tap: Split tap_ip6_send() into UDP and ICMP variants

tap_ip6_send() has special case logic to compute the checksums for UDP
and ICMP packets, which is a mild layering violation.  By using a suitable
helper we can split it into tap_udp6_send() and tap_icmp6_send() functions
without greatly increasing the code size, this removing that layering
violation.

We make some small changes to the interface while there.  In both cases
we make the destination IPv6 address a parameter, which will be useful
later.  For the UDP variant we make it take just the UDP payload, and it
will generate the UDP header.  For the ICMP variant we pass in the ICMP
header as before.  The inconsistency is because that's what seems to be
the more natural way to invoke the function in the callers in each case.

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

1 files changed, 62 insertions, 20 deletions

diff --git a/tap.c b/tap.c
index 0e8c99b..135d799 100644
--- a/tap.c
+++ b/tap.c
@@ -175,21 +175,22 @@ void tap_ip4_send(const struct ctx *c, in_addr_t src, uint8_t proto,
 }
 
 /**
- * tap_ip6_send() - Send IPv6 packet, with L2 headers, calculating L3/L4 checksums
+ * tap_push_ip6h() - Build IPv6 header for inbound packet
  * @c:		Execution context
  * @src:	IPv6 source address
- * @proto:	L4 protocol number
- * @in:		Payload
+ * @dst:	IPv6 destination address
  * @len:	L4 payload length
- * @flow:	Flow label
+ * @proto:	L4 protocol number
+ * @flow:	IPv6 flow identifier
+ *
+ * Return: pointer at which to write the packet's payload
  */
-void tap_ip6_send(const struct ctx *c, const struct in6_addr *src,
-		  uint8_t proto, const char *in, size_t len, uint32_t flow)
+static void *tap_push_ip6h(char *buf,
+			   const struct in6_addr *src,
+			   const struct in6_addr *dst,
+			   size_t len, uint8_t proto, uint32_t flow)
 {
-	char buf[USHRT_MAX];
-	struct ipv6hdr *ip6h =
-		(struct ipv6hdr *)tap_push_l2h(c, buf, ETH_P_IPV6);
-	char *data = (char *)(ip6h + 1);
+	struct ipv6hdr *ip6h = (struct ipv6hdr *)buf;
 
 	ip6h->payload_len = htons(len);
 	ip6h->priority = 0;
@@ -197,24 +198,65 @@ void tap_ip6_send(const struct ctx *c, const struct in6_addr *src,
 	ip6h->nexthdr = proto;
 	ip6h->hop_limit = 255;
 	ip6h->saddr = *src;
-	ip6h->daddr = *tap_ip6_daddr(c, src);
+	ip6h->daddr = *dst;
 	ip6h->flow_lbl[0] = (flow >> 16) & 0xf;
 	ip6h->flow_lbl[1] = (flow >> 8) & 0xff;
 	ip6h->flow_lbl[2] = (flow >> 0) & 0xff;
+	return ip6h + 1;
+}
 
+/**
+ * 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)
+ * @len:	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, const void *in, size_t len)
+{
+	size_t udplen = len + sizeof(struct udphdr);
+	char buf[USHRT_MAX];
+	void *ip6h = tap_push_l2h(c, buf, ETH_P_IPV6);
+	void *uhp = tap_push_ip6h(ip6h, src, dst, udplen, IPPROTO_UDP, flow);
+	struct udphdr *uh = (struct udphdr *)uhp;
+	char *data = (char *)(uh + 1);
+
+	uh->source = htons(sport);
+	uh->dest = htons(dport);
+	uh->len = htons(udplen);
+	csum_udp6(uh, src, dst, in, len);
 	memcpy(data, in, len);
 
-	if (proto == IPPROTO_UDP) {
-		struct udphdr *uh = (struct udphdr *)(ip6h + 1);
+	if (tap_send(c, buf, len + (data - buf)) < 1)
+		debug("tap: failed to send %lu bytes (IPv6)", len);
+}
 
-		csum_udp6(uh, &ip6h->saddr, &ip6h->daddr,
-			  uh + 1, len - sizeof(*uh));
-	} else if (proto == IPPROTO_ICMPV6) {
-		struct icmp6hdr *ih = (struct icmp6hdr *)(ip6h + 1);
+/**
+ * tap_icmp6_send() - Send ICMPv6 packet
+ * @c:		Execution context
+ * @src:	IPv6 source address
+ * @dst:	IPv6 destination address
+ * @in:		ICMP packet, including ICMP header
+ * @len:	ICMP packet length, including ICMP header
+ */
+void tap_icmp6_send(const struct ctx *c,
+		    const struct in6_addr *src, const struct in6_addr *dst,
+		    void *in, size_t len)
+{
+	char buf[USHRT_MAX];
+	void *ip6h = tap_push_l2h(c, buf, ETH_P_IPV6);
+	char *data = tap_push_ip6h(ip6h, src, dst, len, IPPROTO_ICMPV6, 0);
+	struct icmp6hdr *icmp6h = (struct icmp6hdr *)data;
 
-		csum_icmp6(ih, &ip6h->saddr, &ip6h->daddr,
-			   ih + 1, len - sizeof(*ih));
-	}
+	memcpy(data, in, len);
+	csum_icmp6(icmp6h, src, dst, icmp6h + 1, len - sizeof(*icmp6h));
 
 	if (tap_send(c, buf, len + (data - buf)) < 1)
 		debug("tap: failed to send %lu bytes (IPv6)", len);