Type ASSEMBLE
Source Lines : 447
Fixes Applied : 0
Most Recent Version : Tuesday, December 12, 1978
Last Fix ID : [Unmodified]

Module

     DMSAUD

Function

       TO RESERVE SPACE ON DISK FOR  REWRITING A NEW COPY OF
       THE USER  FILE DIRECTORY (UFD)  ON DISK, AND  THEN TO
       UPDATE THE UFD ON DISK.

Attributes

       NUCLEUS RESIDENT, REENTRANT

Operation

       DMSAUD  IS THE  ROUTINE THAT  UPDATES  THE USER  FILE
       DIRECTORY FOR A  GIVEN DISK.  IT IS CALLED  IN ONE OF
       TWO  WAYS:  WHEN  DMSFNSA HAS  CLOSED  THE LAST  OPEN
       OUTPUT  FILE FOR  A GIVEN  DISK, IT  CALLS THE  FIRST
       ENTRY TO  UPDATE THE UFD  FOR THAT DISK;  WHEN DMSERS
       FINDS A FILE
       TO  BE ERASED  IT  FIRST CALLS  THE  SECOND ENTRY  TO
       RESERVE SOME TRACKS, THEN  DOES ITS ERASING FUNCTION,
       THEN CALLS  THE THIRD ENTRY TO  WRITE THE NEW  UFD ON
       DISK.

       THIS LOGIC  MAKES POSSIBLE WHAT  IS CALLED  A "DOUBLE
       DIRECTORY" SCHEME,  WHEREIN THE  OLD DIRECTORY  STILL
       EXISTS  ON  DISK  UNTIL THE  MFD  ITSELF  IS  FINALLY
       REWRITTEN ON RECORD 4 OF THE DISK, COMPLETING THE NEW
       DIRECTORY.  IF THE  SYSTEM IS INTERRUPTED IN  ANY WAY
       IN THE  MIDDLE OF THE  PROCESS, THE OLD  DIRECTORY IS
       STILL INTACT,  AND ANY OLD  FILES POINTED  TO THEREBY
       ARE STILL INTACT.

       DMSAUD, THEN, HAS  BASICALLY TWO STEPS.  ENTRY  (2) -
       CALLED ONLY  BY DMSERS  - DOES  ONLY THE  FIRST STEP;
       ENTRY (3)  - ALSO  CALLED BY DMSERS  - DOES  ONLY THE
       SECOND STEP.

       THE ACTION TAKEN BY EACH STEP IS AS FOLLOWS:

       STEP 1:  AN 800-BYTE BUFFER FOR THE CONSTRUCTING OF A
       NEW MFD IS OBTAINED FROM  FREE STORAGE, AND THE FIRST
       600 BYTES ARE CLEARED.  AVAILABLE DISK-ADDRESSES
       ARE OBTAINED FROM DMSTRKA FOR EACH FST HYPERBLOCK AND
       STORED IN THE MFD, JUST OBTAINED,
       IN SEQUENTIAL HALFWORDS.  THEN, IF  THERE ARE NO MORE
       THAN  215  BYTES  OF SIGNIFICANT  DATA  IN  THE  QMSK
       BITMASK, A  SENTINEL OF  X'FFFF' IS  STORED FOLLOWING
       THESE, AND STEP 1 IS COMPLETE.  IF THE QMSK IS LARGER
       THAN 215  BYTES IN  LENGTH AND  THERE IS  SIGNIFICANT
       DATA  PAST   THE  215TH  BYTE,   HOWEVER,  ADDITIONAL
       DISK-ADDRESSES ARE OBTAINED (AS  MANY AS ARE NEEDED),
       AND  STORED FOLLOWING  A  SENTINEL  OF X'FFFD'.   ALL
       NEEDED DISK-ADDRESSES FOR  THE NEW MFD HAVE  NOW BEEN
       OBTAINED AND  STORED, WITHOUT AFFECTING ANY  OLD DATA
       ON DISK.

       IF ENTRY (2)  WAS CALLED BY DMSERS,  DMSAUD EXITS  AT
       THIS POINT.

       STEP 2: NOW  WE CONTINUE  IN LINE,  OR ENTER  HERE IF
       ENTRY (3) IS CALLED BY DMSERS.

       DMSAUD NOW CYCLES THROUGH THE
       OLD MFD (IF ANY) LEFT IN  CORE BY THE FILE MANAGEMENT
       PROGRAMS,  AND RETURNS  OLD DISK-ADDRESSES  CONTAINED
       THEREIN BY CALLING
       DMSTRKX
       TO RETURN  THEM TO  THE QMSK TABLE.   THE OLD  MFD IS
       THEN RETURNED TO FREE STORAGE VIA FRET.

       NOW  THE  FST  HYPERBLOCKS IN  CORE,  AND  ANY  PQMSK
       EXTENSIONS ARE  WRITTEN ON DISK, CALLING  WRTK, USING
       THE DISK-ADDRESSES  RESERVED ABOVE IN STEP  1.  NEXT,
       ALL THE DISK COUNTS (ADTNUM, ADTCYL, ETC.), THE FIRST
       215 BYTES (OR  LESS) OF THE QMSK, THE  QQMSK, AND THE
       UNIT-TYPE  BYTE ARE  MOVED TO  THE MFD,  AND THE  MFD
       FINALLY  WRITTEN  BACK  ON  RECORD  4  OF  THE  DISK,
       COMPLETING THE NEW UFD ON DISK.

       FINALLY, THE SIGNIFCANT PART OF THE NEW MFD, STILL IN
       CORE,  INCLUDING   THE  DISK-ADDRESSES  OF   THE  FST
       HYPERBLOCKS, THE FFFF  OR THE FFFD SENTINEL,  AND THE
       DISK-ADDRESSES OF THE QMSK  EXTENSION(S) ARE RETAINED
       IN CORE (IN THE HIGH-NUMBERED  END OF THE BUFFER THAT
       WAS  USED FOR  THE  NEW MFD),  AND  THE  REST OF  THE
       800-BYTE BUFFER GIVEN BACK TO FREE
       STORAGE VIA DMSFRET.

       NOTES:  IF A PERMANENT DISK  ERROR OCCURS WRITING THE
            NEW UFD AT ANY POINT, OR IF NECESSARY
            FREE STORAGE CANNOT BE OBTAINED, THE
            DMSAUD ROUTINE PURPOSELY TRANSFERS TO
            THE DMSFNSD CODE, SO THAT THE OLD
            DIRECTORY WILL  BE INTACT  UNTIL THE  DISK ERROR
            CAN BE CORRECTED, OR A LARGER VIRTUAL
            MACHINE DEFINED.

       SEE ALSO "DMSAUDUP" AND  "DMSAUDL", WHICH STILL SERVE
       A USEFUL PURPOSE, AND  ARE RETAINED FOR COMPATIBILITY
       WITH  EXISTING PROGRAMS.   DMSAUDUP  AND DMSAUDL  ARE
       INCLUDED AS ENTRY-POINTS IN THE DMSAUD ROUTINE.

Calls to Other Routines

     DMSFREE, DMSFRET, DMSTRKA, DMSTRKX, DMSDIOW, DMSFNSD