linux-kernel - [PATCH] rtnetlink: return the newly created link in response to newlink

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Message-Id: <1391087144-24490-1-git-send-email-teg@jklm.no>
Date:	Thu, 30 Jan 2014 14:05:44 +0100
From:	Tom Gundersen <teg@...m.no>
To:	netdev@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	John Fastabend <john.r.fastabend@...el.com>,
	Thomas Graf <tgraf@...g.ch>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Vlad Yasevich <vyasevich@...il.com>,
	Tom Gundersen <teg@...m.no>,
	Marcel Holtmann <marcel@...tmann.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH] rtnetlink: return the newly created link in response to newlink

Userspace needs to reliably know the ifindex of the netdevs it creates,
as we cannot rely on the ifname staying unchanged.

Earlier, a simlpe NLMSG_ERROR would be returned, but this returns the
corresponding RTM_NEWLINK on success instead.

Signed-off-by: Tom Gundersen <teg@...m.no>
Cc: Marcel Holtmann <marcel@...tmann.org>
Cc: David S. Miller <davem@...emloft.net>
---
 net/core/rtnetlink.c | 100 ++++++++++++++++++++++++++-------------------------
 1 file changed, 52 insertions(+), 48 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index cf67144..31c1322 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1725,6 +1725,54 @@ static int rtnl_group_changelink(struct net *net, int group,
 	return 0;
 }
 
+static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr* nlh)
+{
+	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;
+	int err;
+	u32 ext_filter_mask = 0;
+
+	err = nlmsg_parse(nlh, sizeof(*ifm), tb, IFLA_MAX, ifla_policy);
+	if (err < 0)
+		return err;
+
+	if (tb[IFLA_IFNAME])
+		nla_strlcpy(ifname, tb[IFLA_IFNAME], IFNAMSIZ);
+
+	if (tb[IFLA_EXT_MASK])
+		ext_filter_mask = nla_get_u32(tb[IFLA_EXT_MASK]);
+
+	ifm = nlmsg_data(nlh);
+	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, ext_filter_mask), GFP_KERNEL);
+	if (nskb == NULL)
+		return -ENOBUFS;
+
+	err = rtnl_fill_ifinfo(nskb, dev, RTM_NEWLINK, NETLINK_CB(skb).portid,
+			       nlh->nlmsg_seq, 0, 0, ext_filter_mask);
+	if (err < 0) {
+		/* -EMSGSIZE implies BUG in if_nlmsg_size */
+		WARN_ON(err == -EMSGSIZE);
+		kfree_skb(nskb);
+	} else
+		err = rtnl_unicast(nskb, net, NETLINK_CB(skb).portid);
+
+	return err;
+}
+
 static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh)
 {
 	struct net *net = sock_net(skb->sk);
@@ -1871,63 +1919,19 @@ replay:
 			goto out;
 		}
 
+		ifm->ifi_index = dev->ifindex;
+
 		err = rtnl_configure_link(dev, ifm);
 		if (err < 0)
 			unregister_netdevice(dev);
+		else
+			rtnl_getlink(skb, nlh);
 out:
 		put_net(dest_net);
 		return err;
 	}
 }
 
-static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr* nlh)
-{
-	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;
-	int err;
-	u32 ext_filter_mask = 0;
-
-	err = nlmsg_parse(nlh, sizeof(*ifm), tb, IFLA_MAX, ifla_policy);
-	if (err < 0)
-		return err;
-
-	if (tb[IFLA_IFNAME])
-		nla_strlcpy(ifname, tb[IFLA_IFNAME], IFNAMSIZ);
-
-	if (tb[IFLA_EXT_MASK])
-		ext_filter_mask = nla_get_u32(tb[IFLA_EXT_MASK]);
-
-	ifm = nlmsg_data(nlh);
-	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, ext_filter_mask), GFP_KERNEL);
-	if (nskb == NULL)
-		return -ENOBUFS;
-
-	err = rtnl_fill_ifinfo(nskb, dev, RTM_NEWLINK, NETLINK_CB(skb).portid,
-			       nlh->nlmsg_seq, 0, 0, ext_filter_mask);
-	if (err < 0) {
-		/* -EMSGSIZE implies BUG in if_nlmsg_size */
-		WARN_ON(err == -EMSGSIZE);
-		kfree_skb(nskb);
-	} else
-		err = rtnl_unicast(nskb, net, NETLINK_CB(skb).portid);
-
-	return err;
-}
-
 static u16 rtnl_calcit(struct sk_buff *skb, struct nlmsghdr *nlh)
 {
 	struct net *net = sock_net(skb->sk);
-- 
1.8.5.3

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