[openib-general] Re: [PATCH v2] [RFC] - example user mode rdma ping/pongprogram using CMA

[Roland Dreier]

    Steve> So what's up with these access flags on qp?  You cannot set
    Steve> them on qp creation...only on qp modify.  That seems
    Steve> strange.  Since rdma read/writes work without these
    Steve> attributes set, I'm wondering what they really do?

I'm not sure how things interact with the RDMA CM abstraction, but the
underlying IB modify QP operation allows the QP access flags to be set
in the RESET -> INIT state transition.  A QP cannot generate or
process any messages until it is in the INIT state (actually, until it
is in the RTR state, which can only be reached through the INIT
state), so there's no problem setting them early enough.

RDMA operations should not work without the QP access flags set and
I'm pretty sure that I've seen RDMAs fail without them in practice, so
there's still a bit of a mystery with rping.

 - R.