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: head/share/man/man4/virtio.4 273515 2014-10-23 04:47:32Z bryanv $ 26.\" 27.Dd July 30, 2017 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.Ed 39.Pp 40Alternatively, to load VirtIO support as modules at boot time, place the 41following lines in 42.Xr loader.conf 5 : 43.Bd -literal -offset indent 44virtio_pci_load="YES" 45.Ed 46.Sh DESCRIPTION 47VirtIO is a specification for para-virtualized I/O in a virtual machine (VM). 48Traditionally, the hypervisor emulated real devices such as an Ethernet 49interface or disk controller to provide the VM with I/O. 50This emulation is often inefficient. 51.Pp 52VirtIO defines an interface for efficient I/O between the hypervisor and VM. 53The 54.Nm 55module provides a shared memory transport called a virtqueue. 56The 57.Nm virtio_pci 58device driver represents an emulated PCI device that the hypervisor makes 59available to the VM. 60This device provides the probing, configuration, and 61interrupt notifications needed to interact with the hypervisor. 62.Dx 63supports the following VirtIO devices: 64.Bl -hang -offset indent -width xxxxxxxx 65.It Nm Ethernet 66An emulated Ethernet device is provided by the 67.Xr vtnet 4 68device driver. 69.It Nm Block 70An emulated disk controller is provided by the 71.Xr virtio_blk 4 72device driver. 73.It Nm SCSI 74An emulated SCSI HBA is provided by the 75.Xr virtio_scsi 4 76device driver. 77.\".It Nm Balloon 78.\"A pseudo-device to allow the VM to release memory back to the hypervisor is 79.\"provided by the 80.\".Xr virtio_balloon 4 81.\"device driver. 82.El 83.Sh LOADER TUNABLES 84Tunables can be set at the 85.Xr loader 8 86prompt before booting the kernel or stored in 87.Xr loader.conf 5 . 88.Bl -tag -width "xxxxxx" 89.It Va hw.virtio.pci.disable_msix 90This tunable disables MSI-X interrupt usage. 91The default value is 0 (use MSI-X interrupts if available). 92.El 93.Sh SEE ALSO 94.\".Xr virtio_balloon 4 , 95.Xr virtio_blk 4 , 96.\".Xr virtio_console 4 , 97.Xr virtio_scsi 4 , 98.Xr vtnet 4 99.Sh HISTORY 100Support for VirtIO first appeared in 101.Fx 9.0 . 102.Sh AUTHORS 103.An -nosplit 104.Fx 105support for VirtIO was first added by 106.An Bryan Venteicher Aq Mt bryanv@FreeBSD.org . 107