bonding: ban stacked bonding support

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@gmail.com>
---

 drivers/net/bonding/bond_main.c |    5 +++++
 1 file changed, 5 insertions(+)

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Alexey Dobriyan <adobriyan@gmail.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@gmail.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.

>---
>
> 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@canonical.com>

	This is probably a good candidate for -stable as well.

	-J

---
	-Jay Vosburgh, jay.vosburgh@canonical.com
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On Fri, Feb 20, 2015 at 03:14:00PM -0800, Jay Vosburgh wrote:
> Alexey Dobriyan <adobriyan@gmail.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@gmail.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.

Completely agree.

> 
> >---
> >
> > 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:
I would say adding the check for netif_is_bond_master() is critical
since a check for only IFF_MASTER would fail when trying to add a bridge
to a bond and that failure would not be desireable.

Fix that and you can also add:

Signed-off-by: Andy Gospodarek <gospo@cumulusnetworks.com>

to your next post.

> 
> Signed-off-by: Jay Vosburgh <jay.vosburgh@canonical.com>
> 
> 	This is probably a good candidate for -stable as well.
Agree

(Though netif_is_bond_master() was added in 3.10; luckily it would be an
easy backport.)

> 
> 	-J
> 
> ---
> 	-Jay Vosburgh, jay.vosburgh@canonical.com
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Sat, Feb 21, 2015 at 12:14:00AM CET, jay.vosburgh@canonical.com wrote:
>Alexey Dobriyan <adobriyan@gmail.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@gmail.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@canonical.com>
>
>	This is probably a good candidate for -stable as well.
>
>	-J
>
>---
>	-Jay Vosburgh, jay.vosburgh@canonical.com
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On Fri, Feb 20, 2015 at 03:14:00PM -0800, Jay Vosburgh wrote:
> 	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");

I think separate error messages are better (kernel can distinguish between
two anyway).
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