Description of problem:

vol-dumpxml get wrong format type when check volume info which created by qemu-img 

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

# rpm -qf /sbin/libvirtd && rpm -q qemu-kvm qemu-img
libvirt-daemon-1.2.5-1.fc20.x86_64
qemu-kvm-1.6.2-5.fc20.x86_64
qemu-img-1.6.2-5.fc20.x86_64

How reproducible:

100%

Steps to Reproduce:

1.prepare an dir type pool
# virsh pool-list dir
 Name                 State      Autostart 
-------------------------------------------
 default              active     no 

2.create qcow2 format volume by qemu-img

# qemu-img create -f qcow2 /var/lib/libvirt/images/qcow2.img 1G 
Formatting '/var/lib/libvirt/images/qcow2.img', fmt=qcow2 size=1073741824 encryption=off cluster_size=65536 lazy_refcounts=off

3.check format by vol-dumpxml

# virsh pool-refresh default 
Pool default refreshed

# virsh vol-dumpxml /var/lib/libvirt/images/qcow2.img
<volume type='file'>
  <name>qcow2.img</name>
  <key>/var/lib/libvirt/images/qcow2.img</key>
  <source>
  </source>
  <capacity unit='bytes'>1073741824</capacity>
  <allocation unit='bytes'>200704</allocation>
  <target>
    <path>/var/lib/libvirt/images/qcow2.img</path>
    <format type='raw'/>
    <permissions>
..

4. create qcow2 format volume with backing file

# qemu-img create -f qcow2 /var/lib/libvirt/images/qcow2.s1 -b /var/lib/libvirt/images/qcow2.img 1G 
Formatting '/var/lib/libvirt/images/qcow2.s1', fmt=qcow2 size=1073741824 backing_file='/var/lib/libvirt/images/qcow2.img' encryption=off cluster_size=65536 lazy_refcounts=off 

5. check format by vol-dumpxml

# virsh pool-refresh default 
Pool default refreshed

# virsh vol-dumpxml /var/lib/libvirt/images/qcow2.s1
<volume type='file'>
  <name>qcow2.s2</name>
  <key>/var/lib/libvirt/images/qcow2.s1</key>
  <source>
  </source>
  <capacity unit='bytes'>1073741824</capacity>
  <allocation unit='bytes'>200704</allocation>
  <target>
    <path>/var/lib/libvirt/images/qcow2.s1</path>
    <format type='raw'/>
    <permissions>
      <mode>0644</mode>
      <owner>0</owner>
      <group>0</group>
      <label>unconfined_u:object_r:virt_image_t:s0</label>
    </permissions>
    <timestamps>
      <atime>1401935440.477721377</atime>
      <mtime>1401935437.888694457</mtime>
      <ctime>1401935437.888694457</ctime>
    </timestamps>
  </target>
  <backingStore>
    <path>/var/lib/libvirt/images/qcow2.img</path>
    <format type='qcow2'/>
    <permissions>
..


Actual results:

The "format type" in step3 and step5 is wrong

Expected results:


Additional info:

can't meet this error when create volume by vol-create/vol-create-as