[libvirt] Questions on libvirt storage internals

Hi All I am working on integrating GlusterFS with OpenStack so that VM volumes can be placed on shared GlusterFS volumes. I would highly appreciate if you please help me find the answers to some questions: 1. Whats the difference between a storage driver and a storage backend driver? 2. Why does virDomainAttachDevice code path call the corresponding domainAttach function in the hypervisor driver and not the volume or pool creation method if a disk is being attached? Does it assume that the volume has already been created before this call? 3. Which part of libvirtd source handles receiving messages from the libvirt client? Thanks -Shehjar