tap: break out building of udp header from tap_udp6_send function

We will need to build the UDP header at other locations than in function
tap_udp6_send(), so we break that part out to a separate function.

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

2 files changed, 35 insertions, 9 deletions

diff --git a/tap.c b/tap.c
index 57d0795..7082620 100644
--- a/tap.c
+++ b/tap.c
@@ -265,7 +265,7 @@ void *tap_push_ip6h(struct ipv6hdr *ip6h,
 }
 
 /**
- * tap_udp6_send() - Send UDP over IPv6 packet
+ * tap_push_uh6() - Build UDPv6 header with checksum
  * @c:		Execution context
  * @src:	IPv6 source address
  * @sport:	UDP source port
@@ -274,18 +274,15 @@ void *tap_push_ip6h(struct ipv6hdr *ip6h,
  * @flow:	Flow label
  * @in:		UDP payload contents (not including UDP header)
  * @dlen:	UDP payload length (not including UDP header)
+ *
+ * Return: pointer at which to write the packet's payload
  */
-void tap_udp6_send(const struct ctx *c,
+void *tap_push_uh6(struct udphdr *uh,
 		   const struct in6_addr *src, in_port_t sport,
 		   const struct in6_addr *dst, in_port_t dport,
-		   uint32_t flow, void *in, size_t dlen)
+		   void *in, size_t dlen)
 {
 	size_t l4len = dlen + sizeof(struct udphdr);
-	char buf[USHRT_MAX];
-	struct ipv6hdr *ip6h = tap_push_l2h(c, buf, ETH_P_IPV6);
-	struct udphdr *uh = tap_push_ip6h(ip6h, src, dst,
-					  l4len, IPPROTO_UDP, flow);
-	char *data = (char *)(uh + 1);
 	const struct iovec iov = {
 		.iov_base = in,
 		.iov_len = dlen
@@ -296,8 +293,33 @@ void tap_udp6_send(const struct ctx *c,
 	uh->dest = htons(dport);
 	uh->len = htons(l4len);
 	csum_udp6(uh, src, dst, &payload);
-	memcpy(data, in, dlen);
+	return (char *)uh + sizeof(*uh);
+}
 
+/**
+ * tap_udp6_send() - Send UDP over IPv6 packet
+ * @c:		Execution context
+ * @src:	IPv6 source address
+ * @sport:	UDP source port
+ * @dst:	IPv6 destination address
+ * @dport:	UDP destination port
+ * @flow:	Flow label
+ * @in:	UDP payload contents (not including UDP header)
+ * @dlen:	UDP payload length (not including UDP header)
+ */
+void tap_udp6_send(const struct ctx *c,
+		   const struct in6_addr *src, in_port_t sport,
+		   const struct in6_addr *dst, in_port_t dport,
+		   uint32_t flow, void *in, size_t dlen)
+{
+	size_t l4len = dlen + sizeof(struct udphdr);
+	char buf[USHRT_MAX];
+	struct ipv6hdr *ip6h = tap_push_l2h(c, buf, ETH_P_IPV6);
+	struct udphdr *uh = tap_push_ip6h(ip6h, src, dst,
+					  l4len, IPPROTO_UDP, flow);
+	char *data = tap_push_uh6(uh, src, sport, dst, dport, in, dlen);
+
+	memcpy(data, in, dlen);
 	tap_send_single(c, buf, dlen + (data - buf));
 }
 
diff --git a/tap.h b/tap.h
index 9ac17ce..b53a5b8 100644
--- a/tap.h
+++ b/tap.h
@@ -50,6 +50,10 @@ void *tap_push_ip4h(struct iphdr *ip4h, struct in_addr src,
 void *tap_push_uh4(struct udphdr *uh, struct in_addr src, in_port_t sport,
 		   struct in_addr dst, in_port_t dport,
 		   const void *in, size_t dlen);
+void *tap_push_uh6(struct udphdr *uh,
+		   const struct in6_addr *src, in_port_t sport,
+		   const struct in6_addr *dst, in_port_t dport,
+		   void *in, size_t dlen);
 void *tap_push_ip4h(struct iphdr *ip4h, struct in_addr src,
 		    struct in_addr dst, size_t l4len, uint8_t proto);
 void tap_udp4_send(const struct ctx *c, struct in_addr src, in_port_t sport,