[PATCH 07/10] tcp: Remove ugly address union from struct tcp_conn

[David Gibson <david@gibson.dropbear.id.au>]

We now only extract the v4 part of the tcp_conn::a union in one place.
Make this neater by using a helper to extract the IPv4 address from the
mapped address in that place.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp.c  | 40 +++++++++++++++-------------------------
 util.c | 13 +++++++++++++
 util.h |  1 +
 3 files changed, 29 insertions(+), 25 deletions(-)

diff --git a/tcp.c b/tcp.c
index 3816a1c..6634abb 100644
--- a/tcp.c
+++ b/tcp.c
@@ -416,10 +416,7 @@ struct tcp6_l2_head {	/* For MSS6 macro: keep in sync with tcp6_l2_buf_t */
  * @ws_to_tap:		Window scaling factor advertised to tap/guest
  * @sndbuf:		Sending buffer in kernel, rounded to 2 ^ SNDBUF_BITS
  * @seq_dup_ack_approx:	Last duplicate ACK number sent to tap
- * @a.a6:		IPv6 remote address, can be IPv4-mapped
- * @a.a4.zero:		Zero prefix for IPv4-mapped, see RFC 6890, Table 20
- * @a.a4.one:		Ones prefix for IPv4-mapped
- * @a.a4.a:		IPv4 address
+ * @addr:		IPv6 remote address, can be IPv4-mapped
  * @tap_port:		Guest-facing tap port
  * @sock_port:		Remote, socket-facing port
  * @wnd_from_tap:	Last window size from tap, unscaled (as received)
@@ -489,15 +486,8 @@ struct tcp_conn {
 	uint8_t		seq_dup_ack_approx;
 
 
-	union {
-		struct in6_addr a6;
-		struct {
-			uint8_t zero[10];
-			uint8_t one[2];
-			struct in_addr a;
-		} a4;
-	} a;
-#define CONN_V4(conn)		IN6_IS_ADDR_V4MAPPED(&conn->a.a6)
+	struct in6_addr addr;
+#define CONN_V4(conn)		IN6_IS_ADDR_V4MAPPED(&conn->addr)
 #define CONN_V6(conn)		(!CONN_V4(conn))
 
 	in_port_t	tap_port;
@@ -960,7 +950,7 @@ static int tcp_rtt_dst_low(const struct tcp_conn *conn)
 	int i;
 
 	for (i = 0; i < LOW_RTT_TABLE_SIZE; i++)
-		if (IN6_ARE_ADDR_EQUAL(&conn->a.a6, low_rtt_dst + i))
+		if (IN6_ARE_ADDR_EQUAL(&conn->addr, low_rtt_dst + i))
 			return 1;
 
 	return 0;
@@ -982,7 +972,7 @@ static void tcp_rtt_dst_check(const struct tcp_conn *conn,
 		return;
 
 	for (i = 0; i < LOW_RTT_TABLE_SIZE; i++) {
-		if (IN6_ARE_ADDR_EQUAL(&conn->a.a6, low_rtt_dst + i))
+		if (IN6_ARE_ADDR_EQUAL(&conn->addr, low_rtt_dst + i))
 			return;
 		if (hole == -1 && IN6_IS_ADDR_UNSPECIFIED(low_rtt_dst + i))
 			hole = i;
@@ -994,10 +984,10 @@ static void tcp_rtt_dst_check(const struct tcp_conn *conn,
 	if (hole == -1)
 		return;
 
-	memcpy(low_rtt_dst + hole++, &conn->a.a6, sizeof(conn->a.a6));
+	memcpy(low_rtt_dst + hole++, &conn->addr, sizeof(conn->addr));
 	if (hole == LOW_RTT_TABLE_SIZE)
 		hole = 0;
-	memcpy(low_rtt_dst + hole, &in6addr_any, sizeof(conn->a.a6));
+	memcpy(low_rtt_dst + hole, &in6addr_any, sizeof(conn->addr));
 #else
 	(void)conn;
 	(void)tinfo;
@@ -1285,7 +1275,7 @@ static int tcp_hash_match(const struct tcp_conn *conn,
 			  const struct in6_addr *addr,
 			  in_port_t tap_port, in_port_t sock_port)
 {
-	if (IN6_ARE_ADDR_EQUAL(&conn->a.a6, addr)		&&
+	if (IN6_ARE_ADDR_EQUAL(&conn->addr, addr)		&&
 	    conn->tap_port == tap_port && conn->sock_port == sock_port)
 		return 1;
 
@@ -1330,7 +1320,7 @@ static void tcp_hash_insert(const struct ctx *c, struct tcp_conn *conn)
 {
 	int b;
 
-	b = tcp_hash(c, &conn->a.a6, conn->tap_port, conn->sock_port);
+	b = tcp_hash(c, &conn->addr, conn->tap_port, conn->sock_port);
 	conn->next_index = tc_hash[b] ? tc_hash[b] - tc : -1;
 	tc_hash[b] = conn;
 	conn->hash_bucket = b;
@@ -1660,7 +1650,7 @@ do {									\
 		ip_len = plen + sizeof(struct ipv6hdr) + sizeof(struct tcphdr);
 
 		b->ip6h.payload_len = htons(plen + sizeof(struct tcphdr));
-		b->ip6h.saddr = conn->a.a6;
+		b->ip6h.saddr = conn->addr;
 		if (IN6_IS_ADDR_LINKLOCAL(&b->ip6h.saddr))
 			b->ip6h.daddr = c->ip6.addr_ll_seen;
 		else
@@ -1684,7 +1674,7 @@ do {									\
 
 		ip_len = plen + sizeof(struct iphdr) + sizeof(struct tcphdr);
 		b->iph.tot_len = htons(ip_len);
-		b->iph.saddr = conn->a.a4.a.s_addr;
+		b->iph.saddr = decode_ip4mapped_ip6(&conn->addr).s_addr;
 		b->iph.daddr = c->ip4.addr_seen.s_addr;
 
 		if (check)
@@ -2202,12 +2192,12 @@ static void tcp_conn_from_tap(struct ctx *c, int af, const void *addr,
 		sa = (struct sockaddr *)&addr4;
 		sl = sizeof(addr4);
 
-		encode_ip4mapped_ip6(&conn->a.a6, addr);
+		encode_ip4mapped_ip6(&conn->addr, addr);
 	} else {
 		sa = (struct sockaddr *)&addr6;
 		sl = sizeof(addr6);
 
-		memcpy(&conn->a.a6,      addr, sizeof(conn->a.a6));
+		memcpy(&conn->addr,      addr, sizeof(conn->addr));
 	}
 
 	conn->sock_port = ntohs(th->dest);
@@ -2869,7 +2859,7 @@ static void tcp_conn_from_sock(struct ctx *c, union epoll_ref ref,
 			memcpy(&sa6.sin6_addr, src, sizeof(*src));
 		}
 
-		memcpy(&conn->a.a6, &sa6.sin6_addr, sizeof(conn->a.a6));
+		memcpy(&conn->addr, &sa6.sin6_addr, sizeof(conn->addr));
 
 		conn->sock_port = ntohs(sa6.sin6_port);
 		conn->tap_port = ref.r.p.tcp.tcp.index;
@@ -2888,7 +2878,7 @@ static void tcp_conn_from_sock(struct ctx *c, union epoll_ref ref,
 		    IN4_ARE_ADDR_EQUAL(&sa4.sin_addr, &c->ip4.addr_seen))
 			sa4.sin_addr = c->ip4.gw;
 
-		encode_ip4mapped_ip6(&conn->a.a6, &sa4.sin_addr);
+		encode_ip4mapped_ip6(&conn->addr, &sa4.sin_addr);
 
 		conn->sock_port = ntohs(sa4.sin_port);
 		conn->tap_port = ref.r.p.tcp.tcp.index;
diff --git a/util.c b/util.c
index 257d0b6..ec7f57f 100644
--- a/util.c
+++ b/util.c
@@ -502,3 +502,16 @@ void encode_ip4mapped_ip6(struct in6_addr *ip6, const void *ip4)
 	memset(&a->one, 0xff, sizeof(a->one));
 	memcpy(&a->a4, ip4, sizeof(a->a4));
 }
+
+/**
+ * decode_ip4mapped_ip6() - Decode an IPv4-mapped IPv6 address
+ * @ip6:	IPv6 address
+ *
+ * Returns:	IPv4 address
+ */
+struct in_addr decode_ip4mapped_ip6(const struct in6_addr *ip6)
+{
+	const struct ip4mapped_ip6 *a = (const struct ip4mapped_ip6 *)ip6;
+
+	return a->a4;
+}
diff --git a/util.h b/util.h
index f7d6a6f..103211d 100644
--- a/util.h
+++ b/util.h
@@ -210,5 +210,6 @@ int __daemon(int pidfile_fd, int devnull_fd);
 int fls(unsigned long x);
 int write_file(const char *path, const char *buf);
 void encode_ip4mapped_ip6(struct in6_addr *ip6, const void *ip4);
+struct in_addr decode_ip4mapped_ip6(const struct in6_addr *ip6);
 
 #endif /* UTIL_H */
-- 
@@ -210,5 +210,6 @@ int __daemon(int pidfile_fd, int devnull_fd);
 int fls(unsigned long x);
 int write_file(const char *path, const char *buf);
 void encode_ip4mapped_ip6(struct in6_addr *ip6, const void *ip4);
+struct in_addr decode_ip4mapped_ip6(const struct in6_addr *ip6);
 
 #endif /* UTIL_H */
-- 
2.38.1