Subject: Re: [PATCH v2 net-next 2/4] net: dsa: Link aggregation support

From: Tobias Waldekranz <[email-masked]>
Date: Tue, 01 Dec 2020 22:48:34 +0100

On Tue, Dec 01, 2020 at 22:04, Vladimir Oltean <[email-masked]> wrote:
> On Tue, Dec 01, 2020 at 03:29:53PM +0100, Tobias Waldekranz wrote:
>> On Tue, Dec 01, 2020 at 16:03, Vladimir Oltean <[email-masked]> wrote:
>> > On Mon, Nov 30, 2020 at 03:06:08PM +0100, Tobias Waldekranz wrote:
>> >> When a LAG joins a bridge, the DSA subsystem will treat that as each
>> >> individual port joining the bridge. The driver may look at the port's
>> >> LAG pointer to see if it is associated with any LAG, if that is
>> >> required. This is analogue to how switchdev events are replicated out
>> >> to all lower devices when reaching e.g. a LAG.
>> >
>> > Agree with the principle. But doesn't that mean that this code:
>> >
>> > static int dsa_slave_switchdev_blocking_event(struct notifier_block *unused,
>> > 					      unsigned long event, void *ptr)
>> > {
>> > 	struct net_device *dev = switchdev_notifier_info_to_dev(ptr);
>> > 	int err;
>> >
>> > 	switch (event) {
>> > 	case SWITCHDEV_PORT_OBJ_ADD:
>> > 		err = switchdev_handle_port_obj_add(dev, ptr,
>> > 						    dsa_slave_dev_check,
>> > 						    dsa_slave_port_obj_add);
>> > 		return notifier_from_errno(err);
>> > 	case SWITCHDEV_PORT_OBJ_DEL:
>> > 		err = switchdev_handle_port_obj_del(dev, ptr,
>> > 						    dsa_slave_dev_check,
>> > 						    dsa_slave_port_obj_del);
>> > 		return notifier_from_errno(err);
>> > 	case SWITCHDEV_PORT_ATTR_SET:
>> > 		err = switchdev_handle_port_attr_set(dev, ptr,
>> > 						     dsa_slave_dev_check,
>> > 						     dsa_slave_port_attr_set);
>> > 		return notifier_from_errno(err);
>> > 	}
>> >
>> > 	return NOTIFY_DONE;
>> > }
>> >
>> > should be replaced with something that also reacts to the case where
>> > "dev" is a LAG? Like, for example, I imagine that a VLAN installed on a
>> > bridge port that is a LAG should be propagated to the switch ports
>> > beneath that LAG. Similarly for all bridge attributes.
>>
>> That is exactly what switchdev_handle_* does, no? It is this exact
>> behavior that my statement about switchdev event replication references.
>
> I'm sorry, I don't mean to be overly obtuse, but _how_ does the current
> code propagate a VLAN to a physical port located below a bond? Through
> magic? The dsa_slave_dev_check is passed as a parameter to
> switchdev_handle_port_obj_add _exactly_ because the code has needed so
> far to match only on DSA interfaces and not on bonding interfaces. So
> the code does not react to VLANs added on a bonding interface. Hence my
> question.

There is no magic involved, here is the relevant snippet from
__switchdev_handle_port_obj_add:

	/* Switch ports might be stacked under e.g. a LAG. Ignore the
	 * unsupported devices, another driver might be able to handle them. But
	 * propagate to the callers any hard errors.
	 *
	 * If the driver does its own bookkeeping of stacked ports, it's not
	 * necessary to go through this helper.
	 */
	netdev_for_each_lower_dev(dev, lower_dev, iter) {
		if (netif_is_bridge_master(lower_dev))
			continue;

		err = __switchdev_handle_port_obj_add(lower_dev, port_obj_info,
						      check_cb, add_cb);
		if (err && err != -EOPNOTSUPP)
			return err;
	}

> ip link del bond0
> ip link add bond0 type bond mode 802.3ad
> ip link set swp1 down && ip link set swp1 master bond0 && ip link set swp1 up
> ip link set swp2 down && ip link set swp2 master bond0 && ip link set swp2 up
> ip link del br0
> ip link add br0 type bridge
> ip link set bond0 master br0
> ip link set swp0 master br0
>
> This should propagate the VLANs to swp1 and swp2 but doesn't:
> bridge vlan add dev bond0 vid 100

I ran through this on my setup and it is indeed propagated to all ports.

Just a thought, when you rebased the ocelot specific stuff to v2, did
you add the number of supported LAGs to ds->num_lags? If not, DSA will
assume that the hardware does not support offloading.

> It's perfectly acceptable to say that this patch set doesn't deal with
> that. But your commit message seems to suggest that it's me who's
> misunderstanding something.

I understand, that is why I explicitly mentioned the lack of static FDB
support for example. But it absolutely should deal with the full list I
specified, so thanks for testing it.