Re: RDMAoE verbs questions

[Eli Cohen <eli-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>]

On Fri, Dec 04, 2009 at 08:03:31PM -0800, Roland Dreier wrote:
> 
>  > Yes, every Linux arch aligns structs to the min alignment for the
>  > members, so at least 32 in this case.
>  > 
>  > However, it doesn't really matter, look at ibv_cmd_query_port, it
>  > doesn't zero the padding. So there must be an ABI bump to ensure that
>  > new code links to a library that doesn't fill the new member with
>  > garbage.
>  > 
>  > This is a messy one, the low level libraries have to be reved somehow too..
>  > ops.query_port2() I guess.
> 
> Actually I think we can fix this in libibverbs without having to break
> anything.  It's a little bit devious, but if we do something like:
> 
> // ... add link_layer member in padding of struct ibv_port_attr
> 
> enum {
> 	IBV_LINK_LAYER_UNSPECIFIED,
> 	IBV_LINK_LAYER_INFINIBAND,
> 	IBV_LINK_LAYER_ETHERNET,
> };
> 
> static inline int __ibv_query_port(struct ibv_context *context, uint8_t port_num,
> 				   struct ibv_port_attr *port_attr)
> {
> 	port_attr->link_layer = IBV_LINK_LAYER_UNSPECIFIED;
> 	return ibv_query_port(context, port_num, port_attr);
> }
> 
> // ... rest of file...
> 
> #define ibv_query_port(context, port_num, port_attr) \
> 	__ibv_query_port(context, port_num, port_attr)
> 
> then I think legacy apps should be OK (port_attr size doesn't change,
> binary compat is still there), and new apps that do check link_layer
> should also be OK ... if they use an old library and/or old driver,
> they'll see LINK_LAYER_UNSPECIFIED, which means that IBoE is not supported.
> 
> What do you think, does this work?
> 
>  - R.

It looks good to me. Thanks, I will take it for RDMAoE.
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