[RFC net-next] net: dsa: Remove indirect function call for flow dissection

[Florian Fainelli <f.fainelli@gmail.com>]

We only need "static" information to be given for DSA flow dissection,
replace the call to .flow_dissect() with an unsigned integer given us
the offset into the packet that we must de-reference to obtain the
protocol number.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
Alexander,

This should probably require us to fix all DSA taggers to provide a
valid proto_off otherwise we would be incorrectly dissecting a flow, but
that still sounds like an improvement to me.

Thanks!

 include/net/dsa.h         |  3 +--
 net/core/flow_dissector.c | 13 ++++++++-----
 net/dsa/tag_dsa.c         | 10 +---------
 net/dsa/tag_edsa.c        | 10 +---------
 net/dsa/tag_mtk.c         | 11 +----------
 net/dsa/tag_qca.c         | 11 +----------
 6 files changed, 13 insertions(+), 45 deletions(-)

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 6767dc3f66c0..8e3e1fa06d75 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -70,14 +70,13 @@ struct dsa_device_ops {
 	struct sk_buff *(*xmit)(struct sk_buff *skb, struct net_device *dev);
 	struct sk_buff *(*rcv)(struct sk_buff *skb, struct net_device *dev,
 			       struct packet_type *pt);
-	int (*flow_dissect)(const struct sk_buff *skb, __be16 *proto,
-			    int *offset);
 	/* Used to determine which traffic should match the DSA filter in
 	 * eth_type_trans, and which, if any, should bypass it and be processed
 	 * as regular on the master net device.
 	 */
 	bool (*filter)(const struct sk_buff *skb, struct net_device *dev);
 	unsigned int overhead;
+	unsigned int proto_off;
 	const char *name;
 	enum dsa_tag_protocol proto;
 };
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index d524a693e00f..9037ebdddac1 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -972,13 +972,16 @@ bool __skb_flow_dissect(const struct net *net,
 		if (unlikely(skb->dev && netdev_uses_dsa(skb->dev) &&
 			     proto == htons(ETH_P_XDSA))) {
 			const struct dsa_device_ops *ops;
-			int offset = 0;
+			unsigned int overhead;
+			unsigned int proto_off;
 
 			ops = skb->dev->dsa_ptr->tag_ops;
-			if (ops->flow_dissect &&
-			    !ops->flow_dissect(skb, &proto, &offset)) {
-				hlen -= offset;
-				nhoff += offset;
+			overhead = ops->overhead;
+			proto_off = ops->proto_off;
+			if (overhead && likely(proto_off < skb->len)) {
+				hlen -= overhead;
+				nhoff += overhead;
+				proto = ((__be16 *)skb->data)[proto_off];
 			}
 		}
 #endif
diff --git a/net/dsa/tag_dsa.c b/net/dsa/tag_dsa.c
index 7ddec9794477..4a970e959fef 100644
--- a/net/dsa/tag_dsa.c
+++ b/net/dsa/tag_dsa.c
@@ -142,21 +142,13 @@ static struct sk_buff *dsa_rcv(struct sk_buff *skb, struct net_device *dev,
 	return skb;
 }
 
-static int dsa_tag_flow_dissect(const struct sk_buff *skb, __be16 *proto,
-				int *offset)
-{
-	*offset = 4;
-	*proto = ((__be16 *)skb->data)[1];
-	return 0;
-}
-
 static const struct dsa_device_ops dsa_netdev_ops = {
 	.name	= "dsa",
 	.proto	= DSA_TAG_PROTO_DSA,
 	.xmit	= dsa_xmit,
 	.rcv	= dsa_rcv,
-	.flow_dissect   = dsa_tag_flow_dissect,
 	.overhead = DSA_HLEN,
+	.proto_off = 1,
 };
 
 MODULE_LICENSE("GPL");
diff --git a/net/dsa/tag_edsa.c b/net/dsa/tag_edsa.c
index e8eaa804ccb9..c7cb0df17287 100644
--- a/net/dsa/tag_edsa.c
+++ b/net/dsa/tag_edsa.c
@@ -161,21 +161,13 @@ static struct sk_buff *edsa_rcv(struct sk_buff *skb, struct net_device *dev,
 	return skb;
 }
 
-static int edsa_tag_flow_dissect(const struct sk_buff *skb, __be16 *proto,
-				 int *offset)
-{
-	*offset = 8;
-	*proto = ((__be16 *)skb->data)[3];
-	return 0;
-}
-
 static const struct dsa_device_ops edsa_netdev_ops = {
 	.name	= "edsa",
 	.proto	= DSA_TAG_PROTO_EDSA,
 	.xmit	= edsa_xmit,
 	.rcv	= edsa_rcv,
-	.flow_dissect   = edsa_tag_flow_dissect,
 	.overhead = EDSA_HLEN,
+	.proto_off = 3,
 };
 
 MODULE_LICENSE("GPL");
diff --git a/net/dsa/tag_mtk.c b/net/dsa/tag_mtk.c
index b5705cba8318..c96354f12317 100644
--- a/net/dsa/tag_mtk.c
+++ b/net/dsa/tag_mtk.c
@@ -89,22 +89,13 @@ static struct sk_buff *mtk_tag_rcv(struct sk_buff *skb, struct net_device *dev,
 	return skb;
 }
 
-static int mtk_tag_flow_dissect(const struct sk_buff *skb, __be16 *proto,
-				int *offset)
-{
-	*offset = 4;
-	*proto = ((__be16 *)skb->data)[1];
-
-	return 0;
-}
-
 static const struct dsa_device_ops mtk_netdev_ops = {
 	.name		= "mtk",
 	.proto		= DSA_TAG_PROTO_MTK,
 	.xmit		= mtk_tag_xmit,
 	.rcv		= mtk_tag_rcv,
-	.flow_dissect	= mtk_tag_flow_dissect,
 	.overhead	= MTK_HDR_LEN,
+	.proto_off	= 1,
 };
 
 MODULE_LICENSE("GPL");
diff --git a/net/dsa/tag_qca.c b/net/dsa/tag_qca.c
index c95885215525..a88849d211f0 100644
--- a/net/dsa/tag_qca.c
+++ b/net/dsa/tag_qca.c
@@ -90,22 +90,13 @@ static struct sk_buff *qca_tag_rcv(struct sk_buff *skb, struct net_device *dev,
 	return skb;
 }
 
-static int qca_tag_flow_dissect(const struct sk_buff *skb, __be16 *proto,
-                                int *offset)
-{
-	*offset = QCA_HDR_LEN;
-	*proto = ((__be16 *)skb->data)[0];
-
-	return 0;
-}
-
 static const struct dsa_device_ops qca_netdev_ops = {
 	.name	= "qca",
 	.proto	= DSA_TAG_PROTO_QCA,
 	.xmit	= qca_tag_xmit,
 	.rcv	= qca_tag_rcv,
-	.flow_dissect = qca_tag_flow_dissect,
 	.overhead = QCA_HDR_LEN,
+	.proto_offset = 0,
 };
 
 MODULE_LICENSE("GPL");
-- 
2.17.1