[openib-general] RDMA CM and loopback addresses

[Sean Hefty]

I created a test program to determine how sockets handles local system
connections.  The server side was configured to listen in 1 of 3 ways: on any
address, a local address, or the loopback address.  The client side connected in
1 of 4 ways (bound address to server address): any address to a local address,
loopback to local, local to loopback, or loopback to loopback.  The results were
that all 12 combinations resulted in a connection.

To obtain similar behavior with the RDMA CM, I propose the following:

1. Binding to the loopback address will no longer result in acquiring a local
RDMA device.  (This will be deferred to rdma_resolve_addr().)
2. Listening on a loopback address will result in listening across all RDMA
devices.
3. Connections from a loopback address will acquire a device based on the
destination address.  If the destination address is also a loopback address, the
CMA will simply pick the first one in the list.

I hope to have a patch for this by the end of the week.

- Sean