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Date:   Sun, 18 Oct 2020 00:36:01 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     andrew@...n.ch, f.fainelli@...il.com, vivien.didelot@...il.com,
        kuba@...nel.org, Christian Eggers <ceggers@...i.de>,
        Kurt Kanzenbach <kurt@...utronix.de>
Subject: [RFC PATCH 03/13] net: dsa: tag_ksz: don't allocate additional memory for padding/tagging

From: Christian Eggers <ceggers@...i.de>

The caller (dsa_slave_xmit) guarantees that the frame length is at least
ETH_ZLEN and that enough memory for tail tagging is available.

Signed-off-by: Christian Eggers <ceggers@...i.de>
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 net/dsa/tag_ksz.c | 73 ++++++-----------------------------------------
 1 file changed, 9 insertions(+), 64 deletions(-)

diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
index 945a9bd5ba35..e78a783bb841 100644
--- a/net/dsa/tag_ksz.c
+++ b/net/dsa/tag_ksz.c
@@ -14,46 +14,6 @@
 #define KSZ_EGRESS_TAG_LEN		1
 #define KSZ_INGRESS_TAG_LEN		1
 
-static struct sk_buff *ksz_common_xmit(struct sk_buff *skb,
-				       struct net_device *dev, int len)
-{
-	struct sk_buff *nskb;
-	int padlen;
-
-	padlen = (skb->len >= ETH_ZLEN) ? 0 : ETH_ZLEN - skb->len;
-
-	if (skb_tailroom(skb) >= padlen + len) {
-		/* Let dsa_slave_xmit() free skb */
-		if (__skb_put_padto(skb, skb->len + padlen, false))
-			return NULL;
-
-		nskb = skb;
-	} else {
-		nskb = alloc_skb(NET_IP_ALIGN + skb->len +
-				 padlen + len, GFP_ATOMIC);
-		if (!nskb)
-			return NULL;
-		skb_reserve(nskb, NET_IP_ALIGN);
-
-		skb_reset_mac_header(nskb);
-		skb_set_network_header(nskb,
-				       skb_network_header(skb) - skb->head);
-		skb_set_transport_header(nskb,
-					 skb_transport_header(skb) - skb->head);
-		skb_copy_and_csum_dev(skb, skb_put(nskb, skb->len));
-
-		/* Let skb_put_padto() free nskb, and let dsa_slave_xmit() free
-		 * skb
-		 */
-		if (skb_put_padto(nskb, nskb->len + padlen))
-			return NULL;
-
-		consume_skb(skb);
-	}
-
-	return nskb;
-}
-
 static struct sk_buff *ksz_common_rcv(struct sk_buff *skb,
 				      struct net_device *dev,
 				      unsigned int port, unsigned int len)
@@ -90,23 +50,18 @@ static struct sk_buff *ksz_common_rcv(struct sk_buff *skb,
 static struct sk_buff *ksz8795_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct dsa_port *dp = dsa_slave_to_port(dev);
-	struct sk_buff *nskb;
 	u8 *tag;
 	u8 *addr;
 
-	nskb = ksz_common_xmit(skb, dev, KSZ_INGRESS_TAG_LEN);
-	if (!nskb)
-		return NULL;
-
 	/* Tag encoding */
-	tag = skb_put(nskb, KSZ_INGRESS_TAG_LEN);
-	addr = skb_mac_header(nskb);
+	tag = skb_put(skb, KSZ_INGRESS_TAG_LEN);
+	addr = skb_mac_header(skb);
 
 	*tag = 1 << dp->index;
 	if (is_link_local_ether_addr(addr))
 		*tag |= KSZ8795_TAIL_TAG_OVERRIDE;
 
-	return nskb;
+	return skb;
 }
 
 static struct sk_buff *ksz8795_rcv(struct sk_buff *skb, struct net_device *dev,
@@ -155,18 +110,13 @@ static struct sk_buff *ksz9477_xmit(struct sk_buff *skb,
 				    struct net_device *dev)
 {
 	struct dsa_port *dp = dsa_slave_to_port(dev);
-	struct sk_buff *nskb;
 	__be16 *tag;
 	u8 *addr;
 	u16 val;
 
-	nskb = ksz_common_xmit(skb, dev, KSZ9477_INGRESS_TAG_LEN);
-	if (!nskb)
-		return NULL;
-
 	/* Tag encoding */
-	tag = skb_put(nskb, KSZ9477_INGRESS_TAG_LEN);
-	addr = skb_mac_header(nskb);
+	tag = skb_put(skb, KSZ9477_INGRESS_TAG_LEN);
+	addr = skb_mac_header(skb);
 
 	val = BIT(dp->index);
 
@@ -175,7 +125,7 @@ static struct sk_buff *ksz9477_xmit(struct sk_buff *skb,
 
 	*tag = cpu_to_be16(val);
 
-	return nskb;
+	return skb;
 }
 
 static struct sk_buff *ksz9477_rcv(struct sk_buff *skb, struct net_device *dev,
@@ -211,24 +161,19 @@ static struct sk_buff *ksz9893_xmit(struct sk_buff *skb,
 				    struct net_device *dev)
 {
 	struct dsa_port *dp = dsa_slave_to_port(dev);
-	struct sk_buff *nskb;
 	u8 *addr;
 	u8 *tag;
 
-	nskb = ksz_common_xmit(skb, dev, KSZ_INGRESS_TAG_LEN);
-	if (!nskb)
-		return NULL;
-
 	/* Tag encoding */
-	tag = skb_put(nskb, KSZ_INGRESS_TAG_LEN);
-	addr = skb_mac_header(nskb);
+	tag = skb_put(skb, KSZ_INGRESS_TAG_LEN);
+	addr = skb_mac_header(skb);
 
 	*tag = BIT(dp->index);
 
 	if (is_link_local_ether_addr(addr))
 		*tag |= KSZ9893_TAIL_TAG_OVERRIDE;
 
-	return nskb;
+	return skb;
 }
 
 static const struct dsa_device_ops ksz9893_netdev_ops = {
-- 
2.25.1

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