If register 0 is positive upon entry into POINT is assumed
and ROSNTPTB loads a TTR from the address in register 0 and calls TTRCNVRT and SETXTNT to convert the TTR to a CCHHR. Then contrel
returns to the calling routine.
If register 0 is negative upon entry into DMSROS, BSP (BACKSPACE) is
assumed. The backsFace code checks to determine if the current
position is the beginning of a track. If not, the backspace code
decrements the record number by one and control then returns to the
calling routine. If the current position is the beginning of a
track, the backspace code calls CHRCNVRT to get the current ceHB.
The backspace code then calls rdcnt to get the current record number
of the last record on the new track, calls setxtnt to set the new
extent boundaries, and returns control to the calling routine. • NOTE Routine -- Upon entry to note, DMSSCT checks to determine if the DCB refers to an OS disk. If it does, DMSSCT calls DMSROS (ROSRTPTE) to get the current TTR. Control then returns to the user. • POINT Routine -- Upon entry to point, DMSSCT checks to determine if
the DCB refers to an OS disk. If it does, DMSSCT calls (ROSNTPTB) to reset the current TTR, calls CKCONCAT and returns
control to the calling • CKCONCAT Routine Upon entry to CKCONCAT, DMSSCT checks to
determine if the FCB MACLIB CORCAT bit is on. If it is on, DCBRELAD+3 sets the correct OS FST pointer the FCB and returns
control to the calling routine. If the FCE CCNCAT bit is off,
control returns to the calling routine. • FIND (type_C) Routine If the DCB refers to an OS disk, DMSSCT TTR and control returns to the • calls DMSROS (ROSNTPTB) to update the
calling routine. EOBROUTN Routine If the FCB OS bit OSREAD. Otherwise, if no special I/O FCBPROC, control passes to EOB2 in DMSSEB. is on,
routine
control passes
is specified
to
in • OSREAD Routine -- DMSSEB calls DMSROS to perform a read or write and
then control passes to EOBRETRN which, in turn, passes control back
to DMSSBS. DMSSBS passes control back to the routine calling the
read or write macro operation. -- If the MACLIB CONCAT option is on in the CMSCB, OPEN checks the MACLIB names in the global list and fills in the addresses of OS FSTS for any MACLIBS on os disks. The CMSCB of the first MACLIB in
the global list merges and initializes CMSCBS. If the CMSCB refers to a data set on an OS disk, DMSSCP checks to ensure
that the data set is accessible and the DCB dees not specify output, BDAM, or a key length. If any errors occur, error message DMSSOP036E appears and DMSSOP does not open the DCB. DMSSOP fills them in from the
os PST for the data set5 CMS Method of Operation and Program Organization 2-135

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