Access Methods

OPEN and CLOSE

This release of the Tachyon Operating System has the following limitations:

• OPEN recognizes the DCB exit list (EXLST) entry for the DCB OPEN exit. RDJFCB recognizes the JFCB and ARL entries. All other EXLST entries are ignored.
• Files are not automatically closed at task termination. Any data in buffers when a program ends will not be written.
• The FREE=CLOSE DD parameter and the FREE option on the CLOSE macro are ignored and the data set is not deallocated.

BSAM and QSAM

The Tachyon Operating System supports the BSAM and QSAM access methods for sequential, SYSIN, SYSOUT, DUMMY, UNIX files and simulated partitioned data set members and directories. Most of BSAM and QSAM is supported, with the following limitations:

• There is no support for any device other than DASD, so device-specific services for tape or 3800 printers are not supported.
• There is no support for subsystem data sets other than SYSIN and SYSOUT.
• The OPEN mode INOUT is processed as INPUT.
• User totaling, user labels and QSAM parallel access are not supported.
• Because data sets are stored in workstation files and not on devices with physical blocks, the NOTE and POINT services return a relative byte number for FILEDATA=TEXT and RECFM=U, V, VB, VS and VBS data sets. This limits the use of the NOTE and POINT services on these data sets to the first 16 megabytes.
• Spanned records are not supported by QSAM.
• Concatenated sequential data sets are supported, but the DCB’s end-of-data (EODAD) routine is entered upon encountering end-of-file on the first data set in a concatenation.

BDAM

The Tachyon Operating System supports the BDAM access method to access sequential files with fixed-length, unkeyed records (RECFM=F,KEYLEN=0,FILEDATA=RECORD) that were previously loaded using BSAM or QSAM. The CHECK, CLOSE, OPEN, READ and WRITE services are supported for a BDAM DCB. Requests for CHECK are ignored because all I/O is marked as completed after a READ or WRITE request, allowing WAIT to be used for the DECB. The BDAM DCB must have MACRF of RI, RIC, WI, WIC, (RI,WI) or (RIC,WIC). MACRF codes A, K, S and X are not supported nor are OPTCD=E and LIMCT. Only READ DI, READ DIF, WRITE DI and WRITE DIF are supported. The FREEDBUF and RELEX services are not supported.

BPAM

The Tachyon Operating System supports the BPAM access method to access simulated partitioned data sets in input mode. The BLDL, CHECK, CLOSE, DEBCHK, FIND, LINK(X), LOAD, NOTE, OPEN, POINT, READ, RDJFCB and XCTL(X) services are supported for a BPAM DCB. The limitations on NOTE and POINT for BSAM also apply to BPAM. TTRs are defined similarly to the way they are in z/OS’s PDSE support.

VSAM

The Tachyon Operating System supports the VSAM access method to access VSAM files in input mode. The OPEN and CLOSE services are supported for VSAM ACBs. The CHECK, ENDREQ, GET and POINT services are supported for VSAM RPLs. The BLDVRP and DLVRP services are ignored. The GENCB, MODCB, SHOWCB and TESTCB services are supported for VSAM control blocks. Most of VSAM for input is supported, with the following limitations:

• Because the number of buffers and strings cannot be set in the AMP parameter of the DD statement and are not supported for VSAM file definition, the ACB is the only place where the number of buffers and strings can be set. The Tachyon Operating System does not support the System Managed Buffers facility of DFSMS. The Tachyon Operating System also does not support dynamic string addition, so the STRNO field of the ACB must be large enough for all concurrent requests.
• If MAREA and MLEN are specified in the VSAM ACB, the message area will be cleared but no messages will be placed in the message area if the OPEN or CLOSE fails.
• Because this release of the Tachyon Operating System does not support output and update access and alternate indexes, the MACRF=(OUT) and MACRF=(RST) options are not allowed and the VSAM file must contain records loaded by the tosvsam utility. Also the BSTRNO field and the MACRF=(NRM|AIX), MACRF=(DDN|DSN) and MACRF=(NIS|SIS) options are ignored.
• This release of the Tachyon Operating System does not support Local Shared Resources, but it will ignore the MACRF=(LSR), MACRF=(DFR|NDF) and MACRF=(LEW|NLW) options and the SHRPOOL field to allow programs using LSR to run. Global Shared Resources and Record Level Sharing are not supported, so MACRF=(GSR) and MACRF=(RLS) are not allowed.
• The OPEN service completely ignores any bits set in the ACBINFLG field as well as the MACRF=(CFX|NFX) option.
• The following VSAM services are not supported: DIV (Data In Virtual), Media Manager, catalog services (SVC 26) and SHOWCAT.
• VSAM requests support the EODAD and LERAD exits unless the “,L” option is specified for the exit. All other EXLST entries are ignored.