>  a) don't chroot anything.
>  b) init never chroots itself, but does run /etc/rc in a chroot,

Unless someone has fixed a bunch of stuff in the kernel, then at least
the part of /etc/rc that handles fsck / and mounting it rw, needs to be 
unchrooted.   For this purpose I don't run /etc/rc chroot'd, but move the
bulk of the functionality to a separate rc (rc.chroot), then /etc/rc runs
that chroot'd (using the value of $CHROOT passed from init) after 
making / writable. 

>  d) init chroots itself, and then execs /sbin/init inside the
>     chroot.

This is a bit like what I do but the chroot is done in the "real" init.

--sjg