[ewg] Re: [PATCH v3] libibmad: Handle MAD redirection

[Jason Gunthorpe]

On Wed, Jul 01, 2009 at 03:39:01PM -0400, Hal Rosenstock wrote:

> > Clearly the only sane way this can work is if the GID is always
> > filled in for the redirection case.
> 
> Why is that ? Why must the redirector provide GRH info when it's not
> required for subnet local cases ?

Because the redirector doesn't know what the initiator will do. It
could include a GRH, or maybe not. It must include the GID to cover
both cases.

> >> Futhermore, RedirectLID can be non zero but GID redirection is still
> >> being used as indicated by the RedirectLID description indicating that
> >> a non zero RedirectLID will in general not be valid.
> >
> > The spec says if it is not zero the requester shall use it. I don't
> > see an ambiguity here.
> 
> To me, the ambiguity is several lines below it where it states that
> the RedirectLID might not be valid and says to obtain a PathRecord
> when RedirectGID is supplied rather than relying on the RedirectLID is
> non zero.

Whoever authored this should not have mixed 'will in general not be
valid' and 'they must be replaced' in the same sentance - but I think
the meaning is still clear. With a 0 RedirectLID only the RedirectGID,
QP and P_Key are to be used by the receiver. When RedirectLID is not 0
then all of the Redirect fields must contain correct data and should
be used as necessary by the receiver.

It never says to obtain a Path Record when a GID is supplied. It says
to obtain a path record with RedirectLID is 0.

Jason