Re: TCP RDMA option to accelerate NFS, CIFS, SCSI, etc.

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

> understand all the protocols that are amased over TCP. To do it in silicon
> it will probably make sense for a subset.

You dont want to do it in silicon. Forget doing all this in silicon. We have
this funky stuff called software. The silicon needs no RDMA support to do
sensible work in the API and the underlying OS are sensibly designed.

> You can look at it as a simple way to enable the protocl stack and the
> application to completely separate the protocol state machine (defined by
> headers and/or trailers) from the payload.

The two are tied together. You have to parse the TCP option stream to get
the ident in the first place. You can't act on the RDMAID until you
have checked the packet is syntactically valid and you've processed
the options including handling the SACK data mixed in with it.

It might also be fragmented of course.


> As for the vulnerability to attacks with a good size RDMAID and some
> imagination you can get the same level of protection as with the TCP
> sequence number (even a bit better because sequence numbers can be guessed
> from context).

The tcp sequence number protects against ordering errors not against DMAing
crap into the wrong buffer.

Different game, different cost if you lose.

Alan