1.\" Copyright (c) 2011 Bryan Venteicher 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD: src/share/man/man4/virtio.4,v 1.5 2012/11/17 01:50:49 svnexp Exp $ 26.\" 27.Dd January 6, 2013 28.Dt VIRTIO 4 29.Os 30.Sh NAME 31.Nm virtio 32.Nd VirtIO Device Support 33.Sh SYNOPSIS 34To compile VirtIO device support into the kernel, place the following lines 35in your kernel configuration file: 36.Bd -ragged -offset indent 37.Cd "device virtio" 38.Cd "device virtio_pci" 39.Ed 40.Pp 41Alternatively, to load VirtIO support as modules at boot time, place the 42following lines in 43.Xr loader.conf 5 : 44.Bd -literal -offset indent 45virtio_load="YES" 46virtio_pci_load="YES" 47.Ed 48.Sh DESCRIPTION 49VirtIO is a specification for para-virtualized I/O in a virtual machine (VM). 50Traditionally, the hypervisor emulated real devices such as an Ethernet 51interface or disk controller to provide the VM with I/O. 52This emulation is often inefficient. 53.Pp 54VirtIO defines an interface for efficient I/O between the hypervisor and VM. 55The 56.Nm 57module provides a shared memory transport called a virtqueue. 58The 59.Nm virtio_pci 60device driver represents an emulated PCI device that the hypervisor makes 61available to the VM. 62This device provides the probing, configuration, and 63interrupt notifications needed to interact with the hypervisor. 64.Dx 65supports the following VirtIO device(s): 66.Bl -hang -offset indent -width xxxxxxxx 67.It Nm Ethernet 68An emulated Ethernet device is provided by the 69.Xr vtnet 4 70device driver. 71.It Nm Block 72An emulated disk controller is provided by the 73.Xr virtio_blk 4 74device driver. 75.\".It Nm SCSI 76.\"An emulated SCSI HBA is provided by the 77.\".Xr virtio_scsi 4 78.\"device driver. 79.\".It Nm Balloon 80.\"A pseudo-device to allow the VM to release memory back to the hypervisor is 81.\"provided by the 82.\".Xr virtio_balloon 4 83.\"device driver. 84.El 85.Sh LOADER TUNABLES 86Tunables can be set at the 87.Xr loader 8 88prompt before booting the kernel or stored in 89.Xr loader.conf 5 . 90.Bl -tag -width "xxxxxx" 91.It Va hw.virtio.pci.disable_msix 92This tunable disables MSI-X interrupt usage. 93The default value is 0 (use MSI-X interrupts if available). 94.El 95.Sh SEE ALSO 96.\".Xr virtio_balloon 4 , 97.Xr virtio_blk 4 98.\".Xr virtio_scsi 4 , 99.Xr vtnet 4 100.Sh HISTORY 101Support for VirtIO first appeared in 102.Fx 9.0 . 103.Sh AUTHORS 104.An -nosplit 105.Fx 106support for VirtIO was first added by 107.An Bryan Venteicher Aq Mt bryanv@daemoninthecloset.org . 108