STREAMS-UX Programmer's Guide (February 2007)

Appendix C
239
C Message Types
This section describes the fixed set of message types recognized by STREAMS/UX. As described in Chapter 3,
“Messages,” STREAMS messages can be classified as ordinary (non-priority) messages that are subject to flow
control, and high priority messages that are not subject to flow-control.
STREAMS defined message types differ in their intended purposes, their treatment at the stream head, and
their message queueing priority. STREAMS does not prevent a module or driver from generating any
message type or sending it in any direction on the stream. However, established processing and direction
rules should be observed. Stream head processing is fixed according to the message type, although certain
parameters can be altered.