[libvirt] USB pass-through only works after many disconnects at the beginning

Hi, I want to pass through a USB device to a KVM guest (Windows 2000). My host OS is a standard Fedora 10, 64 bit. However, the device is only passed to the guest when I use qemu monitor directly and only after several tries... The device has no Linux drivers ('AVM GmbH ISDN-Controller FRITZ!Card v2.0') so I think I don't have to tell the kernel not to use it. I have KVM 74 and tried initially with libvirt 0.5.1 so from what I read this should be ok. At first I added this to my domain xml via virsh: <hostdev mode='subsystem' type='usb'> <source> <vendor id='0x....'/> <product id='0x....'/> </source> </hostdev> However, the device did not turn up in the guest. Therefore I updated libvirt/-python 0.6.1 and python-virtinst from updates-testing and recompiled virt-manager 0.7 from F11 because I read that virt-manager 0.7 had some support for USB pass-through. Now I had some new UI, but it turned out that using that did not produce better results... After that I called qemu-kvm directly with '-usb -usbdevice host:...:...'. qemu produced this output on my terminal: husb: open device 2.9 husb: config #1 need -1 husb: 1 interfaces claimed for configuration -1 husb: grabbed usb device 2.9 husb: config #1 need 1 USBDEVFS_DISCONNECT: No such device husb: device 2.9 disconnected When I used qemu monitor to re-attach the device, something liek that happened (re-attached multiple times): husb: open device 2.11 husb: config #1 need -1 husb: 1 interfaces claimed for configuration -1 husb: grabbed usb device 2.11 husb: config #1 need 1 husb: 1 interfaces claimed for configuration 1 husb: config #1 need 1 USBDEVFS_DISCONNECT: No such device husb: config #1 need 1 USBDEVFS_DISCONNECT: No such device husb: config #1 need 1 USBDEVFS_DISCONNECT: No such device husb: device 2.11 disconnected ... Eventually (after several tries), the device was attached and no more disconnects happened. After that I could use the device as expected. However plain qemu is not what I would like to have. I read about 'virsh attach-device' so I tried to use my usb hostdev snippet but to no avail (even after 10s of tries). So how can I use USB pass through? Could this be Windows-related? Judging from all the other threads (like [1]) it should be really easy to use. fs [1] https://www.redhat.com/archives/libvir-list/2009-February/msg00387.html