[ovs-dev] [PATCH 1/6] ofproto-dpif: New function ofproto_receive().

[Ben Pfaff]

On Thu, Dec 27, 2012 at 11:37:31AM -0800, Ethan Jackson wrote:
> > Why shouldn't we give up in trace, as we do in the packet receive
> > path, if the port can't be found?  "trace" is supposed to match the
> > packet receive path (otherwise it isn't as useful).  I guess the
> > reason is that we don't have to, since the user specified the ofproto
> > name, but I think that we should anyway.
> >
> 
> There seems to be some contention on this point.  Currently, the unit tests
> rely on this behavior.  Specifically, you can do a trace without specifying
> an in_port and it will implicitly use OFPP_NONE.  In previous rounds of
> review, I had suggested that we remove this option, and require a valid
> in_port to trace.  Jesse suggested that this feature is important.  I
> really don't care either way.  Could you two please make a decision on the
> point?

We have to be able to deal with flows that have no in_port to support
OpenFlow "ofp_packet_out", which allows no in_port to be specified.
But that's different from "trace" because ofp_packet_out doesn't do a
flow table lookup (it includes its own list of actions).  I'm not sure
that it's really necessary to support "no input port" here.

Jesse, comments?