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

[Sean Hefty]

>> Are you trying to have each port join the same multicast group?
>
>Possibly - could make some implementation easier, though for performance
>  probably not.

If you only want to join a group once per system, then using the following calls
from the RDMA CM should work:

rdma_create_id();
rdma_resolve_addr(multicast IP address);
/* At this point, you'll have a device */
rdma_create_qp();
rdma_join_multicast();

You would only need to know the address of the multicast group to join, which is
somewhat equivalent to knowing the MGID.

> > How are you determining the multicast group parameters?
>
>Which parameters are you referring to?

The values in the MCMemberRecord needed when creating or joining the multicast
group: MGID, pKey, qKey, SL, flow label, traffic class, etc.

>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.

I'll think about this some, but I'm not sure there's much else that can be done.
At some point, you need an address / identifier for the multicast group.

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

Ibverbs doesn't really help establish connections, but I'm guessing that you
exchange QP information over TCP sockets.

- Sean