[libvirt] Downloading and wiping assumes volume is a device or file

Hi, I'm still working on the RBD (RADOS / Ceph) storage driver for libvirt and I noticed the virStorageVolDownload and virStorageVolWipe methods. I assumed those would be passed on to the storage backend, but it doesn't. In the storageDriver the method storageVolumeDownload simply opens a file descriptor and reads the device. Until now libvirt only had support for storage drivers who presented regular files or block devices, but RBD doesn't. (Well, RBD could, but I'm currently going for Qemu-RBD). In the future we might see more storage drivers in libvirt for a project like Sheepdog as well. Sheepdog and RBD both have drivers in Qemu. What would the way be to approach this? Should the download, upload and wipe methods be moved to the storage backends? There could also be an exception? If virStoragePoolType matches VIR_STORAGE_POOL_RBD or VIR_STORAGE_POOL_SHEEPDOG the storage backend could be invoked instead of opening the file descriptor? Any thoughts on this? Thanks, Wido