[openib-general] RDMA CM and loopback addresses

[Jason Gunthorpe]

On Thu, Mar 30, 2006 at 01:06:21PM -0800, Sean Hefty wrote:
> It will be difficult, if not impossible, to fully match IP semantics.  
> Before a connection can occur, hardware resources need to be allocated, 
> which requires a specific device.  So, for the purpose of RDMA, we may need 
> to treat an address as a property of a device, rather than the host.

Well, if you have to know the HW devices at bind() rather than at
connect()/accept() (in socket speak) then your right, I don't think
you can ever match the full semantics for IP routing in linux :< This
maybe isn't so bad for IB (only 1 IP subnet), but it seems regrettable
for iwarp.

Does that also mean if you choose to use a wildcard listen address
then you cannot pre-allocate QPs/etc? Or are true wildcard RDMA
listen connections just not supported?

> or connection requests are then restricted to that specific hardware 
> device.  I.e. connections requests that come over an IB device, are 
> restricted to that IB device.

This is inevitable, but all the route selection stuff can apply to the
client side to choose the local device and on the server to vett that
an incoming connection is administratively valid.

Jason