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>

1 files changed, 75 insertions, 0 deletions

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index bc13616e7fdc..520859622af5 100644
--- a/net/sunrpc/xprt.c
+++ b/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
@@ -81,6 +84,78 @@ 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
  *