net: ip6_gre: Split up ip6gre_changelink()

Extract from ip6gre_changelink() a reusable function
ip6gre_changelink_common(). This will allow introduction of
ERSPAN-specific _changelink() function with not a lot of code
duplication.

Fixes: 5a963eb61b7c ("ip6_gre: Add ERSPAN native tunnel support")
Signed-off-by: Petr Machata <petrm@mellanox.com>
Acked-by: William Tu <u9012063@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_gre.c

@@ -1924,37 +1924,52 @@ static int ip6gre_newlink(struct net *src_net, struct net_device *dev,
 	return err;
 }
 
-static int ip6gre_changelink(struct net_device *dev, struct nlattr *tb[],
-			     struct nlattr *data[],
-			     struct netlink_ext_ack *extack)
+static struct ip6_tnl *
+ip6gre_changelink_common(struct net_device *dev, struct nlattr *tb[],
+			 struct nlattr *data[], struct __ip6_tnl_parm *p_p,
+			 struct netlink_ext_ack *extack)
 {
 	struct ip6_tnl *t, *nt = netdev_priv(dev);
 	struct net *net = nt->net;
 	struct ip6gre_net *ign = net_generic(net, ip6gre_net_id);
-	struct __ip6_tnl_parm p;
 	struct ip_tunnel_encap ipencap;
 
 	if (dev == ign->fb_tunnel_dev)
-		return -EINVAL;
+		return ERR_PTR(-EINVAL);
 
 	if (ip6gre_netlink_encap_parms(data, &ipencap)) {
 		int err = ip6_tnl_encap_setup(nt, &ipencap);
 
 		if (err < 0)
-			return err;
+			return ERR_PTR(err);
 	}
 
-	ip6gre_netlink_parms(data, &p);
+	ip6gre_netlink_parms(data, p_p);
 
-	t = ip6gre_tunnel_locate(net, &p, 0);
+	t = ip6gre_tunnel_locate(net, p_p, 0);
 
 	if (t) {
 		if (t->dev != dev)
-			return -EEXIST;
+			return ERR_PTR(-EEXIST);
 	} else {
 		t = nt;
 	}
 
+	return t;
+}
+
+static int ip6gre_changelink(struct net_device *dev, struct nlattr *tb[],
+			     struct nlattr *data[],
+			     struct netlink_ext_ack *extack)
+{
+	struct ip6gre_net *ign = net_generic(dev_net(dev), ip6gre_net_id);
+	struct __ip6_tnl_parm p;
+	struct ip6_tnl *t;
+
+	t = ip6gre_changelink_common(dev, tb, data, &p, extack);
+	if (IS_ERR(t))
+		return PTR_ERR(t);
+
 	ip6gre_tunnel_unlink(ign, t);
 	ip6gre_tnl_change(t, &p, !tb[IFLA_MTU]);
 	ip6gre_tunnel_link(ign, t);