udp: add udp gso

Implement generic segmentation offload support for udp datagrams. A
follow-up patch adds support to the protocol stack to generate such
packets.

UDP GSO is not UFO. UFO fragments a single large datagram. GSO splits
a large payload into a number of discrete UDP datagrams.

The implementation adds a GSO type SKB_UDP_GSO_L4 to differentiate it
from UFO (SKB_UDP_GSO).

IPPROTO_UDPLITE is excluded, as that protocol has no gso handler
registered.

[ Export __udp_gso_segment for ipv6. -DaveM ]

Signed-off-by: Willem de Bruijn <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/skbuff.h

···
 	SKB_GSO_ESP = 1 << 15,
 
 	SKB_GSO_UDP = 1 << 16,
+
+	SKB_GSO_UDP_L4 = 1 << 17,
 };
 
 #if BITS_PER_LONG > 32

include/net/udp.h

···
 				 struct udphdr *uh, udp_lookup_t lookup);
 int udp_gro_complete(struct sk_buff *skb, int nhoff, udp_lookup_t lookup);
 
+struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
+				  netdev_features_t features,
+				  unsigned int mss, __sum16 check);
+
 static inline struct udphdr *udp_gro_udphdr(struct sk_buff *skb)
 {
 	struct udphdr *uh;

net/core/skbuff.c

···
 		thlen = tcp_hdrlen(skb);
 	} else if (unlikely(skb_is_gso_sctp(skb))) {
 		thlen = sizeof(struct sctphdr);
+	} else if (shinfo->gso_type & SKB_GSO_UDP_L4) {
+		thlen = sizeof(struct udphdr);
 	}
 	/* UFO sets gso_size to the size of the fragmentation
 	 * payload, i.e. the size of the L4 (UDP) header is already

net/ipv4/udp_offload.c

···
 }
 EXPORT_SYMBOL(skb_udp_tunnel_segment);
 
+struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
+				  netdev_features_t features,
+				  unsigned int mss, __sum16 check)
+{
+	struct sk_buff *segs, *seg;
+	unsigned int hdrlen;
+	struct udphdr *uh;
+
+	if (gso_skb->len <= sizeof(*uh) + mss)
+		return ERR_PTR(-EINVAL);
+
+	hdrlen = gso_skb->data - skb_mac_header(gso_skb);
+	skb_pull(gso_skb, sizeof(*uh));
+
+	segs = skb_segment(gso_skb, features);
+	if (unlikely(IS_ERR_OR_NULL(segs)))
+		return segs;
+
+	for (seg = segs; seg; seg = seg->next) {
+		uh = udp_hdr(seg);
+		uh->len = htons(seg->len - hdrlen);
+		uh->check = check;
+
+		/* last packet can be partial gso_size */
+		if (!seg->next)
+			csum_replace2(&uh->check, htons(mss),
+				      htons(seg->len - hdrlen - sizeof(*uh)));
+	}
+
+	return segs;
+}
+EXPORT_SYMBOL_GPL(__udp_gso_segment);
+
+static struct sk_buff *__udp4_gso_segment(struct sk_buff *gso_skb,
+					  netdev_features_t features)
+{
+	const struct iphdr *iph = ip_hdr(gso_skb);
+	unsigned int mss = skb_shinfo(gso_skb)->gso_size;
+
+	if (!can_checksum_protocol(features, htons(ETH_P_IP)))
+		return ERR_PTR(-EIO);
+
+	return __udp_gso_segment(gso_skb, features, mss,
+				 udp_v4_check(sizeof(struct udphdr) + mss,
+					      iph->saddr, iph->daddr, 0));
+}
+EXPORT_SYMBOL_GPL(__udp4_gso_segment);
+
 static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 					 netdev_features_t features)
 {
···
 		goto out;
 	}
 
-	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP))
+	if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_UDP | SKB_GSO_UDP_L4)))
 		goto out;
 
 	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 		goto out;
+
+	if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
+		return __udp4_gso_segment(skb, features);
 
 	mss = skb_shinfo(skb)->gso_size;
 	if (unlikely(skb->len <= mss))

net/ipv6/ip6_offload.c

···
 
 	if (skb->encapsulation &&
 	    skb_shinfo(skb)->gso_type & (SKB_GSO_IPXIP4 | SKB_GSO_IPXIP6))
-		udpfrag = proto == IPPROTO_UDP && encap;
+		udpfrag = proto == IPPROTO_UDP && encap &&
+			  (skb_shinfo(skb)->gso_type & SKB_GSO_UDP);
 	else
-		udpfrag = proto == IPPROTO_UDP && !skb->encapsulation;
+		udpfrag = proto == IPPROTO_UDP && !skb->encapsulation &&
+			  (skb_shinfo(skb)->gso_type & SKB_GSO_UDP);
 
 	ops = rcu_dereference(inet6_offloads[proto]);
 	if (likely(ops && ops->callbacks.gso_segment)) {

net/ipv6/udp_offload.c

···
 #include <net/ip6_checksum.h>
 #include "ip6_offload.h"
 
+static struct sk_buff *__udp6_gso_segment(struct sk_buff *gso_skb,
+					  netdev_features_t features)
+{
+	const struct ipv6hdr *ip6h = ipv6_hdr(gso_skb);
+	unsigned int mss = skb_shinfo(gso_skb)->gso_size;
+
+	if (!can_checksum_protocol(features, htons(ETH_P_IPV6)))
+		return ERR_PTR(-EIO);
+
+	return __udp_gso_segment(gso_skb, features, mss,
+				 udp_v6_check(sizeof(struct udphdr) + mss,
+					      &ip6h->saddr, &ip6h->daddr, 0));
+}
+
 static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
 					 netdev_features_t features)
 {
···
 		const struct ipv6hdr *ipv6h;
 		struct udphdr *uh;
 
-		if (!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP))
+		if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_UDP | SKB_GSO_UDP_L4)))
 			goto out;
 
 		if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 			goto out;
+
+		if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
+			return __udp6_gso_segment(skb, features);
 
 		/* Do software UFO. Complete and fill in the UDP checksum as HW cannot
 		 * do checksum of UDP packets sent as multiple IP fragments.