[ofa-general] creating QP with zero wr and/or null CQ

[Roland Dreier]

 > Calling ibv_create_qp() to create RC QP with max_send/recv_wr set to zero
 > fails, however if only one of them is set to zero, its working fine.

Not too surprising.

 > Also, if either of recv_cq or send_cq is NULL then the program crashes,
 > where it seems the crash relates to these lines at ibv_cmd_create_qp()
 > 
 > 	cmd->send_cq_handle  = attr->send_cq->handle;
 > 	cmd->recv_cq_handle  = attr->recv_cq->handle;

Makes sense.

 > So, are these limitations originating from the spec or from the implementation?

I'm not sure what the spec says about 0-sized QPs.  However for the
create QP verb, the spec does say that the required inputs include:

    The QP attributes that must be specified at QP create time are:
        . The CQ to be associated with the Send Queue.
        . The CQ to be associated with the Receive Queue.

and I'm not sure it's worth adding special cases to deal with null CQs
for QPs that don't have a send/receive queue.  And I'm not sure how
much it's worth worrying about 0-sized QPs either.

 - R.