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Programming Interface Information:
This information is NOT intended to be used as Programming Interfaces of z/VM. |
ALOCEXT
Control Block Contents
ALOCEXT DSECT
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' 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)
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 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
Copyright IBM Corporation, 1990, 2007