Description of problem:

I have a kvm-guest machine using the qcow2 format image and it works fine.
Now I want to creat a new image to take the place of this old image,use the old disk image as as a readonly 'backing store'.

I run the command "virsh vol-create default new.xml" with the following new.xml:
<volume>
  <name>new.img</name>
  <capacity>1000000000</capacity>
  <allocation>0</allocation>
  <target>
    <format type='qcow2'/>
  </target>
  <backingStore>
    <path>/var/lib/libvirt/images/myoriginal.img</path>
  </backingStore>
</volume>

And then I repoint this kvm-guest to the new disk image,but can't the start the guest with the error " internal error unable to start guest: qemu: could not open disk image /var/lib/libvirt/images/new1.img "

By the way, the command "virsh vol-create --pool default new.xml"  in the Test_Day:2009-09-17_Virtualization_qcow2 doesn't work with the error "'vol-create' need <file> option",so I remove --pool and it works.


Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
1.virsh vol-create default new.xml
2.virsh edit myguest_name,repoint the disk image to the new one
3.start the guest.
  
Actual results:
Can not start the guest with the error "internal error unable to start guest: qemu: could not open disk image /var/lib/libvirt/images/new1.img "

Expected results:
Can start the guest

Additional info: