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

[Steve Wise]

On Thu, 2006-02-09 at 18:42 -0800, Roland Dreier wrote:
>     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.

After poking around, I think CMA sets these via ib_cm_init_qp_attr()
called by rdma_init_qp_attr(). 

Stevo.