We already have this, its called inotify (and if I'm not mistaken,
beagle already uses it). Several years ago when it was still a little
flakey patch, I built a custom filesystem indexer into an enterprise
search engine using it (I needed to pull apart Unix mbox files). The
only trouble of course is the action is triggered immediately, which
may not always be ideal (but that's a userspace problem)
--
Matt
-