Programming Interface Information: This information is NOT intended to be used as Programming Interfaces of z/VM.

#### MDISK

Prolog

Control Block Contents
MDISK DSECT

Storage Layout

Cross Reference (Contains links to field and bit definitions)

#### MDISK Prolog

     Name       : Minidisk Control Block
     Description: Mini-disk Control Block
     DSECT      : MDISK
     Function   : This control block maps a defined minidisk for
                  a virtual machine.
     Located by : VDEVMDSK - Mini-disk block for Reserve/Release
     Created by : HCPVDSLK
     Deleted by : HCPDTDEV

#### MDISK Control Block Content

#### MDISK DSECT

    Hex   Dec Type/Val   Lng Label (dup)    Comments
    ---- ---- --------- ---- -------------- --------
    0000    0 Structure      MDISK          Mini-disk Control Block
         **      FIELDS FOR ATTACH / DETACH
    0000    0 Signed       4 MDINEXT        NEXT MDISK ON THIS REAL DEVICE
    0004    4 Signed       4 MDILINKS       NUMBER OF LINKS TO THIS EXTENT
         **      FIELDS FOR RELEASE PROCESSING
    0008    8 Dbl-Word     8 MDISIOQS (0)   NORMAL START REQUEST QUEUES
    0008    8 Signed       4 MDIDEOWD       ANCHOR FOR QUEUE OF UNSOLICITED
                                            IORBKS OWED TO DEVICES
    000C   12 Signed       4 MDIDEPND       ANCHOR FOR QUEUE OF PENDING
                                            UNSOLICITED IORBKS
    0010   16 Address      4 MDIRTRQ        ADDRESS OF TIMER REQUEST BLOCK
    0014   20 Address      4 *              RESERVED FOR FUTURE IBM USE
    0018   24 Dbl-Word     8 MDIDIAQS (0)   DIAGNOSE I/O QUEUES
    0018   24 Address      4 MDIQWAIT       ANCHOR FOR QUEUE OF IORBKS
                                            WAITING FOR RELEASE TO RETRY
                                            DIAGNOSE I/O
    001C   28 Address      4 *              RESERVED FOR FUTURE IBM USE
         **      LOCKS FOR ACCESS TO THE MINIDISK EXTENT
    0020   32 Dbl-Word     8 MDILLOCK (0)   LOGICAL LOCK --- DEVICE RESERVED
    0020   32 Signed       4 MDIRSVD (0)    VDEVBK HOLDING DEVICE RESERVED
    0020   32 Address      4 MDIRVDEV       ADDRESS OF VDEV RESERVING
                                            MINI-DISK (BASE VDEV IF MULTIPLE
                                            EXPOSURE DEVICE)
    0024   36 Bitstring    1 MDISTAT        STATUS FLAGS
              1... ....      MDIRESVD       X'80' INDICATES ACTIVE RESERVE
              .1.. ....      MDIRRSVP       X'40' REAL RESERVE IS PENDING
              ..1. ....      MDIRELPD       X'20' REAL RELEASE IS PENDING
              ...1 ....      MDIWRKAL       X'10' Virtual working allegiance
                                            is to be simulated MIDWRKAL
                                            interacts with MDIRESVD and
                                            MDIRVDEV like this : Case I:
                                            MDIRESVD = OFF and MDIWRKAL = ON
                                            Working allegiance is active and
                                            If MDIRVDEV = 0 Then The minidisk
                                            is available. Else MDIRVDEV = the
                                            owning vdev address Case II:
                                            MDIRESVD = ON and MDIWRKAL = OFF
                                            The device is currently reserved
                                            MDIRVDEV = the owning vdev
                                            address MDIRVDEV cannot be zero
                                            Case III: MDIRESVD = ON and
                                            MDIWRKAL = ON The device is
                                            currently reserved MDIRVDEV = the
                                            owning vdev address Working
                                            allegiance may or may not be
                                            active. If the channel program
                                            ended without a Release CCW
                                            issued, then working allegiance
                                            is over but the device is still
                                            unavailable.
    0025   37 Bitstring    1 MDILPUM        MASK FOR LOGICAL PATH ON WHICH
                                            RESERVE WAS MADE
    0026   38 Bitstring    1 MDIMDCFL       Flag byte for minidisk caching
              1... ....      MDITHUD        X'80' MDC purge on backend is
                                            required
              .1.. ....      MDIOVLAP       X'40' Mini-disk overlapped -
                                            purge cache
              ..11 ....      MDIMDCA        X'30' MDC authorization bits used
                                            only when setting MDIHSHID
              ...1 ....      MDIMDCD        X'10' MDC default authorization
                                            MDC will be prohibited ("SET MDC
                                            MDISK ON" disabled) if: -
                                            minidisk includes CP-system
                                            cylinders. CP's I/O to PAGE,
                                            SPOL, and DRCT space will clash
                                            with any user I/O that is cached.
              .... 1...      MDIMDCP        X'08' MDC prohibited for this
                                            mdisk
              .... .1..      MDIRECAC       X'04' Do record caching for this
                                            mdisk
    0027   39 Bitstring    1 MDISMFLG       miscellaneous MDISK flags
              1... ....      MDISMFPO       X'80' The minidisk has a full
                                            pack overlay link to it
              .1.. ....      MDIEXCLU       X'40' Exclusive link held on
                                            minidisk
              ..1. ....      MDIDVFP        X'20' Minidisk created using
                                            DEVNO option
              ...1 ....      MDIQDSK        X'10' Minidisk is a Vdisk
              .... 1...      MDIQDSKP       X'08' Minidisk is a PRIVATE Vdisk
    0028   40 Dbl-Word     8 MDILOCK (0)    LOCKWORD FOR RESERVE/RELEASE
                                            STATUS
    0028   40 Dbl-Word     8 MDIPLOCK (3)   PHYSICAL LOCK --- EXTENT IN USE
    0040   64 Dbl-Word     8 MDIQLOCK (3)   LOCKWORD FOR QUEUE MANIPULATION
           MDISK extent in cylinders (if CKD or ECKD)
                           or blocks (if FBA)
           These values are unique for this real device; no other
           MDISK block represents this exact extent, although other
           MDISK block extents may overlap this extent.
           Warning: some CKD/ECKD-only routines cannot handle cylinder
           numbers larger than 65535; FBA routines can handle 2**32-1.
    0058   88 Dbl-Word     8 MDIVEXTN (0)   Virtual DASD cylinder/block
                                            extents
    0058   88 Signed       4 MDIVSEXT       Virtual DASD start cylinder/block
    005C   92 Signed       4 MDIVEEXT       Virtual DASD end cylinder/block
           All MDISK blocks representing existing virtual dasds
           (whether "minidisks" or "tdisks" but not "dedicated dasds")
           are chained in no particular order from the RDEV block.
           The virtual dasd VDEV blocks in use on this extent are
           doubly-chained from this MDISK block in descending "link
           access mode" order.  The first VDEV's backward pointer
           points to the end of the chain.
    0060   96 Signed       4 MDIVLINK       Pointer to next linked VDEV
           Counts representing the sum of all VDEVs chained from
           this MDISK having the specified "link access mode."
           See also MDIEXCLU bit in MDISMFPO byte.
           MDILINKS = MDIRDCNT + MDIWRCNT.
           A stable-read link would be counted once in each of
           MDIRDCNT and MDISTCNT.
           These counts summarize the thousands of VDEVs that could
           be chained from this MDISK block.
    0064  100 Signed       4 MDIRDCNT       Read link count for minidisk
    0068  104 Signed       4 MDIWTCNT       Write link count to minidisk
    006C  108 Signed       4 MDISTCNT       Stable link count for minidisk
           The minidisk owner is either the user who has the MDISK
           statement in the directory or the user who created this
           extent (not using the directory).
    0070  112 Character    8 MDIOUSER       Mini-disk owner userid
    0078  120 Signed       2 MDIOVDEV       Mini-disk owner VDEV number
           MDIHSHID may contain one of the following values:
           Zero    - This minidisk isn't eligible for MDC caching
          RDEVHSID - when positive, the minidisk is eligible
                     for MDC caching and this field is used to create
                     the MDC hash key.  When negative (bit 0 is on),
                     MDC caching is not permitted for this minidisk.
           X'FFFF' - this minidisk is an FBA device and is not page
                     aligned and is not eligible for MDC caching.
           Note that if MDIHSHID is positve, caching is allowed
           provided that it permitted at the system level.
    007A  122 Signed       2 MDIHSHID       MDC Hash ID
           MDISK blocks representing tdisks are chained in extent-order
           from the CPVOLume extent EXTBK within which they reside.
           This mechanism is used to distinguish free tdisk space from
           tdisk space in use.
    007C  124 Signed       4 MDITNEXT       Ptr to next MDISK on EXTBK chain
    0080  128 Signed       4 MDIEXTBK       Ptr to parent EXTBK
           MDISK blocks representing Vdisks use the following field
           to chain in the Qdisk block.
    0084  132 Address      4 MDIQDISK       Address of QDISK block for Vdisk
           Miscellanea
    0088  136 Signed       4 MDICYLMP       Minidisk cache cylinder map. If
                                            high order bit on, points to
                                            address of cyl map indicating the
                                            format of each cylinder. If off,
                                            then so far entire mdisk is std
                                            and this field contains the DPSBK
                                            address for that size. Updated
                                            with Compare and Swap.
              00000012       MDISIZE        ((*-MDISK+7)/8) SIZE IN DWS FOR
                                            FREE/FRET

#### MDISK Storage Layout

    *** MDISK - Mini-disk Control Block
    *
    *     +---------------------------+---------------------------+
    *   0 |         MDINEXT           |         MDILINKS          |
    *     +---------------------------+---------------------------+
    *   8 |         MDIDEOWD          |         MDIDEPND          |
    *     +---------------------------+---------------------------+
    *  10 |         MDIRTRQ           |///////////////////////////|
    *     +---------------------------+---------------------------+
    *  18 |         MDIQWAIT          |///////////////////////////|
    *     +---------------------------+------+------+------+------+
    *  20 |         MDIRVDEV          |:STAT |:LPUM |:MDCFL|:SMFLG|
    *     +---------------------------+------+------+------+------+
    *  28 |                                                       |
    *     =                       MDIPLOCK                        =
    *     |                                                       |
    *     +-------------------------------------------------------+
    *  40 |                                                       |
    *     =                       MDIQLOCK                        =
    *     |                                                       |
    *     +---------------------------+---------------------------+
    *  58 |         MDIVSEXT          |         MDIVEEXT          |
    *     +---------------------------+---------------------------+
    *  60 |         MDIVLINK          |         MDIRDCNT          |
    *     +---------------------------+---------------------------+
    *  68 |         MDIWTCNT          |         MDISTCNT          |
    *     +---------------------------+---------------------------+
    *  70 |                       MDIOUSER                        |
    *     +-------------+-------------+---------------------------+
    *  78 |  MDIOVDEV   |  MDIHSHID   |         MDITNEXT          |
    *     +-------------+-------------+---------------------------+
    *  80 |         MDIEXTBK          |         MDIQDISK          |
    *     +---------------------------+---------------------------+
    *  88 |         MDICYLMP          | 8C
    *     +---------------------------+
    *
    *** MDISK - Mini-disk Control Block

#### MDISK Cross Reference

    Symbol         Dspl Value
    -------------- ---- -----
    MDICYLMP       0088
    MDIDEOWD       0008
    MDIDEPND       000C
    MDIDIAQS       0018
    MDIDVFP        0027 20
    MDIEXCLU       0027 40
    MDIEXTBK       0080
    MDIHSHID       007A
    MDILINKS       0004
    MDILLOCK       0020
    MDILOCK        0028
    MDILPUM        0025
    MDIMDCA        0026 30
    MDIMDCD        0026 10
    MDIMDCFL       0026
    MDIMDCP        0026 08
    MDINEXT        0000
    MDIOUSER       0070
    MDIOVDEV       0078
    MDIOVLAP       0026 40
    MDIPLOCK       0028
    MDIQDISK       0084
    MDIQDSK        0027 10
    MDIQDSKP       0027 08
    MDIQLOCK       0040
    MDIQWAIT       0018
    MDIRDCNT       0064
    MDIRECAC       0026 04
    MDIRELPD       0024 20
    MDIRESVD       0024 80
    MDIRRSVP       0024 40
    MDIRSVD        0020
    MDIRTRQ        0010
    MDIRVDEV       0020
    MDISIOQS       0008
    MDISIZE        0088 00000012
    MDISMFLG       0027
    MDISMFPO       0027 80
    MDISTAT        0024
    MDISTCNT       006C
    MDITHUD        0026 80
    MDITNEXT       007C
    MDIVEEXT       005C
    MDIVEXTN       0058
    MDIVLINK       0060
    MDIVSEXT       0058
    MDIWRKAL       0024 10
    MDIWTCNT       0068

This information is based on z/VM V5R2.0. Last updated on 12 Apr 2006 at 17:04:59 EDT.
Copyright IBM Corporation, 1990, 2005