I had my Ph.D. student (Andrew Ohana) spend a while last summer implementing exactly this using python-inotify, since I wanted it to greatly improve the efficiency of https://cloud.sagemath.com, which makes very frequent snapshots. It's pretty solid and is on github: https://github.com/ohanar/bup/tree/bup-watch He's been busy with his actual math thesis work and teaching, so hasn't got this upstreamed into bup. It also depends on changes he made to bup to store the index using sqlite instead of some custom format.