"Now, the purpose of a module's entry and exit routines
is simple: it's your job to invoke everything that needs to happen
upon module loading (allocating memory, registering devices, etc.),
as well as module unloading (returning memory, unregistering
devices, etc.), and here's the most important part: You have to
clean up after yourself completely.
"Let me say that again, with feeling: Whatever you choose to do
in a module's entry routine must be explicitly undone upon exit.
Unlike what you might be used to in user space programming, you
can't leave open files lying around or space dynamically allocated,
knowing that someone is going to tidy up after you when your
program eventually terminates. This is kernel space programming--no
one is there to pick up after you. If you forget to deallocate some
space that was dynamically allocated with, say, kmalloc(), then
you've just introduced a memory leak, and other kernel programmers
will not look kindly upon that."
