[openib-general] Re: [PATCH 3/3] iWARP CM - iWARPConnectionManager

[Caitlin Bestler]

openib-general-bounces at openib.org wrote:
>>> For example, as soon as the user calls connect(), can they receive a
>>> CLOSE event, even before the connect() call returns?
>> 
>> No.  connect results in a CONNECT_REPLY event always. Not a CLOSE
>> event.
> 
> What if the remote side sends the reply, then decides to abort or
> disconnect? I'm considering a case where multiple events may be
> queued. I.e. after calling connect(), what events can a user see
> without making any other calls?
> 

One of the differences here is that for iWARP there is a natural
ordering of events that is unambiguous. TCP connection follows
a certain sequence, and after that there is the TCP sequence
itself (or the equivalent SCTP features).

So if the remote side sends the reply and *then* decides to
abort or disconnect that step will unambiguously be an abort
or disconnection of an *established* connection (because the
sequence numbers will be greater). There isn't the problem
that IB can face where a disconnect might be received before
the connection acceptance.

So the only possible race conditions are between locally
initiated events and remote ones. These have been worked
through in forums such as RDMAC, DAPL and RNIC-PI. It relies
on atomic state transitioning, but it otherwise simple.
I'm not claiming to have done a by-hand software proof,
but I haven't spotted anything in IW-CM that contradicts
my understanding of the relevant state machines.

A formal state model is a bit tricky to present because
there are multiple objects involved on the passive side
in each connection establishment. By the time you are
accurate the state model is no longer informative to
a first time reader.