> >The presence of a kernel header does not mean that it's a published or
> >stable API. It's unfortunate, but vbetool shouldn't be using machine/pio.h
> >and it should be fixed.
> 
> What API should it be using?

presumably, not the underscore-prefixed versions - e.g.
outb() instead of __outb,
inb() instead of __inb, etc.