVM-state --diskspec
> hda,snapshot=external,file=overlay.qcow2 --disk-only --atomic
> 
> Any pointers will be greatly appreciated!
> 
> Hakan Duran