Subject: Re: Bonding on bond

From: Jiri Bohac <[email-masked]>
Date: Thu, 20 Jan 2011 16:31:10 +0100

On Wed, Jan 19, 2011 at 09:33:19PM +0100, Nicolas de Pesloüan wrote:
> Even if it is possible to test for slave and for master with a
> single condition (IFF_BONDING), I suggest to split the tests and the
> error messages, to give end user the best possible diagnostic.

OK, why not. The below patch still uses IFF_BONDING to detect a
master is being enslaved, because IFF_MASTER is also used by the
eql driver. No idea if it works / someone ever uses it with
bonding, but it might collide.

bonding: prohibit enslaving of bonding masters

Nested bonding is not supported and will result in strange problems, e.g.:
- netif_receive_skb() will not properly change skb->dev to point to the
  uppoer-most bonding master
- arp monitor will not work (dev->last_rx is only updated by hardware drivers)
- accidentally enslaving a bonding master to itself will cause an infinite
  recursion in the TX path

This patch prevents this by prohibiting a bonding master from being further enslaved.

Signed-off-by: Jiri Bohac <[email-masked]>

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index b1025b8..b117dd8 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -1453,6 +1453,12 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
 		return -EBUSY;
 	}
 
+	/* cannot enslave a master */
+	if (slave_dev->priv_flags & IFF_BONDING) {
+		pr_debug("Error, cannot enslave a bonding master\n");
+		return -EBUSY;
+	}
+
 	/* vlan challenged mutual exclusion */
 	/* no need to lock since we're protected by rtnl_lock */
 	if (slave_dev->features & NETIF_F_VLAN_CHALLENGED) {

-- 
Jiri Bohac <[email-masked]>
SUSE Labs, SUSE CZ