Programming Interface Information:
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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
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