This is a very minimal IRIX loadable device driver, written back when I had a nice little SGI O2. The best thing about the O2 was it took standard PCI cards offering the ability to extend the machine using standard PC cards.
The article describing how this all works is here.
Sadly I no longer have any SGI machines, let alone the O2 so I can't check that this code still compiles. The best place to go if you're interested in old SGI stuff is nekochan.