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Recently a question was posted regarding SubSystem Datasets,
more appropriatly the use of a SUBSYS= parameter on a DD statement.
//DD1   DD SUBSYS=(ssn,'parms').
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I believe this information was once documented in GG66-3131 
(the SubSystem Interface in MVS/SP Version 3) and documented
the SSI function codes for Allocation, Converter, Open, Close and GET).
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After several days of reserach I do see that IXGSEXIT 
(log stream subsystem exit) may be the documentation that 
replaced GG66-3131. IXGSEXIT can support applications that use QSAM and BSAM 
(GET and READ) requests to sequential dataset.
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IXGSEXIT documents similar exit points for Allocation, ConVerter, Open, Close, 
GET, and unallocate.
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In either case both documents provide similiar functionality with respect to 
processing SubSystem Dataset via the SUBSYS= parameter on a DD statement.
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However neither technology provides a PUT/WRITE function/exit.
So how does the SubSystem Address Space process a PUT/WRITE from an application 
that has a DD SUBSYS=xxxx statement ?
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How does the Subsystem Address Space get notified that a record was written to 
it ? 
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Simple Example:
Lets say for this discussion I want to transfer all I/O from a an applications 
SYSOUT DD with SUBSYS=xxxx to a 64Bit Memory Chunk.
Once I have all my exits established, Each I/O from an application with the 
appropriate SUBSYS statement should be directed to my
SubSystem Address Space. Do I understand this correctly ?
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How does the subsystem address space receive/obtain the data from the 
Applications PUT/WRITE statement, so that the SubSystem Address Space can 
populate the 64Bit Memory Chunk ?
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Paul D'Angelo
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