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Programming Interface Information:
This information is NOT
intended to be
used as Programming Interfaces of VM/ESA. It is to be used for diagnosis only. |
FREBK
Cross Reference (Contains links to field and bit definitions)
FREBK Prolog
NAME : HCPFREBK
DESCRIPTION: FREE STORAGE BLOCK
DSECT : FREBK
FUNCTION :
MAPS A FREE STORAGE BLOCK HEADER AND TRAILER
FOR BOTH ACTIVE AND INACTIVE FREE STORAGE BLOCKS.
CREATED BY : HCPFREE OR HCPFREVM WHEN A BLOCK IS
REQUESTED. THIS BLOCK IS NEVER ALLOCATED
AS A SEPARATE BLOCK.
DELETED BY : HCPFRET WHEN A BLOCK IS RETURNED TO
FREE STORAGE. THIS BLOCK IS NEVER
DEALLOCATED AS A SEPARATE BLOCK.
SERIALIZED :
IT IS THE RESPONSIBILITY OF THE REQUESTOR TO
ENSURE THAT ACCESS TO THE FREE STORAGE BLOCK IS
SERIALIZED.
NOTES : WHEN A FREE STORAGE BLOCK IS ISSUED TO SATISFY A
FREE STORAGE REQUEST, THE FREE STORAGE MANAGER
PLACES A ONE DOUBLEWORD HEADER AND A TWO
DOUBLEWORD TRAILER AROUND THE BLOCK. THESE AREAS
ARE USED FOR DEBUGGING PURPOSES.
WHEN THE BLOCK IS RETURNED, THESE AREAS ARE
EXAMINED. IF EITHER OR BOTH HAVE BEEN CORRUPTED, AN
ABEND IS ISSUED.
FREBK Control Block Content
FREBK DSECT
Hex Dec Type/Val Lng Label (dup) Comments ---- ---- --------- ---- -------------- -------- 0000 0 Structure FREBK FREE STORAGE BLOCK THIS IS A PICTURE OF HOW THE FIELDS IN THIS DSECT ARE ACTUALLY USED: +-------------------------------------------------------+ * 0 | FREHEADR | * +-------------------------------------------------------+ * 8 : : : (CONTROL BLOCK) : * : : * +-------------------------------------------------------+ * XX | FRETRALR | * | | +-------------------------------------------------------+ * XX+10 THE FREE STORAGE HEADER (FREHEADR) AND FREE STORAGE TRAILERS (FRETRALR) AREA PROVIDED AS DEBUGGING AIDS FOR FREE STORAGE RELATED PROBLEMS. THE FREE STORAGE HEADER IMMEDIATELY PRECEDES THE START OF THE FREE STORAGE BLOCK ISSUED IN RESPONSE TO AN HCPFREE OR HCPFREVM CALL. THE TRAILER IMMEDIATELY FOLLOWS THE FREE STORAGE REQUESTED BY THE CALLER. THE EXACT FORMAT/CONTENT OF THESE FIELDS DEPENDS ON WHETHER THE FREE STORAGE BLOCK IS ACTIVE OR INACTIVE. 0000 0 Dbl-Word 8 FRESTRT (0) START OF VARIABLE LENGTH DATA 0000 0 Dbl-Word 8 FREHEADR FREE STORAGE BLOCK HEADER 00000008 FREHEADL *-FREHEADR LENGTH OF HEADER IN BYTES 0000 0 Dbl-Word 8 FRETRALR (2) FREE STORAGE BLOCK TRAILER 00000010 FRETRALL *-FRETRALR LENGTH OF TRAILER IN BYTES 00000003 FRERECL (FREHEADL+FRETRALL+7)/8 SIZE IN DOUBLE WORDS 0000 0 Signed 4 FREESIZE (0) # OF DWORDS OF STORAGE REQUESTED 0000 0 Signed 2 * Mini-eyecatcher for SPS else zero 0002 2 Signed 2 FREHSIZE Actual count of DWs requested Notes : The maximum allowable size value for FRETSIZE is the number of doublewords which can fit into a single 4K page (not counting the free storage header and trailer), or 509 doublewords, x'1FD'. A FREHSIZE value of x'FAB' in active subpooled free storage blocks is not a size, but is used to indicate that the block is an active "fast allocated block". 0004 4 Signed 4 FRESUBBK (0) Address of SUBBK for subpool blk 0004 4 Character 4 FREESFLG ALLOCATED BLOCK CHARACTER STRING 0000 0 Character 4 FREEID CONTROL BLOCK'S IDENTIFIER (THE FIRST CHARACTER IS '<', AND THE ID FOR UNDEFINED BLOCKS IS '<<<<' ) 0004 4 Signed 4 FREFSCBK (0) Addr of storage obtainers FSCBK 0004 4 Character 4 FREEEFLG CHARACTER STRING '<<<<' 0008 8 Signed 4 FREEDISP REQUEST'S OFFSET IN CALLING MODULE (1ST HALF WORD = X'00 00') 000C 12 Character 4 FREEMOD MODULE ID OF CALLING MODULE THE FIRST BYTE'S ALWAYS SET TO 0 0000 0 Signed 4 FREEPNT PNTR TO NEXT BLOCK IN FREE STORAGE CHAIN OR 0 (IF END-OF-CHAIN) 0004 4 Signed 4 FRETSIZE Size of available block in DWs or the size in bytes for a larger than subpool size block that is on the free storage chain Notes : For for subpooled free storage, FRETSIZE as such is not used. Instead the address of the SUBBK which represents this subpool remains here in the second word of the free storage header (as field FRESUBBK). Since the maximum allowable value for FRETSIZE for normal free storage is 509 (x'1FD'), any larger value in this field indicates that the block in question is in a frame used for subpooled free storage (since SUBBKs can't reside in low prefix page addresses like x'1FD' and below). However, in order to use this fact to distinguish between types, caution must be used, since the high order bit of the SUBBK address is used as a free storage garbage collection flag. Also note that in *active* subpooled free storage blocks, a value of x'FAB' in the actual requested size in dws (in FREHSIZE) is not a size, but an indicator that the block is an active "fast allocated block". 0000 0 Character 4 FRETID CONTROL BLOCK'S IDENTIFIER (THE FIRST CHARACTER IS '<', AND THE ID FOR UNDEFINED BLOCKS IS '<<<<' ) THIS FIELD IS PRESERVED FROM THE HCPFREE CALL WHICH ORIGINALLY OBTAINED THIS CONTROL BLOCK 0004 4 Character 4 FRETMOD MODID OF HCPFRET CALLER THE FIRST BYTE'S ALWAYS SET TO 0 0008 8 Signed 2 FRETDISP DISPL INTO MODID OF HCPFRET CALL 000A 10 Bitstring 1 FREECALL (6) LOW-ORDER 2 BYTES OF "FREEDISP" AND "FREEMOD PRESERVED FROM THE HCPFREE CALL WHICH ORIGINALLY OBTAINED THIS CONTROL BLOCK
FREBK Storage Layout
*** FREBK - FREE STORAGE BLOCK * * +-------------------------------------------------------+ * 0 | | * = FRESTRT = * | | * +-------------------------------------------------------+ * *** FREBK - FREE STORAGE BLOCK *** Overlay for FRESTRT in FREBK * * +-------------------------------------------------------+ * 0 | FREHEADR | * +-------------------------------------------------------+ * 8 * *** Overlay for FRESTRT in FREBK *** Overlay for FRESTRT in FREBK * * +-------------------------------------------------------+ * 0 | FRETRALR | * | | * +-------------------------------------------------------+ * 10 * *** Overlay for FRESTRT in FREBK *** Overlay for FREHEADR in FREBK * * +-------------+-------------+---------------------------+ * 0 |/////////////| FREHSIZE | FREESFLG | * +-------------+-------------+---------------------------+ * 8 * *** Overlay for FREHEADR in FREBK *** Overlay for FRETRALR in FREBK * * +---------------------------+---------------------------+ * 0 | FREEID | FREEEFLG | * +---------------------------+---------------------------+ * 8 | FREEDISP | FREEMOD | * +---------------------------+---------------------------+ * 10 * *** Overlay for FRETRALR in FREBK *** Overlay for FREHEADR in FREBK * * +---------------------------+---------------------------+ * 0 | FREEPNT | FRETSIZE | * +---------------------------+---------------------------+ * 8 * *** Overlay for FREHEADR in FREBK *** Overlay for FRETRALR in FREBK * * +---------------------------+---------------------------+ * 0 | FRETID | FRETMOD | * +-------------+-------------+---------------------------+ * 8 | FRETDISP | FREECALL | * +-------------+-----------------------------------------+ * 10 * *** Overlay for FRETRALR in FREBK
FREBK Cross Reference
(contains links to field and bit definitions)Symbol Dspl Value -------------- ---- -----FREECALL 000A
FREEDISP 0008
FREEEFLG 0004
FREEID 0000
FREEMOD 000C
FREEPNT 0000
FREESFLG 0004
FREESIZE 0000
FREFSCBK 0004
FREHEADL 0000 00000008
FREHEADR 0000
FREHSIZE 0002
FRERECL 0000 00000003
FRESTRT 0000
FRESUBBK 0004
FRETDISP 0008
FRETID 0000
FRETMOD 0004
FRETRALL 0000 00000010
FRETRALR 0000
FRETSIZE 0004
Last updated on 3 Aug 1999 at 11:55:54 EDT.
Copyright IBM Corporation, 1990, 1999