[ofa-general] Re: [PATCH] core/cm: improve requestmessage interpretation of subnet local fields

[Jason Gunthorpe]

On Mon, Sep 17, 2007 at 11:39:46AM -0700, Sean Hefty wrote:
> >I'm with Hal on this - why does this cause a problem? There is no IB
> >packet verification check that tests if a GRH is present, only if it
> >is presen it must be valid - so how can an extra correctly filled in
> >GRH cause anything but degraded performance?
> 
> ib_init_ah_from_path() uses the hop_limit in the path record to
> determine if a GRH should be used.  It sets the address handle
> attributes (used to configure the QP) based on hop_limit > 1.  If
> hop_limit is set incorrectly in the CM REQ, the path record formed
> by the CM based on data carried in the REQ could have invalid GRH
> values.

But using this hop limit this was is just a convention we have
adopted. There is nothing in IBA that allows the active side to send a
REQ with invalid GIDs/etc in any situation. The passive side should
always be able to form a correct GRH based on any REQ.

Jason