[libvirt] How to get the fully qualified path for network disks

Some background: Looking @ the comments in https://review.openstack.org/#/c/192736/8/nova/virt/libvirt/driver.py we need a way to construct the fully qualified path for a 'network' type disk which can then be passed to qemu-img for the rebase cmd. Checking with some folks offline and on IRC, i was suggested to bring this up here. Is there a way in libvirt to get the full path of network disk that can work with qemu-img given the virDomain pointer ? thanx, deepak