rtnetlink: rtnl_setlink() and rtnl_getlink() changes

rtnl_getlink() & rtnl_setlink() run with RTNL held, we can use
__dev_get_by_index() and __dev_get_by_name() variants and avoid
dev_hold()/dev_put()

Adds to rtnl_getlink() the capability to find a device by its name,
not only by its index.
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -910,9 +910,9 @@ static int rtnl_setlink(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 	err = -EINVAL;
 	ifm = nlmsg_data(nlh);
 	if (ifm->ifi_index > 0)
-		dev = dev_get_by_index(net, ifm->ifi_index);
+		dev = __dev_get_by_index(net, ifm->ifi_index);
 	else if (tb[IFLA_IFNAME])
-		dev = dev_get_by_name(net, ifname);
+		dev = __dev_get_by_name(net, ifname);
 	else
 		goto errout;
 
@@ -922,11 +922,9 @@ static int rtnl_setlink(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 	}
 
 	if ((err = validate_linkmsg(dev, tb)) < 0)
-		goto errout_dev;
+		goto errout;
 
 	err = do_setlink(dev, ifm, tb, ifname, 0);
-errout_dev:
-	dev_put(dev);
 errout:
 	return err;
 }
@@ -1154,6 +1152,7 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
 {
 	struct net *net = sock_net(skb->sk);
 	struct ifinfomsg *ifm;
+	char ifname[IFNAMSIZ];
 	struct nlattr *tb[IFLA_MAX+1];
 	struct net_device *dev = NULL;
 	struct sk_buff *nskb;
@@ -1163,19 +1162,23 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
 	if (err < 0)
 		return err;
 
+	if (tb[IFLA_IFNAME])
+		nla_strlcpy(ifname, tb[IFLA_IFNAME], IFNAMSIZ);
+
 	ifm = nlmsg_data(nlh);
-	if (ifm->ifi_index > 0) {
-		dev = dev_get_by_index(net, ifm->ifi_index);
-		if (dev == NULL)
-			return -ENODEV;
-	} else
+	if (ifm->ifi_index > 0)
+		dev = __dev_get_by_index(net, ifm->ifi_index);
+	else if (tb[IFLA_IFNAME])
+		dev = __dev_get_by_name(net, ifname);
+	else
 		return -EINVAL;
 
+	if (dev == NULL)
+		return -ENODEV;
+
 	nskb = nlmsg_new(if_nlmsg_size(dev), GFP_KERNEL);
-	if (nskb == NULL) {
-		err = -ENOBUFS;
-		goto errout;
-	}
+	if (nskb == NULL)
+		return -ENOBUFS;
 
 	err = rtnl_fill_ifinfo(nskb, dev, RTM_NEWLINK, NETLINK_CB(skb).pid,
 			       nlh->nlmsg_seq, 0, 0);
@@ -1183,11 +1186,8 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
 		/* -EMSGSIZE implies BUG in if_nlmsg_size */
 		WARN_ON(err == -EMSGSIZE);
 		kfree_skb(nskb);
-		goto errout;
-	}
-	err = rtnl_unicast(nskb, net, NETLINK_CB(skb).pid);
-errout:
-	dev_put(dev);
+	} else
+		err = rtnl_unicast(nskb, net, NETLINK_CB(skb).pid);
 
 	return err;
 }