[openib-general] [PATCH] [RFC] new CM API to format QP attributes

[Sean Hefty]

Sean Hefty wrote:
> Here's a new API to the CM to format QP attributes required to transition
> a QP to a specified state.  Only a transition to the INIT state is coded
> currently.  I'll add in the other transitions shortly.
> 
> +int ib_cm_init_qp_attr(struct ib_cm_id *cm_id,
> +		       struct ib_qp_attr *qp_attr,
> +		       int *qp_attr_mask);
> +

With respect to the QP attributes being set, the CM is missing the 
minimum RNR NAK timer field, which is needed to transition the QP to 
RTR, but not needed by the CM.  A few options:

* Let the CM set the value to a default, such as 1.  I'm leaning 
towards a low value here, because I'm questioning the usefulness of RNR 
NAK.

* Extend the CM API to let the user specify the value.  The CM would 
only use this value to return it in the qp_attr if this call were made. 
  This makes it explicit to the user that they need to provide a value.

* Do nothing and make the user set the value in the qp_attr after 
calling the above function, but before calling ib_modify_qp.

I'm leaning towards the first option at this point.

- Sean