C and real hardware

[utzoo!watmath!bstempleton]

Clearly "Unregister" is not the right name for this kind of type.
In general, you are correct in a need for this type.  Not just for
memory-mapped i/o devices, but also for any machine with multiple
processes sharing memory.   Perhaps the atribute "Shared" is good for
in a way you can consider a memory-mapped i/o location to be shared between
the processor and the device.