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      :
  or 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.
  or FBA and CKD/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 DSECT
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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' ALO370TE 370 FBA allocation
                                        type 'TEMP'
          .... ...1      ALO370PE       X'01' ALO370PE 370 FBA allocation
                                        type 'PERM'
          .... ..1.      ALO370TD       X'02' ALO370TD 370 FBA allocation
                                        type 'TDSK'
          .... .1..      ALO370DR       X'04' ALO370DR 370 FBA allocation
                                        type 'DRCT'
          1... .1..      ALO370AD       X'84' ALO370AD 370 FBA type
                                        in-use DRCT space
          .... 1...      ALO370PA       X'08' ALO370PA 370 FBA allocation
                                        type 'PAGE'
          ...1 ....      ALO370DU       X'10' ALO370DU 370 FBA allocation
                                        type 'DUMP'
          ...1 .1..      ALO370OV       X'14' ALO370OV 370 FBA allocation
                                        type 'OVRD'
          ...1 11..      ALO370AO       X'1C' ALO370AO 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' ALOCEND Marks the end of
                                        the allocation map
          .1.1 .1.1      ALOCFMXX       85 ALOCFMXX Maximum number of
                                        extents allowed in one allocation
                                        map (FBA)
          .1.1 ..11      ALOCFOMX       83 ALOCFOMX Maximum number of
                                        extents allowed in one FBA alloc
                                        map when ownership information is
                                        written after the end of the map
          ALOCENXT       ALOCEMXX       340 ALOCEMXX Maximum number of
                                        extents allowed in one allocation
                                        map (E/CKD)
          ALOCENXT       ALOCMAXCM      4079 ALOCMAXCM 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' ALOCEXTM Indicates this is
                                        the extent based allocation map.
0003    3 Bitstring    1 *              Do not use Part of remap.

          
*** 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

 
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
ALOCFOMX       000C 53
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