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.Dd July 2, 2013 26.Dt VIRTIO_BLK 4 27.Os 28.Sh NAME 29.Nm virtio_blk 30.Nd VirtIO Block driver 31.Sh SYNOPSIS 32To compile this driver into the kernel, 33place the following lines in your 34kernel configuration file: 35.Bd -ragged -offset indent 36.Cd "device virtio_blk" 37.Ed 38.Pp 39Alternatively, to load the driver as a 40module at boot time, place the following line in 41.Xr loader.conf 5 : 42.Bd -literal -offset indent 43virtio_blk_load="YES" 44.Ed 45.Sh DESCRIPTION 46The 47.Nm 48device driver provides support for VirtIO block devices. 49.Sh LOADER TUNABLES 50Tunables can be set at the 51.Xr loader 8 52prompt before booting the kernel or stored in 53.Xr loader.conf 5 . 54.Bl -tag -width indent 55.It Va hw.vtblk.no_ident 56.It Va hw.vtblk. Ns Ar X Ns Va .no_ident 57.Pp 58These tunables disable retrieving the device identification string 59from the hypervisor either globally or per-device. 60The default value is 0. 61.It Va hw.vtblk.writecache_mode 62.It Va hw.vtblk. Ns Ar X Ns Va .writecache_mode 63.Pp 64These tunables determine the write cache mode globally or per-device. 65The mode can changed only if the ConfigWCE feature is negotiated. 66Set to 0 for writethrough mode, 1 for writeback mode, and -1 to leave 67it as-is. 68The default value is to leave as-is. 69.El 70.Sh SYSCTL VARIABLES 71The following variables are available as 72.Xr sysctl 8 73variables. 74.Bl -tag -width indent 75.It Va dev.vtblk. Ns Ar X Ns Va .writecache_mode 76.Pp 77The write cache mode of the device can be either writethrough (0) or 78writeback (1). 79If the ConfigWCE feature is negotiated, the write cache mode can 80be toggled between writethrough and writeback. 81.El 82.Sh SEE ALSO 83.Xr virtio 4 84.Sh HISTORY 85The 86.Nm 87driver was written by 88.An Bryan Venteicher Aq Mt bryanv@FreeBSD.org . 89It first appeared in 90.Fx 9.0 . 91