>This is an implementation details. You should avoid relying on such
>things in a portable MPI applications. The safe assumption here is
>that MPI_Bsend always copy the buffer, as described in the MPI standard.
I'm fully aware of the MPI standard, and the program will be
standard-compliant. However, since performance is somewhat important even
in this emulated mode I want to understand what the OpenMPI implementation
is likely to do.