netdev - Re: [PATCH 04/11] IB/cm: Expose DGID in SIDR request events

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Date:	Mon, 15 Jun 2015 16:08:52 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	"Hefty, Sean" <sean.hefty@...el.com>
Cc:	Haggai Eran <haggaie@...lanox.com>,
	Doug Ledford <dledford@...hat.com>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Liran Liss <liranl@...lanox.com>,
	Guy Shapiro <guysh@...lanox.com>,
	Shachar Raindel <raindel@...lanox.com>,
	Yotam Kenneth <yotamke@...lanox.com>
Subject: Re: [PATCH 04/11] IB/cm: Expose DGID in SIDR request events

On Mon, Jun 15, 2015 at 09:32:53PM +0000, Hefty, Sean wrote:
> >  drivers/infiniband/core/cm.c | 7 +++++++
> >  include/rdma/ib_cm.h         | 2 ++
> >  2 files changed, 9 insertions(+)
> > 
> > diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
> > index c5f5f89e274a..46f99ec4080a 100644
> > +++ b/drivers/infiniband/core/cm.c
> > @@ -2983,6 +2983,13 @@ static void cm_format_sidr_req_event(struct cm_work
> > *work,
> >  	param->pkey = __be16_to_cpu(sidr_req_msg->pkey);
> >  	param->listen_id = listen_id;
> >  	param->service_id = sidr_req_msg->service_id;
> > +	if (work->mad_recv_wc->wc->wc_flags & IB_WC_GRH) {
> > +		param->grh = 1;
> > +		memcpy(&param->dgid, &work->mad_recv_wc->recv_buf.grh->dgid,
> > +		       sizeof(param->dgid));
> > +	} else {
> > +		param->grh = 0;
> 
> What is the use case here?  Are you trying to sort by device?  How does the GID of the GMP relate to the listen?

Ouch, that is getting fugly, it used by cma_save_req_info, which feeds
the data into ib_get_net_dev_by_params - basically it chooses the
alias GUID'd netdev to use.

But how is that going to work? How is the sender to know it should be
sending a GRH with the CM message?

Falling back to use the primary_path sgid seems like a poor
substitute, if APM is being used that might be a totally different
port than the CM message.

I'm also not sure about the pkey, it seems to me that the pkey used to
select the ingress netdevice should be the pkey of the rx'd CM GMP,
not the pkey of the future RDMA channel, so this looks like it should
change:

+static int cma_save_req_info(const struct ib_cm_event *ib_event,
+			     struct cma_req_info *req)
[..]
+	switch (ib_event->event) {
+	case IB_CM_REQ_RECEIVED:
+		req->pkey	= be16_to_cpu(req_param->primary_path->pkey);
[..]
+	case IB_CM_SIDR_REQ_RECEIVED:
+		req->pkey	= sidr_param->pkey;

Some comment for the GID, if the GRH is present, then the DGID from
there should alwas be used, not the content of the REQ.

All this is because the CM IP protocol didn't include the LLADDR of
the target's IPoIB interface.. If we are already looking at a breaking
change to force GRH, how hard would it be to add on the LLADDR
somehow instead?

Jason
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