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Initialization of the Input/Output System
Obviously, someone has to create all the processes just described and
initialize the mail boxes they use to communicate. As a result, the
"systeminit" procedure described
in the discussion of
kernel initialization should
actually be considered part of the code written for your input/output
sub-system. That routine should create all the processes needed for
the input/output system and initialize its data structures.
Somehow or other, we want to let user code get into the
picture. To make this possible, the last thing your "systeminit"
procedure should do is to call a function named "userinit". This
function will be responsible for creating the user processes that will
actually use your kernel and input/output system.