[openib-general] Re: A Couple More CM Queries

[Sean Hefty]

Hal Rosenstock wrote:
>>>2. Should ib_create_cm_id check return an error if cm_handler == NULL
>>>just to make sure ?
>>
>>Personally, I don't think it's worth this check for kernel clients, 
>>unless we want to start checking for NULL parameters everywhere.
> 
> Incoming REQs currently use this capability anyhow.

Incoming REQs use the cm_handler associated with the listen request.

>>While on the CM, I did look at the issue of calling the API out of 
>>order that you had pointed out before (which could result in accessing 
>>a NULL port pointer).  I'm not convinced that a simple check for a NULL 
>>port pointer covers all potential problems.  For example, I'm not sure 
>>how well the codebase will handle the dynamic removal of a device while 
>>users are attempting to access the device.
> 
> We may need to handle this at some point. Guess the changes may be larger
> if/when we get there.

One of the side effects of changing the CM from using a pointer to a QP 
to just the QPN is that the CM can no longer rely on the device being 
around.  And I agree, this will need to be handled at some point, but 
may not be a huge issue as long as the client is reasonable and 
disconnects before destroying their QP.

> It looks like sending private data in REQ/REP/RTU, but incoming private data 
> isn't handled on the receiving side. 

The private_data is given to the user in the cm_event structure.  Look 
for work->cm_event.private_data = in cm_format_req_event, 
cm_format_rep_event, and cm_rtu_handler.  Note that the private_data is 
only available while in the CM event callback.

> Also, in cm_process_send_error(), where the handler is called
> 
> cm_id_priv->id.cm_handler(&cm_id_priv->id, &cm_event);
> 
> might that callback request the CM ID destruction ? If so, some
> code is missing to handle this.

Yep - this is a bug.  Send errors should probably be handled using the 
same cm_process_work routine that the receive handling goes through. 
I'll generate a patch for this, but it'll take me a few days, unless 
this is urgent.

- Sean