net: Add skb_gro_receive

This patch adds the helper skb_gro_receive to merge packets for
GRO.  The current method is to allocate a new header skb and then
chain the original packets to its frag_list.  This is done to
make it easier to integrate into the existing GSO framework.

In future as GSO is moved into the drivers, we can undo this and
simply chain the original packets together.

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

2 files changed, 61 insertions, 0 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index acf17af..cf2cb50 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1687,6 +1687,8 @@ extern int	       skb_shift(struct sk_buff *tgt, struct sk_buff *skb,
 				 int shiftlen);
 
 extern struct sk_buff *skb_segment(struct sk_buff *skb, int features);
+extern int	       skb_gro_receive(struct sk_buff **head,
+				       struct sk_buff *skb);
 
 static inline void *skb_header_pointer(const struct sk_buff *skb, int offset,
 				       int len, void *buffer)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 18e224a..b8d0abb 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2582,6 +2582,65 @@ err:
 
 EXPORT_SYMBOL_GPL(skb_segment);
 
+int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
+{
+	struct sk_buff *p = *head;
+	struct sk_buff *nskb;
+	unsigned int headroom;
+	unsigned int hlen = p->data - skb_mac_header(p);
+
+	if (hlen + p->len + skb->len >= 65536)
+		return -E2BIG;
+
+	if (skb_shinfo(p)->frag_list)
+		goto merge;
+
+	headroom = skb_headroom(p);
+	nskb = netdev_alloc_skb(p->dev, headroom);
+	if (unlikely(!nskb))
+		return -ENOMEM;
+
+	__copy_skb_header(nskb, p);
+	nskb->mac_len = p->mac_len;
+
+	skb_reserve(nskb, headroom);
+
+	skb_set_mac_header(nskb, -hlen);
+	skb_set_network_header(nskb, skb_network_offset(p));
+	skb_set_transport_header(nskb, skb_transport_offset(p));
+
+	memcpy(skb_mac_header(nskb), skb_mac_header(p), hlen);
+
+	*NAPI_GRO_CB(nskb) = *NAPI_GRO_CB(p);
+	skb_shinfo(nskb)->frag_list = p;
+	skb_header_release(p);
+	nskb->prev = p;
+
+	nskb->data_len += p->len;
+	nskb->truesize += p->len;
+	nskb->len += p->len;
+
+	*head = nskb;
+	nskb->next = p->next;
+	p->next = NULL;
+
+	p = nskb;
+
+merge:
+	NAPI_GRO_CB(p)->count++;
+	p->prev->next = skb;
+	p->prev = skb;
+	skb_header_release(skb);
+
+	p->data_len += skb->len;
+	p->truesize += skb->len;
+	p->len += skb->len;
+
+	NAPI_GRO_CB(skb)->same_flow = 1;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(skb_gro_receive);
+
 void __init skb_init(void)
 {
 	skbuff_head_cache = kmem_cache_create("skbuff_head_cache",