See earlier thread on libvir-list:
https://www.redhat.com/archives/libvir-list/2015-September/thread.html#00201
Libvirt >= 1.2.20 supplies the correct dcPath parameter. If it is
available in the libvirt XML, use it, otherwise fall back to the old
method of trying to guess it from the vpx:// path.
Patches 1, 2 and 4 are just refactoring around this change.
Rich.