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 <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 52 insertions, 1 deletions

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index ea6e6e7df0ee..6c2b7640f6f3 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -187,6 +187,54 @@ out_unlock:
 }
 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)
 {
@@ -203,12 +251,15 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 		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))
 		goto out;