[openib-general] comments on DAT registry in OpenIB

[Bob Woodruff]

Catlin wrote, 
>application --------->   DAT Layer -----------> RDMA Verbs -------->
>model-specific code
>               \                                          ^
>                 \                                      /
>                  \------------------------------------/


Tell me how you are going to make the CM transport independent. 
You cannot, they are simply different for IB and iWarp. 

We would have to do something like,

rdma_verbs_connect(xport_type, ....)
{
    if (xport_type == ib) {
       do_sa_queries()
       ib_connect()
     }
    else if (xport_type == iwarp) {
       do_iWarp_connect()
    }
}

Thus all you have done is added another layer, 

>application --------->   DAT Layer --> RDMA Verbs -> ib_specific_routines
-> drv
>model-specific code                               ->
iwarp_specific_routines -> drv
>               \                             ^    -> common routines -> drv
>                 \                          /
>                  \------------------------/


Another approach would be just to:

s/DAT/RDMA and make it as thin as possible

>application --------->  RDMA Verbs -> ib_specific_routines -> drv
>model-specific code                -> iwarp_specific_routines -> drv
>                                   -> common routines -> drv
>              

And we have achieved the same thing.