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Date:	Sat, 21 Feb 2015 17:59:45 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Jay Vosburgh <jay.vosburgh@...onical.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>, davem@...emloft.net,
	vfalico@...il.com, andy@...yhouse.net, netdev@...r.kernel.org
Subject: Re: [PATCH] bonding: ban stacked bonding support

Sat, Feb 21, 2015 at 12:14:00AM CET, jay.vosburgh@...onical.com wrote:
>Alexey Dobriyan <adobriyan@...il.com> wrote:
>
>>Does Linux support it at all?
>>
>>In short: if you add bonding master as a slave, and then release it,
>>it will no longer be a IFF_BONDING creating problems like described at
>>https://bugzilla.kernel.org/show_bug.cgi?id=89541
>>
>>	echo +bond1 >/sys/class/net/bonding_masters
>>	echo 1 >/sys/class/net/bond1/bonding/mode
>>	echo +bond2 >/sys/class/net/bonding_masters
>>	echo +bond2 >/sys/class/net/bond1/bonding/slaves
>>	echo -bond2 >/sys/class/net/bond1/bonding/slaves
>>	echo -bond2 >/sys/class/net/bonding_masters
>>
>>	cat /proc/net/bonding/bond2		# should not exist
>>		[oops]
>>
>>Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
>
>	I think it's time to disallow stacking like this; it never
>really worked quite right as far as I can remember, and I thought it was
>disallowed at some point in the past.  I don't believe the stacked bonds
>function correctly for receive in the current kernel, either, although
>I'd have to test it again to confirm that.
>
>	The usual case for desiring to stack bonds is an active-backup
>pair of LACP / 802.3ad bonds (such as the bugzilla referenced above),
>but the 802.3ad mode handles this situation internally, so no stack is
>necessary.

Exactly. There is no real use-case for stacked bonding.

>
>>---
>>
>> drivers/net/bonding/bond_main.c |    5 +++++
>> 1 file changed, 5 insertions(+)
>>
>>--- a/drivers/net/bonding/bond_main.c
>>+++ b/drivers/net/bonding/bond_main.c
>>@@ -1248,6 +1248,11 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
>> 			    slave_dev->name);
>> 	}
>> 
>>+	if (slave_dev->flags & IFF_MASTER) {
>>+		netdev_dbg(bond_dev, "stacked bonding not supported\n");
>>+		return -EBUSY;
>>+	}
>>+
>> 	/* already enslaved */
>> 	if (slave_dev->flags & IFF_SLAVE) {
>> 		netdev_dbg(bond_dev, "Error: Device was already enslaved\n");
>
>	Instead of a separate block for IFF_MASTER, the IFF_SLAVE line
>could be replaced with something like:
>
>	if (netif_is_bond_slave(slave_dev) || netif_is_bond_master(slave_dev)) {
>		netdev_dbg(bond_dev, "Error: Device is bond slave or master\n");
>
>	With that caveat:
>
>Signed-off-by: Jay Vosburgh <jay.vosburgh@...onical.com>
>
>	This is probably a good candidate for -stable as well.
>
>	-J
>
>---
>	-Jay Vosburgh, jay.vosburgh@...onical.com
>--
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