[mpi-21] Ballot 4 - MPI_File_get_info

[Rolf Rabenseifner]

This is a proposal for MPI 2.1, Ballot 4.

I'm asking especially the implementors to check, whether
this interpretation is implemented in their MPI implementations,
or does not contradict to the existing implementation.

This is a follow up to:
  MPI_File_get_info
  in http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-errata/index.html
with mail discussion not yet existing
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Proposal:
MPI-2.0 Sect. 9.2.8, File Info, page 219, lines 11-13 read:

     MPI_FILE_GET_INFO returns a new info object containing the hints 
  of the file associated with fh. The current setting of all hints 
  actually used by the system related to this open file is returned
  in info_used. 
  The user is responsible for freeing info_used via MPI_INFO_FREE.   

but should read (" or an abort(errorcode)" removed):

     MPI_FILE_GET_INFO returns a new info object containing the hints 
  of the file associated with fh. The current setting of all hints 
  actually used by the system related to this open file is returned
  in info_used. 
  If there does not exist such a hint, MPI_INFO_NULL is returned.
  The user is responsible for freeing info_used via MPI_INFO_FREE
  if info_used is not MPI_INFO_NULL.     
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Rationale for this clarification:
  This text was missing. It was not clear, whether a MPI_Info handle 
  would be returned that would return nkeys=0 from MPI_INFO_GET_NKEYS.
  From user's point of view, this behavior might have been expected
  without this clarification.
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As far as I understand, ROMIO is using for all filesystems some default
hints and therefore "no-hints" is never returned.
MPI_File_set_view and MPI_File_set_info are only modifying values
but do not remove keys.
Therefore, the info handle cannot become empty.

Best regards
Rolf

Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner_at_[hidden]
High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
Nobelstr. 19, D-70550 Stuttgart, Germany . (Office: Allmandring 30)