[openib-general] posting send requests in RTR ( was Re: [PATCH 0/4] Dispatch communication related events to the IB CM)

[Caitlin Bestler]

Michael Tsirkin wrote:

> 
> Not necessarily. CMA consumer at this point is a rare beast,
> but since the issue is not specific to CMA, let's look at
> some IB protocols: IPoIB connected mode can simply drop a
> packet.  So can SRP.  SDP (potential CMA consumer!) simply
> never needs to send any application data before communication
> established event. 
> 

I agree, the simplest and transport neutral rule is that the
application is not guaranteed what will happen if they post
to the send queue before the communication established event,
They MAY get an error, or it MAY be queued, it MAY even be
sent because the QP *is* in RTS mode but the consumer just
hasn't been told yet, or it may cause a packet to be placed
on the wire prematurely with possible adverse effects on the
connection (iWARP on the passive side sending a DDP Segment
before the active side has received the MPA Response can 
indeed result in a broken connection).

So the best rule for the application is to simply always wait
for the communication established event. That always works,
and complying with it is hardly a burden for the application.