netdev - [net v4] veth: advertise peer link once both links are tied together

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Message-Id: <1464676221-4873-1-git-send-email-vincent@bernat.im>
Date:	Tue, 31 May 2016 08:30:21 +0200
From:	Vincent Bernat <vincent@...nat.im>
To:	"David S. Miller" <davem@...emloft.net>,
	Vijay Pandurangan <vijayp@...ayp.ca>,
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:	Vincent Bernat <vincent@...nat.im>
Subject: [net v4] veth: advertise peer link once both links are tied together

When the peer link is created, its "iflink" information is not
advertised through Netlink. Once created, the local device is advertised
with this information but if a user is maintaining a cache from all
updates, it will still miss the iflink for the peer link:

    2: veth0@...E: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default
        link/ether ae:0e:08:af:fb:a0 brd ff:ff:ff:ff:ff:ff
    3: veth1@...h0: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN group default
        link/ether 3a:31:f1:36:2e:e5 brd ff:ff:ff:ff:ff:ff

With this patch, we advertise again the peer link to let any user pick
the appropriate iflink information:

    3: veth0@...E: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default
        link/ether fa:ba:12:26:99:00 brd ff:ff:ff:ff:ff:ff
    3: veth0@...h1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default
        link/ether fa:ba:12:26:99:00 brd ff:ff:ff:ff:ff:ff
    4: veth1@...h0: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN group default
        link/ether ea:e4:e2:26:3c:87 brd ff:ff:ff:ff:ff:ff

Signed-off-by: Vincent Bernat <vincent@...nat.im>
---
v4:
 - use ~0U instead of IFF_SLAVE for ifi_change

v3:
 - send an additional netlink messages once the peer link is tied to
   avoid any chicken/egg problem

v2:
 - ensure the device is unregistered in case of link configuration failure

drivers/net/veth.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index f37a6e61d4ad..aaa1b023b9f2 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -466,6 +466,8 @@ static int veth_newlink(struct net *src_net, struct net_device *dev,
 
 	priv = netdev_priv(peer);
 	rcu_assign_pointer(priv->peer, dev);
+
+	rtmsg_ifinfo(RTM_NEWLINK, peer, ~0U, GFP_KERNEL);
 	return 0;
 
 err_register_dev:
-- 
2.8.1