PM73574: FREAD ON A VARIABLE RECORD FORMAT TAPE DATASET AFTER A REPOSITION MAY RETURN INCORRECT DATA

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• When reading from a variable format tape data set following a
  reposition, the read may return residual data following the
  updated data.
  
  For example, a tape dataset containing 85 records (80 in the
  first block, 5 in the second) and the first block has been
  read (buffer contains records 1-80).  If the application
  gets the first record (via an fread() for instance) and then
  repositions to the second block (location of records 81-85):
  and you fread() these records, you may encounter residual
  data from the first block.  Your output may be:
  
  record 81/85
  record 82/85
  record 83/85
  record 84/85
  record 85/85
  record 6/85
  record 7/85
  ...
  -
  Where after reaching the end of the current block
  incorrect/residual data from the previous block read may
  be returned.
  
  
  Verification Steps:
  1) Ensure data in use resides on a tape device and is in
     a variable format.
  2) Ensure a resposition has been issued prior to encountering
     incorrect data.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: C/C++ applications repositioning or          *
  *                 rewinding variable length record             *
  *                 TAPE datasets.                               *
  ****************************************************************
  * PROBLEM DESCRIPTION: C/C++ applications that reposition or   *
  *                      rewind in variable length record TAPE   *
  *                      datasets may process the current        *
  *                      buffer with an incorrect block size     *
  *                      leading to unpredictable results.       *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  See problem description.
  

Problem conclusion

• The code was changed to fix the problem.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UK90183 UK90184

Modules/Macros

• CELHOSRB CELHOSRW CELQOSRB CELQOSRW EDC4003A
  EDC40038
  

Fix information

• Fixed component name

  LE C LIBRARY

• Fixed component ID

  568819805

Applicable component levels

• R770 PSY UK90183

     UP12/12/27 P F212

• R780 PSY UK90184

     UP12/12/27 P F212

Fix is available

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