[openib-general] [PATCH v2 04/13] Connection Manager

[Steve Wise]

On Tue, 2006-12-05 at 18:59 +0300, Evgeniy Polyakov wrote:
> On Tue, Dec 05, 2006 at 09:39:58AM -0600, Steve Wise (swise at opengridcomputing.com) wrote:
> > > Phrases like "MPA-aware TCP" rises a lot of questions - briefly saying
> > > that hardware (even if it is called ethernet driver) can create and work
> > > with own TCP flows potentially modified in the way it likes which is seen 
> > > in driver. Likely such flows will not be seen by upper layers like OS 
> > > network stack according to hardware descriptions.
> > > 
> > > Is it correct?
> > > 
> > 
> > I don't quite get your point about the driver aspect of this?
> > 
> > The HW manages the iWARP connection including data flow.  It adheres to
> > the MPA, RDDP, and RDMAP protocol specification IDs from the IETF.  The
> > HW manages how data gets pushed out in the RDMA stream.   The RDMA
> > Driver just requests a TCP connection and does the MPA exchange.  Then
> > tells the hardware to move the connection into RDMA mode.  From that
> > point on, the driver simply suffles IO work requests from the consumer
> > application to the hardware and handles asynchronous events while the
> > connection is up and running.
> 
> My main concern about this is the fact, that protocol handling is
> splitted into SF and HW parts, and actually until negotiation is
> completed those parts are completely unrelated to each other, so
> requested TCP connection can leak into main stack and main stack can
> send some packets which can be considered as MPA negotiation.
> 

Ah.  Data from an offloaded connection cannot leak into the main stack
nor vice-verse.  We can take an active RDMA connection establishment as
an example if you want:  Once the message is sent to the HW to "setup a
TCP connection from addr/port a.b to addr/port c.d", then packets on
that connection (that 4-tuple) will always be delivered to the RDMA
driver, not the native stack.  If the the packet received after the
connection is setup is -not- an MPA reply (in this example), then the
connection is aborted.  Once the connection is aborted.  So no leaking
can happen.