Re: SRP issues with OpenSM 3.3.3

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Tue, Dec 15, 2009 at 09:18:19AM -0800, Ira Weiny wrote:
> On Tue, 15 Dec 2009 10:15:32 -0700
> Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org> wrote:
> 
> > > > However, I don't understand the comment "Only set HopLimit if going through a
> > > > router"?
> > > 
> > > This is from '#ifdef ROUTER_EXP' days - as far as I could understand
> > > HopLimit should be set to IB_HOPLIMIT_MAX for inter-subnet MADs.
> > 
> > If HopLimit is 0 then no GRH is required, if it is non 0 then the user
> > of that path needs to apply a GRH. IIRC there are already a few things
> > in the kernel that follow this?
> 
> Is that in the spec somewhere?  The follow on would be that if they specify a
> DGID in the PathRecord query and the result is subnet local they must still
> use a GRH even if the packet is going to stay local?  I think this makes sense
> but I wonder if __everyone__ is following that?

The spec provides no guidance whatsoever on how to tell if a packets
generated from a PR need a GRH or not. The only other choice is to
compare the resulting DGID against all the GID prefixs on the port and
see if any match.

If a router spec is ever written I'm sure it will clarify this matter,
and everyone will follow.

The SM decides what hop limit should be so the SM decides if it needs
a GRH. I belive the original long ago version of this always set the
hop limit to 0 unless the DLID was a router port.

Jason
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