A file system that will record a few pre-determined data structures in one or more files of their file system. Initially it will provide a simple lookup table functions that could be used once a state file has been read into memory. Later on it could be expanded to more complex and exotic off-line data structures such as B-trees [Elmasri94].
Since files in this file system will be completely under the control of the file system, it could be made hidden from users. User processes would not need to be able to modify these files. However, it would be useful for users to be able to list and read them for logging, reporting, and debugging purposes. In other words, it may be a read-only file systems as far as user-processes are concerned.
Statefs itself cannot be directly interposed upon. It can only be accessed within the implementation of another interposeable module (via $0, as described in Table tab-fist-decl). Statefs sole existence is to augment an existing file system's functionality, not to be the functionality itself. Therefore, at the moment, I see no reason to allow Statefs to be directly interposed upon.