[openib-general] Re: [PATCH] CMA: allow/require bind beforeconnect

[Caitlin Bestler]

Sean Hefty wrote:
> Roland Dreier wrote:
>> OK, fair enough.  I was really replying to the first sentence of:
>> 
>>      Caitlin> From the perspective of any given host, IP addresses
>>      are Caitlin> unique across all interface devices. A given
>>      connection Caitlin> can therefore be identified by just the
>>      4-tuple, with no Caitlin> need to explicitly state "via this
>> device". 
>> 
>> IP addresses are not unique.  However, I do agree that a 4-tuple
>> uniquely identifies a TCP connection.
> 
> I agree with this as well.  But the CMA, when running over
> IB, does not establish TCP connections.  It's simply mapping
> addresses.  RDMA connections will end up being identified by QPs.
> 
> If a user tries to establish a connection, the CMA will
> determine which device that connection will go out on.  If
> it's an IB device, there's no need for a local port number.
> If it's an iWarp device, then the iWarp CM will need to
> allocate a usable port number.
> 
> What I'm still trying to understand is why the CMA should
> allocate a port number for active connections.  The port
> space over IB is separate, and the port number is not needed
> for connecting or routing data.  Are there specific
> applications that will run over RDMA that will have a problem with
> this? 
> 

If you are making a relliable connection with an IP address then
it is quite reasonable for system administrators to expect that
it will be identified and controlled just with TCP or SCTP.
That calls for a local port address.

So you either allocate a local port address (for the local
IP address) or you convince every traffic reporting and
management tool ever written to suddenly understand that
the local port space is bigger than their current understanding.
Basically, if you claim to use an IP Address then you need
to claim to use one of the IP Transports.