NAME
random_harvest —
gather entropy from the kernel for the
entropy device
SYNOPSIS
#include
<sys/types.h>
#include <sys/random.h>
void
random_harvest_direct(void
*entropy, u_int size, enum
esource source);
void
random_harvest_fast(void
*entropy, u_int size, enum
esource source);
void
random_harvest_queue(void
*entropy, u_int size, enum
esource source);
DESCRIPTION
Therandom_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.
The caller should pass a pointer pointing to the “random” data in entropy. The argument size contains the number of bytes pointed to. The source is chosen from one of the values enumerated in sys/dev/random.h. and is used to indicate the source of the entropy.
The
random_harvest_direct();
variant is used for early harvesting before any multitasking is enabled.
The
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.
The
random_harvest_queue()
variant is used for general harvesting and is the default choice for most
entropy sources such as interrupts or console events.
Interrupt harvesting has been in part simplified for the kernel
programmer. If a device driver registers an interrupt handler with
BUS_SETUP_INTR(9) or
bus_setup_intr(9), then it is only necessary to include the
INTR_ENTROPY bit in the flags
argument to have that interrupt source be used for entropy harvesting. This
should be done wherever practicable.
SEE ALSO
AUTHORS
The FreeBSD random(4) entropy device and supporting documentation was written by Mark R V Murray.