I checked the capabilities. I do not know why the guest is only for vbox. 
<guest>
    <os_type>hvm</os_type>
    <arch name='i686'>
      <wordsize>32</wordsize>
      <domain type='vbox'>
      </domain>
    </arch>
  </guest>

I want it run qemu-kvm. and when i run virsh define /etc/libvirt/qemu/demo.xml. It shows error: Failed to define domain from /etc/libvirt/qemu/demo.xml
error: unknown OS type hvm

Then I use virsh-install --prompt to install kvm guest, it shows error: libvirtError: this function is not supported by the connection driver: virConnectNumOfDefinedStoragePools

I really do not know how to do, please help me, thanks.

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Have a nice day!

Qian