[openib-general] Making gen2 transport neutral

[Christoph Hellwig]

On Thu, Jun 30, 2005 at 08:52:54AM -0700, Caitlin Bestler wrote:
> structs:
> typically "struct ib_xyz" is transformed as follows:
> 
> 	struct ib_xyz {
> 		/* Only IB specific fields remain */
> 		/* In some cases fields have been split, because
>              * iWARP allows two things to vary that IB had
>              * locked together. SGE limits are the primary
>              * example of this. iWARP can have different
> 	 	 * limits on SGE size for each type of message
> 		 */
> 	};
> 
> 	struct iwarp_xyz {
> 		/* equivalent iWARP specific fields */
> 	};
> 
> 	struct rdma_xyz {
> 		/* Transport neutral fields. Typically
> 		 * a subset of what was in struct ib_xyz before
> 		 */
> 		union {
> 			struct ib_xyz ib;
> 			struct iwarp_xyz iwarp;
> 		} xpt;
> 	};

wrong way around, but we had that before.  It should be

struct ib_foo {
	struct rdma_foo common;
	...
}

struct iwarp_foo {
	struct rdma_foo common;
	...
}

see filesystem and network protocol private data for example where
why historically did it that union way and it didn't work out at all
long-term.

> I am assuming that returning a "not supported" error for irrelevant
> verbs is an acceptable burnden for all providers.

Even better make the methods implementing them optional and let the
upper layer return EOPNOTSUPP when it's not implemeneted.