NAME       : HCPMSDBK
 DESCRIPTION: Monitor Send Block
 DSECT      : MSDBK
 FUNCTION   : To represent a monitor broadcast (IUCV Sends of the
              same information to one or more users).  The counts
              contained in an MSDBK are used to determine when the
              DCSS pages corresponding to that broadcast can be
              released for reuse.
     Data structure   Field location
     MNDI_EV_TOSEND   MNDI_EV_TOSEND_HEAD
                      MNDI_EV_TOSEND_TAIL
     MNDI_EV_SENT     MNDI_EV_SENT.MND_HEAD
                      MNDI_EV_SENT.MND_TAIL
     MNDI_SAM_SENT    MNDI_SAM_SENT.MND_HEAD
                      MNDI_SAM_SENT.MND_TAIL
 LOCATED BY :
 CREATED BY : HCPMOISS
              HCPMNXAE
 DELETED BY : HCPMOISR
              HCPMOIER
              HCPMOVPM
 REFERENCES : none
 SERIALIZED : The appropriate lock must be obtained for any
              manipulations to the list.
 RELOCATION CONSIDERATIONS : None
 COMPATIBILITY AND MIGRATION CONCERNS : The MSDBK is used to link Monitor broadcasts in
              a circular list.  As a result of this circular list
              implentation, it is a requirement that MSDFWDPT and
              MSDBCKPT are the first two words in the list.  This is
              necessary, because the code thinks that the head and
              tail pointers to the list are 'another element of the list'.

 MSDBK DSECT
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Hex   Dec Type/Val   Lng Label (dup)    Comments
---- ---- --------- ---- -------------- --------
0000    0 Structure      MSDBK          Monitor Send Block
0000    0 Address      4 MSDFWDPT       Pointer to the next MDSBK on the
                                        list
0004    4 Address      4 MSDBCKPT       Pointer to the previous MSDBK on
                                        the list
0008    8 Signed       4 MSD_SENT_CT    Count of outstanding messages
000C   12 Signed       4 MSD_PEND_CT    Count of pending messages
0010   16 Bitstring    4 MSD_TRGCL      Target class of this message.
                                        This field fill be used to assign
                                        the TRGCLS parameter of the IUCV
                                        macro when sending data.
0014   20 Bitstring    8 MSD_CTL_ADDR (0)
                                        Control area addresses. This
                                        level exists so that the control
                                        area addressess remain together.
                                        It is necessary they be together
                                        because the data is used as the
                                        PRMMSG for the IUCV SEND.
0014   20 Address      4 MSD_CTLST_GRA  Monitor control area starting
                                        address - guest real address
0018   24 Address      4 MSD_CTLEN_GRA  Monitor control area ending
                                        address - guest real address
          0000001C       MSD$END        * End of MSDBK
          00000004       MSDSIZE        (MSD$END-MSDBK+7)/8 MSDBK size in
                                        doublewords

          
*** MSDBK - Monitor Send Block
*
*     +---------------------------+---------------------------+
*   0 |         MSDFWDPT          |         MSDBCKPT          |
*     +---------------------------+---------------------------+
*   8 |       MSD_SENT_CT         |       MSD_PEND_CT         |
*     +---------------------------+---------------------------+
*  10 |        MSD_TRGCL          |      MSD_CTLST_GRA        |
*     +---------------------------+---------------------------+
*  18 |      MSD_CTLEN_GRA        | 1C
*     +---------------------------+
*
*** MSDBK - Monitor Send Block

 
Symbol         Dspl Value
-------------- ---- -----
MSD$END        0018 0000001C
MSD_CTL_ADDR   0014
MSD_CTLEN_GRA  0018
MSD_CTLST_GRA  0014
MSD_PEND_CT    000C
MSD_SENT_CT    0008
MSD_TRGCL      0010
MSDBCKPT       0004
MSDFWDPT       0000
MSDSIZE        0018 00000004