[ofw] patch: [ibbus] Add A new function to IBAL that allows one to create a multicast group without attaching a QP to it.

[Hefty, Sean]

> I guess that if we want to keep tracking the multicast group (as fab has
> noticed) than we don't have a way to not change the API.

Personally, I'm fine requiring the caller to handle the cleanup (provided the kernel cleans up after user space).

The main issue I see with the existing APIs is that the user has no way to cancel a join request without blowing up everything.  So, I would vote for replacing the existing kernel APIs with something like:

ib_join_mcast(struct ib_mcast_req *req, ib_mcast_handle_t *h_mcast);
ib_free_mcast(ib_mcast_handle_t h_mcast, ib_pfn_destroy_cb_t pfn_destroy_cb);

'leave' is replaced with 'free, which must always be called.  Eventually, I would like these APIs available separately from the rest of ibal, so that winverbs can use them without being forced to use the other ibal APIs.  If the API is being modified, there's no reason to keep the existing calls.  Users should just be moved to the new APIs.

- Sean