If an MFS has been installed onto the file being accessed, the MFS "traps" or "interrupts" the call to the underlying filing system. Instead of calling the BFS, OpenInsight calls the MFS first, passing it the same arguments that would otherwise have been passed to the BFS.
Because the full list of arguments is available to the MFS, including the name of the operation to be performed, the MFS can examine and manipulate any of the arguments.
