net: tso: add UDP segmentation support

Note that like TCP, we do not support additional encapsulations,
and that checksums must be offloaded to the NIC.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/tso.c

@@ -16,7 +16,6 @@ EXPORT_SYMBOL(tso_count_descs);
 void tso_build_hdr(const struct sk_buff *skb, char *hdr, struct tso_t *tso,
 		   int size, bool is_last)
 {
-	struct tcphdr *tcph;
 	int hdr_len = skb_transport_offset(skb) + tso->tlen;
 	int mac_hdr_len = skb_network_offset(skb);
 
@@ -32,21 +31,29 @@ void tso_build_hdr(const struct sk_buff *skb, char *hdr, struct tso_t *tso,
 
 		iph->payload_len = htons(size + tso->tlen);
 	}
-	tcph = (struct tcphdr *)(hdr + skb_transport_offset(skb));
-	put_unaligned_be32(tso->tcp_seq, &tcph->seq);
+	hdr += skb_transport_offset(skb);
+	if (tso->tlen != sizeof(struct udphdr)) {
+		struct tcphdr *tcph = (struct tcphdr *)hdr;
 
-	if (!is_last) {
-		/* Clear all special flags for not last packet */
-		tcph->psh = 0;
-		tcph->fin = 0;
-		tcph->rst = 0;
+		put_unaligned_be32(tso->tcp_seq, &tcph->seq);
+
+		if (!is_last) {
+			/* Clear all special flags for not last packet */
+			tcph->psh = 0;
+			tcph->fin = 0;
+			tcph->rst = 0;
+		}
+	} else {
+		struct udphdr *uh = (struct udphdr *)hdr;
+
+		uh->len = htons(sizeof(*uh) + size);
 	}
 }
 EXPORT_SYMBOL(tso_build_hdr);
 
 void tso_build_data(const struct sk_buff *skb, struct tso_t *tso, int size)
 {
-	tso->tcp_seq += size;
+	tso->tcp_seq += size; /* not worth avoiding this operation for UDP */
 	tso->size -= size;
 	tso->data += size;
 
@@ -64,12 +71,12 @@ EXPORT_SYMBOL(tso_build_data);
 
 int tso_start(struct sk_buff *skb, struct tso_t *tso)
 {
-	int tlen = tcp_hdrlen(skb);
+	int tlen = skb_is_gso_tcp(skb) ? tcp_hdrlen(skb) : sizeof(struct udphdr);
 	int hdr_len = skb_transport_offset(skb) + tlen;
 
 	tso->tlen = tlen;
 	tso->ip_id = ntohs(ip_hdr(skb)->id);
-	tso->tcp_seq = ntohl(tcp_hdr(skb)->seq);
+	tso->tcp_seq = (tlen != sizeof(struct udphdr)) ? ntohl(tcp_hdr(skb)->seq) : 0;
 	tso->next_frag_idx = 0;
 	tso->ipv6 = vlan_get_protocol(skb) == htons(ETH_P_IPV6);