libvirt users - Jul 2015 - Error attaching tape drive device to KVM guest

Hello,

i'm trying to configure a host SCSI device (tape drive) so that it is 
available in a KVM guest VM, but am receiving an error when attempting to 
attach the device.  My guest xml has the following scsi controller 
defined:

<controller type='scsi' index='0'
model='virtio-scsi'>
    <alias name='scsi0'/>
    <address type='pci' domain='0x0000' bus='0x00'
slot='0x04'
function='0x0'/>
</controller>

I created tapedrive.xml with following contents:

<disk type='block' device='lun' sgio='unfiltered'>
    <driver name='qemu' type='raw' cache='none'/>
    <source dev='/dev/st0'/>
    <target dev='st0' bus='scsi'/>
    <address type='drive' controller='0' bus='0'
target='0' unit='0'/>
</disk>

I then attempt to attach using following command, and receive this error:

# virsh attach-device instance-0000002d tapedrive.xml --config
error: Failed to attach device from tapedrive.xml
error: internal error: Invalid harddisk device name: st0

Does anyone know cause of the error?  In <address> section of tape drive 
definition I am using type='drive', I tried type='tape' also but
same
error. is there a different property value I should use here, or general 
advice for attaching tape drive to KVM guest?  Thanks, Jake