For scheduler activations, a way for the kernel to arrange to call a
specific userlevel function is needed, as well as passing it
arguments.

I suspect that once the *context() stuff is done, we can use that.
The application would set up the context, and the kernel can clone it
and restore it when it wants to run again.

Does this seem reasonable?

Usually, kernel info is returned via a device/socket, but we can't
exactly do that in a threads package...

--Michael