The "init" in this project is a small application invoked by the kernel
which does basic system initialization and execs into svchub. It does
few very system-specific things that are difficult to do otherwise and
which do not really belong in svchub. Moving these out of svchub makes
svchub much easier to test and work with, and it also allows replacing
this code to fit the needs of a particular system.

There are two of them here right now, but more might be added.
The two are: `init` which is meant for systems starting from the real
root (i.e. those where the kernel mounts the rootfs), and `rdinit`
for initramfs. Now the `init` one is essentially a stub, it doesn't do
much, but it does effectively replace `rdinit` so the same svchub stuff
can be re-used between initramfs and real-root setups.

One things that these tools have to do (and which is very difficult to do
otherwise) is setting up fds 0, 1 and 2. If Linux fails to initialize
its console devices, it will invoke init with those fds free. Which is no
good since almost everything assumes fd 2 is stderr.

This is probably the right place to put a tool that would wait e.g. for
a USB UART console, but that's implemented right now.


Initramfs specifics
~~~~~~~~~~~~~~~~~~~
See ../../doc/initrd.txt for more information.

The `init` is a small part of `rdinit` which acts as a short-time pid 1
supervisor and also as udev event monitor while the system runs from initrd.
Once it's done switching to the real root, it attempts to invoke svchub
by calling a script in /base/etc/boot.


Real root startup
~~~~~~~~~~~~~~~~~
Without initrd, the kernel would attempt to start /sbin/init or a few other
options outside of /base; `rdinit` skips this step completely, however, if
the system can start without initrd, then `init` can be placed to /sbin
(or symlinked from /sbin) as a bridge to get the system to run svchub.

Since `rdinit` mounts /dev and /sys and `init` is supposed to be a drop-in
replacement, `init` also mounts /dev and /sys. That was deemed acceptable
because the chances or ever running a Linux system without those two are
very small. Anything else has to be mounted in the startup script.