Issue with "integer" arguments in Fortran API for PNetCDF

[John Michalakes]

I'm having a problem adapting parallel NetCDF as an option in the WRF
(Weather Research and Forecast) model I/O API. WRF currently supports
non-parallel NetCDF, and we're now trying to extend the model to use the new
parallel NetCDF code. Have run into a problem with some of the arguments in
the API for parallel-NetCDF:

The original NetCDF Fortran API defines lengths, starts, and other arguments
as INTEGER. PnetCDF recasts some (but not all) of these arguments as
MPI_Offset. We compile WRF with OBJECT_MODE 64 on the IBMs where
KIND=MPI_OFFSET_KIND works out to 8 bytes. Thus, the calls in WRF that pass
these arguments as 32-bit INTEGERs from Fortran are causing PNetCDF to see
garbage in the high four bytes of the dummy argument. For example, the
length argument to NFMPI_DEF_DIM ends up being 73 + a very-large-garbage
value instead of 73.

I was hoping for a relatively quick drop-in of PnetCDF into WRF I/O API but
this now seems unlikely. There is a large amount of NetCDF interface code in
WRF that will need to be gone through.  Or I can write a wrapper lib for all
these routines.

Has anyone done this already? What's needed is for the wrapper routine to
accept INTEGER arguments and copy them to INTEGER(KIND=MPI_OFFSET_KIND) to
be used as arguments to the actual NFMPI_* routines in PNetCDF and (in the
case of return values) copy them back to INTEGER again.

Not arguing, but curious: since PNetCDF is supposed to be a parallel
implementation of the NetCDF API, why was the API altered this way to use
arguments of type MPI_Offset instead of INTEGER? At least for what I'm
trying to do, it is a significant impediment.

I really appreciate that parallel NetCDF is being developed. It is very much
needed, especially now as we try moving to Petascale. Kudos to the
developers.

John

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John Michalakes, Software Engineer        michalak at ucar.edu
NCAR, MMM Division                   voice: +1 303 497 8199
3450 Mitchell Lane                     fax: +1 303 497 8181
Boulder, Colorado 80301 U.S.A.        cell: +1 720 209 2320
        http://www.mmm.ucar.edu/individual/michalakes
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