netlink: support setting devgroup parameters

If a rtnetlink request specifies a negative or zero ifindex and has no
interface name attribute, but has a group attribute, then the chenges
are made to all the interfaces belonging to the specified group.
Signed-off-by: Vlad Dogaru <ddvlad@rosedu.org>
Acked-by: Jamal Hadi Salim <hadi@cyberus.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -1558,6 +1558,24 @@ struct net_device *rtnl_create_link(struct net *src_net, struct net *net,
 }
 EXPORT_SYMBOL(rtnl_create_link);
 
+static int rtnl_group_changelink(struct net *net, int group,
+		struct ifinfomsg *ifm,
+		struct nlattr **tb)
+{
+	struct net_device *dev;
+	int err;
+
+	for_each_netdev(net, dev) {
+		if (dev->group == group) {
+			err = do_setlink(dev, ifm, tb, NULL, 0);
+			if (err < 0)
+				return err;
+		}
+	}
+
+	return 0;
+}
+
 static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 {
 	struct net *net = sock_net(skb->sk);
@@ -1585,10 +1603,16 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 	ifm = nlmsg_data(nlh);
 	if (ifm->ifi_index > 0)
 		dev = __dev_get_by_index(net, ifm->ifi_index);
-	else if (ifname[0])
+	else {
+		if (ifname[0])
 			dev = __dev_get_by_name(net, ifname);
+		else if (tb[IFLA_GROUP])
+			return rtnl_group_changelink(net,
+					nla_get_u32(tb[IFLA_GROUP]),
+					ifm, tb);
 		else
 			dev = NULL;
+	}
 
 	err = validate_linkmsg(dev, tb);
 	if (err < 0)