[openib-general] Alternate Path Migration support?

[Roland Dreier]

    fabbri> 1. Does the openib stack on tavor H/W support APM?  Anyone
    fabbri> played with it?

All the older stacks should support it, and I have tested it.  I still
have not implemented setting of the alternate path in the new mthca
driver (although it is not much work), so the gen2 stack doesn't
support APM yet.

    fabbri> 2. Do I need to supply the alternate path in the
    fabbri> ib_cm_connect, or can I later do a ib_qp_modify to supply
    fabbri> the alternate path?

    fabbri> If ib_qp_modify is sufficient, should this cause the LAP
    fabbri> CM message to be sent, or is that something that the
    fabbri> consumer has request separately (after the call to
    fabbri> qp_modify)?

You can supply an alternate path to ib_cm_connect(), or load an
alternate path after the connection is established using
ib_cm_alternate_path_load(), which will cause a LAP to be sent, which
will make the other side get a TS_IB_CM_LAP_RECEIVED callback, etc.

You shouldn't use ib_qp_modify() while the CM owns the QP state -- in
particular it definitely won't send a LAP.

 - R.