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.\"
.\" Copyright (c) 2002 Mark R V Murray
.\" 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 ``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 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 February 6, 2002
.Dt RANDOM_HARVEST 9
.Os
.Sh NAME
.Nm random_harvest
.Nd gather entropy from the kernel for the entropy device
.Sh SYNOPSIS
.In sys/types.h
.In sys/random.h
.Ft void
.Fo random_harvest
.Fa "void *entropy"
.Fa "u_int size"
.Fa "u_int bits"
.Fa "u_int frac"
.Fa "enum esource source"
.Fc
.Sh DESCRIPTION
The
.Fn random_harvest
function is used by device drivers
and other kernel processes to pass data
that is considered (at least partially) stochastic
to the entropy device.
.Pp
The caller should pass a pointer (to no more than 16 bytes) of
the
.Dq random
data in
.Fa entropy .
The argument
.Fa size
contains the number of bytes pointed to.
The caller should
.Em "very conservatively"
estimate the number of random bits
in the sample,
and pass this in
.Fa bits
or
.Fa frac .
If the estimated number of bits per sample is an integer, then
.Fa bits
is used, and
.Fa frac
is 0.
Otherwise,
for low-entropy samples,
.Dq fractional
entropy can be supplied in
.Fa frac .
(This is considered to be
.Fa frac /
1024 bits of entropy.)
The
.Fa source
is chosen from
.Dv RANDOM_WRITE , RANDOM_KEYBOARD , RANDOM_MOUSE , RANDOM_NET
and
.Dv RANDOM_INTERRUPT ,
and is used to indicate the source of the entropy.
.Pp
Interrupt harvesting has been simplified
for the kernel programmer.
If a device driver registers an interrupt handler
with
.Xr BUS_SETUP_INTR 9
or
.Xr bus_setup_intr 9 ,
then it is only necessary to
include the
.Dv INTR_ENTROPY
bit in the
.Fa flags
argument to have that interrupt source
be used for entropy harvesting.
.Sh SEE ALSO
.Xr random 4 ,
.Xr BUS_SETUP_INTR 9
.Sh AUTHORS
The
.Fx
.Xr random 4
entropy device and supporting documentation was written by
.An Mark R V Murray .
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