l2tp: auto load type modules

It should not be necessary to do explicit module loading when
configuring L2TP. Modules should be loaded as needed instead
(as is done already with netlink and other tunnel types).

This patch adds a new module alias type and code to load
the sub module on demand.
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_core.h

@@ -321,4 +321,7 @@ do {									\
 #define l2tp_dbg(ptr, type, fmt, ...)					\
 	l2tp_printk(ptr, type, pr_debug, fmt, ##__VA_ARGS__)
 
+#define MODULE_ALIAS_L2TP_PWTYPE(type) \
+	MODULE_ALIAS("net-l2tp-type-" __stringify(type))
+
 #endif /* _L2TP_CORE_H_ */

net/l2tp/l2tp_eth.c

@@ -358,3 +358,4 @@ MODULE_LICENSE("GPL");
 MODULE_AUTHOR("James Chapman <jchapman@katalix.com>");
 MODULE_DESCRIPTION("L2TP ethernet pseudowire driver");
 MODULE_VERSION("1.0");
+MODULE_ALIAS_L2TP_PWTYPE(5);

net/l2tp/l2tp_netlink.c

@@ -576,6 +576,13 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
 	if (info->attrs[L2TP_ATTR_MRU])
 		cfg.mru = nla_get_u16(info->attrs[L2TP_ATTR_MRU]);
 
+#ifdef CONFIG_MODULES
+	if (l2tp_nl_cmd_ops[cfg.pw_type] == NULL) {
+		genl_unlock();
+		request_module("net-l2tp-type-%u", cfg.pw_type);
+		genl_lock();
+	}
+#endif
 	if ((l2tp_nl_cmd_ops[cfg.pw_type] == NULL) ||
 	    (l2tp_nl_cmd_ops[cfg.pw_type]->session_create == NULL)) {
 		ret = -EPROTONOSUPPORT;

net/l2tp/l2tp_ppp.c

@@ -1863,3 +1863,4 @@ MODULE_DESCRIPTION("PPP over L2TP over UDP");
 MODULE_LICENSE("GPL");
 MODULE_VERSION(PPPOL2TP_DRV_VERSION);
 MODULE_ALIAS("pppox-proto-" __stringify(PX_PROTO_OL2TP));
+MODULE_ALIAS_L2TP_PWTYPE(11);