[openib-general] Problem is routing CM REQ

[Sean Hefty]

> - A kind of inter-subnet path record query is needed that can
>   return a local and remote GRH and LRH. These four structures need to
>   be *linked* so that:
>    - Side A GRH.SGID = active side's Port GID
>    - Side A GRH.DGID = passive side's Port GID
>    - Side A LRH.SLID = any active side's port LID
>    - Side A LRH.DLID = A subnet router
>    - Side A LRH.SL   = SL to A subnet router
> 
>    - Side B GRH.SGID = Side A GRH.DGID
>    - Side B GRH.DGID = Side A GRH.SGID
>    - Side B LRH.SLID = any passive side's port LID
>    - Side B LRH.DLID = B subnet router
>    - Side B LRH.SL   = SL to B subnet router

Something along this line is what I was considering as well.

>    Off hand I don't see that the existing path record query structure
>    has enough information to do this.. Particularly, in cases
>    where each subnet has more than 1 router port there is no real
>    guarentee that querying for the SGID -> DGID direction and then the
>    DGID -> SGID direction uses the same router ports without providing
>    both router LIDs as part of the query.

I'm trying to figure out a way to get this information, but I'm still at a loss. 
  If there was a way to query both the local SA and remote SA using the same 
SGID/DGID pair, it's possible that the combined path records could be used to 
form this data.  I.e. set SGID = local port, and DGID = remote port for both 
queries.

I don't see a way to issue the SA query to the remote subnet though.

> ** The hackish and simple thing to do right now is to just demand that
>    routers *always* use reversible LRHs with a single SLID and have the
>    passive side pick up the QP lids from the LRH if it is routed..

Yep - we also need to hack the CM to set/replace the SLID/DLID carried in the CM 
REQ.

- Sean