[openib-general] [Fwd: RE: IB mcast question]

[Steve Wise]

On Tue, 2006-08-15 at 14:18 -0700, Sean Hefty wrote:
> > > App 1:
> > > Creates QP with QKey=22
> > > Joins multicast group 1 with QKey=33
> > >
> > > App 2:
> > > Creates QP with QKey=44
> > > Joins multicast group 1
> > > Sends to multicast group but with QKey=22
> >
> >I think that last send is technically an IBA spec violation.
> 
> I'll admit that this definitely seems like a hack, but I haven't found where it
> is violation.  (I'll keep looking.)  From 10.5.2.1, a QP doesn't need to be
> attached to a multicast group to initiate a send, so it seems like any potential
> violation is only that the QKey and MLID wouldn't match.
> 
> - Sean

And I can't find in the IBTA spec where they talk about the qkey field
of a mcast group at all.  qkeys are used to validate an incoming
datagram.  If the qkey in the packet doesn't match the qkey of the qp,
then its dropped. This is an HCA ingress issue, not a mcast issue
really.

>From what I can gather, the sender:

1) Doesn't need to be in the group (as sean pointed out)

2) posts a SEND WR with an address handle for the the mcast group, the
remote_qpn == 0xfffff, and the remote_qkey == to remote qp's qkey.


Now why C10-15 is there, I dunno...but i'm sure somebody around here
does...

:)