In performing the functions requested in this file, AMS may require
execution ofDOSjVS iSAM phases located in the CMSVSAM DCSS. The CMSVSAM DCSS is loaded when AMS opens the VSAM catalog for processing. On return fro. DOS/VS code, DMSAMS purges the CMSAMS DCSS, and issues
DLBL commands for theSYSIPT and SYSLST files to clear the DOSCB's for
these ddnames.Control is then passed to DMSVSR, which
the userprogram was not in the CMSjDOS entered, the SET DOS OFF command is issued DMSVSR, DMSAMS performs minor housekeeping CMS. purges the CMSVSAM DCSS. If
environment whenDMSAMS was by DMSVSR. Upon return from tasks and returns control to
Executing aVSAM Function for a DOS User
When aVSAM function, such as an OPEN or CLOSE macro, is requested from DOS throqgh the CMSDOS ness to the CMSVS!M DCSS, thus giving control to DOS/VS VSAM phases. Figure 20 shows the
relationships in storage between the user program, theCMSDOS DCSS, and
theCMSiSAM DCSS. The description below illustrates the overall logic
of that control flow.CMS/DOS SiC HANDLING
There are fourCMS/DOS routines that handle DMSBOP, DMSCLS, and DMSXCP. Within DMSDOS, support VSAM requests. These are described
EnvironmentUnder CMS." VSAM requests: DMSDOS, several SVC functions
in"Simulating a DOS DMSDOS VSAM processing involves handling of SVC 65 (CDLOAD), which
returns the address of a specified phase to the caller.DMSDOS searches
both the sharedsegment table and the nonshared segment table for the CMSDOS and CMSV?AM segments, because both could be in use. Both of
thesesegment tables contain the name of each phase comprising that
segment followed by thefullvord address of that phase within the
segment.
DuringSVC 65 processing, DMSDOS checks to see if the address of
IKQLAB is being requested. IKQLAB is theVSAM routine that returns the
label information generated by DLBLs andEXTENT cards in DOS/VS systems.
If this is the case,DMSDOS saves the address of IKQLAB in NUCON for
later use byDMSXCP. If VSAM has not been loaded, a DIAGNOSE 64 (LOADSYS) is issued to
load theCMSVSAM DCSS. When DMSBOP is entered to process ACBs, it checks to see if CMSVSAM is
loaded. IfVSAM has not been loaded, DIAGNOSE 64 is issued to load the
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execution of
DLBL commands for the
these ddnames.
the user
environment when
Executing a
When a
relationships in storage between the user program, the
the
of that control flow.
There are four
Environment
in
returns the address of a specified phase to the caller.
both the shared
these
segment followed by the
segment.
During
IKQLAB is being requested. IKQLAB is the
label information generated by DLBLs and
If this is the case,
later use by
load the
loaded. If
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