net: allow to delete a whole device group

With dev group, we can change a batch of net devices,
so we should allow to delete them together too.

Group 0 is not allowed to be deleted since it is
the default group.

Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -1836,6 +1836,42 @@ errout:
 	return err;
 }
 
+static int rtnl_group_dellink(const struct net *net, int group)
+{
+	struct net_device *dev, *aux;
+	LIST_HEAD(list_kill);
+	bool found = false;
+
+	if (!group)
+		return -EPERM;
+
+	for_each_netdev(net, dev) {
+		if (dev->group == group) {
+			const struct rtnl_link_ops *ops;
+
+			found = true;
+			ops = dev->rtnl_link_ops;
+			if (!ops || !ops->dellink)
+				return -EOPNOTSUPP;
+		}
+	}
+
+	if (!found)
+		return -ENODEV;
+
+	for_each_netdev_safe(net, dev, aux) {
+		if (dev->group == group) {
+			const struct rtnl_link_ops *ops;
+
+			ops = dev->rtnl_link_ops;
+			ops->dellink(dev, &list_kill);
+		}
+	}
+	unregister_netdevice_many(&list_kill);
+
+	return 0;
+}
+
 static int rtnl_dellink(struct sk_buff *skb, struct nlmsghdr *nlh)
 {
 	struct net *net = sock_net(skb->sk);
@@ -1859,6 +1895,8 @@ static int rtnl_dellink(struct sk_buff *skb, struct nlmsghdr *nlh)
 		dev = __dev_get_by_index(net, ifm->ifi_index);
 	else if (tb[IFLA_IFNAME])
 		dev = __dev_get_by_name(net, ifname);
+	else if (tb[IFLA_GROUP])
+		return rtnl_group_dellink(net, nla_get_u32(tb[IFLA_GROUP]));
 	else
 		return -EINVAL;