Copyright (c) 2002-2015 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 August 26, 2018 .Dt RANDOM_HARVEST 9 .Os .Sh NAME .Nm random_harvest .Nd gather entropy from the kernel for the entropy device .Sh SYNOPSIS n sys/types.h n sys/random.h .Ft void .Fo random_harvest_direct .Fa "void *entropy" .Fa "u_int size" .Fa "enum esource source" .Fc .Ft void .Fo random_harvest_fast .Fa "void *entropy" .Fa "u_int size" .Fa "enum esource source" .Fc .Ft void .Fo random_harvest_queue .Fa "void *entropy" .Fa "u_int size" .Fa "enum esource source" .Fc .Sh DESCRIPTION The .Fn random_harvest_* functions are used by device drivers and other kernel processes to pass data that is considered (at least partially) stochastic to the entropy device.
p The caller should pass a pointer pointing to the .Dq random data in .Fa entropy . The argument .Fa size contains the number of bytes pointed to. The .Fa source is chosen from one of the values enumerated in
a sys/dev/random.h . and is used to indicate the source of the entropy.
p The .Fo random_harvest_direct .Fc variant is used for early harvesting before any multitasking is enabled.
p The .Fn random_harvest_fast variant is used by sources that should not take a performance hit from harvesting, as they are high-rate sources. Some entropy is sacrificed, but the high rate of supply will compensate for this.
p The .Fn random_harvest_queue variant is used for general harvesting and is the default choice for most entropy sources such as interrupts or console events.
p Interrupt harvesting has been in part 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. This should be done wherever practicable. .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 .