Libvirt and Xen: No consolelog, no qcow2, no boot, no VNC...

Hi all,
I configured my Openstack Folsom installation with Libvirt/Xen. It can now boot ttylinux kernel, but still cannot bring me into shell... :-(
The xend's http server has already been enabled, libvirt is also configured to use xen. When I boot a ami/ari/img image combination from horizon, it CAN launch the kernel, but would failed in a later step:

[ 0.080293] TCP cubic registered
[ 0.080471] NET: Registered protocol family 10
[ 0.081052] lo: Disabled Privacy Extensions
[ 0.081598] NET: Registered protocol family 17
[ 0.081757] registered taskstats version 1
[ 5.180066] XENBUS: Waiting for devices to initialise: 295s...290s...285s...

However, I got this log from "xm console" directly from the compute node. In controller node, both "nova console-log" and horizon's log page are completely blank.
If I try to boot a qcow2 image, it would failed when creating the VM:
In "nova show":

| fault | {u'message': u'NoValidHost', u'code': 500, u'created': u'2012-12-29T17:06:58Z'} |

And in the compute node's nova-conpute.log:

2012-12-30 01:09:15 INFO nova.compute.resource_tracker [req-23e785e5-6a21-4a9d-b78e-17bd056f3423 3ab1fdecbc824ba9b7e2225f44f0f1e7 df4e473d7d644f589eb28274a66ff235] Aborting claim: [Claim 88e57f25-1f8b-4fe2-9600-0b8b964b22e4: 512 MB memory, 0 GB disk, 1 VCPUS]
2012-12-30 01:09:16 ERROR nova.compute.manager [req-23e785e5-6a21-4a9d-b78e-17bd056f3423 3ab1fdecbc824ba9b7e2225f44f0f1e7 df4e473d7d644f589eb28274a66ff235] [instance: 88e57f25-1f8b-4fe2-9600-0b8b964b22e4] Build error: ['Traceback (most recent call last):\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 496, in _run_instance\n injected_files, admin_password)\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 743, in _spawn\n block_device_info)\n', ' File "/usr/lib/python2.7/dist-packages/nova/exception.py", line 117, in wrapped\n temp_level, payload)\n', ' File "/usr/lib/python2.7/contextlib.py", line 24, in __exit__\n self.gen.next()\n', ' File "/usr/lib/python2.7/dist-packages/nova/exception.py", line 92, in wrapped\n return f(*args, **kw)\n', ' File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 1062, in spawn\n block_device_info)\n', ' File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 1888, in _create_domain_and_network\n domain = self._create_domain(xml)\n', ' File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 1867, in _create_domain\n domain.createWithFlags(launch_flags)\n', ' File "/usr/lib/python2.7/dist-packages/eventlet/tpool.py", line 187, in doit\n result = proxy_call(self._autowrap, f, *args, **kwargs)\n', ' File "/usr/lib/python2.7/dist-packages/eventlet/tpool.py", line 147, in proxy_call\n rv = execute(f,*args,**kwargs)\n', ' File "/usr/lib/python2.7/dist-packages/eventlet/tpool.py", line 76, in tworker\n rv = meth(*args,**kwargs)\n', ' File "/usr/lib/python2.7/dist-packages/libvirt.py", line 650, in createWithFlags\n if ret == -1: raise libvirtError (\'virDomainCreateWithFlags() failed\', dom=self)\n', "libvirtError: POST operation failed: xend_post: error from xen daemon: (xend.err 'Device /dev/xvdp (51952, tap) is already connected.')\n"]

Could anyone help me on deploying Xen as my hypervisor?
Any hints are appreciated!