random(4): Simplify RANDOM_LOADABLE

Simplify RANDOM_LOADABLE by removing the ability to unload a LOADABLE
random(4) implementation.  This allows one-time random module selection
at boot, by loader(8).  Swapping modules on the fly doesn't seem
especially useful.

This removes the need to hold a lock over the sleepable module calls
read_random and read_random_uio.

init/deinit have been pulled out of random_algorithm entirely.  Algorithms
can run their own sysinits to initialize; deinit is removed entirely, as
algorithms can not be unloaded.  Algorithms should initialize at
SI_SUB_RANDOM:SI_ORDER_SECOND.  In LOADABLE systems, algorithms install
a pointer to their local random_algorithm context in p_random_alg_context at
that time.

Go ahead and const'ify random_algorithm objects; there is no need to mutate
them at runtime.

LOADABLE kernel NULL checks are removed from random_harvestq by ordering
random_harvestq initialization at SI_SUB_RANDOM:SI_ORDER_THIRD, after
algorithm init.  Prior to random_harvestq init, hc_harvest_mask is zero and
no events are forwarded to algorithms; after random_harvestq init, the
relevant pointers will already have been installed.

Remove the bulk of random_infra shim wrappers and instead expose the bare
function pointers in sys/random.h.  In LOADABLE systems, read_random(9) et
al are just thin shim macros around invoking the associated function
pointer.  We do not provide a registration system but instead expect
LOADABLE modules to register themselves at SI_SUB_RANDOM:SI_ORDER_SECOND.
An example is provided in randomdev.c, as used in the random_fortuna.ko
module.

Approved by:	csprng(markm)
Discussed with:	gordon
Differential Revision:	https://reviews.freebsd.org/D22512

1 files changed, 3 insertions, 0 deletions

diff --git a/UPDATING b/UPDATING
index becf733734869..12adfb6c0a59c 100644
--- a/UPDATING
+++ b/UPDATING
@@ -26,6 +26,9 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 13.x IS SLOW:
 	disable the most expensive debugging functionality run
 	"ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20191226:
+	Kernel-loadable random(4) modules are no longer unloadable.
+
 20191222:
 	Clang, llvm, lld, lldb, compiler-rt, libc++, libunwind and openmp have
 	been upgraded to 9.0.1.  Please see the 20141231 entry below for