You could do worse than Mach ports

[Peter da Silva]

>     I have to say that I can *easily* envision the work involved in taking
>     DragonFly to that goal.  I don't think it makes sense to turn everything
>     into a message port and message...

No, I don't think I meant to imply that. And I don't think that
it's a good idea to put components in separate protection domains
unless we have a reason to. The idea that you *can* take a chunk
of the system (even if not just ANY chunk) and pull it into userland,
though, that's really attractive even though you'll almost never
do it... but when you need to you REALLY need to. :)

>     User mode is not a big deal.  It really isn't.  All it really is is a
>     private MMU context, that just happens to be a bit more expensive to
>     switch into and out of, and which we just happen to feel free to page
>     in and out at will.

Uh-huh. And with a little bit of work we can reduce that cost by
spreading it over more messages.