Message Direction
Various
system calls let the user create messages and send them downstream and prioritize
the messages.
Table 4-3 Send and Receive Messages
| Creates a message from the caller supplied control and data buffers and
sends the message downstream
|
| Does the same as putmsg(2) and
enables the caller to specify a priority band for the message
|
| Retrieves M_DATA, M_PROTO, or M_PCPROTO or high priority messages from the stream head, and places the
contents into two user buffers
|
| Does the same as getmsg(2) and enables the caller to
specify a priority band for the message
|
|
The stream head guarantees that the control part of a message generated by putmsg(2) is at least 64 bytes long. This promotes
reusability of the buffer. When the buffer is a reasonable size, modules and drivers
may reuse the buffer for other headers.
stropts.h contains the
specification of strbuf, which describes the control and data buffers.