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 |
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Does the same as putmsg(2) and enables the caller to specify a priority band for the message |
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Retrieves M_DATA, M_PROTO, or M_PCPROTO or high priority messages from the stream head, and places the contents into two user buffers |
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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.