Description of problem:
I have been trying to pass through a PCI device (a USB hub) to a Xen domU. xen refuses to do so, saying the PCI backend and pci-stub don't own the device.

Version-Release number of selected component (if applicable):
xen-4.1.2-2.fc16.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Create F16 domain using virsh-install
2. Use "virsh edit F16" to add the following lines to the config file

    <hostdev mode='subsystem' type='pci' managed='no'>
      <source>
        <address domain='0x0000' bus='0x00' slot='0x1a' function='0x0'/>
      </source>
    </hostdev>

3. echo -n 0000\:00\:1a.0 >/sys/bus/pci/drivers/ehci_hcd/unbind
4. Start F16 domain using virt-manager
  
Actual results:
Error dialog appears saying:
Error starting domain: POST operation failed: xend_post: error from xen daemon: (xend.err "pci: PCI Backend and pci-stub don't own device 0000:00:1a.0")

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 44, in cb_wrapper
    callback(asyncjob, *args, **kwargs)
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 65, in tmpcb
    callback(*args, **kwargs)
  File "/usr/share/virt-manager/virtManager/domain.py", line 1050, in startup
    self._backend.create()
  File "/usr/lib64/python2.7/site-packages/libvirt.py", line 510, in create
    if ret == -1: raise libvirtError ('virDomainCreate() failed', dom=self)
libvirtError: POST operation failed: xend_post: error from xen daemon: (xend.err "pci: PCI Backend and pci-stub don't own device 0000:00:1a.0")

Expected results:
Domain should start

Additional info:
I am unable to add the PCI device through virt-manager due to bug 771128.