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.

Debian                                           August 26, 2018                               RANDOM_HARVEST(9)