[MACVLAN]: Prevent nesting macvlan devices

[Patrick McHardy <kaber@trash.net>]

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[MACVLAN]: Prevent nesting macvlan devices

Don't allow to nest macvlan devices since it will cause lockdep warnings and
isn't really useful for anything.

Signed-off-by: Patrick McHardy <kaber@trash.net>

---
commit 80a76fbde679793a17482a3dd842386801fca66b
tree 07f67e78ac0ae505a5de81e7e770a1b7d597f120
parent 4d14fded63dcaf9d5dcf78e2a8ea3f5de2c29eb9
author Patrick McHardy <kaber@trash.net> Thu, 10 Jan 2008 16:25:01 +0100
committer Patrick McHardy <kaber@trash.net> Thu, 10 Jan 2008 16:25:01 +0100

 drivers/net/macvlan.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 2e4bcd5..e8dc2f4 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -384,6 +384,13 @@ 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.
+	 */
+	if (lowerdev->rtnl_link_ops == dev->rtnl_link_ops)
+		return -ENODEV;
+
 	if (!tb[IFLA_MTU])
 		dev->mtu = lowerdev->mtu;
 	else if (dev->mtu > lowerdev->mtu)