This allows for configurations where there are a few
known senders in the system (e.g. multiple SoCs on the same
board) along with unlimited external senders.

The source mode devices represent the known senders while
all external senders terminate on passthru device.

Although you can still receive packets on the lower device
without the need for the passthru vlan device, there
are use cases where you need additional packet processing
in the pipeline that hooks via rx_handler. With this the
rx_handler can be attached to the passthru device while
macvlan itself remains attached to the lower device.

We use this to use the same physical link for inter-SoC
networking and external networking. Some of our chips
have no other viable link for inter-SoC traffic.

Signed-off-by: Thomas Martitz <t.martitz@fritz.com>
---
 drivers/net/macvlan.c | 41 ++++++++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 13 deletions(-)

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index c40fa331836bb..d28f9d905a84d 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -1502,15 +1502,6 @@ int macvlan_common_newlink(struct net_device *dev,
 	}
 	port = macvlan_port_get_rtnl(lowerdev);
 
-	/* Only 1 macvlan device can be created in passthru mode */
-	if (macvlan_passthru(port)) {
-		/* The macvlan port must be not created this time,
-		 * still goto destroy_macvlan_port for readability.
-		 */
-		err = -EINVAL;
-		goto destroy_macvlan_port;
-	}
-
 	vlan->lowerdev = lowerdev;
 	vlan->dev      = dev;
 	vlan->port     = port;
@@ -1523,10 +1514,30 @@ int macvlan_common_newlink(struct net_device *dev,
 	if (data && data[IFLA_MACVLAN_FLAGS])
 		vlan->flags = nla_get_u16(data[IFLA_MACVLAN_FLAGS]);
 
+	/* Only 1 macvlan device can be created in passthru mode. There may be
+	 * additional source mode devices but nothing else at the moment.
+	 *
+	 * First check if adding a source mode device to an existing passthru vlan.
+	 */
+	if (macvlan_passthru(port) && vlan->mode != MACVLAN_MODE_SOURCE) {
+		/* The macvlan port must be not created this time,
+		 * still goto destroy_macvlan_port for readability.
+		 */
+		err = -EINVAL;
+		goto destroy_macvlan_port;
+	}
+
+	/* Now check if adding a passthru device to an existing set of source mode
+	 * devices.
+	 */
 	if (vlan->mode == MACVLAN_MODE_PASSTHRU) {
-		if (port->count) {
-			err = -EINVAL;
-			goto destroy_macvlan_port;
+		struct macvlan_dev *p;
+
+		list_for_each_entry(p, &port->vlans, list) {
+			if (p->mode != MACVLAN_MODE_SOURCE) {
+				err = -EINVAL;
+				goto destroy_macvlan_port;
+			}
 		}
 		macvlan_set_passthru(port);
 		eth_hw_addr_inherit(dev, lowerdev);
@@ -1560,7 +1571,11 @@ int macvlan_common_newlink(struct net_device *dev,
 	if (err)
 		goto unregister_netdev;
 
-	list_add_tail_rcu(&vlan->list, &port->vlans);
+	/* macvlan_handle_frame expects the (one and only) passthru device first. */
+	if (vlan->mode == MACVLAN_MODE_PASSTHRU)
+		list_add_rcu(&vlan->list, &port->vlans);
+	else
+		list_add_tail_rcu(&vlan->list, &port->vlans);
 	update_port_bc_queue_len(vlan->port);
 	netif_stacked_transfer_operstate(lowerdev, dev);
 	linkwatch_fire_event(dev);
-- 
2.54.0