[PATCH] macvlan: Support creating macvlans from macvlans

[ebiederm@xmission.com (Eric W. Biederman)]

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>
---
 drivers/net/macvlan.c |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 7e24b50..b5241fc 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;
-- 
1.6.1.2.350.g88cc