[TUN]: Introduce the tun_net structure and init/exit net ops.

This is the first step in making tuntap devices work in net 
namespaces. The structure mentioned is pointed by generic
net pointer with tun_net_id id, and tun driver fills one on 
its load. It will contain only the tun devices list.

So declare this structure and introduce net init and exit hooks.
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -63,6 +63,7 @@
 #include <linux/if_tun.h>
 #include <linux/crc32.h>
 #include <net/net_namespace.h>
+#include <net/netns/generic.h>
 
 #include <asm/system.h>
 #include <asm/uaccess.h>
@@ -106,6 +107,11 @@ struct tun_struct {
 
 /* Network device part of the driver */
 
+static unsigned int tun_net_id;
+struct tun_net {
+	struct list_head dev_list;
+};
+
 static LIST_HEAD(tun_dev_list);
 static const struct ethtool_ops tun_ethtool_ops;
 
@@ -909,6 +915,37 @@ static const struct ethtool_ops tun_ethtool_ops = {
 	.set_rx_csum	= tun_set_rx_csum
 };
 
+static int tun_init_net(struct net *net)
+{
+	struct tun_net *tn;
+
+	tn = kmalloc(sizeof(*tn), GFP_KERNEL);
+	if (tn == NULL)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&tn->dev_list);
+
+	if (net_assign_generic(net, tun_net_id, tn)) {
+		kfree(tn);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static void tun_exit_net(struct net *net)
+{
+	struct tun_net *tn;
+
+	tn = net_generic(net, tun_net_id);
+	kfree(tn);
+}
+
+static struct pernet_operations tun_net_ops = {
+	.init = tun_init_net,
+	.exit = tun_exit_net,
+};
+
 static int __init tun_init(void)
 {
 	int ret = 0;
@@ -916,9 +953,22 @@ static int __init tun_init(void)
 	printk(KERN_INFO "tun: %s, %s\n", DRV_DESCRIPTION, DRV_VERSION);
 	printk(KERN_INFO "tun: %s\n", DRV_COPYRIGHT);
 
+	ret = register_pernet_gen_device(&tun_net_id, &tun_net_ops);
+	if (ret) {
+		printk(KERN_ERR "tun: Can't register pernet ops\n");
+		goto err_pernet;
+	}
+
 	ret = misc_register(&tun_miscdev);
-	if (ret)
+	if (ret) {
 		printk(KERN_ERR "tun: Can't register misc device %d\n", TUN_MINOR);
+		goto err_misc;
+	}
+	return 0;
+
+err_misc:
+	unregister_pernet_gen_device(tun_net_id, &tun_net_ops);
+err_pernet:
 	return ret;
 }
 
@@ -935,6 +985,7 @@ static void tun_cleanup(void)
 	}
 	rtnl_unlock();
 
+	unregister_pernet_gen_device(tun_net_id, &tun_net_ops);
 }
 
 module_init(tun_init);