I agree with Rajeev's plan.  One thing to bear in mind (its in the mails

but might not jump out) is that some I/O applications may need an

MPI_Offset sized datatype extent (HDF5 might be in this group).

Just to clarify my original suggestion -- I think all internal extents and

sizes should be stored as MPI_Offset. If the user requests for the extent,

we can always return an MPI_Aint (ignoring the overflow).

 -- Pavan

--

Pavan Balaji

http://www.mcs.anl.gov/~balaji