If the CMSCB fcbmembr field contains a member name (filled in by FILEDEF
with the member option), DMSSOP issues an OS FIND macro to position the
file pointer to the correct member. If an error occurs on the call to
the FIND macro, error message DMSSOP036E appears and DMSSOP does not
open the DCB. • BSP (backspace) Routine -- Upon entry, backspace checks for the FCB OS bit. If it is on, the BSP routine calls DMSROS (ROSNTPTB) to
backspace the TTR and control returns to the calling routine. • FIND (type_D) Routine -- Upon entry to find, the find routine checks
the FCB OS bit. If it is on, the FIND routine takes the as FST address from the CMSCB or, if the CONCAT bit is on, from the global MlCLIB list. The FIND routine then calls (ROSFIND) to find
the member name and TTR. DMSROS searches for a matching me.ber name or, if the FCBMVPDS option is specified, a higher member na.e. If the returu code G OL 0, uL If the iCBCAThL is not on,
control returns to the calling routine with the return code fro. DMSROS. If the return code is 4 and the FCBCATeL bit is on, DeSSVT checks to determine if all the global M!CLIBS were searched. If they
were, control returns to the calling routine with the DMSROS return
code. If they were not, DMSSVT issues the FIND on the next MACLIB in
the global list. • BLDL Routine--BLDL list = FF LL NAME TTR KZC DATA • If the DCB refers to an as disk, the BLDL routine fills in the TTR, C-byte and data field from the os data set. SEARCH Routine --The search
currently active is included
currently accessible.
routine
in the
ensures that any as
search order of all
disk
disks • DISK Routine --The disk routine displays the status of any or alIOS disks using the following fora: 'MODE(CUU): (NO. CILS.), TIPE RIO - OS.' DMSSTT MODULE -- DMSSTT verifies that the disk being searched is an OS dIsk:- nMSSTT calls DMSLFS to get the FST associated with the data set. Upon return from DMSLFS, DMSSTT checks the return code to ensure that CMS supports the data set attributes. A return code of 81 or 82
indicates that CMS does not support the data set and message DftSSTT229E occurs to that effect. DftSSTT then clears the FST copy with binary
zeros, and moves the filename, filetype, file.ode, BLKSIZE, LRECL, RECFM, and flag byte to the FST copy. From this point on, co.mon code
execution occurs for both CMS and os disks. • CHRCNVRT Routine --The CHRNCVRT routine converts a CCHH address to a
relative track address.
2-136 IBM VM/370 System Logic and Program Determination--Volume 2

• CHKSENSE Routine CHKSENSE checks sense bits to determine the
recoverability of a unit check error if one occurs. • CHKITNT Routine CHKITNT checks to determine if the end of split
cylinder or the end of extent occurred, and, if so, updates to the
next split cylinder or extent. • DISKIO Routine -- DISKIO starts I/O operation on a CCW string via a DIAGNOSE X'20'. • GETALT Routine --GETALT switches reading from alternate track to
prime track, and from prime track to alternate track. • RDCNT Routine --RDCNT reads count fields on the track to deter.ine
the last record number on the track. • SETXTNT Routine -- SETITNT sets OSFSTEND to the value of the end of the extent and, if a new extent is specified, sets CCHHR to the value
of the start of the extent. Simulating a DOS Environment under eMS CMS/DOS is a functional enhancement to CMS that provides Des
installations with the interactive capabilities of a VM/370 virtual machine. CMS/DOS operates as the background DOS partition; the other
four partitions are unnecessary, since the CMS/DOS virtual machine is a
one-user machine. CMS/DOS provides read access to real DOS data sets, but not write or
update access. Real DOS private and system relccatable, source
statement, and core-image libraries can be read. This read capability is
supported to the extent required to support the CMS/DOS linkage editor,
the DOS/PLI and DOS/VS COBOL compilers, the FETCH routine, and the RSERV, SSERV, and ESERV commands. No read or write capatility exists fer
the DOS procedure library, except for copying procedures from the
procedure library (via the PSERV command) or displaying the procedure
library (via the DSERV command) • CMS/DOS does not sUPFort the standard label cylinder.
INITIALIZING DOS AND PROCESSING DOS SYSTEM CONTROL COMMANDS Initialization of the CMS/DOS operating environment requires the setting
of flags and the creation of certain data areas in storage. Once initialized, these flags and data areas may then be changed by routines
invoked by the system control commands.
Five modules are described in this section: • DMSSET Activates the CMS/DOS environment control blocks to be used
during CMS/DOS processing. • DMSOPT Sets or resets compiler execution-time options. • DMSASN Relates logical units to physical units. • DMSLLU Lists the assignments of CMS/DOS physical units. • DMSDLB Associates a DTF with a logical unit for CMS/DOS processing. eMS Method of Operation and Program Organization 2-137