EXTBK Back to Index page
 
Prolog 
Control Block Contents 
   EXTBK DSECT
Storage Layout 
Cross Reference (Contains links to field and bit definitions)
Programming Interface Information:
This information is NOT intended to be
used as Programming Interfaces of z/VM.


  EXTBK Prolog Top of page
 
 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
 RELOCATION CONSIDERATIONS : None
 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 Top of page
 

 EXTBK DSECT Top of page
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' EXTFULL Indicates entire extent is in use .1.. .... EXTLOG1 X'40' EXTLOG1 This EXTBK is the first in a series of EXTBKs associated with 1 physical extent on the DASD ..1. .... EXTLOGEX X'20' EXTLOGEX 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 Top of page
 
          
*** 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 Top of page
 
 
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 7.3.0 Last updated on 22 Jun 2022 at 15:50:22 EDT.
Copyright IBM Corporation, 1990, 2022