[libvirt] Curl/HTTP block device

Hi, I've noticed newer version of curl in last qemu changelog. It seems that its needed for curl block device. Unfortunatelly, I was not able to find out more. I tried to look into qemu source code and to some patches but I am not much wiser. As I understand it, qemu could be able to use a curl compatible URL as block device. Probably only in readonly mode but it still would be very usefull for i.e. ISO images. Can anyone point me in the right direction and more importantly, is this feature available via Libvirt? I checked the documentation on libvirt.org and it seems that remode disk can be only nbd/rbd/sheepdog. Radek