Open Stack

> Why accept it?
> 
> * It's low risk but needed refactoring that will make the code that has
> been a source of occasional bugs.
> * It is very low risk internal refactoring that uses code that has been
> in tree for some time now (BDM objects).
> * It has seen it's fair share of reviews

Yeah, this has been conflict-heavy for a long time. If it hadn't been, I
think it'd be merged by now.

The bulk of this is done, the bits remaining have seen a *lot* of real
review. I'm happy to commit to reviewing this, since I've already done
so many times :)

--Dan