rxrpc: Permit multiple service binding

Permit bind() to be called on an AF_RXRPC socket more than once (currently
maximum twice) to bind multiple listening services to it.  There are some
restrictions:

 (1) All bind() calls involved must have a non-zero service ID.

 (2) The service IDs must all be different.

 (3) The rest of the address (notably the transport part) must be the same
     in all (a single UDP socket is shared).

 (4) This must be done before listen() or sendmsg() is called.

This allows someone to connect to the service socket with different service
IDs and lays the foundation for service upgrading.

The service ID used by an incoming call can be extracted from the msg_name
returned by recvmsg().

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/Documentation/networking/rxrpc.txt b/Documentation/networking/rxrpc.txt
index 1b63bbc6b94f..b7115ec55e04 100644
--- a/Documentation/networking/rxrpc.txt
+++ b/Documentation/networking/rxrpc.txt
@@ -600,6 +600,10 @@ A server would be set up to accept operations in the following manner:
 	};
 	bind(server, &srx, sizeof(srx));
 
+     More than one service ID may be bound to a socket, provided the transport
+     parameters are the same.  The limit is currently two.  To do this, bind()
+     should be called twice.
+
  (3) The server is then set to listen out for incoming calls:
 
 	listen(server, 100);