PQ02305: CFTP SERVER HANGS ON PUT REQUESTS THROUGH OFFLOAD

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• The FTP server connection will hang when receiving data from
  the client across an offload device.  The FTP server issues a
  receive on the data connection with WAITALL set which results
  in a receive request being sent to offload.  When the offload
  response arrives, if WAITALL is on the socket will block.  This
  prevents another receive request from being sent to the offload
  to retrieve more data.
  The code in TCPREQU at seq 07703000 has a calculation to
  determine if the original read length (ftp server) is larger
  than the data buffer size multiplied by the number of buffers
  allowed for this socket.  If the read length is larger, WAITALL
  is set turned off and another receive response will be sent
  down to the offload.
  VERIFICATION STEPS:
  The hang will only occur during a put process up to the server
  since WAITALL is only used when the server is receiving on the
  data connection.
  The server trace will show the following messages prior to the
  hang:
  MV1684 seq_open_file: stream 89DE024 has maxreclen 23440
  RU0898 get_buffer: file buffer 089BA000 (allocated for
                     processor xx)
  RS4570 WrtStreamFastIO entered with brfsize 131072
  RS4578 FIO: record format is VB, data type is A
  If a moretrace socket and offload is run, the following
  messages need to be found:
  EZB8355I 7May WaitAll TRUE
  EZB8357I xxxx bytes available, NonBlocking FALSE, WaitAll TRUE
  EZB7258I SkBlockRequest: Client FTPSRV02, Msgid 5, Retryable T
  KEYWORDS:
  msgEZB8355I msgEZB8357I msgEZB7258I WAIT HANG MSG WAIT ALL
  MSGWAIT MSGWAITALL  DATABUFFER POOLSIZE
  

Local fix

• Setting the DATABUFFERPOOLSIZE buffer size in the TCP/IP
  profile to 24576 or smaller will ensure TCPREQU will set
  WAITALL to false and prevent the hang.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of TCP/IP for MVS; Offload and FTP *
  ****************************************************************
  * PROBLEM DESCRIPTION: FTP server hangs on PUT requests        *
  *                      through OFFLOAD.                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The FTP server connection can hang when receiving data from the
  client across an Offload device. The FTP server issues a receive
  on the data connection with a flag set that results in a receive
  request being sent to Offload. When the Offload response
  arrives, if the flag is set and there is data available to read,
  the socket will block. This prevents another receive request
  from being sent to the Offload device to retrieve more data.
  

Problem conclusion

• TCPREQU has been amended to turn off the WaitAll flag if reading
  data from an Offload device.
  
  The TCP/IP for MVS Version 3 Release 2 Messages and Codes
  (SC31-7132-03) manual should have the following message added:
  
  ----------------------------------------------------------------
   EZB8358I WaitAll changed to false in an Offload environment.
  
   Severity: Informational.
  
   Explanation: TCP/IP has detected that data is being received
   from an Offload device and has turned off the WaitAll flag so
   that another read will be issued to the device.
  
   System Action: None.
  
   User or Operator Response: None.
  
   System Programmer Response: None.
  
   Source Data Set:  TCPREQU
  
   Procedure Name:   HPNSWrapUpDataDelivered
  ----------------------------------------------------------------
  
  The equivalent softcopy file will also be updated.
  
  * Cross Reference between External and Internal Names
  EZAAA00K (MSTCP   )  EZABB035 (TCPREQU )
  

Temporary fix

• *********
  * HIPER *
  *********
  

Comments

APAR Information

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

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

  UQ05676

Modules/Macros

•    EZAAA00K EZABB035
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R320 PSY UQ05676

     UP97/06/10 P F706 Ž

Fix is available

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