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Directing the System to Determine Block Size z/OS DFSMS Installation Exits SC23-6850-01 |
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If DCBLRECL has been set up and DCBRECFM specifies either F, V, or D you can write a routine as part of the IFG0EX0B exit to have the system determine the block size for the data set. Do this by setting the user's block size field to zero before the exit returns to its caller. If you are requesting a system determined block size, the DCBBLKSI field in the DCB and the DCBEBLKSI field in the DCBE, if present, should be set to zero. A sample is shown in Example of the IFG0EX0B Exit Routine. The user's block size value is in the 2-byte DCBBLKSI in the DCB if both of the following are true:
The user's block size value is in the 4-byte DCBEBLKSI in the DCBE if all of the following are true:
For an EXCP DCB that is not using the DCBE BLKSIZE field, your exit can use the BLKSIZE field in the JFCB but the application program might not use it. If a system-determined block size is used, open turns on the reblockable indicator in the format-1 DSCB (bit 2 of the DS1SMSFG field). When the data set is opened for OUTPUT or OUTIN and the merging of the block size fields occurs, open checks the indicator. If the block size is a system-determined block size, and the logical record length or record format have changed from those specified in the data set label, open determines the block size again. |
Copyright IBM Corporation 1990, 2014
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