-- file Core.mesa
-- Last edited by Brotz, November 20, 1981  2:39 PM.

DIRECTORY
  AltoFileDefs USING [FP],
  VMDefs USING [FileHandle];

Core: DEFINITIONS =

BEGIN


-- Core is a remnant of the once mighty Laurel CoreDefs.  It now provides a thin veneer
--   over the VM package to make it suitable for use in Laurel.  The major functions
--   provided by this interface are:

-- (1) To give a uniform way to open files on the local disk or on remote servers.
--   The file name format is: [Site]<Directory>SimpleName.Extension

-- (2) To guard against opening files illegally, both those files that should never be touched
--   by a client (such as DiskDescriptor, Laurel.run, etc.) and those files that are currently
--   open by the client.

-- Core provides a file name cache, which contains the names of all currently open files, the
--   names of files that must not be opened under any circumstances, and if room permits
--   (up to the cache limits), a mapping of file name to Alto FP for certain commonly used
--   files that are not currently open.

-- Exported variable --

localCacheHead: CacheHeader;


-- Procedures --


Login: PROCEDURE [user: DMSUser];
-- Notifies the Core of the new name, registry and password to be used on subsequent
--   Open's.


Open: PROC [filename: STRING, mode: OpenMode] RETURNS [handle: VMDefs.FileHandle];
-- Opens "filename" in "mode", and returns a handle to the opened file.
-- ERRORS:
-- VMDefs.CantOpen (notFound, alreadyExists, accessDenied, illegalFileName)
-- VMDefs.Error (io, resources, credentials) [io = unrecoverable disk error or communications
--   failure for remote files, resources = disk full or directory limit on remote server,
--   credentials = credentials presented at Login were not sufficient to permit this Open].


Close: PROCEDURE [handle: VMDefs.FileHandle];
-- Closes the file associated with "handle".  "handle" must not be re-used by the caller.


Delete: PROCEDURE [handle: VMDefs.FileHandle];
-- Deletes the file associated with "handle".  "handle" must not be re-used by the caller.


InsertInFileCache: PROC [name: STRING, fp: AltoFileDefs.FP, open: BOOLEAN _ TRUE]
  RETURNS [entry: LocalCacheEntry];
-- Inserts "name" and "fp" in the Alto file name cache.
-- To protect a file from being opened, "open" should be TRUE.  In this case, subsequent
--   Open's on this file will fail with VMDefs.Error[alreadyExists].
-- Possible uses of this procedure are to provide faster Open's and to protect critical files as
--   described above.


LookupInFileCache: PROCEDURE [name: STRING] RETURNS [fp: AltoFileDefs.FP];
-- Returns the FP associated with the name (or NullFP if no such file).


FreeCacheEntry: PROCEDURE [name: STRING];
-- Removes the cache entry for "name" from the local file cache (if it existed).
-- May call SysBug if that file is marked open.


-- Data Structures and Types.


DMSUserBlk: TYPE = RECORD [name: STRING, registry: STRING, password: STRING];
DMSUser: TYPE = POINTER TO DMSUserBlk;

OpenMode: TYPE = {read, update};
-- read: Read only; the file must exist
-- update: Read + Write + Append; if the file exists then the old version is referenced,
--   otherwise, a new file is created.

CacheHeaderBlk: TYPE = RECORD
  [server: STRING,
  firstEntry: CacheEntry,
  lastEntry: CacheEntry,
  next: CacheHeader,
  prev: CacheHeader];
CacheHeader: TYPE = POINTER TO CacheHeaderBlk;

CacheEntryBlk: TYPE = RECORD
  [next: CacheEntry,
  prev: CacheEntry,
  name: STRING,
  handle: VMDefs.FileHandle,
  open: BOOLEAN,
  vp: SELECT location: Location FROM
    local => [fp: AltoFileDefs.FP],
    remote => [loginEpoch: CARDINAL],
    ENDCASE];
CacheEntry: TYPE = POINTER TO CacheEntryBlk;
LocalCacheEntry: TYPE = POINTER TO local CacheEntryBlk;
RemoteCacheEntry: TYPE = POINTER TO remote CacheEntryBlk;

Location: TYPE = {local, remote};


END.  -- of Core --z20461(529)\f1