[openib-general] RDMA connection and address translation API

[James Lentini]

On Wed, 24 Aug 2005, Roland Dreier wrote:

>     James> You need to consider what makes sense for *both* ib and
>     James> iwarp. Keep in mind that the correct API will allow a
>     James> consumer to use ib and iwarp devices transparently. In
>     James> other words their will be one code path that support both.
> 
>     James> If we were to adopt your proposal, the consumer would need
>     James> to perform unnecessary operations on iWARP.
> 
> No, I think we just need to realize that a perfectly transport neutral
> protocol implementation is not achievable.  

It is achievable. Although the IB and iWARP protocols are different, 
they can provide the same services to NFS-RDMA.

IB is missing one service that iWARP has, namely that nodes can be 
identified with IP addresses. The ATS mechanism provides this 
capability for IB networks. If there are better mechanisms that do the 
same thing, then NFS-RDMA can use them. 

The important things is not to push this up into the ULPs. The NFS-RDMA 
protocol is being standardized in the IETF. There is no reason to 
upset that process. If an additional IB specific protocol is 
necessary, it should be standardized in the IBTA.

> It's unfortunate that kDAPL fooled people by hiding the details of 
> the wire protocol under a supposedly "neutral API," but the fact is 
> that mapping an abstract RDMA transport to a real implementation 
> will always involve arbitrary transport-dependent choices.

The kDAPL API *is* transport neutral. This has been demonstrated at 
several interoperability tests at which the same applications were run 
on both IB and iWARP.

kDAPL isn't the only transport neutral networking API. The Sockets API 
supports UDP and TCP transports via the same interface. 

I believe we are very close to reaching agreement on a transport 
neutral RDMA connection API. Comparing your API proposal to the API 
that we proposed at the BOF, they are very similar. The most important 
similarity is that both use IP addressing. 

The only real point of debate is over how to perform the address 
translation (IP <-> GID) on IB. I believe we should separate that from 
the API discussion.