`rngd` seems to be the root cause for slow boot issues, and its functionality is
redundant since kernel v3.17 (2014), which introduced a `krngd` task (in kernel
space) that takes care of pulling in data from hardware RNGs:
> commit be4000bc4644d027c519b6361f5ae3bbfc52c347
> Author: Torsten Duwe <duwe@lst.de>
> Date: Sat Jun 14 23:46:03 2014 -0400
>
> hwrng: create filler thread
>
> This can be viewed as the in-kernel equivalent of hwrngd;
> like FUSE it is a good thing to have a mechanism in user land,
> but for some reasons (simplicity, secrecy, integrity, speed)
> it may be better to have it in kernel space.
>
> This patch creates a thread once a hwrng registers, and uses
> the previously established add_hwgenerator_randomness() to feed
> its data to the input pool as long as needed. A derating factor
> is used to bias the entropy estimation and to disable this
> mechanism entirely when set to zero.
Closes: #96067
It looks like the cpu type part of modalias might have changed, my
systems (4.4.20 and 4.7.2) show something like the following:
```
cpu:type:x86,ven0000fam0006mod003F:feature:,0000,0001,0002,0003,0004,0005,0006,0007,0008,0009,000B,000C,000D,000E,000F,0010,0011,0013,0017,0018,0019,001A,001C,002B,0034,003B,003D,0068,006F,0070,0072,0074,0075,0076,007D,0080,0081,0089,008C,008D,0091,0093,0094,0095,0096,0097,0098,0099,009A,009B,009C,009D,009E,009F,00C0,00C5,0120,0123,0125,0127,0128,0129,012A,0140
```
Update the rngd modalias rule to match this so udev properly has
systemd start rngd.
Only one process can interact with the TPM module and
that process should be tcsd. The tpm_rng kernel module
should instead be loaded and /dev/hwrnd be used to
read the TPM random generator.
Also, log which random generator devices are used by
rngd on startup.
Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
