SUNRPC: Provide a new API for registering transport implementations

To allow transport capabilities to be loaded dynamically, provide an API
for registering and unregistering the transports with the RPC client.
Eventually xprt_create_transport() will be changed to search the list of
registered transports when initializing a fresh transport.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Tom Talpey <tmt@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/xprt.h

@@ -208,6 +208,15 @@ struct rpc_xprtsock_create {
 	struct rpc_timeout *	timeout;	/* optional timeout parameters */
 };
 
+struct xprt_class {
+	struct list_head	list;
+	unsigned short		family;
+	int			protocol;
+	struct rpc_xprt *	(*setup)(struct rpc_xprtsock_create *);
+	struct module		*owner;
+	char			name[32];
+};
+
 /*
  * Transport operations used by ULPs
  */
@@ -239,6 +248,8 @@ static inline __be32 *xprt_skip_transport_header(struct rpc_xprt *xprt, __be32 *
 /*
  * Transport switch helper functions
  */
+int			xprt_register_transport(struct xprt_class *type);
+int			xprt_unregister_transport(struct xprt_class *type);
 void			xprt_set_retrans_timeout_def(struct rpc_task *task);
 void			xprt_set_retrans_timeout_rtt(struct rpc_task *task);
 void			xprt_wake_pending_tasks(struct rpc_xprt *xprt, int status);

net/sunrpc/xprt.c

@@ -62,6 +62,9 @@ static inline void	do_xprt_reserve(struct rpc_task *);
 static void	xprt_connect_status(struct rpc_task *task);
 static int      __xprt_get_cong(struct rpc_xprt *, struct rpc_task *);
 
+static spinlock_t xprt_list_lock = SPIN_LOCK_UNLOCKED;
+static LIST_HEAD(xprt_list);
+
 /*
  * The transport code maintains an estimate on the maximum number of out-
  * standing RPC requests, using a smoothed version of the congestion
@@ -80,6 +83,78 @@ static int      __xprt_get_cong(struct rpc_xprt *, struct rpc_task *);
 
 #define RPCXPRT_CONGESTED(xprt) ((xprt)->cong >= (xprt)->cwnd)
 
+/**
+ * xprt_register_transport - register a transport implementation
+ * @transport: transport to register
+ *
+ * If a transport implementation is loaded as a kernel module, it can
+ * call this interface to make itself known to the RPC client.
+ *
+ * Returns:
+ * 0:		transport successfully registered
+ * -EEXIST:	transport already registered
+ * -EINVAL:	transport module being unloaded
+ */
+int xprt_register_transport(struct xprt_class *transport)
+{
+	struct xprt_class *t;
+	int result;
+
+	result = -EEXIST;
+	spin_lock(&xprt_list_lock);
+	list_for_each_entry(t, &xprt_list, list) {
+		/* don't register the same transport class twice */
+		if (t == transport)
+			goto out;
+	}
+
+	result = -EINVAL;
+	if (try_module_get(THIS_MODULE)) {
+		list_add_tail(&transport->list, &xprt_list);
+		printk(KERN_INFO "RPC: Registered %s transport module.\n",
+			transport->name);
+		result = 0;
+	}
+
+out:
+	spin_unlock(&xprt_list_lock);
+	return result;
+}
+EXPORT_SYMBOL_GPL(xprt_register_transport);
+
+/**
+ * xprt_unregister_transport - unregister a transport implementation
+ * transport: transport to unregister
+ *
+ * Returns:
+ * 0:		transport successfully unregistered
+ * -ENOENT:	transport never registered
+ */
+int xprt_unregister_transport(struct xprt_class *transport)
+{
+	struct xprt_class *t;
+	int result;
+
+	result = 0;
+	spin_lock(&xprt_list_lock);
+	list_for_each_entry(t, &xprt_list, list) {
+		if (t == transport) {
+			printk(KERN_INFO
+				"RPC: Unregistered %s transport module.\n",
+				transport->name);
+			list_del_init(&transport->list);
+			module_put(THIS_MODULE);
+			goto out;
+		}
+	}
+	result = -ENOENT;
+
+out:
+	spin_unlock(&xprt_list_lock);
+	return result;
+}
+EXPORT_SYMBOL_GPL(xprt_unregister_transport);
+
 /**
  * xprt_reserve_xprt - serialize write access to transports
  * @task: task that is requesting access to the transport