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.