Huge cleanup of random(4) code.
rS284959
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Description

Huge cleanup of random(4) code.

GENERAL
Update copyright.
Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna
If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks.
Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird.
Adjust arc4random stirring a bit - the existing code looks a little suspect.
Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks.
Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack.
Move stuff out of locked regions when it does not need to be there.
Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose.
Use SYSINIT to sequence the startup.
Fix init/deinit sysctl stuff.
Make relevant sysctls also tunables.
Add different harvesting "styles" to allow for different requirements (direct, queue, fast).
Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code.
Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code.
Fix the random(9) manpage.
Loadable modules are not present for now. These will be re-engineered when the dust settles.
Use macros for locks.
Fix comments.

src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h
Remove; plugability is no longer used. Compile-time algorithm selection is the way to go.

src/sys/dev/random/uint128.h
Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL.

src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h
Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea.
This is still a long way off a proper unit test.

src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h
Improve messy union to just uint128_t.
Remove unneeded 'static struct fortuna_start_cache'.
Tighten up up arithmetic.
Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing.
Assert that locks are held correctly.
Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks.
Turn into self-sufficient module (no longer requires randomdev_soft.[ch])

src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h
Improve messy union to just uint128_t.
Remove unneeded 'staic struct start_cache'.
Tighten up up arithmetic.
Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing.
Assert that locks are held correctly.
Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks.
Turn into self-sufficient module (no longer requires randomdev_soft.[ch])
Fix some magic numbers elsewhere used as FAST and SLOW.

Differential Revision: https://reviews.freebsd.org/D2025
Reviewed by: vsevolod,delphij,rwatson,trasz,jmg
Approved by: so (delphij)