A C D D P Q R
R
R
R
R S S S S T C 0 C E U U E E E E T E E E E E C N L S R
I C J P S R N T T V S E N B C G E E E L U V D C M E T
IUCV P E F R
E S I C Y B M A R C r1acro T C R I C V T E F A S M Param- T B E E R S K P eters E K L
ALL X X X ANSBUF X X ANSLEN X X
BUFFER X X X
BUFLEN X X CP X X X X X X X X X X X X X
DATA X X FCNCD X MASK X X
MF X X X X X X X X X X X X X X X MSGID X X X X X 1M X X MSGTAG X PATHID X X X X X X X X X X PRMDATA X
v A PRMLIST X X X X X X X X X X X X X X X PRMf1SG X X PRTY X X X X QUIESCE X X SRCCLS X X X TRGCLS X X X X TYPE X
USERDTA X X X X X USERID X
Vt'1B LOK X X X X X X X X X X X X X
Notes:
1. PRMLIST is a required parameter (others are optional).
2. The QUERY and TEST MESSAGE functions do not use parameters.
Figure 18. IUCV Function and IUCV Macro Parameter Relationships Inter-User Communications Vehicle 139

Invoking Communications between CP and a Virtual Machine Specify CP=NO when invoking an IUCV function from a virtual machine. The IUCV instruction is generated. If a label is specified for the parameter list, it must
be relocatable and addressable. The code generated by CP=NO modifies general
register 0. When the function is executed, the virtual machine must be in supervi­
sor state. CP=NO is the default. CP system services invoke the IUCV macro instruction specifying CP= YES. CP= YES generates a CALL linkage directly to the IUCV processing module (DMKIUACP). If a label is specified for the parameter list, it must be relocatable
and addressable. The code generated by CP= YES modifies general registers 0, 1
and 15. The invoker must supply an EXTRN statement for the entry point DMKIUACP. If VMBLOK= USER is specified with CP= YES, then a CALL linkage is generated
directly to the IUCV processing module (DMKIUACU). The invoker must supply
an EXTRN statement for the entry point DMKIUACU. Requests Initiated by the Virtual Machine
When a virtual machine wishes to establish communications with a CP system ser­
vice, it invokes the CONNECT function specifying the name of the desired CP service as the target virtual machine ID.
The IUCV communication processor receives control from the CONNECT func­
tion, gathers the external interrupt information and determines which service is
desired. The communication processor then locates the CONNECT entry point for
that service and, using CALL linkage, passes control to that entry point.
The CONNECT entry point for the requested CP system service inspects the
external interrupt data. It must either accept the connection or reject the con­
nection. To accept the connection, it invokes the ACCEPT function, specifying CP= YES. To reject the connection, it invokes the SEVER function specifying CP= YES. When the service module has finished responding to the incoming con­
nection request, it issues an EXIT (SVC 12) to return control to the communi­
cations processor.
When an incoming message for a CP system service is encountered, the communi­
cations processor gathers the external interrupt information and determines which
service is desired. The communication processor locates the entry point that proc­
esses incoming messages for the desired service and, using CALL linkage, passes
control to it.
The message processing module of the CP service then inspects the external inter­
rupt data. The CP service module must invoke the RECEIVE function, specifying CP= YES, to obtain the actual message. When the RECEIVE function completes,
the message data will have been moved to the address specified in the RECEIVE
parameter list. The CP service module then interprets the message data and ser­
vices the request. When the request has been satisfied, the CP service module
invokes the REPL Y function to satisfy the two-way message protocol. When the REPLY function completes, the reply has beer. queued back to the source commu­
nicator. When the CP service module cGi.iipletes processing of the message, it
issues an EXIT (SVC 12) to return to the communications processor. 140 VM/SP System Programmer's Guide ,/