.\"     $OpenBSD: viornd.4,v 1.2 2015/02/17 16:29:16 bentley Exp $
.\"
.\" Copyright (c) 2014 Stefan Fritsch <sf@sfritsch.de>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: February 17 2015 $
.Dt VIORND 4
.Os
.Sh NAME
.Nm viornd
.Nd VirtIO random number device
.Sh SYNOPSIS
.Cd "viornd* at virtio? flags 0x00"
.Sh DESCRIPTION
The
.Nm
driver provides a virtual random number generator using a
.Xr virtio 4
entropy device provided by QEMU 1.3 and later, and possibly by other
hypervisors.
.Pp
As there is currently no way for
.Nm
to determine how much entropy is needed, the second byte of the flags value
can be used to configure how often it should request more entropy from the
host.
If the second lowest byte of the flags has a value from 1 to 15,
.Nm
will ask for 16 bytes of entropy every 15 * (1 << value) seconds.
For example, flags == 0x100 means an interval of 30 seconds,
0x500 means 8 minutes, 0xa00 means 256 minutes, and 0xf00 means about 6 days.
For flags == 0, a default value will be used (currently 8 minutes).
If the bit 0x1000 is set in the flags,
.Nm
will only request entropy from the host once during system boot.
.Sh SEE ALSO
.Xr intro 4 ,
.Xr virtio 4
.Sh HISTORY
The
.Nm
driver first appeared in
.Ox 5.5 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was written by
.An Stefan Fritsch Aq Mt sf@sfritsch.de .