As you can see, the policy is mostly independent from the qemu implementation and even from the kernel implementation. Naming the macvtap code in qemu '-net vepa' would completely mix up things for people that want to use vepa with an SR-IOV card, or macvtap in bridge mode!
Qemu can continue to name the interface '-net tap'. libvrt can invoke it as '-net tap, fd=x', whether the fd is of type tap or macvtap. The SR-IOV/VMdq/macvlan are all 'offloading' the briding function to a particular physical device. In the case of the 'vepa' (or even the pepa) mode the offload is to an external switch on the network. The sriov nic's embedded bridge can also be put into VEPA mode or be used as a bridge for packets among the virtual functions. The embedded bridge might even support the 'pepa' mode. Similarly, the 'macvlan' driver can support the bridge mode for packets among the macvlan interfaces, or support vepa/pepa modes where the packes are sent out on the wire without bridging function. Therefore, we define an interface type that can be linked to a specific NIC (source dev), and a set of supported modes defined. Expanding on Daniel's suggestion earlier in this thread on 'physical' type, we can do the following: <interface type ='physical' name='somename'/> <source dev='eth0'/> <type='sr-iov|vmdq|ethernet'/> // it can be of one type <mode='vepa|pepa|bridge'/> </interface> The 'mode' can be left blank since the same NIC can support differnt modes per VM's network inteface defined in the domain xml. The 'mode' can however be used to restrict the supported modes for the particular named instance. With the above, in the domain xml, we specify: <interface type='physical'/> <name='somename'/> <type='macvtap|tap'/> // one of the two to be specified <target mode='vepa|pepa|bridge'/> //specify the mode needed for the VM </interface> With the above, when instantiating a guest libvirt will determine the type of interface. Example: for a 'vepa' on device eth0, libvirt will create a macvtap interface while setting the mode to vepa. This fd is what is passed to qemu. Since macvtap/tap appear the same to qemu we should not have to modify anything beyond libvirt. thoughts? Vivek/Stefan/Gerhard __ Vivek Kashyap Linux Technology Center, IBM