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

ALOCEXT

Prolog  

Control Block Contents  
   ALOCEXT DSECT

Storage Layout  

Cross Reference (Contains links to field and bit definitions)  


ALOCEXT Prolog

 Name       : HCPALOC
 Description: DASD allocation record mapping for
              EXTENT-BASED ALLOCATION MAPPING.
 DSECT      : ALOCEXT
 Function   : Maps the DASD allocation record for system owned
              volumes with EXTENT-BASED ALLOCATION MAPPING.
 Located by : n/a
              exists only temporarily in storage,
              resides in block numbers 3 and 4 of
              an FBA DASD formatted for CP use
              For CKD and ECKD DASD, resides on
              cylinder 0, head 0, record 4.
 Created by : ICKDSF
              when an FBA DASD is formatted for ESA
              CP use, or a CKD/ECKD DASD with
              more than ALOCMAXCM cylinders is
              formatted for CP use.
 Deleted by : n/a
              exists in storage only until the in
              storage allocation map is built
 Notes      :
 For FBA
              The FBA allocation record resides on FBA volumes formatted
              for CP use in the reserved pages, blocks 3 & 4.  There are
              two versions of the FBA allocation record, one for volumes
              formatted for 370 CP (which ESA CP can use), and one for
              volumes formatted for ESA CP.  The two versions map almost
              exactly the same.  The ESA version has an indicator that
              this is an extent-based allocation map as well as ESA
              allocation types.
              Volumes which are formatted for ESA CP use are marked by
              the presence of the string "CPVOL" in the volume owner
              area of the OS volume label record (block 1).
              FBA volumes which are formatted for 370 CP use are marked
              by the presence of the string "CP370" in the volume owner
              area of the OS volume label record (block 1).  FBA volumes
              formatted for 370 CP are usable by ESA CP without
              reformatting.
              The layout of the blocks in the reserved pages of FBA
              volumes is:
              0 - IPL record
              1 - OS VOL1 volume label record
              2 - VTOC - OS FORMAT 4 & FORMAT 5 labels
              3-4 - Allocation Record extent map
              5-12 - Initialized to 0
              13-31 - Reserved, initialized to 0.
 For FBA and  KD/ECKD
              Note that the length of the allocation record is variable
              depending on the number of extents.  The overall length of
              the allocation record is determined by multiplying the
              number of entries (found in bytes 3-4 of the first entry)
              by the length of an entry, and adding one (the next byte
              after the last entry is marked with X'FF').
              The allocation type values for all DASD formatted for ESA
              CP are the same for all types of DASD (CKD, ECKD, FBA).

 

ALOCEXT Control Block Content


ALOCEXT DSECT

Hex   Dec Type/Val   Lng Label (dup)    Comments
---- ---- --------- ---- -------------- --------
0000    0 Structure      ALOCEXT        DASD allocation record mapping
                                        for
0000    0 Bitstring   12 ALOCEENT (0)   Extent map entry
0000    0 Bitstring    1 ALOCETYP       Extent allocation type
          .... ....      ALO370TE       X'00' 370 FBA allocation type
                                        'TEMP'
          .... ...1      ALO370PE       X'01' 370 FBA allocation type
                                        'PERM'
          .... ..1.      ALO370TD       X'02' 370 FBA allocation type
                                        'TDSK'
          .... .1..      ALO370DR       X'04' 370 FBA allocation type
                                        'DRCT'
          1... .1..      ALO370AD       X'84' 370 FBA type in-use DRCT
                                        space
          .... 1...      ALO370PA       X'08' 370 FBA allocation type
                                        'PAGE'
          ...1 ....      ALO370DU       X'10' 370 FBA allocation type
                                        'DUMP'
          ...1 .1..      ALO370OV       X'14' 370 FBA allocation type
                                        'OVRD'
          ...1 11..      ALO370AO       X'1C' 370 FBA type in-use OVRD
                                        space
0001    1 Bitstring    1 ALOCECNT       Volume allocation contents -
                                        contains all of the extent map
                                        entry ALOCETYP bytes ORed
                                        together (valid only in first
                                        extent map entry on ESA formatted
                                        volumes, not valid for volumes
                                        formatted for 370)
0002    2 Signed       2 ALOCEECT       Count of allocation extent map
                                        entries. Also, has indicator that
                                        this is an extent-based map.
                                        (Both count and indicator are
                                        valid only in 1st extent map
                                        entry.)
0004    4 Signed       4 ALOCESTR       Extent start slot number FBA
                                        Extent start cyl number E/CKD
0008    8 Signed       4 ALOCEEND       Extent end slot number FBA Extent
                                        end cyl number E/CKD
000C   12 Bitstring    1 ALOCENXT (0)   Next extent entry
          1111 1111      ALOCEND        X'FF' Marks the end of the
                                        allocation map
          .1.1 .1.1      ALOCFMXX       85 Maximum number of extents
                                        allowed in one allocation map
                                        (FBA)
          ALOCENXT       ALOCEMXX       340 Maximum number of extents
                                        allowed in one allocation map
                                        (E/CKD)
          ALOCENXT       ALOCMAXCM      4079 Maximum number of cylinders
                                        for a cylinder based map.
          0000000C       ALOCEENL       *-ALOCEENT Length of an extent
                                        entry
0002    2 Bitstring    1 ALOCEFLG       Holds flag indicating this is the
                                        extent-based allocation map. Note
                                        that the other bits in this byte
                                        are NOT available to use as this
                                        field overlaps ALOCEECT.
          1... ....      ALOCEXTM       X'80' Indicates this is the
                                        extent based allocation map.
0003    3 Bitstring    1 *              Do not use Part of remap.

 

ALOCEXT Storage Layout

          
*** ALOCEXT - DASD allocation record mapping for
*
*     +------+------+-------------+---------------------------+
*   0 |:CETYP|:CECNT|  ALOCEECT   |         ALOCESTR          |
*     +------+------+-------------+---------------------------+
*   8 |         ALOCEEND          |
*     +---------------------------+
*
*** ALOCEXT - DASD allocation record mapping for
          
*** Overlay for ALOCEECT in ALOCEXT
*
*                   +------+------+
*   0 ...         2 |:CEFLG|//////| 4
*                   +------+------+
*
*** Overlay for ALOCEECT in ALOCEXT

 

ALOCEXT Cross Reference

Symbol         Dspl Value
-------------- ---- -----
ALOCECNT       0001
ALOCEECT       0002
ALOCEEND       0008
ALOCEENL       000C 0000000C
ALOCEENT       0000
ALOCEFLG       0002
ALOCEMXX       000C ALOCENXT
ALOCEND        000C FF
ALOCENXT       000C
ALOCESTR       0004
ALOCETYP       0000
ALOCEXTM       0002 80
ALOCFMXX       000C 55
ALOCMAXCM      000C ALOCENXT
ALO370AD       0000 84
ALO370AO       0000 1C
ALO370DR       0000 04
ALO370DU       0000 10
ALO370OV       0000 14
ALO370PA       0000 08
ALO370PE       0000 01
ALO370TD       0000 02
ALO370TE       0000 00

This information is based on z/VM V5R2.0. Last updated on 12 Apr 2006 at 17:37:48 EDT.
Copyright IBM Corporation, 1990, 2005