Re: [PATCH v2 01/17] IB/Verbs: Implement new callback query_transport() for each HW

From: Doug Ledford
Date: Fri Apr 10 2015 - 14:25:31 EST

On Fri, 2015-04-10 at 12:04 -0600, Jason Gunthorpe wrote:
> On Fri, Apr 10, 2015 at 01:38:38PM -0400, ira.weiny wrote:
> Hiding meaning is to say 'only run on IB or OPA': WHY are we limited
> to those two?

For something else, I might agree with this. But, for the specific case
of IPoIB, it's pretty fair. IPoIB is more than just an ULP. It's a
spec. And it's very IB specific. It will only work with OPA because
OPA is imitating IB. To run it on another fabric, you would need more
than just to make it work. If the new fabric doesn't have a broadcast
group, or has multicast registration like IB does, you need the
equivalent of IBTA, whatever that may be for this new fabric, buy in on
the pre-defined multicast groups and you might need firmware support in
the switches.

> We can see how this might work in future, lets say OPAv2 *requires* the
> 32 bit LID, for that case cap_ib_address = 0 cap_opa_address = 1. If
> we don't update IPoIB and it uses the tests from above then it
> immediately, and correctly, stops running on those OPAv2 devices.
> Once patched to support cap_op_address then it will begin working
> again. That seems very sane..

It is very sane from an implementation standpoint, but from the larger
interoperability standpoint, you need that spec to be extended to the
new fabric simultaneously.

Doug Ledford <dledford@xxxxxxxxxx>

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