Some additional information that I have found since yesterday:
When I create a volume like this:
<volume>
<name>coreos00.disk</name>
<capacity unit="bytes">9116319744</capacity>
<target>
<format type="raw"></format>
<permissions>
<mode>644</mode>
</permissions>
</target>
<backingStore>
<path>vmdisks/coreos_2023</path>
<format type="raw"></format>
</backingStore>
</volume>
Which does not seem to work with the backing store either as it creates
an empty volume without the underlying parent. But when I now delete
the volume via rbd and create a new clone it shows up in libvirt and
can be used by the machine.
# rbd -p vmdisks rm coreos00.disk
# rbd clone vmdisks/coreos_2023@basis vmdisks/coreos00.disk
Sadly this is not a very efficient way to create the clones I would
say.
Anyone got any, like literally any, ideas what might be wrong in this
setup?