IBM System/360 System Programmer's Guide

HOW TO READ A JOB FILE CONTROL BLOCK
To accomplish the functicns that are performed as a result of an OPEN
macro-instruction, the OPEN routine requires access to information that
you have supplied in a data definition (DO) statement. This information
is stored by the system in a job file control block (JFCB).
usually, the programmer is not concerned with the JFCB itself. In
special applications, however, you may find it necessary to modify the
contents of a JFCB before issuing an OPEN nacro-instruction. To assist
you, the system provides the RDJFCB rr.acro-instruction. This macro-
instruction causes a specified JFCB to be read into main storage from
the job queue in which it has been stored. Forroat and field description
of the JFCB is contained in the System Control Block publication.
When subsequently issuing the OPEN rracro-instruction, you must
indicate, by specifying the TYPE=J option, that you have supplied a
modified JFCB to be used during the initialization process.
The JFCB is returned to the job queue by the OPEN routine or the
OPENJ routine, if any of the modifications in the following list occur.
These modifications can occur only if the inforroation is not originally
in the JFCB.
• Expiration date field and creation date field merged into the JFCB
from the DSCB.
•
Secondary quantity field merged into the JFCB from the DSCB.
•
DCB fields merged
into the
JFCB
from the
DSCB.
•
DCB fields merged into the
JFCB
from
the
DCB.
•
Volume serial number fields
added to the JFCB.
•
Data
set sequence
number field added to the JFCB.
•
Number of volumes
field added to the JFCB.
If you make these, or any other rocdifications, and you want the JFCB
returned tc the job queue, you must set the high-order bit of field
JFCBMASK+4 to one. This field is in the JFCB. Setting the high-order
bit of field JFCBMASK+4 to zero does not necessarily suppress the return
of the JFCB to the job queue. If the OPEN or OPENJ routines have made
any of the above modif~cations, the JFCB is returned to the job queue.
OPEN -- Prepare the Data Control Block for Processing (S)
The OPEN macro-instruction initializes one or more data control
blocks so that their associated data sets can be processed.
A full explanation of the operands of the OPEN macro-instruction,
except for the TYPE=J option, is contained in the publication IBM
System/360 Operating System: Control Prograro Services. The TYPE=J
option, because it is used in conjunction with modifying a JFCB, should
be used only by the system programmer or only under his supervision.
r----------T----------T------------------------------------------------,
I Name I Operation I Operand I
~----------+----------+------------------------------------------------~
I [symJ:::ol] I OPEN I ({ dcb-addr, [ (optl. -code [ , opt
2
-code] ) 1 , } ••. ) I
I I I
[,TYPE=J] I
L __________ L __________ L ________________________________________________ J
130

IBM System/360 Specifications

General

Brand	IBM
Model	System/360
Category	Desktop
Language	English