[ofa-general] [RFC] host stack IB-to-IB router support

[Sean Hefty]

Based on previous e-mail threads, this is my plan for implementing IB-to-IB
router support in the host stack capable of supporting RC communication.  Note
that this work is part of the PathForward project aimed at supporting early
IB-to-IB router development.  It is not intended to define IB router
architecture.

1. Extend struct ib_cm_req_param:

       struct ib_cm_req_param {
		struct ib_sa_path_rec	*primary_path;
		struct ib_sa_path_rec	*alternate_path;
	+	struct ib_sa_path_rec	*remote_primary_path;
	+	struct ib_sa_path_rec	*remote_alternate_path;

   The remote path information would be valid only if the provided paths had
   a hop_limit > 1, but could also be used to support paths where
   reversible = 0.

2. Add an ib_remote_sa module.

   This module would be responsible for obtaining remote path information.
   Because the architecture does not define how this information is obtained,
   my intent is to encapsulate this functionality into a single module to
   simplify out of tree maintenance.  Its basic operation is:

   a. Local ib_remote_sa sends query request to remote ib_remote_sa.
   b. Remote ib_remote_sa queries its local SA.
   c. Remote ib_remote_sa sends query response to local ib_remote_sa.

   I expect the ib_remote_sa implementation to be a temporary solution only.
   It will layer above either the ib_mad or ib_cm services, whichever ends
   up being easier.

3. Extend the rdma_cm route resolution to include remote route lookup.

- Sean