Comment 2 for bug 1906266

Ah apologies it's still there in master:

https://github.com/libvirt/libvirt/blob/84dc367e2a6febfcc4aeea4c52e44c52aea298fc/src/util/virstoragefile.c#L5265-L5270

So we will need to workaround this within the libvirt driver using the following:

https://libvirt.org/kbase/backing_chains.html#vm-refuses-to-start-due-to-misconfigured-backing-store-format

This should be easy enough to wire up in the qcow2 imagebackend during cache() assuming it doesn't impact already running domains/instances using the backing file.