[libvirt] libvirt-libxl driver defaulting to tap disk and not working (ubuntu 12.10 + xen 4.5 + libvirt 1.2.3 + openstack)

HI I am an openstacker, when I used the latest libvirt and xen code to run the openstack. Can not create the vm. there is an error in libxl log, you can see the log: Os : Ubuntu 12.10 Compiled against library: libvirt 1.2.3 Using library: libvirt 1.2.3 Using API: Xen 1.2.3 Running hypervisor: Xen 4.5.0 libxl: debug: libxl_create.c:1356:do_domain_create: ao 0x7f7894002810: create: how=(nil) callback=(nil) poller=0x7f7894001bb0 libxl: debug: libxl_device.c:251:libxl__device_disk_set_backend: Disk vdev=xvda spec.backend=tap libxl: debug: libxl_device.c:210:disk_try_backend: Disk vdev=xvda, backend tap unsuitable because blktap not available libxl: error: libxl_device.c:289:libxl__device_disk_set_backend: no suitable backend for disk xvda libxl: debug: libxl_event.c:1739:libxl__ao_complete: ao 0x7f7894002810: complete, rc=-3 libxl: debug: libxl_create.c:1370:do_domain_create: ao 0x7f7894002810: inprogress: poller=0x7f7894001bb0, flags=ic libxl: debug: libxl_event.c:1711:libxl__ao__destroy: ao 0x7f7894002810: destroy The blktap does work, and I also find the same error someone has posted, (http://www.redhat.com/archives/libvir-list/2013-February/msg01124.html) When I change the type to "phy", it also doesnot work. And try to change the type to other options, also does not work. Can someone give me some suggestions? Thanks ! The XML from the openstack is : <domain type="xen"> <uuid>9e9ed86c-8892-40da-acd1-31ec6303abfe</uuid> <name>instance-00000001</name> <memory>524288</memory> <vcpu>1</vcpu> <os> <type>xen</type> <kernel>/opt/stack/data/nova/instances/9e9ed86c-8892-40da-acd1-31ec6303abfe/kernel</kernel> <initrd>/opt/stack/data/nova/instances/9e9ed86c-8892-40da-acd1-31ec6303abfe/ramdisk</initrd> <cmdline>ro root=/dev/xvda</cmdline> </os> <features> <acpi/> <apic/> </features> <clock offset="utc"/> <devices> <disk type="file" device="disk"> <driver name="tap2" type="raw" cache="none"/> <source file="/opt/stack/data/nova/instances/9e9ed86c-8892-40da-acd1-31ec6303abfe/disk"/> <target bus="xen" dev="xvda"/> </disk> <disk type="file" device="cdrom"> <driver name="tap2" type="raw" cache="none"/> <source file="/opt/stack/data/nova/instances/9e9ed86c-8892-40da-acd1-31ec6303abfe/disk.config"/> <target bus="ide" dev="xvdd"/> </disk> <interface type="bridge"> <mac address="fa:16:3e:d8:c3:c0"/> <source bridge="br100"/> <filterref filter="nova-instance-instance-00000001-fa163ed8c3c0"/> </interface> <console type="pty"/> <graphics type="vnc" autoport="yes" keymap="en-us" listen="127.0.0.1"/> <video> <model type="xen"/> </video> </devices> </domain> Best regards, Tian, Shuangtai