atch descriptor.

    @param fd: The file descriptor returned by C{libc.inotify_init}.
    @type fd: L{int}

    @param path: The path to watch via inotify.
    @type path: L{twisted.python.filepath.FilePath}

    @param mask: Bitmask specifying the events that inotify should monitor.
    @type mask: L{int}
    r