A filesystem "change journal" and other topics

But it should have worked since inotify was introduced. It's not really even up to knfsd, the notification hooks are mostly in lower level vfs code that knfsd calls. (And of course userspace servers like Ganesha couldn't avoid notifying even if they wanted to.)

Before inotify was introduced, there was dnotify, was was a poor fit since as I understand it only allowed directories. Sending the notification for a write to the parent directory is a little strange to start off with, for knfsd it's often impossible. Nevertheless looking through the history I see Neil Brown added code that attempts to do this on read and write in early 2004. Even on dnotify I expect notifications for other operations worked since it was introduced.

The harder problem again is notifying one client about changes that occurred on another. Yeah, in theory I guess you could do that with a separate protocol implemented in userspace. Sounds painful to me.