[ofw] [RFC] Generate IBAT path records in IPoIB

[Fab Tillier]

Hi Alex,

> I think this should work fine along with your previous patch. Couple
> questions though. Why broadcast broup record values could be different
> from path query record?

I don't think there's anything in the IB spec that requires them to be the same.  The packet rate can for sure be different if you have mixed rate ports in the broadcast group.  The broadcast group could be comprised of SDR, DDR, and QDR HCAs in which case it would have a SDR packet rate.  This wouldn't give optimal performance between two DDR or QDR HCAs. Same goes for the MTU, if you have a mix of 2K and 4K MTU HCAs in the fabric.  The packet lifetime might be too big for a RC connection too, but won't be too small.

I think for local subnet operations the traffic class, flow label, and hop limit are likely ignored, so probably not a big deal since there are likely bigger issues related to routing than this (like needing the LID pair on both the source and destination subnet).  The service level might also need to be different for MPI traffic vs. IPoIB traffic, but this needs to be handled locally to the node anyway.

> If so, maybe path query could be left as an
> option for Customer?

Callers can still call the existing MAC to GID IOCTL in IPoIB and then do a path query to the SA.  Alternatively, clients could extract the GID pairs from the returned path and perform an SA query.  I either case, clients have the freedom to use the returned path or do an SA query. The difference between the MAC to GID IOCTL and the MAC to PATH IOCTL is the output buffer size, 32 vs. 64  bytes respectively.

> Pkey is set to default - why not to get it from
> broadcast record as well?

Good point, thanks!

-Fab