[openib-general] RFC userspace CMA

[Caitlin Bestler]

> -----Original Message-----
> From: openib-general-bounces at openib.org 
> [mailto:openib-general-bounces at openib.org] On Behalf Of Tom Tucker
> Sent: Wednesday, October 26, 2005 5:01 AM
> To: Sean Hefty
> Cc: openib
> Subject: Re: [openib-general] RFC userspace CMA
> 
> Sean:
> 
> FYI, I've started writing the iw_cm that sits below the 
> rdma_cm. Here's the general picture I have in mind.
> 
> 	+---------+
> 	| RDMA CM |
> 	+-+-----+-+
> 	  |     |
>      +----+     +----+
>      |               |
> +---------+     +----+----+
> | IB CM   |     | IW CM   |
> +----+----+     +----+----+
>      |               |
>  ____+_____      ____+_____
> +---------+|    +---------+|
> | IB devs ||    | IW devs ||
> +---------+     +---------+
> 
> The purpose of the IW CM is to abstract the two different 
> connection models used by the iWARP side: offloaded and host 
> integrated, and to act as a shim between device specific 
> connection data structures and the rdma_cm data structures.
> 

How much logic is really in the RDMA CM?

If it is sufficiently small, which is what my expectation is,
would it make sense to simply make the IB CM and IW CM conform
to the same polymorphic interface? (Making the "RDMA CM" little
more than a re-directing inline function).

But if there is any substantial portion of common logic
then the above structure definitely makes sense.

My main concern is that the Connection Request reported
up from here has the same semantics over IB CM as it does
over IW CM. The remote IP Address of an established 
connection is pretty fairly validated. It originated
from privileged code on the remote side (presumably
the kernel) and the routers actually got packets
back to that machine using that address.

So a daemon using that address for client validation
is totally reasonable, over an IP network. An equivalent
degree of reliability should be there for IB. Using the
SM to validate a translation achieved that. There are
certainly other ways to achieve it. But we need to be
clear that it is part of what the application is 
expecting when it is told that remote IP Address X
is requesting a connection.