SO_MREADOFF and M_STOP

The SO_MREADOFF and M_STOP messages request devices to start or stop their output. They are used to produce momentary pauses in a device's output, not to turn devices on or off.

The message format is not defined by STREAMS and its use is developer dependent. These messages may be considered special cases of an M_CTL message. These messages cannot be generated by a user-level process and each is always discarded if passed to the stream head.