Loosely based on wenxu's patches:

"nf_flow_table_offload: offload the vlan/PPPoE encap in the flowtable".

Fixed double vlan and pppoe packets, almost entirely rewriting the patch.

After this patch, it is possible to transmit packets in the fastpath with
outgoing encaps, without using vlan- and/or pppoe-devices.

This makes it possible to use more different kinds of network setups.
For example, when bridge tagging is used to egress vlan tagged
packets using the forward fastpath. Another example is passing 802.1q
tagged packets through a bridge using the bridge fastpath.

This also makes the software fastpath process more similar to the
hardware offloaded fastpath process, where encaps are also pushed.

After applying this patch, always info->outdev = info->hw_outdev,
so the netfilter code can be further cleaned up by removing:
 * hw_outdev from struct nft_forward_info
 * out.hw_ifindex from struct nf_flow_route
 * out.hw_ifidx from struct flow_offload_tuple

Signed-off-by: Eric Woudstra <ericwouds@gmail.com>
---
 net/netfilter/nf_flow_table_ip.c | 96 +++++++++++++++++++++++++++++++-
 net/netfilter/nft_flow_offload.c |  6 +-
 2 files changed, 96 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/nf_flow_table_ip.c b/net/netfilter/nf_flow_table_ip.c
index 98edcaa37b38..9221ddb6f07a 100644
--- a/net/netfilter/nf_flow_table_ip.c
+++ b/net/netfilter/nf_flow_table_ip.c
@@ -302,6 +302,92 @@ static bool nf_flow_skb_encap_protocol(struct sk_buff *skb, __be16 proto,
 	return false;
 }
 
+static inline int nf_flow_vlan_inner_push(struct sk_buff *skb, __be16 proto, u16 id)
+{
+	struct vlan_hdr *vhdr;
+
+	if (skb_cow_head(skb, VLAN_HLEN))
+		return -1;
+
+	__skb_push(skb, VLAN_HLEN);
+	skb_reset_network_header(skb);
+
+	vhdr = (struct vlan_hdr *)(skb->data);
+	vhdr->h_vlan_TCI = htons(id);
+	vhdr->h_vlan_encapsulated_proto = skb->protocol;
+	skb->protocol = proto;
+
+	return 0;
+}
+
+static inline int nf_flow_ppoe_push(struct sk_buff *skb, u16 id)
+{
+	struct ppp_hdr {
+		struct pppoe_hdr hdr;
+		__be16 proto;
+	} *ph;
+	int data_len = skb->len + 2;
+	__be16 proto;
+
+	if (skb_cow_head(skb, PPPOE_SES_HLEN))
+		return -1;
+
+	if (skb->protocol == htons(ETH_P_IP))
+		proto = htons(PPP_IP);
+	else if (skb->protocol == htons(ETH_P_IPV6))
+		proto = htons(PPP_IPV6);
+	else
+		return -1;
+
+	__skb_push(skb, PPPOE_SES_HLEN);
+	skb_reset_network_header(skb);
+
+	ph = (struct ppp_hdr *)(skb->data);
+	ph->hdr.ver  = 1;
+	ph->hdr.type = 1;
+	ph->hdr.code = 0;
+	ph->hdr.sid  = htons(id);
+	ph->hdr.length = htons(data_len);
+	ph->proto = proto;
+	skb->protocol = htons(ETH_P_PPP_SES);
+
+	return 0;
+}
+
+static int nf_flow_encap_push(struct sk_buff *skb,
+			      struct flow_offload_tuple_rhash *tuplehash,
+			      unsigned short *type)
+{
+	int i = 0, ret = 0;
+
+	if (!tuplehash->tuple.encap_num)
+		return 0;
+
+	if (tuplehash->tuple.encap[i].proto == htons(ETH_P_8021Q) ||
+	    tuplehash->tuple.encap[i].proto == htons(ETH_P_8021AD)) {
+		__vlan_hwaccel_put_tag(skb, tuplehash->tuple.encap[i].proto,
+				       tuplehash->tuple.encap[i].id);
+		i++;
+		if (i >= tuplehash->tuple.encap_num)
+			return 0;
+	}
+
+	switch (tuplehash->tuple.encap[i].proto) {
+	case htons(ETH_P_8021Q):
+		*type = ETH_P_8021Q;
+		ret = nf_flow_vlan_inner_push(skb,
+					      tuplehash->tuple.encap[i].proto,
+					      tuplehash->tuple.encap[i].id);
+		break;
+	case htons(ETH_P_PPP_SES):
+		*type = ETH_P_PPP_SES;
+		ret = nf_flow_ppoe_push(skb,
+					tuplehash->tuple.encap[i].id);
+		break;
+	}
+	return ret;
+}
+
 static void nf_flow_encap_pop(struct sk_buff *skb,
 			      struct flow_offload_tuple_rhash *tuplehash)
 {
@@ -331,6 +417,7 @@ static void nf_flow_encap_pop(struct sk_buff *skb,
 
 static unsigned int nf_flow_queue_xmit(struct net *net, struct sk_buff *skb,
 				       const struct flow_offload_tuple_rhash *tuplehash,
+				       struct flow_offload_tuple_rhash *other_tuplehash,
 				       unsigned short type)
 {
 	struct net_device *outdev;
@@ -339,6 +426,9 @@ static unsigned int nf_flow_queue_xmit(struct net *net, struct sk_buff *skb,
 	if (!outdev)
 		return NF_DROP;
 
+	if (nf_flow_encap_push(skb, other_tuplehash, &type) < 0)
+		return NF_DROP;
+
 	skb->dev = outdev;
 	dev_hard_header(skb, skb->dev, type, tuplehash->tuple.out.h_dest,
 			tuplehash->tuple.out.h_source, skb->len);
@@ -458,7 +548,8 @@ nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
 		ret = NF_STOLEN;
 		break;
 	case FLOW_OFFLOAD_XMIT_DIRECT:
-		ret = nf_flow_queue_xmit(state->net, skb, tuplehash, ETH_P_IP);
+		ret = nf_flow_queue_xmit(state->net, skb, tuplehash,
+					 &flow->tuplehash[!dir], ETH_P_IP);
 		if (ret == NF_DROP)
 			flow_offload_teardown(flow);
 		break;
@@ -753,7 +844,8 @@ nf_flow_offload_ipv6_hook(void *priv, struct sk_buff *skb,
 		ret = NF_STOLEN;
 		break;
 	case FLOW_OFFLOAD_XMIT_DIRECT:
-		ret = nf_flow_queue_xmit(state->net, skb, tuplehash, ETH_P_IPV6);
+		ret = nf_flow_queue_xmit(state->net, skb, tuplehash,
+					 &flow->tuplehash[!dir], ETH_P_IPV6);
 		if (ret == NF_DROP)
 			flow_offload_teardown(flow);
 		break;
diff --git a/net/netfilter/nft_flow_offload.c b/net/netfilter/nft_flow_offload.c
index e8f800788c4a..bb15aa55e6fb 100644
--- a/net/netfilter/nft_flow_offload.c
+++ b/net/netfilter/nft_flow_offload.c
@@ -124,13 +124,12 @@ static void nft_dev_path_info(const struct net_device_path_stack *stack,
 				info->indev = NULL;
 				break;
 			}
-			if (!info->outdev)
-				info->outdev = path->dev;
 			info->encap[info->num_encaps].id = path->encap.id;
 			info->encap[info->num_encaps].proto = path->encap.proto;
 			info->num_encaps++;
 			if (path->type == DEV_PATH_PPPOE)
 				memcpy(info->h_dest, path->encap.h_dest, ETH_ALEN);
+			info->xmit_type = FLOW_OFFLOAD_XMIT_DIRECT;
 			break;
 		case DEV_PATH_BRIDGE:
 			if (is_zero_ether_addr(info->h_source))
@@ -158,8 +157,7 @@ static void nft_dev_path_info(const struct net_device_path_stack *stack,
 			break;
 		}
 	}
-	if (!info->outdev)
-		info->outdev = info->indev;
+	info->outdev = info->indev;
 
 	info->hw_outdev = info->indev;
 
-- 
2.45.2