[PATCH v2 net-next 03/10] net: dsa: tag_8021q: Create helper function for removing VLAN header

[Vladimir Oltean <olteanv@gmail.com>]

This removes the existing implementation from tag_sja1105, which was
partially incorrect (it was not changing the MAC header offset, thereby
leaving it to point 4 bytes earlier than it should have).

This overwrites the VLAN tag by moving the Ethernet source and
destination MACs 4 bytes to the right. Then skb->data (assumed to be
pointing immediately after the EtherType) is temporarily pushed to the
beginning of the new Ethernet header, the new Ethernet header offset and
length are recorded, then skb->data is moved back to where it was.

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
---
Changes in v2:

Patch is new.

 include/linux/dsa/8021q.h |  7 +++++++
 net/dsa/tag_8021q.c       | 15 +++++++++++++++
 net/dsa/tag_sja1105.c     |  3 +--
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/include/linux/dsa/8021q.h b/include/linux/dsa/8021q.h
index 3911e0586478..463378812f18 100644
--- a/include/linux/dsa/8021q.h
+++ b/include/linux/dsa/8021q.h
@@ -31,6 +31,8 @@ int dsa_8021q_rx_switch_id(u16 vid);
 
 int dsa_8021q_rx_source_port(u16 vid);
 
+struct sk_buff *dsa_8021q_remove_header(struct sk_buff *skb);
+
 #else
 
 int dsa_port_setup_8021q_tagging(struct dsa_switch *ds, int index,
@@ -71,6 +73,11 @@ int dsa_8021q_rx_source_port(u16 vid)
 	return 0;
 }
 
+struct sk_buff *dsa_8021q_remove_header(struct sk_buff *skb)
+{
+	return NULL;
+}
+
 #endif /* IS_ENABLED(CONFIG_NET_DSA_TAG_8021Q) */
 
 #endif /* _NET_DSA_8021Q_H */
diff --git a/net/dsa/tag_8021q.c b/net/dsa/tag_8021q.c
index 65a35e976d7b..0ce680ef8e83 100644
--- a/net/dsa/tag_8021q.c
+++ b/net/dsa/tag_8021q.c
@@ -261,6 +261,21 @@ struct sk_buff *dsa_8021q_rcv(struct sk_buff *skb, struct net_device *netdev,
 }
 EXPORT_SYMBOL_GPL(dsa_8021q_rcv);
 
+struct sk_buff *dsa_8021q_remove_header(struct sk_buff *skb)
+{
+	u8 *from = skb_mac_header(skb);
+	u8 *dest = from + VLAN_HLEN;
+
+	memmove(dest, from, ETH_HLEN - VLAN_HLEN);
+	skb_push(skb, ETH_HLEN);
+	skb_reset_mac_header(skb);
+	skb_reset_mac_len(skb);
+	skb_pull(skb, ETH_HLEN);
+
+	return skb;
+}
+EXPORT_SYMBOL_GPL(dsa_8021q_remove_header);
+
 static const struct dsa_device_ops dsa_8021q_netdev_ops = {
 	.name		= "8021q",
 	.proto		= DSA_TAG_PROTO_8021Q,
diff --git a/net/dsa/tag_sja1105.c b/net/dsa/tag_sja1105.c
index d43737e6c3fb..535d8a1aabe1 100644
--- a/net/dsa/tag_sja1105.c
+++ b/net/dsa/tag_sja1105.c
@@ -106,8 +106,7 @@ static struct sk_buff *sja1105_rcv(struct sk_buff *skb,
 	 * it there, see dsa_switch_rcv: skb_push(skb, ETH_HLEN).
 	 */
 	if (is_tagged)
-		memmove(skb->data - ETH_HLEN, skb->data - ETH_HLEN - VLAN_HLEN,
-			ETH_HLEN - VLAN_HLEN);
+		skb = dsa_8021q_remove_header(skb);
 
 	return skb;
 }
-- 
2.17.1