51. VDEV_NETVSC driver

The VDEV_NETVSC driver (librte_net_vdev_netvsc) provides support for NetVSC interfaces and associated SR-IOV virtual function (VF) devices found in Linux virtual machines running on Microsoft Hyper-V (including Azure) platforms.

51.1. Implementation details

Each instance of this driver effectively needs to drive two devices: the NetVSC interface proper and its SR-IOV VF (referred to as “physical” from this point on) counterpart sharing the same MAC address.

Physical devices are part of the host system and cannot be maintained during VM migration. From a VM standpoint they appear as hot-plug devices that come and go without prior notice.

When the physical device is present, egress and most of the ingress traffic flows through it; only multicasts and other hypervisor control still flow through NetVSC. Otherwise, NetVSC acts as a fallback for all traffic.

To avoid unnecessary code duplication and ensure maximum performance, handling of physical devices is left to their original PMDs; this virtual device driver (also known as vdev) manages other PMDs as summarized by the following block diagram:

        .------------------.
        | DPDK application |
        `--------+---------'
                 |
          .------+------.
          | DPDK ethdev |
          `------+------'       Control
                 |                 |
    .------------+------------.    v    .--------------------.
    |       failsafe PMD      +---------+ vdev_netvsc driver |
    `--+-------------------+--'         `--------------------'
       |                   |
       |          .........|.........
       |          :        |        :
  .----+----.     :   .----+----.   :
  | tap PMD |     :   | any PMD |   :
  `----+----'     :   `----+----'   : <-- Hot-pluggable
       |          :        |        :
.------+-------.  :  .-----+-----.  :
| NetVSC-based |  :  | SR-IOV VF |  :
|   netdevice  |  :  |   device  |  :
`--------------'  :  `-----------'  :
                  :.................:

This driver implementation may be temporary and should be improved or removed either when hot-plug will be fully supported in EAL and bus drivers or when a new NetVSC driver will be integrated.

51.2. Run-time parameters

This driver is invoked automatically in Hyper-V VM systems unless the user invoked it by command line using --vdev=net_vdev_netvsc EAL option.

The following device parameters are supported:

  • iface [string]

    Provide a specific NetVSC interface (netdevice) name to attach this driver to. Can be provided multiple times for additional instances.

  • mac [string]

    Same as iface except a suitable NetVSC interface is located using its MAC address.

  • force [int]

    If nonzero, forces the use of specified interfaces even if not detected as NetVSC.

  • ignore [int]

    If nonzero, ignores the driver running (actually used to disable the auto-detection in Hyper-V VM).

Note

Not specifying either iface or mac makes this driver attach itself to all unrouted NetVSC interfaces found on the system. Specifying the device makes this driver attach itself to the device regardless the device routes.