Re: [PATCH v4] rdma/cm: support option to allow manually setting IB path

[Or Gerlitz <ogerlitz-smomgflXvOZWk0Htik3J/w@public.gmane.org>]

Sean Hefty wrote:
> Future changes to the rdma cm can expand on this framework to support the full range of features allowed by the IB CM, such as separate forward and reverse paths and APM
Sean,

Before enhancing the rdma-cm to support the full feature set of the IB 
CM, something which I personally don't see the actual need for (but I 
will be happy to get educated what applications will or can migrate to 
rdma-cm once this is implemented), how about trying to allow for reduced 
QoS scheme also when the entity that resolved this patch didn't 
consulted with the SA?

IB QoS is based on the query providing the <SGID, DGID, PKEY, SID, TOS> 
tuple and the SA returning a <SLID, DLID, SL, MTU, ....> QoS tuple. Now 
I'd like to see how can we let the application / querying middleware to 
take advantage of the knowledge on what partition it runs and use the SL 
associated with the IPv4 (e.g AF_INET rdma-cm ID's) IPoIB broadcast 
group. This way, one can still program a QoS scheme at the SA which is 
based on partitions.

Looking on mckey, the user space code (e.g ACM), could just do rdma_bind 
to an IP address of an IPoIB NIC that uses this partition and then 
rdma_join to an unmapped multicast address which correspond to the 
broadcast group, take the SL and leave the group, makes sense?

Or.

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