SPI Common Extensions Manual

Subsystem Control Point

SPI Common Extensions Manual—427508-001

3-2

SCP Command-Message Processing

An SCP process can support up to 1000 management applications and 256

subsystems at a time. Using an SCP process to route commands and responses

relieves a subsystem from maintaining many concurrent openers—a single open from

the SCP process might suffice.

Message Size

The message buffer in your application, which holds both command messages and

responses, must have a length of ZCOM-VAL-MAX-RSP-BUFLEN. The command

message cannot have a length longer than ZCOM-VAL-MAX-REQ-BUFLEN. If it does,

the SCP process returns a response with the error number ZCOM-ERR-SPI-ERR.

Message Routing

A command routed through an SCP process must contain the identity of the subsystem

manager process to which the command is directed. The SCP process uses this

information to forward the command message to the correct subsystem process. In

C-series systems, the SCP process extracts this information from either the

ZCOM-TKN-OBJNAME token or the ZSPI-TKN-MANAGER token. In D-series

environments, the variable length string token ZCOM-TKN-XMGR conveys the

manager process name. (For subsystem-specific information about the appropriate

method of specifying the manager process name, see the subsystem’s management

programming manual.)

Only one ZCOM-TKN-XMGR token or ZSPI-TKN-MANAGER token is allowed in a

request.

To use SCP to derive the manager process name from the tokens in the request buffer:

1. If ZCOM-TKN-XMGR appears in the request, SCP uses its value as the identity of

the manager process. Otherwise, the search continues with Step 2. (If there is

more than one XMGR token or if ZSPI-TKN-MANAGER is also present, the

request is rejected.)

2. If Step 1 fails and ZSPI-TKN-MANAGER appears in the request, SCP uses its

value as the identity of the manager process. Otherwise, the search continues with

Step 3. (If the request includes more than one MANAGER token, or if an XMGR

token is also present, the request is rejected.)

3. If Steps 1 and 2 fail, ZCOM-TKN-OBJNAME appears in the request, and SCP can

extract a name of the form \node.$proc or $proc from the value of its first

occurrence in the buffer, SCP uses this value as the identity of the manager

process. Otherwise, the request is rejected.

If the process name sent in any of these three tokens is invalid or if the process does

not exist, SCP returns an error, and the command is rejected.