NAME

       random_harvest — gather entropy from the kernel for the entropy device

SYNOPSIS

       #include <sys/types.h>
       #include <sys/random.h>

       void
       random_harvest(void *entropy, u_int size, u_int bits, u_int frac, enum esource source);

DESCRIPTION

       The  random_harvest()  function is 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 (to no more than 16  bytes)  of  the  “random”  data  in  entropy.   The
       argument  size  contains  the number of bytes pointed to.  The caller should very conservatively estimate
       the number of random bits in the sample, and pass this in bits or frac.  If the estimated number of  bits
       per  sample  is  an  integer,  then  bits  is  used,  and frac is 0.  Otherwise, for low-entropy samples,
       “fractional” entropy can be supplied in frac.  (This is considered to be frac / 1024  bits  of  entropy.)
       The  source  is chosen from RANDOM_WRITE, RANDOM_KEYBOARD, RANDOM_MOUSE, RANDOM_NET and RANDOM_INTERRUPT,
       and is used to indicate the source of the entropy.

       Interrupt harvesting has been 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.

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                                          February 6, 2002                               RANDOM_HARVEST(9)