[openib-general] [PATCH] [RFC] librdmacm: expose device list to users

[Andrew Friedley]

Sean Hefty wrote:
>>Yes, that's what I've been doing, though you recommended using the RDMA
>>CM to set up multicast groups.  What interface should I be using then?
> 
> 
> That's the problem.  There is no raw userspace SA query interface.  The only
> other alternative is to send MADs directly to the SA through the SA MAD
> interface, but doing so would bypass the kernel ib_multicast module which is
> responsible for tracking multicast join / leave requests.  (In fact, the
> userspace MAD interface should eventually prevent a userspace app from sending
> raw join/leave requests.)

I'd rather not do all that.

> Are you trying to have each port join the same multicast group?  

Possibly - could make some implementation easier, though for performance 
  probably not.

 > Are you trying to join the same multicast group multiple times from 
the same port?

Almost certainly not.

 > How are you determining the multicast group parameters?

Which parameters are you referring to?

 > And who creates the multicast group?

Don't know yet :)  Right now I just have a few ideas I want to play 
around with, but first I need to be able to just set up and use 
IB/multicast with an API that meshes well with Open MPI.

RDMA CM just about does it right - except for how interfaces/ports are 
presented.  I just need to be able to get a list of rdma_cm_id's for the 
available interfaces.

Really, ibverbs is sufficient (and does well) for what I need to do 
CM-wise, other than support for multicast.

Andrew

> - Sean