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