virtio_blk_data_plane配置方式

xml中加上如下配置：

  <iothreads>1</iothreads>
  <iothreadids>
    <iothread id='2'/>
  </iothreadids>
  ------
  <driver name='qemu' type='qcow2' cache='directsync' io='native' iothread='2'/>

qemu命令行中有如下内容：

 -object iothread,id=iothread2
 -drive file=/vms/images/E0306H02_clone,format=qcow2,if=none,id=drive-virtio-disk0,cache=directsync,aio=native -device virtio-blk-pci,iothread=iothread2