Description of problem:
On i386 xen,run 
virsh domblkstat rhel4u8-x86_64 hda
error: Failed to get block stats rhel4u8-x86_64 hda
error: internal error read_bd_stats: Frontend block device not connected

Version-Release number of selected component (if applicable):
libvirt-0.8.2-12.el5
kvm-83-207.el5

How reproducible:
always

Steps to Reproduce:
1. virsh dumpxml rhel4u8-x86_64
<domain type='xen' id='1'>
  <name>rhel4u8-x86_64</name>
  <uuid>25f4bc07-1c62-ea5a-ec28-9ec524877bd3</uuid>
  <memory>4194304</memory>
  <currentMemory>4194304</currentMemory>
  <vcpu>8</vcpu>
  <os>
    <type>hvm</type>
    <loader>/usr/lib/xen/boot/hvmloader</loader>
    <boot dev='cdrom'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/lib64/xen/bin/qemu-dm</emulator>
    <disk type='file' device='disk'>
      <driver name='file'/>
      <source file='/var/lib/xen/images/rhel4u8-x86_64'/>
      <target dev='hda' bus='ide'/>
    </disk>
    <interface type='bridge'>
      <mac address='54:52:00:80:2a:f4'/>
      <source bridge='virbr0'/>
      <script path='vif-bridge'/>
      <target dev='vif1.0'/>
    </interface>
    <serial type='pty'>
      <source path='/dev/pts/0'/>
      <target port='0'/>
    </serial>
    <console type='pty' tty='/dev/pts/0'>
      <source path='/dev/pts/0'/>
      <target port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='5901' autoport='yes' keymap='en-us'/>
  </devices>
</domain>

2.virsh domblkstat rhel4u8-x86_64 hda
error: Failed to get block stats rhel4u8-x86_64 hda
error: internal error read_bd_stats: Frontend block device not connected

3.
  
Actual results:


Expected results:

Additional info:
On rhel6 it can work well.