It is not hard but it hasn't caught on because having userspace scripts or daemons running tagging and indexing passes on the files in an existing file system is nowhere near transparent. Even if you use inotify or something to keep track of teh changses in real time, the illusion of transparency will leak sooner than later. And that's when your users' confidence and trust will vanish into the air.
Indexing has to be built in to the filesystem to make the searchs match the state of the filesystem 1-in-1. There's no other way.
I've seen this working live only in the Be Filesystem, or BFS. There you can be sure that if you add an image somewhere, another view of the filesystem will instantly contain the new file and removing it will again banish the image from all other views. The file either exists or doesn't, and you will never notice that a search returned information that isn't no more.
Indexing has to be built in to the filesystem to make the searchs match the state of the filesystem 1-in-1. There's no other way.
I've seen this working live only in the Be Filesystem, or BFS. There you can be sure that if you add an image somewhere, another view of the filesystem will instantly contain the new file and removing it will again banish the image from all other views. The file either exists or doesn't, and you will never notice that a search returned information that isn't no more.