This type of file system is the most natural to generate as a user level file system. In-core kernel-resident file systems keep state that can be regenerated -- a vnode for every interposed file. An interesting observation is that inside NFS file systems, similar state is kept associated with an NFS file handle. That is exactly how Hlfsd and Amd are written: there exist nfs_fhandle structures for every file that is being represented by the file system.