It seems virsh 0.8.3 cannot connect to libvirtd 0.6.3.
Machine 1: iibvirtd is 0.6.3
Machine 2: virsh 0.6.1
virsh -c xen+ssh://root@192.168.1.78 list
Connecting to uri: qemu:///session
Id Name State
----------------------------------
0 Domain-0 running
1 shanxi idle
Machine 3: virsh 0.8.3
virsh -c xen+ssh://root@192.168.1.78 list
error: server closed connection:
error: failed to connect to the hypervisor