Message Classes

The concept of message class has been included to accommodate possible SAF extensions. The messages described above are all class 1 messages. None of these messages contains a variable data portion; all pertinent information is contained in the message header.

If new messages are added to the protocol, they will be defined as new message classes (for example, class 2). The first message the sac sends to a port monitor will always be a class 1 message. Since all port monitors, by definition, understand class 1 messages, the first message the sac sends is guaranteed to be understood. In its response to the sac, the port monitor sets the pm_maxclass field to the maximum message class number for that port monitor. The sac will not send messages to a port monitor from a class with a larger number than the value of pm_maxclass. Requests that require messages of a higher class than the port monitor can understand will fail. For Solaris, always set pm_maxclass to 1.

For any given port monitor, messages of class pm_maxclass and messages of all classes with values lower than pm_maxclass are valid. Thus, if the pm_maxclass field is set to 3, the port monitor understands messages of classes 1, 2, and 3. Port monitors may not generate messages; they may only respond to messages. A port monitor's response must be of the same class as the originating message.

Since only the sac can generate messages, this protocol will function even if the port monitor is capable of dealing with messages of a higher class than the sac can generate.

pm_size (an element of the pmmsg structure) and sc_size (an element of the sacmsg structure) indicate the size of the optional data part of the message. The format of this part of the message is undefined. Its definition is inherent in the type of message. For Solaris, always set both sc_size and pm_size to 0.