Comment 5 for bug 1567807

Yes, it is still possible to create an instance after changing only the delete method. The generated libvirt domain XML looks like this:

  <os>
    <type arch='aarch64' machine='virt'>hvm</type>
    <loader readonly='yes' type='pflash'>/usr/share/AAVMF/AAVMF_CODE.fd</loader>
    <nvram template='/usr/share/AAVMF/AAVMF_CODE.fd'>/var/lib/libvirt/qemu/nvram/instance-00000005_VARS.fd</nvram>
    <boot dev='hd'/>
  </os>

That is, the nvram file is copied from a global template to an instance-specific file -- it's that file under /var/lib/libvirt/qemu/nvram that VIR_DOMAIN_UNDEFINE_NVRAM removes. It should arguably be using template=AAVMF_VARS.fd rather than AAVMF_CODE.fd, but that's unrelated to this and doesn't really matter.

The most annoying part of this change is feature detection. I think delete_configuration might have to know to try unsetting flags until the method works, as older libvirts don't support VIR_DOMAIN_UNDEFINE_NVRAM and I can't see a way to test at runtime. But in our environment we know the libvirt version, so we just pass the flag in unconditionally.