[PATCH 02/10] tcp: Helper to encode IPv4-mapped IPv6 addresses

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

In the tcp_conn structure we have space for an IPv6 address, and use
IPv4-mapped IPv6 addresses to describe IPv4 connections.  We open code
the construction of those IPv4-mapped address in two places.

Avoid the duplication with a helper function.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp.c  |  9 ++-------
 util.c | 20 ++++++++++++++++++++
 util.h |  1 +
 3 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/tcp.c b/tcp.c
index 3d48d6e..26dd268 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2217,9 +2217,7 @@ static void tcp_conn_from_tap(struct ctx *c, int af, const void *addr,
 		sa = (struct sockaddr *)&addr4;
 		sl = sizeof(addr4);
 
-		memset(&conn->a.a4.zero, 0,    sizeof(conn->a.a4.zero));
-		memset(&conn->a.a4.one,  0xff, sizeof(conn->a.a4.one));
-		memcpy(&conn->a.a4.a,    addr, sizeof(conn->a.a4.a));
+		encode_ip4mapped_ip6(&conn->a.a6, addr);
 	} else {
 		sa = (struct sockaddr *)&addr6;
 		sl = sizeof(addr6);
@@ -2902,15 +2900,12 @@ static void tcp_conn_from_sock(struct ctx *c, union epoll_ref ref,
 
 		memcpy(&sa4, &sa, sizeof(sa4));
 
-		memset(&conn->a.a4.zero,   0, sizeof(conn->a.a4.zero));
-		memset(&conn->a.a4.one, 0xff, sizeof(conn->a.a4.one));
-
 		if (IN4_IS_ADDR_LOOPBACK(&sa4.sin_addr) ||
 		    IN4_IS_ADDR_UNSPECIFIED(&sa4.sin_addr) ||
 		    IN4_ARE_ADDR_EQUAL(&sa4.sin_addr, &c->ip4.addr_seen))
 			sa4.sin_addr = c->ip4.gw;
 
-		conn->a.a4.a = sa4.sin_addr;
+		encode_ip4mapped_ip6(&conn->a.a6, &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 514bd44..257d0b6 100644
--- a/util.c
+++ b/util.c
@@ -482,3 +482,23 @@ int write_file(const char *path, const char *buf)
 	close(fd);
 	return len == 0 ? 0 : -1;
 }
+
+struct ip4mapped_ip6 {
+	uint8_t zero[10];
+	uint8_t one[2];
+	struct in_addr a4;
+};
+
+/**
+ * encode_ip4mapped_ip6() - Convert an IPv4 address to an IPv4-mapped IPv6 address
+ * @ip6:	Buffer to store the IPv4-mapped IPv6 address
+ * @ip4:	IPv4 address, network order
+ */
+void encode_ip4mapped_ip6(struct in6_addr *ip6, const void *ip4)
+{
+	struct ip4mapped_ip6 *a = (struct ip4mapped_ip6 *)ip6;
+
+	memset(&a->zero, 0, sizeof(a->zero));
+	memset(&a->one, 0xff, sizeof(a->one));
+	memcpy(&a->a4, ip4, sizeof(a->a4));
+}
diff --git a/util.h b/util.h
index 2d4e1ff..f7d6a6f 100644
--- a/util.h
+++ b/util.h
@@ -209,5 +209,6 @@ void write_pidfile(int fd, pid_t pid);
 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);
 
 #endif /* UTIL_H */
-- 
@@ -209,5 +209,6 @@ void write_pidfile(int fd, pid_t pid);
 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);
 
 #endif /* UTIL_H */
-- 
2.38.1