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

[Hal Rosenstock]

On Wed, Jul 1, 2009 at 4:00 PM, Jason
Gunthorpe<jgunthorpe at obsidianresearch.com> wrote:
> 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.

It could restrict what the initiator can do by doing this. Nothing
wrong with that AFAIT. I agree that this is not what you'd want if the
requester were not subnet local. I'm only talking about the subnet
local case.

>> >> 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.

In looking at this some more, I agree with you on this part now since
all that text is part of the RedirectLID 0 paragraph.

-- Hal

> Jason
>