SUNRPC: xprt_load_transport() needs to support the netid "rdma6"

According to RFC5666, the correct netid for an IPv6 addressed RDMA
transport is "rdma6", which we've supported as a mount option since
Linux-4.7. The problem is when we try to load the module "xprtrdma6",
that will fail, since there is no modulealias of that name.

Fixes: 181342c5eb ("xprtrdma: Add rdma6 option to support NFS/RDMA IPv6")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

include/linux/sunrpc/xprt.h

@@ -330,6 +330,7 @@ struct xprt_class {
 	struct rpc_xprt *	(*setup)(struct xprt_create *);
 	struct module		*owner;
 	char			name[32];
+	const char *		netid[];
 };
 
 /*

net/sunrpc/xprt.c

@@ -151,31 +151,64 @@ out:
 }
 EXPORT_SYMBOL_GPL(xprt_unregister_transport);
 
+static void
+xprt_class_release(const struct xprt_class *t)
+{
+	module_put(t->owner);
+}
+
+static const struct xprt_class *
+xprt_class_find_by_netid_locked(const char *netid)
+{
+	const struct xprt_class *t;
+	unsigned int i;
+
+	list_for_each_entry(t, &xprt_list, list) {
+		for (i = 0; t->netid[i][0] != '\0'; i++) {
+			if (strcmp(t->netid[i], netid) != 0)
+				continue;
+			if (!try_module_get(t->owner))
+				continue;
+			return t;
+		}
+	}
+	return NULL;
+}
+
+static const struct xprt_class *
+xprt_class_find_by_netid(const char *netid)
+{
+	const struct xprt_class *t;
+
+	spin_lock(&xprt_list_lock);
+	t = xprt_class_find_by_netid_locked(netid);
+	if (!t) {
+		spin_unlock(&xprt_list_lock);
+		request_module("rpc%s", netid);
+		spin_lock(&xprt_list_lock);
+		t = xprt_class_find_by_netid_locked(netid);
+	}
+	spin_unlock(&xprt_list_lock);
+	return t;
+}
+
 /**
  * xprt_load_transport - load a transport implementation
- * @transport_name: transport to load
+ * @netid: transport to load
  *
  * Returns:
  * 0:		transport successfully loaded
  * -ENOENT:	transport module not available
  */
-int xprt_load_transport(const char *transport_name)
+int xprt_load_transport(const char *netid)
 {
-	struct xprt_class *t;
-	int result;
+	const struct xprt_class *t;
 
-	result = 0;
-	spin_lock(&xprt_list_lock);
-	list_for_each_entry(t, &xprt_list, list) {
-		if (strcmp(t->name, transport_name) == 0) {
-			spin_unlock(&xprt_list_lock);
-			goto out;
-		}
-	}
-	spin_unlock(&xprt_list_lock);
-	result = request_module("xprt%s", transport_name);
-out:
-	return result;
+	t = xprt_class_find_by_netid(netid);
+	if (!t)
+		return -ENOENT;
+	xprt_class_release(t);
+	return 0;
 }
 EXPORT_SYMBOL_GPL(xprt_load_transport);
 

net/sunrpc/xprtrdma/module.c

@@ -24,6 +24,7 @@ MODULE_DESCRIPTION("RPC/RDMA Transport");
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_ALIAS("svcrdma");
 MODULE_ALIAS("xprtrdma");
+MODULE_ALIAS("rpcrdma6");
 
 static void __exit rpc_rdma_cleanup(void)
 {

net/sunrpc/xprtrdma/transport.c

@@ -768,6 +768,7 @@ static struct xprt_class xprt_rdma = {
 	.owner			= THIS_MODULE,
 	.ident			= XPRT_TRANSPORT_RDMA,
 	.setup			= xprt_setup_rdma,
+	.netid			= { "rdma", "rdma6", "" },
 };
 
 void xprt_rdma_cleanup(void)

net/sunrpc/xprtsock.c

@@ -3059,6 +3059,7 @@ static struct xprt_class	xs_local_transport = {
 	.owner		= THIS_MODULE,
 	.ident		= XPRT_TRANSPORT_LOCAL,
 	.setup		= xs_setup_local,
+	.netid		= { "" },
 };
 
 static struct xprt_class	xs_udp_transport = {
@@ -3067,6 +3068,7 @@ static struct xprt_class	xs_udp_transport = {
 	.owner		= THIS_MODULE,
 	.ident		= XPRT_TRANSPORT_UDP,
 	.setup		= xs_setup_udp,
+	.netid		= { "udp", "udp6", "" },
 };
 
 static struct xprt_class	xs_tcp_transport = {
@@ -3075,6 +3077,7 @@ static struct xprt_class	xs_tcp_transport = {
 	.owner		= THIS_MODULE,
 	.ident		= XPRT_TRANSPORT_TCP,
 	.setup		= xs_setup_tcp,
+	.netid		= { "tcp", "tcp6", "" },
 };
 
 static struct xprt_class	xs_bc_tcp_transport = {
@@ -3083,6 +3086,7 @@ static struct xprt_class	xs_bc_tcp_transport = {
 	.owner		= THIS_MODULE,
 	.ident		= XPRT_TRANSPORT_BC_TCP,
 	.setup		= xs_setup_bc_tcp,
+	.netid		= { "" },
 };
 
 /**