Access to files

Access to files is executed by calling action macros for the various access methods. DMS also handles the opening and closing of files (OPEN/CLOSE processing) as a function of the access method involved.

DMS macros for file processing (“service macros”)

The DMS macros for file processing (i.e. the “service macros”) are macro calls which are valid for all access methods.

Macro	Brief description
CLOSE	closes one or more files.
EXLST	defines error exits.
EXRTN	implements a return from EXLST routines.
FCB	creates a file control block (FCB).
FCBAD	creates the FCB in the literal pool of a program.
LBRET	implements a return from user label handling routines (tape processing).
OPEN	opens a file.

Macros specific to the access methods

A distinction is made between the following access methods:

• BTAM

• DIV

• EAM

• FASTPAM

• SAM

• ISAM

• UPAM

Access takes place in the familar way for encrypted files (with plain text content). Decryption when reading and encryption when writing are performed internally and automatically. The macros for file access in a program do not need to be modified for this purpose. Before a file is opened it is only necessary to enter the associated crypto password in the crypto password table of the accessing task. This can be done before the program is started.

In the tables below, the macros used for file access are assigned to the various access methods.

BTAM (Basic Tape Access Method)

BTAM is an access method for block-oriented tape processing; it can also be used to process tape files which were not created with BTAM. During processing of a tape file, the direction in which the file is processed can be changed as desired within the file, and tapes can be positioned to any desired block or section. BTAM processes files with or without standard blocks.

Macro	Brief description
BTAM	controls all BTAM actions.
FEOV	initiates a tape swap.
NDWERINF	interrogates the status bytes.

DIV (Data In Virtual)

The basis for file processing for a user is 4KB blocks. DIV can also be used to process files that were not created with DIV.

Macro	Brief description
DIV	Process files with the DIV access method open a file define a window (i.e. a work area in virtual address space) write modified pages from the window back to the file on disk undo changes in the window release windows in virtual address space close a file, releasing any existing windows with default values, if applicable

EAM (Evanescent Access Method)

EAM is used to process task-specific temporary files in the SYSEAM area. It is a block-oriented access method and is particularly suitable for rapid processing of task-specific work files.

Macro	Brief description
EAM	Controls all EAM accesses

FASTPAM (Fast Primary Access Method)

FASTPAM is a block-oriented access method which always works with 4KB blocks. FASTPAM can also be used to process files that were not created with FASTPAM.

Macro	Brief description
FPAMACC	File access functions
	read and write blocks synchronously read and write blocks asynchronously wait for the end of asynchronous I/O jobs report the end of asynchronous I/O jobs
FPAMSRV	Management functions
	enable the system environment (FASTPAM environment) enable I/O areas (FASTPAM I/O area pool) open a file for processing close a file opened with FPAMSRV disable the system environment (FASTPAM environment) disable I/O areas (FASTPAM I/O area pool)

SAM (Sequential Access Method)

SAM is a record-oriented access method. The records are stored sequentially in the file. SAM lets users process records sequentially in either direction (beginning-of-file to end-of-file or vice versa). For tape processing, SAM complies with all requirements of DIN 66029 up to exchange level 3. Files with either standard or nonstandard blocks can be processed.

Macro	Brief description
FEOV	initiates a tape swap.
GET	retrieves the next record.
PUT	writes the next record.
PUTX	(locate mode only) replaces a record read by means of GET.
RELSE	terminates a data block.
SETL	positions to beginning-of-file, to end-of-file, or to a record.

ISAM (Indexed-Sequential Access Method)

The basis for file processing is the structure of an ISAM file with its index and data sections. Each record contains a key and the keys are the criterion for sorting the record. For index and data blocks, see the “Introductory Guide to DMS” [1].

Macro	Brief description
ADDPLNK	assigns a pool link name to a user ISAM pool.
CREAIX	creates a secondary index for an ISAM file.
CREPOOL	sets up a user ISAM pool.
DELAIX	deletes secondary indices of an ISAM file.
DELPOOL	deletes a user ISAM pool.
ELIM	deletes a record from the file.
GET	reads the records from the file sequentially.
GETFL	if flagged ISAM keys are used: reads the next record within the flag range (sequentially).
GETKY	reads the first record with the specified key.
GETR	reads the records sequentially in reverse order.
INSRT	inserts a record into the file with a new ISAM key.
ISREQ	clears an ISAM lock.
OSTAT	informs the caller about the number and type of concurrent file accesses.
PUT	sequentially writes records to the end of the file (and also checks that the keys are in the right order).
PUTX	replaces a record read previously.
REMPLNK	deletes the pool link name.
RETRY	after execution of the EXLST PGLOCK exit, resets the ISAM pointer and repeats the last macro.
SETL	positions the ISAM pointer to the beginning of the file, to the end of the file or to a specific record for subsequent processing.
SHOPLNK	provides information about the assignment of ISAM pools to pool link names.
SHOPOOL	provides information about attributes and assignment status of ISAM pools.
SHOWAIX	provides information about secondary indices of an ISAM file.
STORE	inserts a record with a new ISAM key into the file, or overwrites a record with an existing ISAM key if duplicate ISAM keys are not permitted, or inserts into the file a record with an existing ISAM key as the last record with this key.

UPAM (User Primary Access Method)

UPAM is a block-oriented access method. The basis of UPAM is the standard block (= PAM page). UPAM can also be used to process files that were not created with UPAM.

Macro	Brief description
PAM	Controls all UPAM accesses

For event-driven processing, the following macros are also significant (for detailed descriptions, see the “Executive Macros” [2] manual).

Macro	Brief description
CHKEI	checks the queue status for an event item.
CONTXT	accesses the register set of the interrupted task/process.
DISCO	closes the routine for the contingency process.
DISEI	disconnects the user program from the event item.
ENACO	opens a routine as a contingency process and assigns it a name and a priority.
ENAEI	creates an event item and/or establishes the link between the calling process and the event item.
FECB	creates a file event control block.
LEVCO	changes the priority of the called process.
POSSIG	signals an event.
RETCO	terminates the calling contingency process.
SOLSIG	requests a signal from the event item.
SUSPEND	places the calling process in an interruptible wait state.