AMSERV MODULE BALRIDCAMS CMSVSAM DCSS CMSAMS DCSS ---I IDCAMS: I AMS Root I B-disk
for OS or DOS I- -l J Uses _____ ---,I F CMS A-disk
Figure 19. Relationship in Storage between the efts Interface ftodule DMSAMS and the CMSAMS and CftSVS!ft Desss DMSAMS first determines whether the user is in the CMS/DOS environment. If not, a SET DOS ON (VSAM) command is issued to load the CMSDOS segment and initialize the eMS/DOS environment. In this case, DMSAMS must also issue ASSGB co.mands for the disk modes in the DOSCB chain created by the as user's DLBL commands. An ASSGB is also issued
for SYSCAT, the iSAK master catalog. DKS!MS then issues the ASSGN co.mand for the SYSIPT and SYSLST files,
assigning them to the user's A-disk. DLBL commands are then issued
associating these units with files on the user's A-disk. Input to the AKSERV processor is the SYSIPT file, which has the filetype AftSERV. Output from AMSERV processing is placed in the SYSLST file, which has a
filetype of LISTING. DIAGNOSE 64 (LOADSYS) is then issued to load the CftSAftS DCSS, which
contains the DOS/VS AMS code. A DOS/VS SVC 65 is issued to find the
address of the DOS/VS AKS root phase, IDCAftS. When the SVC returns with
the address of IDCAMS, a branch is made to IDCAftS, giving control to
"live" DOS/VS routines. rnCAKS expects parameters to be passed to it when it receives
control. DMSAKS passes duma, parameters in the list labeled AftSP1BMS. After the rcot phase IDCAKS receives control, the functions in the
file specified by the filename on the AftSERV coamand are executed. efts Method of operation and Program Organization 2-115

In performing the functions requested in this file, AMS may require
execution of DOSjVS 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 the SYSIPT and SYSLST files to clear the DOSCB's for
these ddnames. Control is then passed to DMSVSR, which
the user program 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 when DMSAMS was by DMSVSR. Upon return from tasks and returns control to
Executing a VSAM Function for a DOS User
When a VSAM 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, the CMSDOS DCSS, and
the CMSiSAM DCSS. The description below illustrates the overall logic
of that control flow. CMS/DOS SiC HANDLING
There are four CMS/DOS routines that handle DMSBOP, DMSCLS, and DMSXCP. Within DMSDOS, support VSAM requests. These are described
Environment Under 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 shared segment table and the nonshared segment table for the CMSDOS and CMSV?AM segments, because both could be in use. Both of
these segment tables contain the name of each phase comprising that
segment followed by the fullvord address of that phase within the
segment.
During SVC 65 processing, DMSDOS checks to see if the address of
IKQLAB is being requested. IKQLAB is the VSAM routine that returns the
label information generated by DLBLs and EXTENT cards in DOS/VS systems.
If this is the case, DMSDOS saves the address of IKQLAB in NUCON for
later use by DMSXCP. If VSAM has not been loaded, a DIAGNOSE 64 (LOADSYS) is issued to
load the CMSVSAM DCSS. When DMSBOP is entered to process ACBs, it checks to see if CMSVSAM is
loaded. If VSAM has not been loaded, DIAGNOSE 64 is issued to load the
2-116 IBM VM/370 System Logic and program Determination--Volume 2