Environment

Review Function Routines/Function Codes, which describes both the general environment on entry to your function routine and other programming considerations that your function routine should take into account.

If you decide to set up your subsystem to handle DOM processing calls, make sure that your function routine is in place before you enable the subsystem to handle SSI function code 14. IBM® recommends that you use the IEFSSVT macro to notify MVS™ that your subsystem should be given control whenever DOM Processing calls are made. IEFSSVT macro services are available only to dynamic subsystems. Subsystems that are not dynamic can use the IEFJSVEC service; see Building the SSVT and Enabling Your Subsystem for New Functions for more information.

DOMs occur frequently with MVS. Function routines should therefore be as efficient as possible. Do not code a function routine that enters an explicit WAIT or uses a system service that enters a WAIT because entering a wait can cause degraded system performance.

Data areas commonly referenced are mapped by the following mapping macros. IBM recommends you include them in your function routine:

IEFSSOBH
IEFJSSIB
IEFJSSOB
IEFSSDM
IHADOMC

The delete operator message mapped by IHADOMC represents a DOM.

The function routine receives control in the following environment:

Environment variable	Value
Minimum authorization	Supervisor state with PSW key 0
Dispatchable unit mode	Task
AMODE	24-bit or 31-bit
Cross memory mode	PASN=HASN=SASN
ASC mode	Primary
Interrupt status	Enabled for I/O and external interrupts
Locks	No locks held
Control parameters	The SSOB, SSIB, and SSDM control blocks reside in storage below 16 megabytes.
Recovery	The function routine should provide an ESTAE-type recovery environment. See z/OS MVS Programming: Authorized Assembler Services Reference EDT-IXG for more information on these macros. Failure to establish a recovery environment ends the processing of the current DOM if an abend occurs. The function routine's recovery should specify a retry point (address) and return 4 on the SETRP macro before returning to the system. Use the retry point to complete a normal return to the function routine's caller. When the function routine returns to its caller under these circumstances, it should indicate to the system, by setting both register 15 and the SSOBRETN to zero, to take no action against the message. See the next topic, Input Register Information, for how to specify to the system the action you want your function routine to take. Note: Although the system supports AMODE=24 SSI routines monitoring function code 14, IBM recommends converting these SSI routines to AMODE=31. In a future release, IBM may change the location of the SSOB, SSIB, and SSDM control blocks to reside in 31-bit storage.