macvlan: Support creating macvlans from macvlans

When running in a network namespace whose only link to
the outside world is a macvlan device, not being
able to create another macvlan is a real pain.

So modify macvlan creation to allow automatically forward
a creation of a macvlan on a macvlan to become a creation
of a macvlan on the underlying network device.

Signed-off-by: Eric Biederman <ebiederm@aristanetworks.com>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 5 deletions

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 7e24b5048686..b5241fc0f512 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -461,12 +461,13 @@ static int macvlan_newlink(struct net_device *dev,
         if (lowerdev == NULL)
                 return -ENODEV;
 
-        /* Don't allow macvlans on top of other macvlans - its not really
-         * wrong, but lockdep can't handle it and its not useful for anything
-         * you couldn't do directly on top of the real device.
+        /* When creating macvlans on top of other macvlans - use
+         * the real device as the lowerdev.
          */
-        if (lowerdev->rtnl_link_ops == dev->rtnl_link_ops)
-                return -ENODEV;
+        if (lowerdev->rtnl_link_ops == dev->rtnl_link_ops) {
+                struct macvlan_dev *lowervlan = netdev_priv(lowerdev);
+                lowerdev = lowervlan->lowerdev;
+        }
 
         if (!tb[IFLA_MTU])
                 dev->mtu = lowerdev->mtu;