VLAN filtering with DSA

[Vladimir Oltean <olteanv@gmail.com>]

Hi,

Problem background:

Most DSA switch tags shift the EtherType to the right, causing the
master to not parse the VLAN as VLAN.
However, not all switches do that (example: tail tags), and if the DSA
master has "rx-vlan-filter: on" in ethtool -k, then we have a problem.
Therefore, I was thinking we could populate the VLAN table of the
master, just in case, so that it can work with a VLAN filtering master.
It would look something like this:

diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 19b98a7231ec..b8aca2301c59 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -307,9 +307,10 @@ static int dsa_slave_vlan_add(struct net_device *dev,
 			      const struct switchdev_obj *obj,
 			      struct switchdev_trans *trans)
 {
+	struct net_device *master = dsa_slave_to_master(dev);
 	struct dsa_port *dp = dsa_slave_to_port(dev);
 	struct switchdev_obj_port_vlan vlan;
-	int err;
+	int vid, err;
 
 	if (obj->orig_dev != dev)
 		return -EOPNOTSUPP;
@@ -336,6 +337,12 @@ static int dsa_slave_vlan_add(struct net_device *dev,
 	if (err)
 		return err;
 
+	for (vid = vlan.vid_begin; vid <= vlan.vid_end; vid++) {
+		err = vlan_vid_add(master, htons(ETH_P_8021Q), vid);
+		if (err)
+			return err;
+	}
+
 	return 0;
 }
 
@@ -379,8 +386,10 @@ static int dsa_slave_port_obj_add(struct net_device *dev,
 static int dsa_slave_vlan_del(struct net_device *dev,
 			      const struct switchdev_obj *obj)
 {
+	struct net_device *master = dsa_slave_to_master(dev);
 	struct dsa_port *dp = dsa_slave_to_port(dev);
 	struct switchdev_obj_port_vlan *vlan;
+	int vid, err;
 
 	if (obj->orig_dev != dev)
 		return -EOPNOTSUPP;
@@ -396,7 +405,14 @@ static int dsa_slave_vlan_del(struct net_device *dev,
 	/* Do not deprogram the CPU port as it may be shared with other user
 	 * ports which can be members of this VLAN as well.
 	 */
-	return dsa_port_vlan_del(dp, vlan);
+	err = dsa_port_vlan_del(dp, vlan);
+	if (err)
+		return err;
+
+	for (vid = vlan->vid_begin; vid <= vlan->vid_end; vid++)
+		vlan_vid_del(master, htons(ETH_P_8021Q), vid);
+
+	return 0;
 }
 
 static int dsa_slave_port_obj_del(struct net_device *dev,
@@ -1241,6 +1257,7 @@ static int dsa_slave_get_ts_info(struct net_device *dev,
 static int dsa_slave_vlan_rx_add_vid(struct net_device *dev, __be16 proto,
 				     u16 vid)
 {
+	struct net_device *master = dsa_slave_to_master(dev);
 	struct dsa_port *dp = dsa_slave_to_port(dev);
 	struct switchdev_obj_port_vlan vlan = {
 		.obj.id = SWITCHDEV_OBJ_ID_PORT_VLAN,
@@ -1294,12 +1311,13 @@ static int dsa_slave_vlan_rx_add_vid(struct net_device *dev, __be16 proto,
 	if (ret)
 		return ret;
 
-	return 0;
+	return vlan_vid_add(master, proto, vid);
 }
 
 static int dsa_slave_vlan_rx_kill_vid(struct net_device *dev, __be16 proto,
 				      u16 vid)
 {
+	struct net_device *master = dsa_slave_to_master(dev);
 	struct dsa_port *dp = dsa_slave_to_port(dev);
 	struct switchdev_obj_port_vlan vlan = {
 		.vid_begin = vid,
@@ -1332,7 +1350,13 @@ static int dsa_slave_vlan_rx_kill_vid(struct net_device *dev, __be16 proto,
 	/* Do not deprogram the CPU port as it may be shared with other user
 	 * ports which can be members of this VLAN as well.
 	 */
-	return dsa_port_vlan_del(dp, &vlan);
+	ret = dsa_port_vlan_del(dp, &vlan);
+	if (ret)
+		return ret;
+
+	vlan_vid_del(master, proto, vid);
+
+	return 0;
 }
 
 struct dsa_hw_port {
-- 
2.25.1


Ok, now the problem.
This works, except when the master is another DSA switch.
You see, I hit this -EBUSY condition:

static int dsa_slave_vlan_rx_add_vid(struct net_device *dev, __be16 proto,
				     u16 vid)
{
	...

	/* Check for a possible bridge VLAN entry now since there is no
	 * need to emulate the switchdev prepare + commit phase.
	 */
	if (dp->bridge_dev) {
		...
		/* br_vlan_get_info() returns -EINVAL or -ENOENT if the
		 * device, respectively the VID is not found, returning
		 * 0 means success, which is a failure for us here.
		 */
		ret = br_vlan_get_info(dp->bridge_dev, vid, &info);
		if (ret == 0)
			return -EBUSY;
	}
}

Introduced by:

commit 061f6a505ac33659eab007731c0f6374df39ab55
Author: Florian Fainelli <f.fainelli@gmail.com>
Date:   Wed Feb 20 14:35:39 2019 -0800

    net: dsa: Add ndo_vlan_rx_{add, kill}_vid implementation

    In order to properly support VLAN filtering being enabled/disabled on a
    bridge, while having other ports being non bridge port members, we need
    to support the ndo_vlan_rx_{add,kill}_vid callbacks in order to make
    sure the non-bridge ports can continue receiving VLAN tags, even when
    the switch is globally configured to do ingress/egress VID checking.

    Since we can call dsa_port_vlan_{add,del} with a bridge_dev pointer
    NULL, we now need to check that in these two functions.

    We specifically deal with two possibly problematic cases:

    - creating a bridge VLAN entry while there is an existing VLAN device
      claiming that same VID

    - creating a VLAN device while there is an existing bridge VLAN entry
      with that VID

    Those are both resolved with returning -EBUSY back to user-space.

    Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>

Florian, can you please reiterate what is the problem with calling
vlan_vid_add() with a VLAN that is installed by the bridge?

The effect of vlan_vid_add(), to my knowledge, is that the network
interface should add this VLAN to its filtering table, and not drop it.
So why return -EBUSY?

Thanks,
-Vladimir