.\" Copyright (c) 2011 Bryan Venteicher
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.\" $FreeBSD: head/share/man/man4/virtio.4 273515 2014-10-23 04:47:32Z bryanv $
.\"
.Dd January 22, 2012
.Dt VIRTIO 4
.Os
.Sh NAME
.Nm virtio
.Nd VirtIO Device Support
.Sh SYNOPSIS
To compile VirtIO device support into the kernel, place the following lines
in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "device virtio"
.Cd "device virtio_pci"
.Ed
.Pp
Alternatively, to load VirtIO support as modules at boot time, place the
following lines in
.Xr loader.conf 5 :
.Bd -literal -offset indent
virtio_load="YES"
virtio_pci_load="YES"
.Ed
.Sh DESCRIPTION
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.
.Pp
VirtIO defines an interface for efficient I/O between the hypervisor and VM.
The
.Nm
module provides a shared memory transport called a virtqueue.
The
.Xr 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.
.Fx
supports the following VirtIO devices:
.Bl -hang -offset indent -width xxxxxxxx
.It Nm Ethernet
An emulated Ethernet device is provided by the
.Xr vtnet 4
device driver.
.It Nm Block
An emulated disk controller is provided by the
.Xr virtio_blk 4
device driver.
.It Nm SCSI
An emulated SCSI HBA is provided by the
.Xr virtio_scsi 4
device driver.
.It Nm Balloon
A pseudo-device to allow the VM to release memory back to the hypervisor is
provided by the
.Xr virtio_balloon 4
device driver.
.El
.Sh SEE ALSO
.Xr virtio_balloon 4 ,
.Xr virtio_blk 4 ,
.Xr virtio_console 4 ,
.Xr virtio_scsi 4 ,
.Xr vtnet 4
.Sh HISTORY
Support for VirtIO first appeared in
.Fx 9.0 .
.Sh AUTHORS
.An -nosplit
.Fx
support for VirtIO was first added by
.An Bryan Venteicher Aq Mt bryanv@FreeBSD.org .