gtpi1m4i | System Installation Support Reference |
The select a host user exit, UAPN, allows you to select the TPF processor
in the loosely coupled complex to assign to a new LU-LU session. UAPN
is also valuable in a uniprocessor TPF environment because it allows you to
select a path (link) for the session.
The TPF system invokes UAPN when a session activation request (LOCATE
command) is received on the CP-CP sessions.
Input
- R1
- RVT1 address of the remote LU
- R2
- RVT1 address of the local TPF LU
- R5
- Pointer to the table containing active links for the TPF loosely coupled
complex. The ITAPST DSECT maps out the entries in this table.
- EBW000
- Indicator byte (zero or more bits can be set)
- X'80'
- The TPF LU is processor-unique, or the remote LU is an LU 6.2 node
that already has one or more sessions with a TPF processor; therefore,
the TPF processor has been selected.
- X'40'
- The APPN network provided a suggested route for the LU-LU session.
- EBW001
- The CPU ID of the selected or suggested TPF processor. The value of
this field is based on the value of the EBW000 field as follows:
- If EBW000 is 0, EBW001 is not defined.
- If EBW000 bit X'80' is on, then EBW001 contains the selected TPF
processor and this value cannot be changed by the user exit.
- If EBW000 bit X'80' is off and bit X'40' is on, EBW001
contains the suggested TPF processor, which was determined by the suggested
link provided by the APPN network. You can choose to not use the
selected link and change this value.
- EBW010-EBW017
- Mode name of the session
- EBW020-EBW027
- The ALS name of the suggested link. This field is defined only when
bit X'40' in field EBW000 is set.
Programming Considerations
- IBM provides sample code for UAPN, which sets the return code in field
EBW002 to 0 indicating that the TPF system should select the TPF processor to
use for the LU-LU session. A round-robin method is used to
distribute session activation requests among the active processors in the
loosely coupled complex that are in CRAS state or above.
- Data levels D0 and D1 must not be modified. All other data levels
are available for use by the user exit.
- If the TPF processor has been chosen (EBW000 bit X'80' is on), you
cannot change the selected TPF processor. However, you can select which
link to use.
- If the remote LU is the SLU, the APPN network may have included a
suggested path in the LOCATE. If so, the name of the suggested ALS,
along with the TPF processor connected to that link, are passed as input to
this user exit in fields EBW020-EBW027 and EBW001 respectively.
You have three choices in this case:
- Use the suggested link.
- Choose a different link, TPF processor, or both.
- Tell the TPF system to select the TPF processor (the APPN network will
select).
Return Values
- EBW002
- Option chosen by the user exit:
- 0
- The user exit did not select a TPF processor or a link. If the TPF
system has not already selected the TPF processor (EBW000 bit X'80' is
not set), the default logic in the TPF system will be used to select a TPF
processor. Regardless of the value of field EBW000, the APPN network
will select the link.
- 1
- The user exit selected a TPF processor and, optionally, a link.
If the TPF system has not already selected the TPF processor (EBW000 bit
X'80' is not set), field EBW001 must contain the CPU ID of the TPF
processor you selected. The processor you selected must be in CRAS
state or above.
If you also selected a link, field EBW020-EBW027 must contain the
name of the selected ALS.
- 2
- The user exit chose to use the suggested path. This return code is
valid only if EBW000 bit X'40' was set on input to UAPN.
- EBW001
- CPU ID of the selected TPF processor.
- EBW020-EBW027
- ALS name of the link selected for the LU-LU session.