virtio4

Usage

Overview

VirtIO is a specification for para-virtualized I/O in a virtual machine (VM). Traditionally, the hypervisor emulated real devices such as an Ethernet interface or disk controller to provide the VM with I/O. This emulation is often inefficient.

VirtIO defines an interface for efficient I/O between the hypervisor and VM. The virtio module provides a shared memory transport called a virtqueue. The virtio_pci device driver represents an emulated PCI device that the hypervisor makes available to the VM. This device provides the probing, configuration, and interrupt notifications needed to interact with the hypervisor. FreeBSD supports the following VirtIO devices:

Ethernet

An emulated Ethernet device is provided by the vtnet(4) device driver.

Block

An emulated disk controller is provided by the virtio_blk(4) device driver.

Console

Provided by the virtio_console(4) driver.

Entropy

Provided by the virtio_random(4) driver.

Balloon

A pseudo-device to allow the VM to release memory back to the hypervisor is provided by the virtio_balloon(4) device driver.

GPU

Graphics support is provided by the virtio_gpu(4) device driver.

SCSI

An emulated SCSI HBA is provided by the virtio_scsi(4) device driver.

Loader tunables

Tunables can be set at the loader(8) prompt before booting the kernel or stored in loader.conf(5).

hw.virtio.pci.disable_msix

If set to 1, disables MSI-X. The default value is 0.

hw.virtio.pci.transitional

For a transitional virtio device, this tunable specifies whether to negotiate modern mode and use the modern virtio driver (1) or to negotiate legacy mode and use the legacy virtio driver (0). The default value is 1.