Nick Stephen posted this URL for HTML documentation on the kernel
interfaces:

   http://www.osf.org/RI/MC/AD3/KI_REF/HTML/index.html 

There's also these four PostScript books available at:

   http://www-cgi.cs.cmu.edu/afs/cs/project/mach/public/www/doc/osf.html 

The books are far more comprehensive, but they're huge (all together they
fill two 3" binders), and I think they're a little out of date relative
to the current kernel.

jonh@cs.dartmouth.edu