Subject: [PATCH] net: 8021q: resolve forwarding path for vlan devices
From: Pablo Neira Ayuso <[email-masked]>
Date: Wed, 24 Mar 2021 02:30:33 +0100

Add .ndo_fill_forward_path for vlan devices.

For instance, assuming the following topology:

                   IP forwarding
                  /             \
            eth0.100             eth0
            |
            eth0
            .
            .
            .
           ethX
     ab:cd:ef:ab:cd:ef

For packets going through IP forwarding to eth0.100 whose destination
MAC address is ab:cd:ef:ab:cd:ef, dev_fill_forward_path() provides the
following path:

        eth0.100 -> eth0

Signed-off-by: Pablo Neira Ayuso <[email-masked]>
---

--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -855,11 +855,18 @@ typedef u16 (*select_queue_fallback_t)(s
 
 enum net_device_path_type {
 	DEV_PATH_ETHERNET = 0,
+	DEV_PATH_VLAN,
 };
 
 struct net_device_path {
 	enum net_device_path_type	type;
 	const struct net_device		*dev;
+	union {
+		struct {
+			u16		id;
+			__be16		proto;
+		} encap;
+	};
 };
 
 #define NET_DEVICE_PATH_STACK_MAX	5
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -770,6 +770,20 @@ static int vlan_dev_get_iflink(const str
 	return real_dev->ifindex;
 }
 
+static int vlan_dev_fill_forward_path(struct net_device_path_ctx *ctx,
+				      struct net_device_path *path)
+{
+	struct vlan_dev_priv *vlan = vlan_dev_priv(ctx->dev);
+
+	path->type = DEV_PATH_VLAN;
+	path->encap.id = vlan->vlan_id;
+	path->encap.proto = vlan->vlan_proto;
+	path->dev = ctx->dev;
+	ctx->dev = vlan->real_dev;
+
+	return 0;
+}
+
 static const struct ethtool_ops vlan_ethtool_ops = {
 	.get_link_ksettings	= vlan_ethtool_get_link_ksettings,
 	.get_drvinfo	        = vlan_ethtool_get_drvinfo,
@@ -808,6 +822,7 @@ static const struct net_device_ops vlan_
 #endif
 	.ndo_fix_features	= vlan_dev_fix_features,
 	.ndo_get_iflink		= vlan_dev_get_iflink,
+	.ndo_fill_forward_path	= vlan_dev_fill_forward_path,
 };
 
 static void vlan_dev_free(struct net_device *dev)