freebsd man page for random_harvest

RANDOM_HARVEST(9)					   BSD 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(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) sto-
     chastic 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.

BSD
								 February 6, 2002							       BSD