[libvirt] 'attach-interface' failure and RHEL6 qemu-kvm

I've run up against a small issue with the 'attach-interface' facility in later versions of libvirt. It doesn't appear to work with the vanilla qemu-kvm package in RHEL6 (which reports as version 0.12.1). For both attach-interface and attach-device I'm getting the same error. virsh attach-interface srv-vvh2o network vir0001 error: Failed to attach interface error: internal error unable to add host net: unknown command: 'host_net_add' virsh # attach-device srv-vvh2o fred.xml error: Failed to attach device from fred.xml error: internal error unable to add host net: unknown command: 'host_net_add' Looking at qemu monitor the 'qemu-kvm' is indeed short of the 'host_net_add' command and it all seems to be down to an entry in 'qemu_capabilities.c' which switches off 'netdev' for qemu versions less than 13. Is there a reason that the RHEL6 version - which seems to have functioning -netdev parameters and 'netdev_add' qemu commands - has been excluded? If its a RHEL6 special patched version is there a way to special case detect it in the code? Thanks Neil