Filip Štědronský <r.lkml@xxxxxxxxxx>: > there are basically two classes of uses for a fantotify-like > interface: > > (1) Keeping an up-to-date representation of the file system. For this, > superblock watches are clearly what you want. > > [...] > > All those factors speak greatly in favour of superblock > watches. > > (2) Tracking filesystem *activity*. Now you are not building > an image of current filesystem state but rather a log of what > happened. Perhaps you are also interested in who > (user/process/...) did what. Permission events also fit mostly in > this category. > > For those it *might* make sense to have mount-scoped watches, for > example if you want to monitor only one container or a subset of > processes. > > We both concentrate on the first but we shouldn't forget about the > second, which was one of the original motivations for fanotify. My (employer's) needs are centered around (2). We definitely crave permission events with a filesystem scope. At the moment, you can avoid permission checks with a simple unshare command (<URL: https://lkml.org/lkml/2016/12/21/144>). So I must be able to see everything that is happening in my universe. It might also be useful to monitor a subuniverse of mine, but the former need is critical at the moment. As for "who (user/process/...) did what", the fanotify API is flawed in that we don't have a CLOSE_WRITE_PERM event. The hit-and-run process is long gone by the time we receive the event. That's more of a rule than an exception. Marko
