Yes, Yes, I know... old thread...
But still... The Apple source code for fs_usage is available online, it's quite possible to compile it yourself. Of course, there ARE some caveats...
It's based on the Apple OS X's netbsd system calls, so some (ha!) editing would be needed...
Even comes with a complimentary Makefile (netbsd flavored, alas).
But if you call within the next 10 minutes, they'll even throw in a usable man page... all for free!
I've been watching too much late night infomercials.
(No refunds, batteries not included, do not return to store, some assembly required)
(and after looking through the code, and seeing your example, I do believe something could be created to do a 'subset' of fs_usage's features pretty quickly... let me tinker...)
I've got a working program, beginning to look similar to what you're looking for, have to do some more work on it to get closer, but you're all welcome to try it.
Bitbucket Hg Repository - fs_usage