SNAX/XF and SNAX/APN Configuration and Management Manual

PTrace Reference for SNAX/XF and SNAX/APN
SNAX/XF and SNAX/APN Configuration and Management Manual—425836-006
15-6
Message-System Overview

LU Network Services (LUNS)

Passthrough control
The service manager receives protocol communications from the line handler through
SNAX level 4. It receives SPI requests and responses, from SCF and other
management applications, through the Subsystem Control Point (SCP).
The service-manager functions do not generate separate trace-record types. However,
the service-manager trace-record displays identify the names of the functions and
services invoked.
Message-System Overview
As described in the SNAX/XF Application Programming Manual and the SNAX/APN
Application Programming Manual, applications using SNAX send and receive SNA
protocol communications through the Guardian file-system interface. The file system,
in turn, uses the services of the message-system interface within the NonStop Kernel.
In addition, SNAX and related NonStop processes perform some internal
communications using the message-system interface.
The details of the message-system interface are not published and are subject to
change. However, because the names of message-system functions are displayed in
some SNAX trace records, a basic understanding of this interface can be useful when
you are analyzing traces.
The message-system functions of interest for SNAX traces are LINK, LISTEN,
WRITELINK, LDONE, and LCAN. The use of these functions is as follows:
1. The entity initiating a communication performs a LINK to send a request to the
responding entity.
2. The responding entity is notified that a request is pending. It then performs a
LISTEN to receive the request.
3. The responding entity processes the request.
4. The responding entity performs a WRITELINK to send its response to the initiating
entity.
5. The initiating entity is notified that a completion message is pending. It performs
LDONE processing to retrieve the completion information.
6. If the initiating entity, having sent a request via LINK, subsequently wants to cancel
its request before completion, it performs LCAN processing. Both the initiating
entity and the responding entity may need to perform some cleanup, depending on
how much processing was done before the LCAN occurred.