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+.\" Copyright (c) 2011 Bryan Venteicher
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd July 2, 2013
+.Dt VIRTIO_BLK 4
+.Os
+.Sh NAME
+.Nm virtio_blk
+.Nd VirtIO Block driver
+.Sh SYNOPSIS
+To compile this driver into the kernel,
+place the following lines in your
+kernel configuration file:
+.Bd -ragged -offset indent
+.Cd "device virtio_blk"
+.Ed
+.Pp
+Alternatively, to load the driver as a
+module at boot time, place the following line in
+.Xr loader.conf 5 :
+.Bd -literal -offset indent
+virtio_blk_load="YES"
+.Ed
+.Sh DESCRIPTION
+The
+.Nm
+device driver provides support for VirtIO block devices.
+.Sh LOADER TUNABLES
+Tunables can be set at the
+.Xr loader 8
+prompt before booting the kernel or stored in
+.Xr loader.conf 5 .
+.Bl -tag -width indent
+.It Va hw.vtblk.no_ident
+.It Va hw.vtblk. Ns Ar X Ns Va .no_ident
+.Pp
+These tunables disable retrieving the device identification string
+from the hypervisor either globally or per-device.
+The default value is 0.
+.It Va hw.vtblk.writecache_mode
+.It Va hw.vtblk. Ns Ar X Ns Va .writecache_mode
+.Pp
+These tunables determine the write cache mode globally or per-device.
+The mode can changed only if the ConfigWCE feature is negotiated.
+Set to 0 for writethrough mode, 1 for writeback mode, and -1 to leave
+it as-is.
+The default value is to leave as-is.
+.El
+.Sh SYSCTL VARIABLES
+The following variables are available as
+.Xr sysctl 8
+variables.
+.Bl -tag -width indent
+.It Va dev.vtblk. Ns Ar X Ns Va .writecache_mode
+.Pp
+The write cache mode of the device can be either writethrough (0) or
+writeback (1).
+If the ConfigWCE feature is negotiated, the write cache mode can
+be toggled between writethrough and writeback.
+.El
+.Sh SEE ALSO
+.Xr virtio 4
+.Sh HISTORY
+The
+.Nm
+driver was written by
+.An Bryan Venteicher Aq bryanv@FreeBSD.org .
+It first appeared in
+.Fx 9.0 .