SUNRPC: Introduce transport switch callout for pluggable rpcbind

Introduce a clean transport switch API for plugging in different types of
rpcbind mechanisms.  For instance, rpcbind can cleanly replace the
existing portmapper client, or a transport can choose to implement RPC
binding any way it likes.

Test plan:
Destructive testing (unplugging the network temporarily).  Connectathon
with UDP and TCP.  NFSv2/3 and NFSv4 mounting should be carefully checked.
Probably need to rig a server where certain services aren't running, or
that returns an error for some typical operation.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/clnt.h

@@ -106,7 +106,7 @@ struct rpc_clnt *rpc_clone_client(struct rpc_clnt *);
 int		rpc_shutdown_client(struct rpc_clnt *);
 int		rpc_destroy_client(struct rpc_clnt *);
 void		rpc_release_client(struct rpc_clnt *);
-void		rpc_getport(struct rpc_task *, struct rpc_clnt *);
+void		rpc_getport(struct rpc_task *);
 int		rpc_register(u32, u32, int, unsigned short, int *);
 
 void		rpc_call_setup(struct rpc_task *, struct rpc_message *, int);

include/linux/sunrpc/xprt.h

@@ -105,6 +105,7 @@ struct rpc_xprt_ops {
 	void		(*set_buffer_size)(struct rpc_xprt *xprt, size_t sndsize, size_t rcvsize);
 	int		(*reserve_xprt)(struct rpc_task *task);
 	void		(*release_xprt)(struct rpc_xprt *xprt, struct rpc_task *task);
+	void		(*rpcbind)(struct rpc_task *task);
 	void		(*set_port)(struct rpc_xprt *xprt, unsigned short port);
 	void		(*connect)(struct rpc_task *task);
 	void *		(*buf_alloc)(struct rpc_task *task, size_t size);

net/sunrpc/clnt.c

@@ -774,7 +774,6 @@ call_encode(struct rpc_task *task)
 static void
 call_bind(struct rpc_task *task)
 {
-	struct rpc_clnt	*clnt = task->tk_client;
 	struct rpc_xprt *xprt = task->tk_xprt;
 
 	dprintk("RPC: %4d call_bind (status %d)\n",
@@ -784,7 +783,7 @@ call_bind(struct rpc_task *task)
 	if (!xprt_bound(xprt)) {
 		task->tk_action = call_bind_status;
 		task->tk_timeout = xprt->bind_timeout;
-		rpc_getport(task, clnt);
+		xprt->ops->rpcbind(task);
 	}
 }
 

net/sunrpc/pmap_clnt.c

@@ -81,13 +81,13 @@ static inline void pmap_wake_portmap_waiters(struct rpc_xprt *xprt)
 /**
  * rpc_getport - obtain the port for a given RPC service on a given host
  * @task: task that is waiting for portmapper request
- * @clnt: controlling rpc_clnt
  *
  * This one can be called for an ongoing RPC request, and can be used in
  * an async (rpciod) context.
  */
-void rpc_getport(struct rpc_task *task, struct rpc_clnt *clnt)
+void rpc_getport(struct rpc_task *task)
 {
+	struct rpc_clnt *clnt = task->tk_client;
 	struct rpc_xprt *xprt = task->tk_xprt;
 	struct sockaddr_in *sap = &xprt->addr;
 	struct portmap_args *map;

net/sunrpc/xprtsock.c

@@ -1262,6 +1262,7 @@ static struct rpc_xprt_ops xs_udp_ops = {
 	.set_buffer_size	= xs_udp_set_buffer_size,
 	.reserve_xprt		= xprt_reserve_xprt_cong,
 	.release_xprt		= xprt_release_xprt_cong,
+	.rpcbind		= rpc_getport,
 	.set_port		= xs_set_port,
 	.connect		= xs_connect,
 	.buf_alloc		= rpc_malloc,
@@ -1278,6 +1279,7 @@ static struct rpc_xprt_ops xs_udp_ops = {
 static struct rpc_xprt_ops xs_tcp_ops = {
 	.reserve_xprt		= xprt_reserve_xprt,
 	.release_xprt		= xs_tcp_release_xprt,
+	.rpcbind		= rpc_getport,
 	.set_port		= xs_set_port,
 	.connect		= xs_connect,
 	.buf_alloc		= rpc_malloc,