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The Question is:
How i can perform analog of DCL command
SET FILE/ATTRIBUTE=RFM:STMLF
in my C program, which must executed as
a detached process(i cannot use a system() call)?
Where i can found function description?
My problem is - i can't understand how to
modify FAB in easy way, because i think,
what file descriptor structure can be
accessed only for read.
The Answer is :
The stock file record format created by C routines is stream LF.
While system() and lib$spawn are not available to a detached process
lacking a CLI, a lib$creprc() creation of a subprocess running the
LOGINOUT image is permitted. (Please see the OpenVMS FAQ for some
related information.)
The file-level record attributes are generally accessed via an
IO$_ACPCONTROL call, specifying the ATR and FAT item blocks. For
details on this API, please see the I/O User's Reference Manual.
In this particular case, the required ATR block would contain a
reference to ATR$C_RECATTR code which would reference a FAT block
where the FAT$V_RTYPE field contains FAT$C_STREAMLF.
The following example sets the DIRECTORY bit via the IO$C_MODIFY.
This involves using ATR$C_UCHAR rather than the ATR$C_RECATTR
code needed to access the FAT$C_STREAMLF field, but is otherwise
rather similar to what would need to be done to alter the record
attributes.
--
.title SETDIRBIT fixes the DIRECTORY bit
;
; this program is used to turn on the "DIRECTORY" bit in the
; file header. The file (more correctly directory) to be
; reset is specified by FID (file identification) and device.
; (The FID can be retrieved from a DIRECTORY/FULL command.)
;
; a) Put the FID into the "fid" buffer, below.
;
; b) The device the FID is from must also be plugged into
; the "dev" descriptor, below.
;
; The UCHAR field is protected -- see the I/O Abuser's Guide,
; Part I, ACP/QIO Interface. (SYSTEM or OWNER access to the
; file (directory) is required.)
;
; 11-Apr-1988 Stephen Hoffman, DIGITAL Equipment Corp.
; This was written up... No claims to style or content:
; intended simply to solve a one-shot problem. MINIMAL
; error checking and user-hostile!
;
.library 'Sys$Library:LIB.Mlb'
$atrdef ; File attribute definitions
$fchdef ; File characteristics
$fibdef ; File Information Block
$iodef ; I/O definitions
$ssdef ; System Service Definitions
.psect data,wrt,noexe,long,noshr,usr
fid: ; A file id (FID) looks like this: [NUM,SEQ,RVN]
.word 652 ; file NUM
.word 9 ; file SEQ
.word 0 ; file RVN
.word 0 ; (so we can use a MOVQ)
;
dev: ; And the name of the disk the file id is from...
.ascid /HSC000$DUA2:/
;
iosb: .blkw 4 ; garden variety IOSB
;
fchan: .blkw 1 ; channel to the disk
;
FIBSIZE=22 ; use the short FIB
fibbuf: .blkb FIBSIZE ; here's the FIB itself
fib: .long FIBSIZE ; here's the FIB descriptor
.address fibbuf
;
uchar: .blkb ATR$S_UCHAR ; the FAT characteristics buffer
fat: ; The File Attributes itemlist follows:
.word ATR$S_UCHAR ; length of the buffer
.word ATR$C_UCHAR ; address of the buffer
.address uchar ; where the UCHAR field is...
.blkq 0 ; zero marks the end...
;
.psect code,nowrt,exe,long,shr,usr
.entry SETDIRBIT, ^M<R2>
;
; Get a channel to the device
;
$ASSIGN_S -
devnam=dev,-
chan=fchan
blbs r0,10$
ret
;
10$: ;
; Move the two important "bits" of trivia out to the FIB.
;
moval fibbuf,R0
movq fid,FIB$W_FID(R0)
movl #FIB$M_WRITE,FIB$L_ACCTL(R0)
;
; Access the file (directory)
;
$QIOW_S -
chan=fchan,-
func=#<IO$_ACCESS!IO$M_ACCESS>,-
iosb=IOSB,-
p1=fib,-
p5=#fat
blbc r0,19$
blbs iosb,20$
19$: ret
;
20$: ;
; Force the DIRECTORY bit on!
;
bisl2 #FCH$M_DIRECTORY,uchar
;
; Write the modified characteristics out...
;
$QIOW_S -
chan=fchan,-
func=#<IO$_MODIFY>,-
iosb=IOSB,-
p1=fib,-
p5=#fat
blbc r0,29$
blbs iosb,30$
29$: ret
;
30$: ;
; And deaccess the file (directory)
;
$QIOW_S -
chan=fchan,-
func=#<IO$_DEACCESS>,-
iosb=IOSB
blbc r0,39$
blbs iosb,40$
39$: ret
;
40$: ;
; Deassign the channel to the disk
;
$DASSGN_S -
chan=fchan
movzwl #SS$_NORMAL,R0
;
; And bail out...
;
ret
.END SETDIRBIT
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