ipv4: Add GRO infrastructure

This patch adds GRO support for IPv4.

The criteria for merging is more stringent than LRO, in particular,
we require all fields in the IP header to be identical except for
the length, ID and checksum.  In addition, the ID must form an
arithmetic sequence with a difference of one.

The ID requirement might seem overly strict, however, most hardware
TSO solutions already obey this rule.  Linux itself also obeys this
whether GSO is in use or not.

In future we could relax this rule by storing the IDs (or rather
making sure that we don't drop them when pulling the aggregate
skb's tail).

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

include/net/protocol.h

@@ -39,6 +39,9 @@ struct net_protocol {
 	int			(*gso_send_check)(struct sk_buff *skb);
 	struct sk_buff	       *(*gso_segment)(struct sk_buff *skb,
 					       int features);
+	struct sk_buff	      **(*gro_receive)(struct sk_buff **head,
+					       struct sk_buff *skb);
+	int			(*gro_complete)(struct sk_buff *skb);
 	unsigned int		no_policy:1,
 				netns_ok:1;
 };

net/ipv4/af_inet.c

@@ -94,6 +94,7 @@
 #include <linux/igmp.h>
 #include <linux/inetdevice.h>
 #include <linux/netdevice.h>
+#include <net/checksum.h>
 #include <net/ip.h>
 #include <net/protocol.h>
 #include <net/arp.h>
@@ -1241,6 +1242,100 @@ out:
 	return segs;
 }
 
+static struct sk_buff **inet_gro_receive(struct sk_buff **head,
+					 struct sk_buff *skb)
+{
+	struct net_protocol *ops;
+	struct sk_buff **pp = NULL;
+	struct sk_buff *p;
+	struct iphdr *iph;
+	int flush = 1;
+	int proto;
+	int id;
+
+	if (unlikely(!pskb_may_pull(skb, sizeof(*iph))))
+		goto out;
+
+	iph = ip_hdr(skb);
+	proto = iph->protocol & (MAX_INET_PROTOS - 1);
+
+	rcu_read_lock();
+	ops = rcu_dereference(inet_protos[proto]);
+	if (!ops || !ops->gro_receive)
+		goto out_unlock;
+
+	if (iph->version != 4 || iph->ihl != 5)
+		goto out_unlock;
+
+	if (unlikely(ip_fast_csum((u8 *)iph, iph->ihl)))
+		goto out_unlock;
+
+	flush = ntohs(iph->tot_len) != skb->len ||
+		iph->frag_off != htons(IP_DF);
+	id = ntohs(iph->id);
+
+	for (p = *head; p; p = p->next) {
+		struct iphdr *iph2;
+
+		if (!NAPI_GRO_CB(p)->same_flow)
+			continue;
+
+		iph2 = ip_hdr(p);
+
+		if (iph->protocol != iph2->protocol ||
+		    iph->tos != iph2->tos ||
+		    memcmp(&iph->saddr, &iph2->saddr, 8)) {
+			NAPI_GRO_CB(p)->same_flow = 0;
+			continue;
+		}
+
+		/* All fields must match except length and checksum. */
+		NAPI_GRO_CB(p)->flush |=
+			memcmp(&iph->frag_off, &iph2->frag_off, 4) ||
+			(u16)(ntohs(iph2->id) + NAPI_GRO_CB(p)->count) != id;
+
+		NAPI_GRO_CB(p)->flush |= flush;
+	}
+
+	NAPI_GRO_CB(skb)->flush |= flush;
+	__skb_pull(skb, sizeof(*iph));
+	skb_reset_transport_header(skb);
+
+	pp = ops->gro_receive(head, skb);
+
+out_unlock:
+	rcu_read_unlock();
+
+out:
+	NAPI_GRO_CB(skb)->flush |= flush;
+
+	return pp;
+}
+
+static int inet_gro_complete(struct sk_buff *skb)
+{
+	struct net_protocol *ops;
+	struct iphdr *iph = ip_hdr(skb);
+	int proto = iph->protocol & (MAX_INET_PROTOS - 1);
+	int err = -ENOSYS;
+	__be16 newlen = htons(skb->len - skb_network_offset(skb));
+
+	csum_replace2(&iph->check, iph->tot_len, newlen);
+	iph->tot_len = newlen;
+
+	rcu_read_lock();
+	ops = rcu_dereference(inet_protos[proto]);
+	if (WARN_ON(!ops || !ops->gro_complete))
+		goto out_unlock;
+
+	err = ops->gro_complete(skb);
+
+out_unlock:
+	rcu_read_unlock();
+
+	return err;
+}
+
 int inet_ctl_sock_create(struct sock **sk, unsigned short family,
 			 unsigned short type, unsigned char protocol,
 			 struct net *net)
@@ -1407,6 +1502,8 @@ static struct packet_type ip_packet_type = {
 	.func = ip_rcv,
 	.gso_send_check = inet_gso_send_check,
 	.gso_segment = inet_gso_segment,
+	.gro_receive = inet_gro_receive,
+	.gro_complete = inet_gro_complete,
 };
 
 static int __init inet_init(void)