random_harvest(9) gather entropy from the kernel for the entropy device


In sys/types.h In sys/random.h Ft void Fo random_harvest Fa void *entropy Fa u_int size Fa u_int bits Fa u_int frac Fa enum esource source Fc


The Fn 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 Fa entropy . The argument Fa 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 Fa bits or Fa frac . If the estimated number of bits per sample is an integer, then Fa bits is used, and Fa frac is 0. Otherwise, for low-entropy samples, ``fractional'' entropy can be supplied in Fa frac . (This is considered to be Fa frac / 1024 bits of entropy.) The Fa 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_INTR9 or bus_setup_intr9, then it is only necessary to include the INTR_ENTROPY bit in the Fa flags argument to have that interrupt source be used for entropy harvesting.


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