I know that it is possible to register a new default VFS, which is in my case a VFS shim forwarding all VFS commands to the previous default VFS, but performing some additional actions. However, a user can overwrite the default VFS by specifying the parameter "vfs=" in the URI on opening a database. What I want to accomplish now, is to respect the "vfs=" parameter, but adding the special VFS shim on top of the user-specified VFS nevertheless. Is that somehow possible? How could that be accomplished? Thanks for any hints.