DSM/Tape Catalog Management Programming Manual

SPI Programming Considerations
DSM/Tape Catalog Management Programming Manual—520481-003
3-6
Components of a Command Buffer
Components of a Command Buffer
A command buffer consists of an SPI message header and zero or more tokens.
These tokens in the command buffer can be parameter tokens, a maximum-response
token, or a context token.
SPI Message Header
The header for a SPI command message indicates that the buffer is for a SPI
command. The buffer header contains the command number and object-type number
for the command. The buffer header also includes positioning information used by
SSGET and SSPUT.
Parameter Tokens
You can supply parameter tokens in the command buffer to provide parameters for a
command. For example, to issue an ADD TAPEVOLUME command, you must include
a ZMCS-TKN-TAPEVOLUME token that contains the name of a tape volume to be
added to the DSM/TC catalog. Because many of the programmatic commands for
MEDIASRV require parameter tokens that are extensible structured tokens, you also
must include the ZMCS-MAP-ADD-TAPEVOLUME token if you issued the ADD
TAPEVOLUME command.
Maximum-Response Token
The command buffer can also contain the ZSPI-TKN-MAXRESP token, which specifies
the maximum number of response records the requester can accept in a single
response buffer received from the MEDIASRV process.
Context Token
The command buffer contains a context token for some commands. The reply to the
command contains the ZSPI-TKN-CONTEXT token if there are more objects in the set
to be processed. To continue the command, the application program copies the ZSPI-
TKN-CONTEXT token to a duplicate of the original command message and resubmits
the command buffer to the MEDIASRV process.
Components of a Response Buffer
The response records in a reply (response) buffer include all of the information that
results from the action of a single command on a single object, plus error or warning
information about the command itself: the message header, response tokens, the
context token, the return token, and error lists.
Message Header
The message header for a response buffer contains the command number and object
type number that resulted in the reply, the DSM/TC subsystem ID, and so on.