[NET]: Add generic segmentation offload

This patch adds the infrastructure for generic segmentation offload.
The idea is to tap into the potential savings of TSO without hardware
support by postponing the allocation of segmented skb's until just
before the entry point into the NIC driver.

The same structure can be used to support software IPv6 TSO, as well as
UFO and segmentation offload for other relevant protocols, e.g., DCCP.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 122 insertions, 5 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 29e3888102b..d293e0f90a0 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -116,6 +116,7 @@
 #include <asm/current.h>
 #include <linux/audit.h>
 #include <linux/dmaengine.h>
+#include <linux/err.h>
 
 /*
  *	The list of packet types we will receive (as opposed to discard)
@@ -1048,7 +1049,7 @@ static inline void net_timestamp(struct sk_buff *skb)
  *	taps currently in use.
  */
 
-void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev)
+static void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct packet_type *ptype;
 
@@ -1186,6 +1187,40 @@ out:
 	return ret;
 }
 
+/**
+ *	skb_gso_segment - Perform segmentation on skb.
+ *	@skb: buffer to segment
+ *	@sg: whether scatter-gather is supported on the target.
+ *
+ *	This function segments the given skb and returns a list of segments.
+ */
+struct sk_buff *skb_gso_segment(struct sk_buff *skb, int sg)
+{
+	struct sk_buff *segs = ERR_PTR(-EPROTONOSUPPORT);
+	struct packet_type *ptype;
+	int type = skb->protocol;
+
+	BUG_ON(skb_shinfo(skb)->frag_list);
+	BUG_ON(skb->ip_summed != CHECKSUM_HW);
+
+	skb->mac.raw = skb->data;
+	skb->mac_len = skb->nh.raw - skb->data;
+	__skb_pull(skb, skb->mac_len);
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(ptype, &ptype_base[ntohs(type) & 15], list) {
+		if (ptype->type == type && !ptype->dev && ptype->gso_segment) {
+			segs = ptype->gso_segment(skb, sg);
+			break;
+		}
+	}
+	rcu_read_unlock();
+
+	return segs;
+}
+
+EXPORT_SYMBOL(skb_gso_segment);
+
 /* Take action when hardware reception checksum errors are detected. */
 #ifdef CONFIG_BUG
 void netdev_rx_csum_fault(struct net_device *dev)
@@ -1222,6 +1257,86 @@ static inline int illegal_highdma(struct net_device *dev, struct sk_buff *skb)
 #define illegal_highdma(dev, skb)	(0)
 #endif
 
+struct dev_gso_cb {
+	void (*destructor)(struct sk_buff *skb);
+};
+
+#define DEV_GSO_CB(skb) ((struct dev_gso_cb *)(skb)->cb)
+
+static void dev_gso_skb_destructor(struct sk_buff *skb)
+{
+	struct dev_gso_cb *cb;
+
+	do {
+		struct sk_buff *nskb = skb->next;
+
+		skb->next = nskb->next;
+		nskb->next = NULL;
+		kfree_skb(nskb);
+	} while (skb->next);
+
+	cb = DEV_GSO_CB(skb);
+	if (cb->destructor)
+		cb->destructor(skb);
+}
+
+/**
+ *	dev_gso_segment - Perform emulated hardware segmentation on skb.
+ *	@skb: buffer to segment
+ *
+ *	This function segments the given skb and stores the list of segments
+ *	in skb->next.
+ */
+static int dev_gso_segment(struct sk_buff *skb)
+{
+	struct net_device *dev = skb->dev;
+	struct sk_buff *segs;
+
+	segs = skb_gso_segment(skb, dev->features & NETIF_F_SG &&
+				    !illegal_highdma(dev, skb));
+	if (unlikely(IS_ERR(segs)))
+		return PTR_ERR(segs);
+
+	skb->next = segs;
+	DEV_GSO_CB(skb)->destructor = skb->destructor;
+	skb->destructor = dev_gso_skb_destructor;
+
+	return 0;
+}
+
+int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+	if (likely(!skb->next)) {
+		if (netdev_nit)
+			dev_queue_xmit_nit(skb, dev);
+
+		if (!netif_needs_gso(dev, skb))
+			return dev->hard_start_xmit(skb, dev);
+
+		if (unlikely(dev_gso_segment(skb)))
+			goto out_kfree_skb;
+	}
+
+	do {
+		struct sk_buff *nskb = skb->next;
+		int rc;
+
+		skb->next = nskb->next;
+		nskb->next = NULL;
+		rc = dev->hard_start_xmit(nskb, dev);
+		if (unlikely(rc)) {
+			skb->next = nskb;
+			return rc;
+		}
+	} while (skb->next);
+	
+	skb->destructor = DEV_GSO_CB(skb)->destructor;
+
+out_kfree_skb:
+	kfree_skb(skb);
+	return 0;
+}
+
 #define HARD_TX_LOCK(dev, cpu) {			\
 	if ((dev->features & NETIF_F_LLTX) == 0) {	\
 		netif_tx_lock(dev);			\
@@ -1266,6 +1381,10 @@ int dev_queue_xmit(struct sk_buff *skb)
 	struct Qdisc *q;
 	int rc = -ENOMEM;
 
+	/* GSO will handle the following emulations directly. */
+	if (netif_needs_gso(dev, skb))
+		goto gso;
+
 	if (skb_shinfo(skb)->frag_list &&
 	    !(dev->features & NETIF_F_FRAGLIST) &&
 	    __skb_linearize(skb))
@@ -1290,6 +1409,7 @@ int dev_queue_xmit(struct sk_buff *skb)
 	      	if (skb_checksum_help(skb, 0))
 	      		goto out_kfree_skb;
 
+gso:
 	spin_lock_prefetch(&dev->queue_lock);
 
 	/* Disable soft irqs for various locks below. Also 
@@ -1346,11 +1466,8 @@ int dev_queue_xmit(struct sk_buff *skb)
 			HARD_TX_LOCK(dev, cpu);
 
 			if (!netif_queue_stopped(dev)) {
-				if (netdev_nit)
-					dev_queue_xmit_nit(skb, dev);
-
 				rc = 0;
-				if (!dev->hard_start_xmit(skb, dev)) {
+				if (!dev_hard_start_xmit(skb, dev)) {
 					HARD_TX_UNLOCK(dev);
 					goto out;
 				}