This patch set re-implements migration with storage for enough new
qemu.
How does this series interact with Li Guang's efforts to add offline
migration? In particular,
1) src -> dest: (QEMU_MIGRATION_PHASE_BEGIN3 ->
QEMU_MIGRATION_PHASE_PREPARE)
<nbd>
<disk src='/var/lib/libvirt/images/f17.img'
size='17179869184'/>
</nbd>
Both sets of patches need to pass size information across in the
cookies; so is tying it to <nbd> appropriate, or should we be
rethinking this XML to be shared between both patches?