Use seedrng for seeding the random number generator

[zx2c4]

The RNG can't actually be seeded from a shell script, due to the
reliance on ioctls. For this reason, the seedrng project provides a
basic script meant to be copy and pasted into projects like OpenRC and
tweaked as needed: https://git.zx2c4.com/seedrng/about/

This commit imports it into OpenRC and wires up /etc/init.d/urandom to
call it. It shouldn't be called by other things on the system, so it
lives in rc_sbindir.

Closes #506.

---

I don't actually have an OpenRC system handy to test this on, so testers would be welcome here.

CC @thesamesam @williamh @vapier

[zx2c4]

@thesamesam @williamh @vapier Any of you should feel free to take over this pull request entirely and add whatever tweaks you think are required.

[ncopa]

I don't actually have an OpenRC system handy to test this on, so testers would be welcome here.

I applied to my workstation and it didn't end up in disaster so far. And output of /dev/urandom still looks random 😃

I am adding this patch to Alpine Linux edge for wider testing. Are there any specific things we should look for?

[zx2c4]

I applied to my workstation and it didn't end up in disaster so far.

@ncopa Would you mind uploading your elog from a few boots, including the first one that uses this? Would be curious to see it progressing.

You also might want to wait until @williamh has had a pass at it. And actually I've already made some changes since your backport.

[thesamesam]

I'm happy, it WFM, and I don't see a problem with letting it sit in ~arch in Gentoo at least for a bit, just like Alpine is doing in edge.

[zx2c4]

Cool, sounds like a plan then. 👍

[zx2c4]

Note that were it not for having to keep those Makefiles around, I would have just split up the urandom init.d/conf.d file into one for Linux and one for BSD, since that seems more possible with Meson, instead of this awkward thing I'm doing now where they're kept together. As a note for the future when the Makefiles go away, we might want to do this.

[zx2c4]

@williamh wants to rewrite this or something, so closing this and letting him handle it.

[zx2c4]

Reopening on the off chance that you want to merge this, as-is, and then apply your own stuff on top of it.