[PATCHi next] veth: advertise peer link relationship for both devices

[Lance Richardson]

Currently, when creating a veth pair, notfications to user
space only include link peer for one end of the veth pair:
   # ip monitor link &
   # ip link add dev vm1 type veth peer name vm2
   30: vm2@NONE: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN
       link/ether be:e3:b7:0e:14:52 brd ff:ff:ff:ff:ff:ff
   31: vm1@vm2: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN
       link/ether da:e6:a6:c5:42:54 brd ff:ff:ff:ff:ff:ff

With this change, netlink notifications are sent with complete
information for both interfaces of the veth pair:

   # 3: vm2@NONE: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN
       link/ether e2:94:54:8a:ac:f5 brd ff:ff:ff:ff:ff:ff
   4: vm1@vm2: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN
       link/ether b2:05:70:e0:fc:35 brd ff:ff:ff:ff:ff:ff
   3: vm2@vm1: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN
       link/ether e2:94:54:8a:ac:f5 brd ff:ff:ff:ff:ff:ff

Signed-off-by: Lance Richardson <lrich...@redhat.com>
---
 drivers/net/veth.c   | 10 +++++++++-
 net/core/rtnetlink.c | 10 ++++++++--
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index f37a6e6..9151686 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -458,7 +458,7 @@ static int veth_newlink(struct net *src_net, struct 
net_device *dev,
        netif_carrier_off(dev);
 
        /*
-        * tie the deviced together
+        * tie the devices together
         */
 
        priv = netdev_priv(dev);
@@ -466,8 +466,16 @@ static int veth_newlink(struct net *src_net, struct 
net_device *dev,
 
        priv = netdev_priv(peer);
        rcu_assign_pointer(priv->peer, dev);
+
+       err = rtnl_configure_link(dev, NULL);
+       if (err < 0)
+               goto err_configure_dev;
+
+       rtmsg_ifinfo(RTM_NEWLINK, peer, 0, GFP_KERNEL);
        return 0;
 
+err_configure_dev:
+       /* nothing to do */
 err_register_dev:
        /* nothing to do */
 err_configure_peer:
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index d69c464..e0956bb 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2165,6 +2165,7 @@ static int rtnl_dellink(struct sk_buff *skb, struct 
nlmsghdr *nlh)
 int rtnl_configure_link(struct net_device *dev, const struct ifinfomsg *ifm)
 {
        unsigned int old_flags;
+       unsigned int gchanges;
        int err;
 
        old_flags = dev->flags;
@@ -2174,9 +2175,14 @@ int rtnl_configure_link(struct net_device *dev, const 
struct ifinfomsg *ifm)
                        return err;
        }
 
-       dev->rtnl_link_state = RTNL_LINK_INITIALIZED;
+       if (dev->rtnl_link_state == RTNL_LINK_INITIALIZING) {
+               dev->rtnl_link_state = RTNL_LINK_INITIALIZED;
+               gchanges = ~0U;
+       } else {
+               gchanges = dev->flags ^ old_flags;
+       }
 
-       __dev_notify_flags(dev, old_flags, ~0U);
+       __dev_notify_flags(dev, old_flags, gchanges);
        return 0;
 }
 EXPORT_SYMBOL(rtnl_configure_link);
-- 
2.5.5