[Mpi3-ft] Piggybacking API

[Terry Dontje]

So I reread the piggybacking document on wiki.  I am not thrilled with 
the amount of new APIs this would be adding to the standard but can also 
see the point of the paper.  I am curious how the new API is expected to 
be used?  The proposal say's this API is needed for user-level fault 
tolerance solutions.  So do we expect a user to change all application 
calls to the MPI library to use the PB calls?  I wonder if a more 
general solution that doesn't require a direct change to the API would work.

I wonder if there might be a way one could register piggybacking with a 
communicator and somehow have the actual piggybacking occur as a  
callback from an implementations messaging layer?

Just a thought,

--td