vdev virtio-net

Synopsis:

vdev  virtio-net options

Options:

intr intr: Signal intr for device interrupts. Not required when the vdev appears as a PCI device.
legacy: Provide the VirtIO legacy interface (0.9.5) rather than the 1.0 standard version.
loc addr: Set the base address of the device registers to addr. If this option isn't specified, the vdev appears as a PCI device.
mac mac_address: Use the mac_address as the Ethernet address for the virtual device in the guest.
name name: Set this side of a peer-to-peer networking connection to name.
peer path: Directly connect to the peer device path (usually of the form /dev/qvm/vm/vnet). In this case, specifying mac and name is highly recommended.; For the name, use the name (system_name) of the system with the peered device (see system in the “VM Configuration Reference” chapter).
peerfeats mask: VirtIO Network feature bits that should be assumed to be supported by the peer, since it is impossible to do proper negotiation (see below).
tapdev host_device_name: Deprecated.

For a list of options available to all vdevs, see “Common vdev options” at the beginning of this chapter.

Description:

Normally the device appears as a PCI device, but if you specify the loc and intr options, the guest will see it as a memory-mapped I/O device at the specified location.

Using the peerfeats option

Feature bits are used to specify the features that are exposed to a peer in a network. They can be defined for each individual virtio-net interface (i.e., each peer connection can have its own feature set).

Peerfeats defines the maximum set of features that will be negotiated between the two TCP stacks connected as peers. The peerfeats bits are specified in Virtual I/O Device (VIRTIO) Version 1.0, Section 5.1.3 (see the document repository at oasis-open.org). This maximum set of bits is currently set at 0x7fc3. The current QNX Neutrino OS TCP stack provided with QNX SDP 7.0 supports a subset of the maximum set. This subset is 0x19c3, or:

0001 1001 1100 0011

with the least-significant bit (bit zero) on the right.

Of particular interest are the bits that support checksumming and Transmit Segmentation Offload (TSO); both these features are supported in the QNX TCP stack (see the table below).

The default peerfeats value for a peer interface is 0x0000.

You should limit the feature bits to the features supported by the guests. For example, if you are configuring two QNX Neutrino OS 7.0 guests to connect as peers, you should specify 0x19c3 as the value for the peerfeats option's mask in the VM configuration for each guest.

When using the peerfeats option:

If you know the peerfeats of both the near-end and the far-end peer interfaces, specify it with the peerfeats option in the VM configurations for each guest.
If you don't know the capabilities supported by both peers, you can set the peerfeats mask to 0x7fc3 and let the connected TCP stacks negotiate the features they will use (check the documentation for your Linux, QNX Neutrino, or other OS for details).
If you are configuring a peer connection to a QNX io-pkt-* bridge, you must set the peerfeats option to 0x0 (zero) to disable all features on both peer nodes.

If one of the peers is in the hypervisor host, configure its interface to disable checksums for TCP/IP and UDP, as follows:
```
ifconfig vp0 -tcp4csum -udp4csum -udp6csum -tcp6csum
```
This is required so that the host bridge does not incorrectly discard or delay packets. Note, however, that you disable checksums only for receiving IP (-rx), so you can still transfer packets with checksums out. If the peer node is properly configured, it should have checksums disabled and be able to receive your packets.

Guest-to-guest and guest-to-host

The table below lists the recommended feature set for guest-to-guest and guest-to host connections:

Bit	Name	Feature
0	VIRTIO_NET_F_CSUM	Device handles packets with partial (or no) checksum.
1	VIRTIO_NET_F_GUEST_CSUM	Driver handles packets with partial (or no) checksum.

Guest-to-guest only

The table below lists the recommended feature set for guest-to-guest connections only:

Bit	Name	Feature
7	VIRTIO_NET_F_GUEST_TSO4	Driver can receive TSOv4.
8	VIRTIO_NET_F_GUEST_TSO6	Driver can receive TSOv6.
11	VIRTIO_NET_F_HOST_TSO4	Device can receive TSOv4.
12	VIRTIO_NET_F_HOST_TSO6	Device can receive TSOv6.

For more information about using the virtio-net vdev, see “Networking” in the “Using a QNX Hypervisor System” chapter.