[PATCH net-next 1/3] net: dsa: don't pass cloned skb's to drivers xmit function

[Christian Eggers <ceggers@arri.de>]

Ensure that the skb is not cloned and has enough tail room for the tail
tag. This code will be removed from the drivers in the next commits.

Signed-off-by: Christian Eggers <ceggers@arri.de>
---
 net/dsa/dsa_priv.h |  3 +++
 net/dsa/slave.c    | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index 12998bf04e55..975001c625b1 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -77,6 +77,9 @@ struct dsa_slave_priv {
 	/* Copy of CPU port xmit for faster access in slave transmit hot path */
 	struct sk_buff *	(*xmit)(struct sk_buff *skb,
 					struct net_device *dev);
+	/* same for tail_tag and overhead */
+	bool tail_tag;
+	unsigned int overhead;
 
 	struct pcpu_sw_netstats	__percpu *stats64;
 
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 3bc5ca40c9fb..49a19a3b0736 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -553,6 +553,7 @@ static netdev_tx_t dsa_slave_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct dsa_slave_priv *p = netdev_priv(dev);
 	struct pcpu_sw_netstats *s;
 	struct sk_buff *nskb;
+	int padlen;
 
 	s = this_cpu_ptr(p->stats64);
 	u64_stats_update_begin(&s->syncp);
@@ -567,6 +568,41 @@ static netdev_tx_t dsa_slave_xmit(struct sk_buff *skb, struct net_device *dev)
 	 */
 	dsa_skb_tx_timestamp(p, skb);
 
+	/* We have to pad he packet to the minimum Ethernet frame size,
+	 * if necessary, before adding the trailer (tail tagging only).
+	 */
+	padlen = (skb->len >= ETH_ZLEN) ? 0 : ETH_ZLEN - skb->len;
+
+	/* To keep the slave's xmit() methods simple, don't pass cloned skbs to
+	 * them. Additionally ensure, that suitable room for tail tagging is
+	 * available.
+	 */
+	if (skb_cloned(skb) ||
+	    (p->tail_tag && skb_tailroom(skb) < (padlen + p->overhead))) {
+		struct sk_buff *nskb;
+
+		nskb = alloc_skb(NET_IP_ALIGN + skb->len +
+				 padlen + p->overhead, GFP_ATOMIC);
+		if (!nskb) {
+			kfree_skb(skb);
+			return NETDEV_TX_OK;
+		}
+		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));
+		consume_skb(skb);
+
+		if (padlen)
+			skb_put_zero(nskb, padlen);
+
+		skb = nskb;
+	}
+
 	/* Transmit function may have to reallocate the original SKB,
 	 * in which case it must have freed it. Only free it here on error.
 	 */
@@ -1814,6 +1850,8 @@ int dsa_slave_create(struct dsa_port *port)
 	p->dp = port;
 	INIT_LIST_HEAD(&p->mall_tc_list);
 	p->xmit = cpu_dp->tag_ops->xmit;
+	p->tail_tag = cpu_dp->tag_ops->tail_tag;
+	p->overhead = cpu_dp->tag_ops->overhead;
 	port->slave = slave_dev;
 
 	rtnl_lock();
-- 
Christian Eggers
Embedded software developer

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