routine fsys_startup (
    bootstrap: mach_port_t;
    RPT
    openflags: int;
    control_port: mach_port_send_t;
    out realnode: mach_port_send_t);

Sent by filesystem on its bootstrap port upon startup. realnode is the node this filesystem is the translator for, opened with flags flags (O_NOTRANS is assumed even if not provided).