Vector lists supplying information to the application

When the application program's OPEN macroinstruction successfully completes, each of two address fields in the ACB is set with a pointer to a variable-length storage area. These areas are located in storage that is read-only for the application program. The storage is addressable from the MVS™ address space in which OPEN is issued.

Each address field contains the address of a vector list. The two vector lists are:

The access-method-support vector list (pointed to by the ACBAMSVL field in the ACB DSECT). This list describes the VTAM® that processed the OPEN macroinstruction.
The resource-information vector list (pointed to by the ACBRIVL field in the ACB DSECT). This list specifies resource identifiers which might be unknown to the application program.

The format for vectors contained in the access-method-support vector list and the resource-information vector list is shown in Figure 1.

Figure 1. Format of vectors built by VTAM during OPEN processing

The diagram shows the format of vectors built by VTAM during OPEN processing. Vectors built by VTAM during OPEN processing have three fields. The first field indicates the total length including this field itself. The second field is the vector ID. The third field contains vector data.

You can reference the vector lists any time after the OPEN macroinstruction completes, and until the CLOSE macroinstruction or equivalent terminations, such as an ABEND, occurs. Information similar to this in the access-method-support vector list is also available at assembly time. See ISTGLBAL macroinstruction for a description of the information available at assembly time.

Applications that use the APPCCMD macroinstruction can also request information from VTAM in the APPCCMD vector list. Refer to the z/OS Communications Server: SNA Programmer's LU 6.2 Guide for more information.