snapshot.xml
  <domainsnapshot>
    <name>snapshot01</name>
    <description>Snapshot of OS install and updates by boh</description>
    <disks>
      <disk name='/data/os-multi/controller.qcow2'>
      </disk>
    </disks>
  </domainsnapshot>

virsh snapshot-create controller snapshot.xml  //建立快照。快照元資訊在/var/lib/libvirt/qemu/snapshot/（destroy後丟失）
virsh snapshot-list controller --tree          //樹形檢視快照。
virsh snapshot-current controller              //檢視當前快照
virsh snapshot-revert controller snapshot02    //恢復快照
virsh snapshot-delete controller snapshot02    //刪除快照

功能引數：
    --quiesce        quiesce guest's file systems
    --atomic         require atomic operation