Sorry if I read this thread too hastily, but why not just keep /proc etc mounted, as was seemingly the way with s6-linux-init <=v0.4.x.x (and therefore slew)? Since the asymmetry is by nature, simply respecting it appears to be one minimalist way.
The umount command basically performs a "umount -a". I can add a list of filesystems that should be kept, but it's more ad-hoc code. It's ugly. But I guess the whole situation is ad-hoc anyway, so elegance isn't exactly what we're going for here :/ -- Laurent
