RANDOM_HARVEST(9)      FreeBSD Kernel Developer's Manual     RANDOM_HARVEST(9)

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
     The 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.

     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
     random(4), BUS_SETUP_INTR(9)

AUTHORS
     The FreeBSD random(4) entropy device and supporting documentation was
     written by Mark R V Murray.

FreeBSD 13.1-RELEASE-p6         August 26, 2018        FreeBSD 13.1-RELEASE-p6