Description

The requirements for the caller are:

To use GETDSAB, the caller must include the DSAB mapping macro (IHADSAB), the CVT mapping macro (CVT), and the JESCT mapping macro (IEFJESCT).

The caller must provide or inherit serialization on the SYSZTIOT resource before calling the GETDSAB macro and while using the output addresses of the macro. The minimum required level of serialization is shared (SHR).

The GETDSAB service does not provide a recovery environment. Because the service runs in task mode, the system will use any recovery environment defined to the caller prior to invoking GETDSAB.

There are no restrictions or limitations for using this macro.

After the caller issues the macro, the system might use some registers as work registers or might change the contents of some registers. When the system returns control to the caller, the contents of these registers are not the same as they were before the macro was issued. Therefore, if the caller depends on these registers containing the same value before and after issuing the macro, the caller must save these registers before issuing the macro and restore them after the system returns control.

On input to the macro, register 13 must contain the address of an 18-word save area.

There are no performance implications related to GETDSAB.

The standard form of the GETDSAB macro follows.

The parameters are described as follows:

FIRST

NEXT

DCBPTR=dcb addr

DDNAME=dd addr

FIRST requests the first DSAB in the DSAB chain. The system uses the DSAB chain associated with the TCB specified by the TCBPTR parameter, or, if none is specified, by the current TCB.

NEXT requests the pointer to the next DSAB in the DSAB chain, following the one pointed to by the initial value in DSABPTR.

DCBPTR=dcb addr specifies the name of a pointer that contains the address of a fullword field. The fullword points to the DCB associated with a DD name. The system retrieves the DSAB pointer associated with the DCB.

When DCBPTR points to an open DCB, DCBPTR and TCBPTR are mutually exclusive.

Do not use the DCBPTR option for a DCB in a DCB OPEN exit, DCB ABEND exit, data management ABEND installation exit or the DCB OPEN installation exit.

When DCBPTR points to a closed DCB, the system selects the DSAB chain associated with the TCB specified by TCBPTR parameter, or, if none is specified, by the current TCB.

DDNAME=dd addr specifies a DD name associated with a DSAB. The system puts the address of the DSAB associated with this DD name into the fullword field specified by the DSABPTR parameter. The DSAB selected is that associated with the TCB specified by the TCBPTR parameter, or, if none is specified, by the current TCB. The dd addr is an 8-character, left-justified field, with trailing blanks. The dd addr may not contain all blanks.

,DSABPTR=dsab addr

Specifies the name of a required fullword field that will be set to the address of the desired DSAB.

When used with the NEXT keyword, DSABPTR must contain the address of a DSAB that was previously obtained by invoking GETDSAB with FIRST, DCBPTR, or DDNAME. The system will replace this initial address with the address of the next DSAB in the DSAB chain.

When used with the keywords FIRST, DCBPTR, or DDNAME, DSABPTR is an output field only.

Upon output, DSABPTR contains the address of the specified DSAB if the return code is zero. If the return code is not zero, DSABPTR contains 0.

,TCBPTR=tcb addr

Specifies the name of a pointer that contains the address of the TCB associated with the task for which DSAB information is requested.

When DCBPTR points to an open DCB, DCBPTR and TCBPTR are mutually exclusive.

The default, TCBPTR=0, requests the current TCB.

,RETCODE=retcode addr

Specifies the location where the system is to store the return code. The return code is also in GPR 15.

,RSNCODE=rsncode addr

Specifies the location where the system is to store the reason code. The reason code is also in GPR 0.

LOC=BELOW

LOC=ANY

Specifies whether or not GETDSAB should limit where it searches to find the DSAB corresponding to the input DDname.

LOC=BELOW, which is the default, searches only those DSABs residing below the 16 MB line

LOC=ANY searches both below and above the 16 MB line.

When control returns from GETDSAB, GPR 15 (and retcode addr, if you coded RETCODE) contains one of the following decimal return codes.

When control returns from GETDSAB, GPR 0 (and rsncode addr, if you coded RSNCODE) might contain one of the following decimal reason codes:

In this example, the first invocation of GETDSAB will set MYDSAB to the address of the first DSAB in the DSAB chain. MYRC will contain the return code.

           GETDSAB FIRST,DSABPTR=MYDSAB,RETCODE=MYRC
            .
            .
            .
           GETDSAB NEXT,DSABPTR=MYDSAB
            .
            .
            .
AUTO       DSECT
MYDSAB     DS   AL4
MYRC       DS   F

This technique can be used to get the DSAB for the first DD in a concatenation and then to step through the DSABs for all other DDs in the concatenation. It is the user's responsibility to determine when the DSAB for the last DD in the concatenation has been fetched, because a subsequent invocation of GETDSAB NEXT will simply return the next DSAB on the chain (if one exists), even if it is for a different DD statement.

If DCBPTR points to an open DCB, DCBPTR and TCBPTR are mutually exclusive. The request will fail with return code 12. MYDSAB will contain 0.

           GETDSAB DCBPTR=MYDCB,DSABPTR=MYDSAB,TCBPTR=MYTCB
            .
            .
            .
AUTO       DSECT
MYDSAB     DS   AL4
MYDCB      DS   AL4
MYTCB      DS   F