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