Once a file is created using keys, additions to the file must not be made without
using keys and specifying the original length.
Note that there is limited support from the CMS file system for BDAM-created
files (sparse). Sparse files are manipulated with CMS commands but are not
treated as sparse files by most CMS commands. The number of records in the
FST are treated as a valid record number.
The number of records in the data set extent must be specified using the
FILEDEF command. The default size is 50 records.
The minimum LRECL for a CMS BDAM file with keys is eight bytes.
Reading OS Data Sets and VSE Files Using OS Macros
The ACCESS Command
CMS users can read as sequential and partitioned data sets that that reside on as
disks. The CMS MOVEFILE command can be used to manipulate those data sets,
and the as QSAM, BP AM macros can be executed under CMS to read them.
The CMS MOVEFILE command can be used to manipulate and read VSE sequen­
tial files that reside on DOS disks. as macros, however, can only be used to read
sequential files from DOS formatted CKD disks. as macros are not supported for
reading sequential files on DOS formatted FB-512 disks.
The following as Release 20.0 BSAM, BP AM, and QSAM macros can be used
with CMS to read as data sets and DOS files:
BLDL BSP CHECK CLOSE DEQ DEVTYPE ENQ
FIND
GET NOTE POINT POST RDJFCB
READ
SYNADAF
SYNADRLS
WAIT
CMS supports the following disk formats for the as and OS/VS sequential and
partitioned access methods:
Split cylinders
User labels
Track overflow
Alternate tracks
As in as, the CMS support of the BSP macro produces a return code of 4 when
attempting to backspace over a tape mark or when a beginning of an extent is
found on an as data set or a VSE file. If the data set or file contains split
cylinders, an attempt to backspace within an extent, resulting in a cylinder switch,
also produces a return code of 4.
Before CMS can read an as data set or VSE file that resides on a non-CMS disk,
you must issue the CMS ACCESS command to make the disk on which it resides
available to CMS. The format of the ACCESS command can be found in the VMjSP CMS Command and Macro Reference. You must not specify options or
file identification when accessing an as or DOS disk.
as Macro Simulation Under eMS 383 .
The FILEDEF Command
You then issue the FILEDEF command to assign a CMS file identification to the
as data set or VSE file so that CMS can read it. The complete format of the
FILEDEF command is found in the VMISP CMS Command and Macro Reference.
If you are issuing a FILEDEF for a VSE file, note that thc as program that will
use the VSE file must have a DCB for it. For "ddname" in the FILEDEF com­
mand line, use the ddname in that DCB. With the DSN operand, enter the file-id
of the VSE file.
Sometimes, CMS issues the FILEDEF command for you. Although the CMS MOVEFILE command, the supported CMS program interfaces, and the CMS OPEN routine each issue a default FILEDEF, you should issue the FILEDEF
command yourself to ensure the appropriate file is defined.
After you have issued the ACCESS and FILEDEF commands for an as sequential
or partitioned data set or as sequential file, CMS commands (such as ASSEMBLE
and STATE) can refer to the as data set or VSE file just as if it were a CMS file.
Several other CMS commands can be used with as data sets and VSE files that do
not reside on CMS disks. See the VMISP CMS Command and Macro Reference
for a complete description of the CMS ACCESS, FILEDEF, LISTDS, MOVEFILE, QUERY, RELEASE, and STATE commands.
For restrictions on reading as data sets and VSE files under CMS, see the VM I SP Planning Guide and Reference.
The CMS FILEDEF command allows you to specify the 110 device and the file
characteristics to be used by a program at execution time. In conjunction with the
as simulation scheme, FILEDEF simulates the functions of the data definition
JCL statement.
FILEDEF may be used only with programs using as macros and functions. For
example:
filedef file 1 disk proga data a 1
After issuing this command, your program referring to FILE 1 would access PROGA DATA on your A-disk.
If you wished to supply data from your terminal for FILEl, you could issue the
command:
filedef file 1 terminal
and enter the data for your program without recompiling.
fi tape in tap2 (recfm fb Irecl50 block 100 9track den 800) After issuing this command, programs referring to T APEIN will access a tape at
virtual address 182. (Each tape unit in the CMS environment has a symbolic name
associated with it.) The tape must have been previously attached to the virtual
machine by the VM/SP operator.
384 VM/SP System Programmer's Guide
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