-- file CoreImpDefs.mesa (See also Core*.mesa.)
-- Last edited by Kierr, February 24, 1978 3:30 PM.
-- Converted to Mesa 5, March 26, 1979 1:46 PM.
-- CoreImpDefs are definitions used in implementation of Core.
-- This file is part of a set. See [IFS]<DMS>Overview.mesa for more information.
DIRECTORY
AltoFileDefs: FROM "AltoFileDefs",
SegmentDefs: FROM "SegmentDefs",
crD: FROM "CoreDefs",
gsD: FROM "GlobalStorageDefs",
ovD: FROM "OverviewDefs";
crID: DEFINITIONS -- [6] Core Division --
SHARES crD = BEGIN
OPEN crD;
-- Purpose: provides an MC style interface to files and raw storage/structures.
--Topology of this file:
--AltoCore: INTERNAL MODULE
--VDATable: INTERNAL MODULE
--FilenameCache: INTERNAL MODULE
--FreePageMonitor: INTERNAL MODULE
---------------------------------------------------------------
-- INTERNAL MODULE: AltoCore.Mesa
-- Purpose: provides support for Alto file system in MC.
AltoReadPages: PROCEDURE
[buffer: gsD.MemoryPagePtr, byteCount: CARDINAL,
pageNumber: UPageNumber, uFH: UFileHandle]
RETURNS [erc: ovD.ErrorCode, bytesRead: CARDINAL];
-- Reads up to "byteCount" bytes of data from the file asscoiated with uFH beginning with page "pageNumber" into the memory page(s) beginning at "buffer". The byteCount must be a multiple of 512 (an even page). The bytesRead returned is the count of bytes actually read and will be equal to the requested byteCount except at EOF, when it may be less. (Note that if pageNumber is beyound the end-of-file then bytesRead=0 is returned.)
-- Error Codes: diskError.
AltoWritePages: PROCEDURE [buffer: gsD.MemoryPagePtr, byteCount: CARDINAL,
pageNumber: UPageNumber, uFH: UFileHandle]
RETURNS [erc: ovD.ErrorCode];
-- Writes byteCount of data from memory, beginning at buffer, to pageNumber of the file aFH. The operation is legal only if the file was opened in update OpenMode. This can be used to extend the file’s size by writing beyond the current end. (Note, however, that the file is never shortened.) The byteCount must always be a multiple of 512, an even page, except on the last page of the file. And it cannot be 0.
-- Regarding byteCount, let "remainder" be (byteCount MOD 512). If non-zero, remainder denotes the number of bytes supplied by the client to be written on the last page of the current transaction. The number of byte actually written will be the MAX[current-bytes-on-that-file-page, remainder]; the value of all bytes beyond remainder are indeterminate.
-- Side effects: Updates the file size in the uFH as needed.
-- Error Codes: diskFull, diskError, fileTooBig.
GetVDA: PROCEDURE [targetPage: AltoPageNumber, aFH: AltoFileHandle]
RETURNS [erc: ovD.ErrorCode, vDA: VDA] ;
-- Get the VDA for the target page, either from the table or, if necessary, by reading the disk.
-- ErrorCodes: DiskError.
MakeFileIndexCanonical: PROCEDURE [page: UPageNumber, byte: CARDINAL]
RETURNS [UPageNumber, CARDINAL[0..512)] ;
-- All FileIndexes (e.g., page,byte) have to property that the corresponding CharIndex is (page*512 + byte). But canonical FileIndexes also have the property that byte is IN [0 .. 512).
MapUToAltoPage: PROCEDURE [page: UPageNumber]
RETURNS [AltoPageNumber] ;
MapAltoToUPage: PROCEDURE [page: AltoPageNumber]
RETURNS [UPageNumber] ;
--------------------------------------------------------------
-- Data Structures and Types for AltoCore: INTERNAL MODULE.
AltoFileHandle: TYPE = POINTER TO alto UFileObject;
UPageNumber: TYPE = PageNumber;
AltoPageNumber: TYPE = SegmentDefs.PageNumber; -- equal 1+UPageNumber
CAsPtr: TYPE = POINTER TO ARRAY [0..0) OF gsD.MemoryPagePtr;
VDA: TYPE = AltoFileDefs.vDA; -- Rename vDA to standard spelling.
-- END of AltoCore: INTERNAL MODULE;
-- VDATable: INTERNAL MODULE =
-- The vDA table is represented as a set of chunks, indexed by a descriptor block.
TableGetVDA: PROCEDURE [vDATable: VDATablePtr, page: AltoPageNumber]
RETURNS [vDA: VDA];
-- Look in vDATable for page. Return the contents of the entry if present; otherwise, return fillinDA.
TablePutVDA: PROCEDURE
[vDATable: VDATablePtr, page: AltoPageNumber, vDA: VDA] ;
-- Puts the pair (page, vDA) in vDATable. The auxilliary entries which overlap between chunks are also stored. Adds a new chunk if necessary.
CallProcedureForChunks: PROCEDURE
[firstPage, lastPage: AltoPageNumber,
aFH: AltoFileHandle,
proc: PROCEDURE
[firstP, lastP: AltoPageNumber, aFH: AltoFileHandle, vDAPtr: VDAsPtr]
RETURNS [erc: ovD.ErrorCode] ]
RETURNS [erc: ovD.ErrorCode] ;
-- The proc is called for each included chunck of the vDA array, unless it asks to be stopped via returning a non-ok ErrorCode. At each call to "proc", the vDAs array and its limits are given as args.
-- The ErrorCode returned is the one returned by proc.
----------------------------------------------
-- Data Structures and Types for VDATable: INTERNAL MODULE.
-- Stuff to define Chunk Table, see also CoreDefs.mesa.
chunkSpan: CARDINAL = 64; -- Number of pages per chunk.
lowerPad: CARDINAL = 1; -- Number of extra entries before chunk.
upperPad: CARDINAL = 1; -- Number of extra entries after a chunk.
chunkSize: CARDINAL = chunkSpan+lowerPad+upperPad; -- Includes extra entries.
maxVDAIndex: CARDINAL = (numberOfChunks*chunkSpan)-1;
-- Chunk addressing structure, an example: Using chunkSpan=32 and numberOfChunks=3, let chunk0,1,2 be the address of memory allocated for the three chunks respectively. Then a VDAArray will have vDAArray[0]=chunk0, cDAArray[1]=(chunk1-32), and vDAArray[2]=(chunk2-64). Assuming that there are no holes, to get to entry i you can say "vDAArray[i/32]↑[i]".
-- END of VDATable: INTERNAL MODULE;
-- FilenameCache: INTERNAL MODULE =
-- Filenames and their associated Mesa FileHandles are cached for faster opening of a file that has been opened previously or inserted in the cache at startup time.
-- Empty. See CoreSS.
-- END of FilenameCache: INTERNAL MODULE;
-- FreePageMonitor: INTERNAL MODULE;
-- This module is responsible for maintaining a free page count and announcing changes to the client.
UpdateFreePageCount: PROCEDURE ;
-- This is called internally to set up (and announce if necessary and enabled) the free page tally by actually counting whenever currentFPC might be wrong.
DecrementFreePageCount: PROCEDURE [deltaFPC: CARDINAL] ;
-- This is called internally to change (and announce if necessary and enabled) the free page tally by subtracting deltaFPC from the current total.
-- END of FreePageMonitor: INTERNAL MODULE;
END.; -- of Core Division implementation.