Right now kqueue, the kernel event mechanism, only attaches to individual files. This works great for sockets and the like but doesn't help for a directory full of files.

The end result should be feature parity with linux's inotify (a single dir worth of notifications, not necessarily sub-dirs) and the design must be good enough to be accepted by other users of kqueue: osx, freebsd, etc

For an overview of inotify start on wikipedia.
Another example API is the windows event api.

I believe most of the work will be around genfs, namei, and vfs.