[fuse-devel] Using FUSE as a filter driver and mount/unmount permission asymmetry

[Jens M. <jen...@le...>]

Hello together,

I am currently investigating how FUSE could be used to implement a filesystem filter (in the same way as it is possible in Windows through filesystem minifilter drivers). I started with a very simple FUSE driver that simply "mirrors" the contents from a directory A to the FUSE mountpoint B (by forwarding the calls to the lower filesystem). No problem, works like a charm. If I use the same approach to mirror the contents of A inside of A itself (which means I am just introducing an indirection through my FUSE driver) it fails (probably because of an endless loop). 

A similar problem would occur if I want to receive inotify notifications from the lower filesystem (which would be triggered by my FUSE driver). I know that I could simply notify myself from the FUSE driver, but since I have the inotify code already it would be an extra effort to add this functionality.

Do you see a way how this could work? 

Another issue I faced during my experiments: is it normal that a user A who mounted a FUSE filesystem (through fuse_mount(), fuse_new(), etc... in an application) is not able to unmount it by himself (through fuse_unmount() in the same application)? User A is not member of the 'fuse' group... and I am a little bit confused: why is a user not allowed to "revert" an action he was able/allowed to do before?

Thanks in advance for your help and comments

Jens