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

[Sean Hefty]

Andrew Friedley wrote:
> I figured you would say that.  So this would be a separate polling 
> interface from a CQ or what the RDMA CM provides?

Yes.  This is one of the issues that I have with the userspace implementation. 
For a raw IB interface, users can end up needing a half-dozen libraries, each 
with their own event interface.

> I see a possible race condition though - consider two processes calling 
> ib_get_mcmember_rec().  Both of them return from this before either can 
> call ib_join_multicast() and create the multicast group.  Is it possible 
> for the same MGID to be returned from ib_get_mcmember_rec() in this 
> scenario?

I probably wasn't being clear.  ib_get_mcmember_rec() would return an 
MCMemberRecord with MGID 0, since that was what was requested.  Other default 
parameters needed to create the group would be filled in.  The actual MGID has 
to come from the SA through the join call.

> Thought I'd try.  Are you saying that just because a join has completed, 
> that doesn't imply the network is fully ready for handling multicast 
> messages for that group?

I believe that is the case.

- Sean