On Tue, 2006-12-05 at 18:59 +0300, Evgeniy Polyakov wrote:
> On Tue, Dec 05, 2006 at 09:39:58AM -0600, Steve Wise ([email protected]) 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.
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