1.\" 2.\" Copyright (c) 2002 Mark R V Murray 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 15.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 18.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 19.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 20.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 21.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 22.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.\" 28.Dd February 6, 2002 29.Dt RANDOM_HARVEST 9 30.Os 31.Sh NAME 32.Nm random_harvest 33.Nd gather entropy from the kernel for the entropy device 34.Sh SYNOPSIS 35.In sys/types.h 36.In sys/random.h 37.Ft void 38.Fo random_harvest 39.Fa "void *entropy" 40.Fa "u_int size" 41.Fa "u_int bits" 42.Fa "u_int frac" 43.Fa "enum esource source" 44.Fc 45.Sh DESCRIPTION 46The 47.Fn random_harvest 48function is used by device drivers 49and other kernel processes to pass data 50that is considered (at least partially) stochastic 51to the entropy device. 52.Pp 53The caller should pass a pointer (to no more than 16 bytes) of 54the 55.Dq random 56data in 57.Fa entropy . 58The argument 59.Fa size 60contains the number of bytes pointed to. 61The caller should 62.Em "very conservatively" 63estimate the number of random bits 64in the sample, 65and pass this in 66.Fa bits 67or 68.Fa frac . 69If the estimated number of bits per sample is an integer, then 70.Fa bits 71is used, and 72.Fa frac 73is 0. 74Otherwise, 75for low-entropy samples, 76.Dq fractional 77entropy can be supplied in 78.Fa frac . 79(This is considered to be 80.Fa frac / 811024 bits of entropy.) 82The 83.Fa source 84is chosen from 85.Dv RANDOM_WRITE , RANDOM_KEYBOARD , RANDOM_MOUSE , RANDOM_NET 86and 87.Dv RANDOM_INTERRUPT , 88and is used to indicate the source of the entropy. 89.Pp 90Interrupt harvesting has been simplified 91for the kernel programmer. 92If a device driver registers an interrupt handler 93with 94.Xr BUS_SETUP_INTR 9 95or 96.Xr bus_setup_intr 9 , 97then it is only necessary to 98include the 99.Dv INTR_ENTROPY 100bit in the 101.Fa flags 102argument to have that interrupt source 103be used for entropy harvesting. 104.Sh SEE ALSO 105.Xr random 4 , 106.Xr BUS_SETUP_INTR 9 107.Sh AUTHORS 108The 109.Fx 110.Xr random 4 111entropy device and supporting documentation was written by 112.An Mark R V Murray . 113