[libvirt] Using -netdev with qemu/kvm rather than old style

I have 0.8.3 installed and my net devices are still being defined via -net rather than -netdev. I have found that using the latter allows my ethernet to properly offload and gives a 35% performance gain. Looking through the libvirt code I find in qemu_conf.c: /* Possible combinations * * 1. Old way: -net nic,model=e1000,vlan=1 -net tap,vlan=1 * 2. Semi-new: -device e1000,vlan=1 -net tap,vlan=1 * 3. Best way: -netdev type=tap,id=netdev1 -device e1000,id=netdev1 * * NB, no support for -netdev without use of -device */ How do I convince virsh/libvirt to use #3, the "Best way"?