Re: RDMAoE verbs questions

[Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>]

 > 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.
--
To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html