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

#### EXTBK

Prolog

Control Block Contents
EXTBK DSECT

Storage Layout

Cross Reference (Contains links to field and bit definitions)

#### EXTBK Prolog

     NAME       : HCPEXTBK
     DESCRIPTION: Extent Block
     DSECT      : EXTBK
     FUNCTION   : Describes a group of contiguous cylinders or slots
                  on a CP-owned DASD containing the same allocation type.
     LOCATED BY : VEXPGEXT
                  VEXSPEXT
                  VEXTDEXT
                  VEXDREXT
                  VEXPEEXT
                  VEX1SEXT
                  EXTMYEXT
                  EXTANYEX
     CREATED BY : HCPRDX when a CP-owned device is attached
                  to the system
     DELETED BY : HCPRDD when a CP-owned device is detached
                  from the system
     REFERENCES : HCPMSABK  - Map for Slot Allocation
                  HCPMDISK  - Minidisk block
     SERIALIZED : Allocation locks
     NOTES      : EXTBKs of type PERM use only the following fields:
                  EXTVEXBK, EXTSTART, EXTEND, EXTANYEX, and EXTMYEXT.
                  EXTBKs are not created for type PARM or UNDF, as
                  they are not needed in the internal representation
                  of the allocation map.

#### EXTBK Control Block Content

#### EXTBK DSECT

    Hex   Dec Type/Val   Lng Label (dup)    Comments
    ---- ---- --------- ---- -------------- --------
    0000    0 Structure      EXTBK          Extent Block
    0000    0 Signed       4 EXTVEXBK       Pointer back to VEXBK
           The following 2 fields vary in units depending
           on the type of device.
    0004    4 Signed       4 EXTSTART       Starting cylinder (CKD/ECKD) or
                                            slot (FBA) for this extent
    0008    8 Signed       4 EXTEND         Ending cylinder (CKD/ECKD) or
                                            slot (FBA) for this extent
    000C   12 Signed       4 EXTINUSE       Number in use in this EXTBK. In
                                            cylinders for E/CKD TDSK and DRCT
                                            extents. In slots for E/CKD PAGE
                                            and SPOL extents and for all FBA
                                            extents. Not used for PERM.
    0010   16 Signed       4 EXTHIGH        Highest slot or cylinder in use
                                            in this extent. Used only by TDSK
                                            and DRCT extents. This number is
                                            relative to the start of the
                                            volume. Query Alloc will actually
                                            report this number relative to
                                            the start of the extent.
    0014   20 Signed       4 EXTSTRCT       Pointer to a structure which
                                            further describes what parts of
                                            the extent are in use. For PAGE
                                            and SPOL this points to a MSABK.
                                            For TDSK, this points to an MDISK
                                            block. Equals 0 for DRCT and PERM
                                            extents.
    0018   24 Signed       4 EXTANYEX       Pointer to next extent on volume
                                            of any type. (for Q ALLOC MAP)
    001C   28 Signed       4 EXTMYEXT       Pointer to next extent on volume
                                            of this type
    0020   32 Signed       4 EXTSTSLT       Slot number of first slot in
                                            EXTBK. Same as EXTSTART for FBA
                                            devices.
    0024   36 Signed       4 EXTENSLT       Slot number of last slot in
                                            EXTBK. Same as EXTEND for FBA
                                            devices.
    0028   40 Signed       4 EXTFREE        Number of free slots in this
                                            extent when stopped allocating
                                            from this extent. Used to
                                            determine if need to get new
                                            CASBKs.
    002C   44 Signed       4 EXTSLOTS       Number of slots in this extent
    0030   48 Bitstring    1 EXTTYPE        Allocation type for this extent
    0031   49 Bitstring    1 EXTFLAG        Flag byte
              1... ....      EXTFULL        X'80' Indicates entire extent is
                                            in use
              .1.. ....      EXTLOG1        X'40' This EXTBK is the first in
                                            a series of EXTBKs associated
                                            with 1 physical extent on the
                                            DASD
              ..1. ....      EXTLOGEX       X'20' This EXTBK belongs to a
                                            series of EXTBKs associated with
                                            1 physical extent on the DASD.
                                            This EXTBK is not the first EXTBK
                                            in the series.
    0032   50 Signed       2 *              Reserved for IBM use
              00000007       EXTSIZE        (*-EXTBK+7)/8 Size, in
                                            doublewords, of EXTBK
              00000034       EXTSIZEB       *-EXTBK Size of EXTBK in bytes
              0000004E       EXTPRPG        (4096-24)/EXTSIZEB Maximum number
                                            of EXTBKs per page

#### EXTBK Storage Layout

    *** EXTBK - Extent Block
    *
    *     +---------------------------+---------------------------+
    *   0 |         EXTVEXBK          |         EXTSTART          |
    *     +---------------------------+---------------------------+
    *   8 |          EXTEND           |         EXTINUSE          |
    *     +---------------------------+---------------------------+
    *  10 |         EXTHIGH           |         EXTSTRCT          |
    *     +---------------------------+---------------------------+
    *  18 |         EXTANYEX          |         EXTMYEXT          |
    *     +---------------------------+---------------------------+
    *  20 |         EXTSTSLT          |         EXTENSLT          |
    *     +---------------------------+---------------------------+
    *  28 |         EXTFREE           |         EXTSLOTS          |
    *     +------+------+-------------+---------------------------+
    *  30 |:TYPE |:FLAG |/////////////| 34
    *     +------+------+-------------+
    *
    *** EXTBK - Extent Block

#### EXTBK Cross Reference

    Symbol         Dspl Value
    -------------- ---- -----
    EXTANYEX       0018
    EXTEND         0008
    EXTENSLT       0024
    EXTFLAG        0031
    EXTFREE        0028
    EXTFULL        0031 80
    EXTHIGH        0010
    EXTINUSE       000C
    EXTLOGEX       0031 20
    EXTLOG1        0031 40
    EXTMYEXT       001C
    EXTPRPG        0032 0000004E
    EXTSIZE        0032 00000007
    EXTSIZEB       0032 00000034
    EXTSLOTS       002C
    EXTSTART       0004
    EXTSTRCT       0014
    EXTSTSLT       0020
    EXTTYPE        0030
    EXTVEXBK       0000

This information is based on z/VM V5R2.0. Last updated on 12 Apr 2006 at 16:53:19 EDT.
Copyright IBM Corporation, 1990, 2005