DFHMIRS executable module

Entry points

DFHMIRNA

Called by

Task initiation

Description

The mirror program is called when a request to access a resource is received from a remote CICS® system with an IPIC over TCP/IP, MRO, or ISC over SNA connection. DFHMIRS controls the receipt of requests and transmission of replies. For non IPIC there is only one transaction which calls the mirror program, but for IPIC connections the Listener task, CIEP handles control flows and attaches a mirror task as required.

DFHMIRS processes requests from these systems:
  • MRO-connected systems
  • LU6.1 connected systems
  • LU6.2 sync level 1 connected systems
  • LU6.2 sync level 2 connected systems
  • IPIC-connected systems

DFHMIRS is defined as a threadsafe program. For IPIC connections only, CICS runs DFHMIRS on an L8 open TCB whenever possible. To enable file control operations to run on the open TCB as well, which can produce performance benefits, you must specify the system initialization parameter FCQRONLY=NO for the CICS system where DFHMIRS runs. For other connection types, CICS does not run DFHMIRS on an open TCB.

For a non-IPIC connection the input to DFHMIRS consists of a TCTTE representing the session between CICS and its session partner and a TIOA containing the function shipping request. The TIOA is passed to DFHXFP (transformer 2) for conversion of the request from transmission format to the parameter list format required for DFHEIP or DFHDLI. If the data requires conversion (transaction CPMI), an EXEC CICS LINK is used to link to the data conversion program DFHCCNV, passing a COMMAREA that contains the EXEC CICS parameter list for the request where applicable. DFHMIRS then passes the request to DFHEIP or DFHDLI for execution.

On return from DFHEIP or DFHDLI, the data conversion program is called to convert the reply (if applicable), and then the transformer program DFHXFP (transformer 3) is called to convert the reply parameter list to transmission format. DFHMIRS then determines the DFC to send with the reply and transmits the reply to the requesting system. If the mirror task has modified protected resources, it continues receiving requests and transmitting replies until a sync point request is received from the remote system.