MFS online error detection

This topic describes how IMS detects input errors, output errors, and paging errors for MFS.

Output errors

MFS output errors are detected after IMS has already sent the response to any preceding input. If an error is detected during MFS MOD or DOF block selection, an error message is sent as ATTACH SYSMSG, and the IMS message is returned to the message queue for retransmission. If the MFS test mode is in effect, it is reset.

Invalid page requests cause error messages to be sent.

Input errors

An error message is sent and the input message is rejected if one of the following occurs:
  • An error is detected during MFS MID or DIF block selection.
  • A nonzero version ID is received in the data descriptor FM header and it does not match the version ID in the MFS descriptor.
  • An error is detected during DPAGE selection (that is, no condition is satisfied on matching the DPAGE label with the DSN in the DD FM header or the COND= with the data).
If one of the following errors is detected during multiple DPAGE input, an error message is sent to the other subsystem, and the input message is rejected:
  • Multiple transmission chains. More data is present in the chain than defined for the DPAGE selected.
  • Any mapped-input LPAGE contains no data segments (as a result of segment routines canceling all segments, for example).
If one of the following errors is detected during a single DPAGE input (that is, multiple DPAGE input is not requested in MFS definitions), an error message is sent and the input message is rejected:
  • A single transmission chain is received and contains more data than defined for the DPAGE selected.
  • Multiple transmission chains are transmitted.
  • The mapped-input message contains no data segments (as a result of segment routines canceling all segments, for example).

If the input message is canceled by the User Segment Edit exit routine, or if a User Segment Edit exit routine failure is detected, an error message is sent to the other subsystem. In the latter case, the input message is rejected.

Paging errors

An error message is sent to the other subsystem when an invalid paging request (QMODEL FM header) is detected:
  • The QNAME parameter on the QGETN or QGET function management header does not match the ATTDQN/SCDDQN parameter on the ATTACH or SCHEDULER FM header sent by IMS. An attached demand-paged output message is returned to the message queue for retransmission. A scheduled demand-paged output message continues to wait for a QGETN with the proper QNAME specified.
  • The QORG parameter on the QGETN or QGET FM header is invalid. The output message is returned to the message queue for retransmission.
  • The QGETN FM header is received and no output message is in progress.
  • A paging request other than QGETN is received as the first input following scheduled demand-paged output (ATTACH SCHEDULER), or a QSTATUS FM header is sent by IMS because of an invalid cursor on a paging request.
  • The QGETN FM header is received for an OLP demand-paged output and current cursor position is at the last page.
The QGET FM header causes a QSTATUS or an error message to be sent in the following cases:
  • Between messages.
  • Non-OLP demand-paged output message is in progress. An error message is sent and the output message is placed on the queue for retransmission.
  • Cursor value does not contain a valid 2-byte binary number. An error message is sent, and the output message is placed on the message queue for retransmission.
  • Cursor value is outside the range for the output message.