net: bridge: move DSA master bridging restriction to DSA

When DSA gains support for multiple CPU ports in a LAG, it will become
mandatory to monitor the changeupper events for the DSA master.

In fact, there are already some restrictions to be imposed in that area,
namely that a DSA master cannot be a bridge port except in some special
circumstances.

Centralize the restrictions at the level of the DSA layer as a
preliminary step.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/bridge/br_if.c

@@ -568,26 +568,6 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
 	    !is_valid_ether_addr(dev->dev_addr))
 		return -EINVAL;
 
-	/* Also don't allow bridging of net devices that are DSA masters, since
-	 * the bridge layer rx_handler prevents the DSA fake ethertype handler
-	 * to be invoked, so we don't get the chance to strip off and parse the
-	 * DSA switch tag protocol header (the bridge layer just returns
-	 * RX_HANDLER_CONSUMED, stopping RX processing for these frames).
-	 * The only case where that would not be an issue is when bridging can
-	 * already be offloaded, such as when the DSA master is itself a DSA
-	 * or plain switchdev port, and is bridged only with other ports from
-	 * the same hardware device.
-	 */
-	if (netdev_uses_dsa(dev)) {
-		list_for_each_entry(p, &br->port_list, list) {
-			if (!netdev_port_same_parent_id(dev, p->dev)) {
-				NL_SET_ERR_MSG(extack,
-					       "Cannot do software bridging with a DSA master");
-				return -EINVAL;
-			}
-		}
-	}
-
 	/* No bridging of bridges */
 	if (dev->netdev_ops->ndo_start_xmit == br_dev_xmit) {
 		NL_SET_ERR_MSG(extack,

net/dsa/slave.c

@@ -2699,6 +2699,46 @@ dsa_slave_prechangeupper_sanity_check(struct net_device *dev,
 	return NOTIFY_DONE;
 }
 
+/* Don't allow bridging of DSA masters, since the bridge layer rx_handler
+ * prevents the DSA fake ethertype handler to be invoked, so we don't get the
+ * chance to strip off and parse the DSA switch tag protocol header (the bridge
+ * layer just returns RX_HANDLER_CONSUMED, stopping RX processing for these
+ * frames).
+ * The only case where that would not be an issue is when bridging can already
+ * be offloaded, such as when the DSA master is itself a DSA or plain switchdev
+ * port, and is bridged only with other ports from the same hardware device.
+ */
+static int
+dsa_bridge_prechangelower_sanity_check(struct net_device *new_lower,
+				       struct netdev_notifier_changeupper_info *info)
+{
+	struct net_device *br = info->upper_dev;
+	struct netlink_ext_ack *extack;
+	struct net_device *lower;
+	struct list_head *iter;
+
+	if (!netif_is_bridge_master(br))
+		return NOTIFY_DONE;
+
+	if (!info->linking)
+		return NOTIFY_DONE;
+
+	extack = netdev_notifier_info_to_extack(&info->info);
+
+	netdev_for_each_lower_dev(br, lower, iter) {
+		if (!netdev_uses_dsa(new_lower) && !netdev_uses_dsa(lower))
+			continue;
+
+		if (!netdev_port_same_parent_id(lower, new_lower)) {
+			NL_SET_ERR_MSG(extack,
+				       "Cannot do software bridging with a DSA master");
+			return notifier_from_errno(-EINVAL);
+		}
+	}
+
+	return NOTIFY_DONE;
+}
+
 static int dsa_slave_netdevice_event(struct notifier_block *nb,
 				     unsigned long event, void *ptr)
 {
@@ -2713,6 +2753,10 @@ static int dsa_slave_netdevice_event(struct notifier_block *nb,
 		if (notifier_to_errno(err))
 			return err;
 
+		err = dsa_bridge_prechangelower_sanity_check(dev, info);
+		if (notifier_to_errno(err))
+			return err;
+
 		err = dsa_slave_prechangeupper(dev, ptr);
 		if (notifier_to_errno(err))
 			return err;