Hardware abstractions: bus_space

Used to abstract the CPU accessing devices, this
is done with opcodes like inw/outw on i386.

A bus_space can relate to a memory space or I/O address space.

First we create the mapping, ask nicely to use a slab of space
at a specified address, then we use the bus_space functions
to access the space.

bus_space_tag_t
Describes the address space we are using

bus_space_handle_t
Describes the subset of the space we are mapping


See the bus_space(9) manual page for more discussion.