[libvirt] block-backup API for libvirt

In qemu there will soon be drive-backup and block-backup commands that allow you to create backups or point-in-time snapshots of VM images. The original feature that drove this was to allow 'image fleecing', which involves creating a light weight mechanism to take a point in time snapshot of the running VM and access that remotely. You can get a good idea of the API from this post: http://lists.gnu.org/archive/html/qemu-devel/2013-10/msg02266.html I would like to see this available via libvirt and wanted to start working on a suitable API. I'm curious if anyone has any input on how they would like to see this done? While I have done some work with and on libvirt I'm no expert on the design philosophy behind the APIs so some direction here before I get coding would be much appreciated. the NBD export call could work but I'd like to hear if that's reasonable. Thanks! Ian