Add VIF_VHOSTUSER vif type to libvirt driver

We propose to add a new VIF type to support the new QEMU vhost-user interface in libvirt dirver. vhost-user is a new QEMU feature that supports efficient Virtio-net I/O between a guest and a user-space vswitch. vhost-user is the userspace equivalent to /dev/vhost-net and is based on a Unix socket for communication instead of a kernel device file.

Problem description

QEMU has a new type of network interface, vhost-user, and we want to make this available to Neutron drivers. This will support deploying high-throughput userspace vswitches for OpenStack-based applications. There are two types of vSwitches that can use vhost-user interface, a generic vhost-user vSwitch and ovs based one, both types should be supported.

Use Cases

This change will allow running userspace vSwitches using vhost-user interface. Both generic vhost-user vSwitches and OVS based vSwtiches will be supported.

Project Priority


Proposed change

We propose to add VIF_VHOSTUSER to Nova for creating network interfaces based on vhost-user. This VIF type would be enabled by Neutron drivers by using portbindings extension and setting the vif_type to VIF_VHOSTUSER. To support both generic and ovs based vSwitches additional information will be passed in vif_details. For ovs based vSwitches plug/unplug methods will create/remove an ovs port if ‘vhost_user_ovs_plug’ is set to True in the vif_details.

VIF_VHOSTUSER driver will allow Neutron mechanism drivers to specify if qemu should work in server or client mode. Mechanism drivers could pass ‘vhost_user_mode’ in vif_details to specify the mode. The name of the socket will be the same as ID of the Neutron port. For ovs based vSwitches name of the socket will be the same as name of the ovs port.


In Juno cycle there were two initiatives to support userspace vhost user in Nova. One was based on vhost-user interface in Qemu the other was based on DPDK implementation. Since DPDK is moving to support vhost-user only one driver is needed.

Alternatively a mechanism for plugging in vif libvirt driver could be used to support vhost-user in libvirt driver. Such mechanism is proposed here:

Data model impact


REST API impact


Security impact


Notifications impact


Other end user impact


Performance Impact

Use of VIF_VHOSTUSER will have no inpact on Openstack performance. Use of userspace vSwitch with vhost-user will improve guest network perforamce.

Other deployer impact

VIF_VHOSTUSER does not have to be enabled by the deployer. Neutron drivers will automatically enable VIF_VHOSTUSER via port binding if this is the appropriate choice for the agent on the compute host.

VIF_VHOSTUSER will require a version of QEMU with vhost-user support, which is currently upstream and will be released in QEMU 2.1.

VIF_VHOSTUSER will also require a version of Libvirt with vhost-user support.

Developer impact




Primary assignee:

Przemyslaw Czesnowicz <pczesno>

Work Items

  • Add VIF_VHOSTUSER support to Nova.


An ml2 dpdk ovs driver is being proposed for Neutron. This feature doesn’t directly depend on it.

This feature depends on bp/virt-driver-large-pages.


VIF_VHOSTUSER will be tested by 3rd party CI for the DPDK Ovs mech driver.

Documentation Impact

No documentation changes for Nova are anticipated. VIF_VHOSTUSER will be automatically enabled by Neutron where appropriate.