Monitoring dynamic LPA processing

Dynamic LPA services allow modules to be added to or deleted from LPA after IPL. Because any product can own LPA modules and have an interest in updating their control structures, an exit (CSVDYLPA) is provided from dynamic LPA services. Providing lists of modules added to or deleted from LPA, the exit is intended to be used as a notification mechanism so that products can update internal control structures with the new module addresses.

The system takes no action as a result of exit routine processing.

CSVDYLPA routine processing. The CSVDYLPA routine, if defined, receives control when the system processes a dynamic LPA services request, either via

the CSVDYLPA macro,
the SETPROG LPA operator command, or
an LPA statement within PROGxx referenced by the SET PROG=xx operator command.

Dynamic LPA services are documented in z/OS MVS Programming: Authorized Assembler Services Reference ALE-DYN. The CSVDYLPA exit routine can be used to update control structures that had captured the addresses of particular LPA modules, upon replacement of a module within LPA.

Installing CSVDYLPA. Use the CSVDYNEX macro to connect a routine to the dynamic LPA processing. For example:

         CSVDYNEX REQUEST=ADD,                                         X
               EXITNAME=THEEXIT,                                       X
               MODNAME=THEMOD
  .
  .
  .
THEEXIT  DC CL16'CSVDYLPA'
THEMOD   DC CL8'DYLPARTN'

The exit routine must be reentrant and AMODE 31.

See Using dynamic exits services for a description of CSVDYNEX processing.

CSVDYLPA routine environment. The routine receives control in the following environment:

In supervisor state with PSW key 0.
In dispatchable unit mode of task, running under the address space, task and request block of the caller of CSVDYLPA.
In cross memory mode of PASN=HASN=SASN.
In AMODE 31.
In primary ASC mode.
Enabled for I/O and external interrupts.
With no locks held.
With parameter areas in the primary address space. The parameter list is described below. The module information area pointed to by the parameter list is mapped by the CSVLPRET macro.
In the address space in which CSVDYLPA REQUEST=ADD was issued, or the master scheduler address space for the SETPROG or SET PROG operator commands.
The exit uses fastpath=yes for CSVDYNEX REQUEST=CALL, and will retry (continue calling) on an exit routine error.
With ENQ resource SYSZCSV.CSVDYLPA held exclusive.
The programmer should not use CSVDYLPA REQUEST=ADD or CSVDYLPA REQUEST=DELETE within the exit routine.

CSVDYLPA routine recovery. The routine should provide its own recovery, using ESTAE, ESTAEX, or SETFRR EUT=YES. If the exit routine ends abnormally, its recovery routine will get control before the recovery routine established by the CSVDYLPA service.

You can use the ADDABENDNUM and ABENDCONSEC parameters on the CSVDYNEX REQUEST=ADD macro to limit the number of times the exit routine abnormally ends before it becomes inactive. An abend is counted under the following conditions:

The exit routine does not provide recovery, or the exit routine does provide recovery but percolates the error.
The system allows a retry, that is, the recovery routine is entered with bit SDWACLUP off.

By default, the system disables the exit routine when it abends on two consecutive calls.

Programming considerations. The programmer should include the CSVLPRET macro which maps one of the input parameters and provides equate symbols for use by the exit routine.

Code the exit routine to be reentrant, and to have AMODE 31.

The exit routine should not modify the parameter areas.

Registers at entry to CSVDYLPA routine. The contents of the registers on entry to a CSVDYLPA routine are:

Register: Contents
0: Contains no information for use by the exit routine
1: Address of parameter area
2-12: Contains no information for use by the exit routine
13: Address of 72-byte standard save area
14: Return address
15: Entry point address

Parameter area at entry to CSVDYLPA routine.

Word 1

Address of fullword containing 0 (symbol CsvdylpaFunctionAdd) if processing an ADD request or 1 (symbol CsvdylpaFunctionDelete) if processing a DELETE request.

Word 2

Address of fullword containing the number of module entries in the area pointed to by parameter list word 3.

Word 3

Address of module information entries. The entries are contiguous, each mapped by DSECT LPMEA in macro CSVLPRET. The entries are not sorted. Only entries with bit LpmeaSuccess on should be processed; others should be skipped. When processing a delete request, the information presented for a deleted entry indicates information about the now-current copy of the entry. If, after the deletion, the entry still exists in LPA, the LpmeaEntryPointAddr, LpmeaLoadPointAddr, and LpmeaModlen fields are provided, if available. If no entry still exists in LPA, then a value of X'7FFFFFFF' is presented in the LpmeaEntryPointAddr field, and the LpmeaLoadPointAddr and LpmeaModlen fields do not contain valid data The exit routine must not modify this area, as doing so would compromise the information provided to subsequent exit routines called for the same event.

Word 4

Address of 512-byte work area on a doubleword boundary. This area can be used as a dynamic area by the module, possibly allowing it to avoid doing GETMAIN/FREEMAIN on entry/exit.

Word 5

Address of 12-byte area that is the DDNAME (bytes 0-7) and DCB (bytes 8-11) address used for the ADD request. The DDNAME will be 0s for the following cases:

a DELETE request;
an ADD request that specified BYADDR=YES; or
an ADD request that specified DCB, DCBPTR, MASKDCB, or MASKDCBPTR.

The DCB address will be 0s for the following cases:

a DELETE request or
an ADD request that specified BYADDR=YES.

The DDNAME and/or DCB address could be used to locate the name of the data set from which the module was fetched, using field LpmeaSuccessConcatNum to identify the number of the data set within the allocated concatenation.

At the time the exit routine is called, the DDNAME will still be allocated and the DCB will still be open.

Registers at exit from CSVDYLPA routine. Upon return from CSVDYLPA processing, the register contents must be:

Register: Contents
0-1: Need not contain any particular value
2-13: Restored to contents at entry
14: Need not contain any particular value
15: 0

Disassociating CSVDYLPA. Disassociate the routines from CSVDYLPA when they should no longer receive control. Use the CSVDYNEX macro to disassociate the routines. For example:

         CSVDYNEX REQUEST=DELETE,                                      X
               EXITNAME=THEEXIT                                        X
               MODNAME=THEMOD
  .
  .
  .
THEEXIT  DC CL16'CSVDYLPA'
THEMOD   DC CL8'DYLPARTN'

Coded example

EXITRTN  CSECT
EXITRTN  AMODE 31
EXITRTN  RMODE ANY
*
* entry linkage
*
         STM   R14,R12,12(R13)
         LR    R12,R15
         USING EXITRTN,R12
*
* Processing
*
         L     R2,0(R1)        Get address of function code
         CLC   0(4,R2),FUNCDEL Is this DELETE?
         BE    DONE            Yes, Done
         L     R2,4(R1)        Get address of number of entries
         ICM   R2,15,0(R2)     Get number of entries
         BZ    DONE            No entries, done
         L     R3,8(R1)        Address of module information area
         USING LPMEA,R3        Establish using
TOP      DS    0H              TOP of loop
         TM    LPMEAOUTPUTFLAGS0,LPMEASUCCESS Is this entry valid?
         BZ    NEXT            No, move on to next
         CLC   LPMEANAME,MYMODULE Is this my module?
         BNE   NEXT            No, move on to next
*
* Put code here possibly to move field LpmeaEntryPointAddr to
* your own data area
*
NEXT     DS    0H              Continue loop
         LA    R3,LPMEA_LEN(R3) Point to next entry
         DROP  R3              Release using
         BCT   R2,TOP          Decrement, see if done
DONE     DS    0H
*
* exit linkage
*
         LM    R14,R12,12(R13)
         SLR   R15,R15
         BR    R14
MYMODULE DC    CL8'MODULEA'
FUNCDEL  DC    A(CSVDYLPAFUNCTIONDELETE)
R1       EQU   1
R2       EQU   2
R3       EQU   3
R4       EQU   4
R12      EQU   12
R13      EQU   13
R14      EQU   14
R15      EQU   15
         CSVLPRET
         END