[openib-general] semantics of process_mad?

[Roland Dreier]

I'm now looking at implementing the process_mad method:

	int	 (*process_mad)(struct ib_device *device,
				int process_mad_flags,
				struct ib_mad *in_mad,
				struct ib_mad *out_mad);

First of all, it seems that a port_num parameter needs to be added.

A QP number parameter might also be good, but maybe we can rely on the
access layer to ensure that the MAD's class and QP number match
appropriately.

Finally, what should the return value be?  There are several
independent things that the process_mad function needs to tell the
access layer:

 - Did the operation succeed?
 - Was the MAD consumed or should it be dispatched to a registered consumer?
 - Was a reply generated or should no reply be sent?

In the Topspin drivers, we handled this by returning an enum
ib_mad_result as below:

	enum ib_mad_result {
		IB_MAD_RESULT_FAILURE      = 0,        // (!SUCCESS is the important flag)
		IB_MAD_RESULT_SUCCESS      = 1 << 0,   // MAD was successfully processed
		IB_MAD_RESULT_REPLY        = 1 << 1,   // Reply packet needs to be sent
		IB_MAD_RESULT_CONSUMED     = 1 << 2    // Packet consumed: stop processing
	};

Thanks,
  Roland