On Wed, 21 Mar 2007 18:27:27 -0600, David Day wrote: > Have not done much VSAM coding, hence the questions. Have an opened ACB in 31 bit storage. Looking at a dump immediately after a successful OPEN for the dataset. TCBDEB points to a DEB where the chain from the DEB to the JFCB is correct(DEB extention to DSAB to SIOT to JFCB)...it's the dataset just opened. At x'14' into the DEBBASIC is a pointer to the ACB, but the field in the DEB is called DEBECBAD. The DEBDCBB field is filled in, but don't recognize what it points to. Are the differences between VSAM and non-VSAM DEB structures and associated control blocks documented somewhere? The field in the DEB that points to an ACB (or DCB) is called DEBDCBAD (not DEBECBAD -- that's the pointer to the plist used to locate the purge ECB for an SVC purge request). And you don't REALLY want to reference the 4-byte DEBDCBAD field -- you should be using the 3-byte DEBDCBB field instead. The high-order byte of DCBDCBAD will often be x'8F' (the 8 represents the task protection key and the F is a constant to identify the control block as a DEB). With that relatively constant x'8F' in the high-order byte of the word you have a tough time mapping above the line, which is where the 24-bit restriction originates. DCBs cannot be located outside of 24-bit virtual storage. I don't believe that ACBs can be located outside of 24-bit virtual storage either, but there is a caveat to this: there are 2 kinds of ACBs (and DCBs) -- Protected and Unprotected. The user's ACB (or DCB) is the Unprotected flavor. The system produces a copy in protected storage (hence the term) which is the actual xCB used by Open/Close/etc. The status of the Protected xCB is reflected back to the user's Unprotected xCB as the I/O operations progress. This is documented (more or less) in the various DFSMS (DFP) publications ... and a whole lot of older, not-completely-obsolete PLMs and FE handbooks. -- Tom Schmidt Madison, WI
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