HP OpenVMS I/O User’s Reference Manual: OpenVMS Version 8.4 > Chapter 2 Disk Drivers
2.5 Disk Driver Programming Example
A sample MACRO
32 disk driver program, DISK_DRIVER.MAR, is shown in Example 2-1. This sample program provides
an example of optimizing access time to a disk file. The program creates
a file using Record Management Services (RMS), stores information
concerning the file, and closes the file. The program then accesses
the file and reads and writes to the file using the Queue I/O ($QIO)
system service. Example 2-1 DISK_DRIVER.MAR Disk Driver Programming Example |
; ********************************************************************
;
.TITLE Disk Driver Programming Example
.IDENT /01/
;
; Define necessary symbols.
;
$FIBDEF ;Define file information block Offsets
$IODEF ;Define I/O function codes
$RMSDEF ;Define RMS-32 Return Status Values
;
; Local storage
;
; Define number of records to be processed.
;
NUM_RECS=100 ;One hundred records
;
; Allocate storage for necessary data structures.
;
; Allocate File Access Block.
;
; A file access block is required by RMS-32 to open and close a
; file.
;
FAB_BLOCK: ;
$FAB ALQ = 100,- ;Initial file size is to be
- ;100 blocks
FAC = PUT,- ;File Access Type is output
FNA = FILE_NAME,- ;File name string address
FNS = FILE_SIZE,- ;File name string size
FOP = CTG,- ;File is to be contiguous
MRS = 512,- ;Maximum record size is 512
- ;bytes
NAM = NAM_BLOCK,- ;File name block address
ORG = SEQ,- ;File organization is to be
- ;sequential
REM = FIX ;Record format is fixed length
;
; Allocate file information block.
;
; A file information block is required as an argument in the
; Queue I/O system service call that accesses a file.
;
FIB_BLOCK: ;
.BLKB FIB$K_LENGTH ;
;
; Allocate file information block descriptor.
;
FIB_DESCR: ;
.LONG FIB$K_LENGTH ;Length of the file
;information block
.LONG FIB_BLOCK ;Address of the file
;information block
;
; Allocate File Name Block
;
; A file name block is required by RMS-32 to return information
; concerning a file (for example, the resultant file name string
; after logical name translation and defaults have been applied).
;
NAM_BLOCK: ;
$NAM ;
;
; Allocate Record Access Block
;
; A record access block is required by RMS-32 for record
; operations on a file.
;
RAB_BLOCK:
$RAB FAB = FAB_BLOCK,- ;File access block address
RAC = SEQ,- ;Record access is to be
- ;sequential
RBF = RECORD_BUFFER,- ;Record buffer address
RSZ = 512 ;Record buffer size
;
; Allocate direct address buffer
;
BLOCK_BUFFER:
.BLKB 1024 ;Direct access buffer is 1024
;bytes
;
; Allocate space to store channel number returned by the $ASSIGN
; Channel system service.
;
DEVICE_CHANNEL: ;
.BLKW 1 ;
;
; Allocate device name string and descriptor.
;
DEVICE_DESCR: ;
.LONG 20$-10$ ;Length of device name string
.LONG 10$ ;Address of device name string
10$: .ASCII /SYS$DISK/ ;Device on which created file
;will reside
20$: ;Reference label to calculate
;length
;
; Allocate file name string and define string length symbol.
;
FILE_NAME: ;
.ASCII /SYS$DISK:MYDATAFIL.DAT/ ;File name string
FILE_SIZE=.-FILE_NAME ;File name string length
;
; Allocate I/O status quadword storage.
;
IO_STATUS: ;
.BLKQ 1 ;
;
; Allocate output record buffer.
;
RECORD_BUFFER: ;
.BLKB 512 ;Record buffer is 512 bytes
;
; ********************************************************************
;
; Start Program
;
; ********************************************************************
;
; The purpose of the program is to create a file called MYDATAFIL.DAT
; using RMS-32; store information concerning the file; write 100
; records, each containing its record number in every byte;
; close the file; and then access, read, and write the file directly,
; using the Queue I/O system service. If any errors are detected, the
; program returns to its caller with the final error status in
; register R0.
.ENTRY DISK_EXAMPLE,^M,R3,R4,R5,R6> ;Program starting
;address
;
; First create the file and open it, using RMS-32.
;
PART_1: ;First part of example
$CREATE FAB = FAB_BLOCK ;Create and open file
BLBC R0,20$ ;If low bit = 0, creation
;failure
;
; Second, connect the record access block to the created file.
;
$CONNECT RAB = RAB_BLOCK ;Connect the record access
;block
BLBC R0,30$ ;If low bit = 0, creation
;failure
;
; Now write 100 records, each containing its record number.
;
MOVZBL #NUM_RECS,R6 ;Set record write loop count
;
; Fill each byte of the record to be written with its record number.
;
10$: SUBB3 R6,#NUM_RECS+1,R5 ;Calculate record number
MOVC5 #0,(R6),R5,#512,RECORD_BUFFER ;Fill record buffer
;
; Now use RMS-32 to write the record into the newly created file.
;
$PUT RAB = RAB_BLOCK ;Put record in file
BLBC R0,30$ ;If low bit = 0, put failure
SOBGTR R6,10$ ;Any more records to write?
;
; The file creation part of the example is almost complete. All that
; remains to be done is to store the file information returned by
; RMS-32 and close the file.
;
MOVW NAM_BLOCK+NAM$W_FID,FIB_BLOCK+FIB$W_FID ;Save file
;identification
MOVW NAM_BLOCK+NAM$W_FID+2,FIB_BLOCK+FIB$W_FID+2 ;Save
;sequence number
MOVW NAM_BLOCK+NAM$W_FID+4,FIB_BLOCK+FIB$W_FID+4 ;Save
;relative volume
$CLOSE FAB = FAB_BLOCK ;Close file
BLBS R0,PART_2 ;If low bit set, successful
;close
20$ RET ;Return with RMS error status
;
; Record stream connection or put record failure.
;
; Close file and return status.
;
30$: PUSHL R0 ;Save error status
$CLOSE FAB = FAB_BLOCK ;Close file
POPL R0 ;Retrieve error status
RET ;Return with RMS error status
;
; The second part of the example illustrates accessing the previously
; created file directly using the Queue I/O system service, randomly
; reading and writing various parts of the file, and then deaccessing
; the file.
;
; First, assign a channel to the appropriate device and access the
; file.
PART_2: ;
$ASSIGN_S DEVNAM = DEVICE_DESCR,- ;Assign a channel to file
CHAN = DEVICE_CHANNEL ;device
BLBC R0,20$ ;If low bit = 0, assign
;failure
MOVL #FIB$M_NOWRITE!FIB$M_WRITE,- ;Set for read/write
FIB_BLOCK+FIB$L_ACCTL ;access
$QIOW_S CHAN = DEVICE_CHANNEL,- ;Access file on device channel
FUNC = #IO$_ACCESS!IO$M_ACCESS,- ;I/O function is
- ;access file
IOSB = IO_STATUS,- ;Address of I/O status
- ;quadword
P1 = FIB_DESCR ;Address of information block
;descriptor
BLBC R0,10$ ;If low bit = 0, access
;failure
MOVZWL IO_STATUS,R0 ;Get final I/O completion
;status
BLBS R0,30$ ;If low bit set, successful
;I/O function
10$: PUSHL R0 ;Save error status
$DASSGN_S CHAN = DEVICE_CHANNEL ;Deassign file device channel
POPL R0 ;Retrieve error status
20$: RET ;Return with I/O error status
;
; The file is now ready to be read and written randomly. Since the
; records are fixed length and exactly one block long, the record
; number corresponds to the virtual block number of the record in the
; file. Thus a particular record can be read or written simply by
; specifying its record number in the file.
;
; The following code reads two records at a time and checks to see
; that they contain their respective record numbers in every byte.
; The records are then written back into the file in reverse order.
; This results in record 1 having the old contents of record 2 and
; record 2 having the old contents of record 1, and so forth. After
; the example has been run, it is suggested that the file dump
; utility be used to verify the change in data positioning.
;
30$ MOVZBL #1,R6 ;Set starting record (block)
;number
;
; Read next two records into block buffer.
;
40$: $QIO_S CHAN = DEVICE_CHANNEL,- ;Read next two records from
- ;file channel
FUNC = #IO$_READVBLK,- ;I/O function is read virtual
- ;block
IOSB = IO_STATUS,- ;Address of I/O status
- ;quadword
P1 = BLOCK_BUFFER,- ;Address of I/O buffer
P2 = #1024,- ;Size of I/O buffer
P3 = R6 ;Starting virtual block of
;transfer
BSBB 50$ ;Check I/O completion status
;
; Check each record to make sure it contains the correct data.
;
SKPC R6,#512,BLOCK_BUFFER ;Skip over equal record
;numbers in data
BNEQ 60$ ;If not equal, data match
;failure
ADDL3 #1,R6,R5 ;Calculate even record number
SKPC R5,#512,BLOCK_BUFFER+512 ;Skip over equal record
;numbers in data
BNEQ 60$ ;If not equal, data match
;failure
;
; Record data matches.
;
; Write records in reverse order in file.
;
$QIOW_S CHAN = DEVICE_CHANNEL,- ;Write even-numbered record in
- ;odd slot
FUNC = #IO$_WRITEVBLK,- ;I/O function is write virtual
- ;block
IOSB = IO_STATUS,- ;Address of I/O status
- ;quadword
P1 = BLOCK_BUFFER+512,- ;Address of even record buffer
P2 = #512,- ;Length of even record buffer
P3 = R6 ;Record number of odd record
BSBB 50$ ;Check I/O completion status
ADDL3 #1,R6,R5 ;Calculate even record number
$QIOW_S CHAN = DEVICE_CHANNEL,- ;Write odd numbered record in
- ;even slot
FUNC = #IO$_WRITEVBLK,- ;I/O function is write virtual
- ;block
IOSB = IO_STATUS,- ;Address of I/O status
- ;quadword
P1 = BLOCK_BUFFER,- ;Address of odd record buffer
P2 = #512,- ;Length of odd record buffer
P3 = R5 ;Record number of even record
BSBB 50$ ;Check I/O completion status
ACBB #NUM_RECS-1,#2,R6,40$ ;Any more records to be read?
BRB 70$ ;
;
; Check I/O completion status.
;
50$: BLBC R0,70$ ;If low bit = 0, service
;failure
MOVZWL IO_STATUS,R0 ;Get final I/O completion
;status
BLBC R0,70$ ;If low bit = 0, I/O function
RSB ;failure
;
; Record number mismatch in data.
;
60$: MNEGL #4,R0 ;Set dummy error status value
;
; All records have been read, verified, and odd/even pairs inverted
;
70$: PUSHL R0 ;Save final status
$QIOW_S CHAN = DEVICE_CHANNEL,- ;Deaccess file
FUNC = #IO$_DEACCESS ;I/O function is deaccess file
$DASSGN_S CHAN = DEVICE_CHANNEL ;Deassign file device channel
POPL R0 ;Retrieve final status
RET ;
.END DISK_EXAMPLE |
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