[PATCH v3 03/11] ip: Introduce unified multi-address data structures

[Jon Maloy <jmaloy@redhat.com>]

As preparation for supporting multiple addresses per interface, we
replace the single addr/prefix_len fields with an array. The
array consists of a new struct inany_addr_entry containing an
address and prefix length, both in inany_addr format.

There are only two functional changes:
- The indicated IPv6 prefix length is now properly stored, instead
  of being ignored and overridden with the hardcoded value 64, as
  as has been the case until now.
- Since even IPv4 addresses now are stored in IPv6 format, we
  also store the corresponding prefix length in that format,
  i.e. using the range [96,128] instead of [0,32].

Signed-off-by: Jon Maloy <jmaloy@redhat.com>

---
v2: -Using inany_addr instead of protocol specific addresses as
     entry address field.

v3: -Merging into one array, directly in struct ctx
    -Changed prefix_len and flags fields in struct inany_addr_entry
     to uint8_t, since that makes the struct directly migratable
---
 arp.c    |   5 +-
 conf.c   | 145 ++++++++++++++++++++++++++++++++-----------------------
 conf.h   |   6 +++
 dhcp.c   |   8 +--
 dhcpv6.c |   6 +--
 fwd.c    |  17 ++++---
 ip.c     |  11 +++--
 ip.h     |   5 ++
 ndp.c    |   6 +--
 passt.h  | 123 +++++++++++++++++++++++++++++++++++++++++++---
 pasta.c  |  15 ++++--
 tap.c    |   5 +-
 12 files changed, 251 insertions(+), 101 deletions(-)

diff --git a/arp.c b/arp.c
index bb042e9..f16beac 100644
--- a/arp.c
+++ b/arp.c
@@ -54,7 +54,8 @@ static bool ignore_arp(const struct ctx *c,
 		return true;
 
 	/* Don't resolve the guest's assigned address, either. */
-	if (!memcmp(am->tip, &c->ip4.addr, sizeof(am->tip)))
+	if (first_v4(c) &&
+	    !memcmp(am->tip, inany_v4(&first_v4(c)->addr), sizeof(am->tip)))
 		return true;
 
 	return false;
@@ -145,7 +146,7 @@ void arp_send_init_req(const struct ctx *c)
 	memcpy(req.am.sha,	c->our_tap_mac,		sizeof(req.am.sha));
 	memcpy(req.am.sip,	&c->ip4.our_tap_addr,	sizeof(req.am.sip));
 	memcpy(req.am.tha,	MAC_BROADCAST,		sizeof(req.am.tha));
-	memcpy(req.am.tip,	&c->ip4.addr,		sizeof(req.am.tip));
+	memcpy(req.am.tip,	inany_v4(&first_v4(c)->addr), sizeof(req.am.tip));
 
 	debug("Sending initial ARP request for guest MAC address");
 	tap_send_single(c, &req, sizeof(req));
diff --git a/conf.c b/conf.c
index 5188c02..bb6bcf8 100644
--- a/conf.c
+++ b/conf.c
@@ -56,7 +56,7 @@
 #define IP4_LL_GUEST_GW		(struct in_addr){ htonl_constant(0xa9fe0202) }
 				/* 169.254.2.2, libslirp default: 10.0.2.2 */
 
-#define IP4_LL_PREFIX_LEN	16
+#define IP4_LL_PREFIX_LEN	112	/* 96 + 16, in IPv6 format */
 
 #define IP6_LL_GUEST_GW		(struct in6_addr)			\
 				{{{ 0xfe, 0x80, 0, 0, 0, 0, 0, 0,	\
@@ -693,11 +693,11 @@ static int conf_ip4_prefix(const char *arg)
 /**
  * conf_ip4() - Verify or detect IPv4 support, get relevant addresses
  * @ifi:	Host interface to attempt (0 to determine one)
- * @ip4:	IPv4 context (will be written)
+ * @c:		Execution context (will be written)
  *
  * Return: interface index for IPv4, or 0 on failure.
  */
-static unsigned int conf_ip4(unsigned int ifi, struct ip4_ctx *ip4)
+static unsigned int conf_ip4(unsigned int ifi, struct ctx *c)
 {
 	if (!ifi)
 		ifi = nl_get_ext_if(nl_sock, AF_INET);
@@ -707,9 +707,9 @@ static unsigned int conf_ip4(unsigned int ifi, struct ip4_ctx *ip4)
 		return 0;
 	}
 
-	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->guest_gw)) {
+	if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.guest_gw)) {
 		int rc = nl_route_get_def(nl_sock, ifi, AF_INET,
-					  &ip4->guest_gw);
+					  &c->ip4.guest_gw);
 		if (rc < 0) {
 			debug("Couldn't discover IPv4 gateway address: %s",
 			      strerror_(-rc));
@@ -717,60 +717,57 @@ static unsigned int conf_ip4(unsigned int ifi, struct ip4_ctx *ip4)
 		}
 	}
 
-	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->addr)) {
+	if (!count_v4(c)) {
+		struct in_addr addr = {0,};
+		int prefix_len = 0;
 		int rc = nl_addr_get(nl_sock, ifi, AF_INET,
-				     &ip4->addr, &ip4->prefix_len, NULL);
+				     &addr, &prefix_len, NULL);
 		if (rc < 0) {
 			debug("Couldn't discover IPv4 address: %s",
 			      strerror_(-rc));
 			return 0;
 		}
-	}
+		if (IN4_IS_ADDR_UNSPECIFIED(&addr))
+			return 0;
 
-	if (!ip4->prefix_len) {
-		in_addr_t addr = ntohl(ip4->addr.s_addr);
-		if (IN_CLASSA(addr))
-			ip4->prefix_len = (32 - IN_CLASSA_NSHIFT);
-		else if (IN_CLASSB(addr))
-			ip4->prefix_len = (32 - IN_CLASSB_NSHIFT);
-		else if (IN_CLASSC(addr))
-			ip4->prefix_len = (32 - IN_CLASSC_NSHIFT);
-		else
-			ip4->prefix_len = 32;
+		c->addrs[c->addr_count].addr = inany_from_v4(addr);
+		c->addrs[c->addr_count].prefix_len = prefix_len + 96;
+		c->addrs[c->addr_count].flags = INANY_ADDR_HOST;
+		c->addr_count++;
+		c->ip4.addr_seen = addr;
 	}
 
-	ip4->addr_seen = ip4->addr;
-
-	ip4->our_tap_addr = ip4->guest_gw;
-
-	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->addr))
-		return 0;
+	c->ip4.our_tap_addr = c->ip4.guest_gw;
 
 	return ifi;
 }
 
 /**
  * conf_ip4_local() - Configure IPv4 addresses and attributes for local mode
- * @ip4:	IPv4 context (will be written)
+ * @c:		Execution context (will be written)
  */
-static void conf_ip4_local(struct ip4_ctx *ip4)
+static void conf_ip4_local(struct ctx *c)
 {
-	ip4->addr_seen = ip4->addr = IP4_LL_GUEST_ADDR;
-	ip4->our_tap_addr = ip4->guest_gw = IP4_LL_GUEST_GW;
-	ip4->prefix_len = IP4_LL_PREFIX_LEN;
+	c->addrs[c->addr_count].addr = inany_from_v4(IP4_LL_GUEST_ADDR);
+	c->ip4.addr_seen = *inany_v4(&c->addrs[c->addr_count].addr);
+	c->ip4.our_tap_addr = c->ip4.guest_gw = IP4_LL_GUEST_GW;
+	c->addrs[c->addr_count].prefix_len = IP4_LL_PREFIX_LEN;
+	c->addr_count++;
 
-	ip4->no_copy_addrs = ip4->no_copy_routes = true;
+	c->ip4.no_copy_addrs = c->ip4.no_copy_routes = true;
 }
 
 /**
  * conf_ip6() - Verify or detect IPv6 support, get relevant addresses
  * @ifi:	Host interface to attempt (0 to determine one)
- * @ip6:	IPv6 context (will be written)
+ * @c:		Execution context (will be written)
  *
  * Return: interface index for IPv6, or 0 on failure.
  */
-static unsigned int conf_ip6(unsigned int ifi, struct ip6_ctx *ip6)
+static unsigned int conf_ip6(unsigned int ifi, struct ctx *c)
 {
+	struct inany_addr_entry *e;
+	union inany_addr addr = {0,};
 	int prefix_len = 0;
 	int rc;
 
@@ -782,8 +779,8 @@ static unsigned int conf_ip6(unsigned int ifi, struct ip6_ctx *ip6)
 		return 0;
 	}
 
-	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->guest_gw)) {
-		rc = nl_route_get_def(nl_sock, ifi, AF_INET6, &ip6->guest_gw);
+	if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.guest_gw)) {
+		rc = nl_route_get_def(nl_sock, ifi, AF_INET6, &c->ip6.guest_gw);
 		if (rc < 0) {
 			debug("Couldn't discover IPv6 gateway address: %s",
 			      strerror_(-rc));
@@ -791,21 +788,28 @@ static unsigned int conf_ip6(unsigned int ifi, struct ip6_ctx *ip6)
 		}
 	}
 
-	rc = nl_addr_get(nl_sock, ifi, AF_INET6,
-			 IN6_IS_ADDR_UNSPECIFIED(&ip6->addr) ? &ip6->addr : NULL,
-			 &prefix_len, &ip6->our_tap_ll);
+	rc = nl_addr_get(nl_sock, ifi, AF_INET6, &addr.a6,
+			 &prefix_len, &c->ip6.our_tap_ll);
 	if (rc < 0) {
 		debug("Couldn't discover IPv6 address: %s", strerror_(-rc));
 		return 0;
 	}
 
-	ip6->addr_seen = ip6->addr;
+	if (!count_v6(c)) {
+		c->addrs[c->addr_count].addr = addr;
+		c->addrs[c->addr_count].prefix_len = prefix_len ? prefix_len : 64;
+		c->addrs[c->addr_count].flags = INANY_ADDR_HOST;
+		c->addr_count++;
+	}
+
+	e = first_v6(c);
+	c->ip6.addr_seen = e->addr.a6;
 
-	if (IN6_IS_ADDR_LINKLOCAL(&ip6->guest_gw))
-		ip6->our_tap_ll = ip6->guest_gw;
+	if (IN6_IS_ADDR_LINKLOCAL(&c->ip6.guest_gw))
+		c->ip6.our_tap_ll = c->ip6.guest_gw;
 
-	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->addr) ||
-	    IN6_IS_ADDR_UNSPECIFIED(&ip6->our_tap_ll))
+	if (IN6_IS_ADDR_UNSPECIFIED(&e->addr.a6) ||
+	    IN6_IS_ADDR_UNSPECIFIED(&c->ip6.our_tap_ll))
 		return 0;
 
 	return ifi;
@@ -813,13 +817,13 @@ static unsigned int conf_ip6(unsigned int ifi, struct ip6_ctx *ip6)
 
 /**
  * conf_ip6_local() - Configure IPv6 addresses and attributes for local mode
- * @ip6:	IPv6 context (will be written)
+ * @c:		Execution context (will be written)
  */
-static void conf_ip6_local(struct ip6_ctx *ip6)
+static void conf_ip6_local(struct ctx *c)
 {
-	ip6->our_tap_ll = ip6->guest_gw = IP6_LL_GUEST_GW;
+	c->ip6.our_tap_ll = c->ip6.guest_gw = IP6_LL_GUEST_GW;
 
-	ip6->no_copy_addrs = ip6->no_copy_routes = true;
+	c->ip6.no_copy_addrs = c->ip6.no_copy_routes = true;
 }
 
 /**
@@ -1145,13 +1149,15 @@ static void conf_print(const struct ctx *c)
 				       buf4, sizeof(buf4)));
 
 		if (!c->no_dhcp) {
+			struct inany_addr_entry *e = first_v4(c);
 			uint32_t mask;
 
-			mask = IN4_MASK(c->ip4.prefix_len);
+			mask = IN4_MASK(e->prefix_len);
 
 			info("DHCP:");
 			info("    assign: %s",
-			     inet_ntop(AF_INET, &c->ip4.addr, buf4, sizeof(buf4)));
+			     inet_ntop(AF_INET, inany_v4(&e->addr),
+				       buf4, sizeof(buf4)));
 			info("    mask: %s",
 			     inet_ntop(AF_INET, &mask,        buf4, sizeof(buf4)));
 			info("    router: %s",
@@ -1189,7 +1195,8 @@ static void conf_print(const struct ctx *c)
 			goto dns6;
 
 		info("    assign: %s",
-		     inet_ntop(AF_INET6, &c->ip6.addr, buf6, sizeof(buf6)));
+		     inet_ntop(AF_INET6, &first_v6(c)->addr.a6,
+			       buf6, sizeof(buf6)));
 		info("    router: %s",
 		     inet_ntop(AF_INET6, &c->ip6.guest_gw, buf6, sizeof(buf6)));
 		info("    our link-local: %s",
@@ -1811,6 +1818,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		}
 		case 'a': {
 			union inany_addr addr = { 0 };
+			struct inany_addr_entry *e;
 			int prefix_len = 0;
 			int af;
 
@@ -1828,13 +1836,20 @@ void conf(struct ctx *c, int argc, char **argv)
 				die("Can't mix CIDR with -n");
 
 			if (af == AF_INET) {
-				c->ip4.addr = *inany_v4(&addr);
-				c->ip4.prefix_len = prefix_len ? prefix_len - 96 :
-					ip4_class_prefix_len(&c->ip4.addr);
+				e = &c->addrs[c->addr_count];
+				e->addr = addr;
+				e->prefix_len = prefix_len ? prefix_len :
+					ip4_class_prefix_len(inany_v4(&addr));
+				e->flags = INANY_ADDR_CONFIGURED;
+				c->addr_count++;
 				if (c->mode == MODE_PASTA)
 					c->ip4.no_copy_addrs = true;
 			} else if (af == AF_INET6) {
-				c->ip6.addr = addr.a6;
+				e = &c->addrs[c->addr_count];
+				e->addr = addr;
+				e->prefix_len = prefix_len ? prefix_len : 64;
+				e->flags = INANY_ADDR_CONFIGURED;
+				c->addr_count++;
 				if (c->mode == MODE_PASTA)
 					c->ip6.no_copy_addrs = true;
 			} else {
@@ -1842,14 +1857,21 @@ void conf(struct ctx *c, int argc, char **argv)
 			}
 			break;
 		}
-		case 'n':
+		case 'n': {
+			struct inany_addr_entry *e;
+			int plen;
+
 			if (prefix_from_cidr)
 				die("Can't use both -n and CIDR prefix length");
-			c->ip4.prefix_len = conf_ip4_prefix(optarg);
-			if (c->ip4.prefix_len < 0)
+			plen = conf_ip4_prefix(optarg);
+			if (plen < 0)
 				die("Invalid netmask: %s", optarg);
+			e = first_v4(c);
+			if (e)
+				e->prefix_len = plen + 96;
 			prefix_from_opt = true;
 			break;
+		}
 		case 'M':
 			parse_mac(c->our_tap_mac, optarg);
 			break;
@@ -1993,9 +2015,9 @@ void conf(struct ctx *c, int argc, char **argv)
 
 	nl_sock_init(c, false);
 	if (!v6_only)
-		c->ifi4 = conf_ip4(ifi4, &c->ip4);
+		c->ifi4 = conf_ip4(ifi4, c);
 	if (!v4_only)
-		c->ifi6 = conf_ip6(ifi6, &c->ip6);
+		c->ifi6 = conf_ip6(ifi6, c);
 
 	if (c->ifi4 && c->mtu < IPV4_MIN_MTU) {
 		warn("MTU %"PRIu16" is too small for IPv4 (minimum %u)",
@@ -2018,14 +2040,14 @@ void conf(struct ctx *c, int argc, char **argv)
 	if (!c->ifi4 && !v6_only) {
 		info("IPv4: no external interface as template, use local mode");
 
-		conf_ip4_local(&c->ip4);
+		conf_ip4_local(c);
 		c->ifi4 = -1;
 	}
 
 	if (!c->ifi6 && !v4_only) {
 		info("IPv6: no external interface as template, use local mode");
 
-		conf_ip6_local(&c->ip6);
+		conf_ip6_local(c);
 		c->ifi6 = -1;
 	}
 
@@ -2134,7 +2156,8 @@ void conf(struct ctx *c, int argc, char **argv)
 	if (!c->ifi6) {
 		c->no_ndp = 1;
 		c->no_dhcpv6 = 1;
-	} else if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr)) {
+	} else if (!first_v6(c) ||
+		   IN6_IS_ADDR_UNSPECIFIED(&first_v6(c)->addr.a6)) {
 		c->no_dhcpv6 = 1;
 	}
 
diff --git a/conf.h b/conf.h
index b45ad74..e86fe96 100644
--- a/conf.h
+++ b/conf.h
@@ -6,6 +6,12 @@
 #ifndef CONF_H
 #define CONF_H
 
+/* Flags indicating origin and role of an address
+ * To be used in struct inany_addr_entry
+ */
+#define CONF_ADDR_CONFIGURED	(1 << 0)	/* User set via -a */
+#define CONF_ADDR_HOST		(1 << 1)	/* From host interface */
+
 enum passt_modes conf_mode(int argc, char *argv[]);
 void conf(struct ctx *c, int argc, char **argv);
 
diff --git a/dhcp.c b/dhcp.c
index c552f01..933a8cf 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -352,7 +352,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	reply.secs		= 0;
 	reply.flags		= m->flags;
 	reply.ciaddr		= m->ciaddr;
-	reply.yiaddr		= c->ip4.addr;
+	reply.yiaddr		= *inany_v4(&first_v4(c)->addr);
 	reply.siaddr		= 0;
 	reply.giaddr		= m->giaddr;
 	memcpy(&reply.chaddr,	m->chaddr,	sizeof(reply.chaddr));
@@ -404,7 +404,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 
 	info("    from %s", eth_ntop(m->chaddr, macstr, sizeof(macstr)));
 
-	mask.s_addr = IN4_MASK(c->ip4.prefix_len);
+	mask.s_addr = IN4_MASK(first_v4(c)->prefix_len);
 	memcpy(opts[1].s,  &mask,                sizeof(mask));
 	memcpy(opts[3].s,  &c->ip4.guest_gw,     sizeof(c->ip4.guest_gw));
 	memcpy(opts[54].s, &c->ip4.our_tap_addr, sizeof(c->ip4.our_tap_addr));
@@ -412,7 +412,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	/* If the gateway is not on the assigned subnet, send an option 121
 	 * (Classless Static Routing) adding a dummy route to it.
 	 */
-	if ((c->ip4.addr.s_addr & mask.s_addr)
+	if ((inany_v4(&first_v4(c)->addr)->s_addr & mask.s_addr)
 	    != (c->ip4.guest_gw.s_addr & mask.s_addr)) {
 		/* a.b.c.d/32:0.0.0.0, 0:a.b.c.d */
 		opts[121].slen = 14;
@@ -469,7 +469,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	if (m->flags & FLAG_BROADCAST)
 		dst = in4addr_broadcast;
 	else
-		dst = c->ip4.addr;
+		dst = *inany_v4(&first_v4(c)->addr);
 
 	tap_udp4_send(c, c->ip4.our_tap_addr, 67, dst, 68, &reply, dlen);
 
diff --git a/dhcpv6.c b/dhcpv6.c
index e4df0db..a1e5f15 100644
--- a/dhcpv6.c
+++ b/dhcpv6.c
@@ -625,7 +625,7 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
 		if (mh->type == TYPE_CONFIRM && server_id)
 			return -1;
 
-		if (dhcpv6_ia_notonlink(data, &c->ip6.addr)) {
+		if (dhcpv6_ia_notonlink(data, &first_v6(c)->addr.a6)) {
 
 			dhcpv6_send_ia_notonlink(c, data, &client_id_base,
 						 ntohs(client_id->l), mh->xid);
@@ -679,7 +679,7 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
 
 	tap_udp6_send(c, src, 547, tap_ip6_daddr(c, src), 546,
 		      mh->xid, &resp, n);
-	c->ip6.addr_seen = c->ip6.addr;
+	c->ip6.addr_seen = first_v6(c)->addr.a6;
 
 	return 1;
 }
@@ -703,5 +703,5 @@ void dhcpv6_init(const struct ctx *c)
 	memcpy(resp_not_on_link.server_id.duid_lladdr,
 	       c->our_tap_mac, sizeof(c->our_tap_mac));
 
-	resp.ia_addr.addr	= c->ip6.addr;
+	resp.ia_addr.addr	= first_v6(c)->addr.a6;
 }
diff --git a/fwd.c b/fwd.c
index 44a0e10..54248a3 100644
--- a/fwd.c
+++ b/fwd.c
@@ -516,7 +516,8 @@ static bool fwd_guest_accessible4(const struct ctx *c,
 	/* For IPv4, addr_seen is initialised to addr, so is always a valid
 	 * address
 	 */
-	if (IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr) ||
+	if ((first_v4(c) &&
+	     IN4_ARE_ADDR_EQUAL(addr, inany_v4(&first_v4(c)->addr))) ||
 	    IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr_seen))
 		return false;
 
@@ -537,7 +538,7 @@ static bool fwd_guest_accessible6(const struct ctx *c,
 	if (IN6_IS_ADDR_LOOPBACK(addr))
 		return false;
 
-	if (IN6_ARE_ADDR_EQUAL(addr, &c->ip6.addr))
+	if (first_v6(c) && IN6_ARE_ADDR_EQUAL(addr, &first_v6(c)->addr.a6))
 		return false;
 
 	/* For IPv6, addr_seen starts unspecified, because we don't know what LL
@@ -586,10 +587,10 @@ static void nat_outbound(const struct ctx *c, const union inany_addr *addr,
 		*translated = inany_loopback4;
 	else if (inany_equals6(addr, &c->ip6.map_host_loopback))
 		*translated = inany_loopback6;
-	else if (inany_equals4(addr, &c->ip4.map_guest_addr))
-		*translated = inany_from_v4(c->ip4.addr);
-	else if (inany_equals6(addr, &c->ip6.map_guest_addr))
-		translated->a6 = c->ip6.addr;
+	else if (first_v4(c) && inany_equals4(addr, &c->ip4.map_guest_addr))
+		*translated = first_v4(c)->addr;
+	else if (first_v6(c) && inany_equals6(addr, &c->ip6.map_guest_addr))
+		translated->a6 = first_v6(c)->addr.a6;
 	else
 		*translated = *addr;
 }
@@ -710,10 +711,10 @@ bool nat_inbound(const struct ctx *c, const union inany_addr *addr,
 		   inany_equals6(addr, &in6addr_loopback)) {
 		translated->a6 = c->ip6.map_host_loopback;
 	} else if (!IN4_IS_ADDR_UNSPECIFIED(&c->ip4.map_guest_addr) &&
-		   inany_equals4(addr, &c->ip4.addr)) {
+		   first_v4(c) && inany_equals(addr, &first_v4(c)->addr)) {
 		*translated = inany_from_v4(c->ip4.map_guest_addr);
 	} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.map_guest_addr) &&
-		   inany_equals6(addr, &c->ip6.addr)) {
+		   first_v6(c) && inany_equals6(addr, &first_v6(c)->addr.a6)) {
 		translated->a6 = c->ip6.map_guest_addr;
 	} else if (fwd_guest_accessible(c, addr)) {
 		*translated = *addr;
diff --git a/ip.c b/ip.c
index 40dc24e..a86753f 100644
--- a/ip.c
+++ b/ip.c
@@ -74,17 +74,18 @@ found:
  * ip4_class_prefix_len() - Get class based prefix length for IPv4 address
  * @addr:	IPv4 address
  *
- * Return: prefix length based on address class, or 32 for other
+ * Return: prefix length in IPv6 format (96 + IPv4 prefix) based on address
+ *         class, or 128 for other
  */
 int ip4_class_prefix_len(const struct in_addr *addr)
 {
 	in_addr_t a = ntohl(addr->s_addr);
 
 	if (IN_CLASSA(a))
-		return 32 - IN_CLASSA_NSHIFT;
+		return 96 + 32 - IN_CLASSA_NSHIFT;
 	if (IN_CLASSB(a))
-		return 32 - IN_CLASSB_NSHIFT;
+		return 96 + 32 - IN_CLASSB_NSHIFT;
 	if (IN_CLASSC(a))
-		return 32 - IN_CLASSC_NSHIFT;
-	return 32;
+		return 96 + 32 - IN_CLASSC_NSHIFT;
+	return 128;
 }
diff --git a/ip.h b/ip.h
index c829d84..91d6d9a 100644
--- a/ip.h
+++ b/ip.h
@@ -137,6 +137,11 @@ static const struct in_addr in4addr_broadcast = { 0xffffffff };
 #define IPV6_MIN_MTU		1280
 #endif
 
+/* Maximum number of addresses per address family */
+#define IP4_MAX_ADDRS		16
+#define IP6_MAX_ADDRS		16
+#define INANY_MAX_ADDRS		(IP4_MAX_ADDRS + IP6_MAX_ADDRS)
+
 int ip4_class_prefix_len(const struct in_addr *addr);
 
 #endif /* IP_H */
diff --git a/ndp.c b/ndp.c
index eb9e313..f60c298 100644
--- a/ndp.c
+++ b/ndp.c
@@ -257,7 +257,7 @@ static void ndp_ra(const struct ctx *c, const struct in6_addr *dst)
 			.valid_lifetime		= ~0U,
 			.pref_lifetime		= ~0U,
 		},
-		.prefix = c->ip6.addr,
+		.prefix = first_v6(c)->addr.a6,
 		.source_ll = {
 			.header = {
 				.type		= OPT_SRC_L2_ADDR,
@@ -466,8 +466,8 @@ void ndp_send_init_req(const struct ctx *c)
 			.icmp6_solicited	= 0, /* Reserved */
 			.icmp6_override		= 0, /* Reserved */
 		},
-		.target_addr = c->ip6.addr
+		.target_addr = first_v6(c)->addr.a6
 	};
 	debug("Sending initial NDP NS request for guest MAC address");
-	ndp_send(c, &c->ip6.addr, &ns, sizeof(ns));
+	ndp_send(c, &first_v6(c)->addr.a6, &ns, sizeof(ns));
 }
diff --git a/passt.h b/passt.h
index 79d01dd..ec5517d 100644
--- a/passt.h
+++ b/passt.h
@@ -64,11 +64,42 @@ enum passt_modes {
 	MODE_VU,
 };
 
+/* Flags indicating origin and role of an address
+ * in struct inany_addr_entry
+ */
+#define INANY_ADDR_CONFIGURED	BIT(0)		/* User set via -a */
+#define INANY_ADDR_HOST		BIT(1)		/* From host interface */
+
+/**
+ * for_each_addr() - Iterate over addresses in unified array
+ * @c:		Pointer to struct ctx
+ * @e:		Pointer variable for current entry (struct inany_addr_entry *)
+ * @af:		Address family filter: AF_INET, AF_INET6, or 0 for all
+ *
+ * Note: @_i is the internal loop counter, uses _next_addr_idx() helper
+ */
+#define for_each_addr(c, e, af)						\
+	for (int _i = _next_addr_idx((c), 0, (af));			\
+	     _i < (c)->addr_count && ((e) = &(c)->addrs[_i], true);	\
+	     _i = _next_addr_idx((c), _i + 1, (af)))
+
+/* first_v4(), first_v6(), count_v4(), count_v6() defined after struct ctx */
+
+/**
+ * struct inany_addr_entry - Unified IPv4/IPv6 address entry
+ * @addr:	IPv4 (as mapped) or IPv6 address
+ * @prefix_len:	Prefix length in IPv6/IPv4-mapped [0,128]/[96,128] format
+ * @flags:	INANY_ADDR_* flags
+ */
+struct inany_addr_entry {
+	union inany_addr addr;
+	uint8_t prefix_len;
+	uint8_t flags;
+};
+
 /**
  * struct ip4_ctx - IPv4 execution context
- * @addr:		IPv4 address assigned to guest
  * @addr_seen:		Latest IPv4 address seen as source from tap
- * @prefixlen:		IPv4 prefix length (netmask)
  * @guest_gw:		IPv4 gateway as seen by the guest
  * @map_host_loopback:	Outbound connections to this address are NATted to the
  *                      host's 127.0.0.1
@@ -84,10 +115,7 @@ enum passt_modes {
  * @no_copy_addrs:	Don't copy all addresses when configuring namespace
  */
 struct ip4_ctx {
-	/* PIF_TAP addresses */
-	struct in_addr addr;
 	struct in_addr addr_seen;
-	int prefix_len;
 	struct in_addr guest_gw;
 	struct in_addr map_host_loopback;
 	struct in_addr map_guest_addr;
@@ -107,7 +135,6 @@ struct ip4_ctx {
 
 /**
  * struct ip6_ctx - IPv6 execution context
- * @addr:		IPv6 address assigned to guest
  * @addr_seen:		Latest IPv6 global/site address seen as source from tap
  * @addr_ll_seen:	Latest IPv6 link-local address seen as source from tap
  * @guest_gw:		IPv6 gateway as seen by the guest
@@ -125,8 +152,6 @@ struct ip4_ctx {
  * @no_copy_addrs:	Don't copy all addresses when configuring namespace
  */
 struct ip6_ctx {
-	/* PIF_TAP addresses */
-	struct in6_addr addr;
 	struct in6_addr addr_seen;
 	struct in6_addr addr_ll_seen;
 	struct in6_addr guest_gw;
@@ -257,6 +282,10 @@ struct ctx {
 	int ifi6;
 	struct ip6_ctx ip6;
 
+	/* Unified address array for both IPv4 (mapped) and IPv6 */
+	struct inany_addr_entry addrs[INANY_MAX_ADDRS];
+	int addr_count;
+
 	char pasta_ifn[IF_NAMESIZE];
 	unsigned int pasta_ifi;
 	int pasta_conf_ns;
@@ -294,6 +323,84 @@ struct ctx {
 	bool migrate_exit;
 };
 
+/**
+ * first_v4() - Get first IPv4 address entry
+ * @c:		Pointer to struct ctx
+ *
+ * Return: pointer to first IPv4 entry, or NULL if none
+ */
+static inline struct inany_addr_entry *first_v4(const struct ctx *c)
+{
+	for (int i = 0; i < c->addr_count; i++)
+		if (inany_v4(&c->addrs[i].addr))
+			return (struct inany_addr_entry *)&c->addrs[i];
+	return NULL;
+}
+
+/**
+ * first_v6() - Get first IPv6 address entry
+ * @c:		Pointer to struct ctx
+ *
+ * Return: pointer to first IPv6 entry, or NULL if none
+ */
+static inline struct inany_addr_entry *first_v6(const struct ctx *c)
+{
+	for (int i = 0; i < c->addr_count; i++)
+		if (!inany_v4(&c->addrs[i].addr))
+			return (struct inany_addr_entry *)&c->addrs[i];
+	return NULL;
+}
+
+/**
+ * count_v4() - Count IPv4 addresses
+ * @c:		Pointer to struct ctx
+ *
+ * Return: number of IPv4 addresses
+ */
+static inline int count_v4(const struct ctx *c)
+{
+	int count = 0;
+
+	for (int i = 0; i < c->addr_count; i++)
+		if (inany_v4(&c->addrs[i].addr))
+			count++;
+	return count;
+}
+
+/**
+ * count_v6() - Count IPv6 addresses
+ * @c:		Pointer to struct ctx
+ *
+ * Return: number of IPv6 addresses
+ */
+static inline int count_v6(const struct ctx *c)
+{
+	int count = 0;
+
+	for (int i = 0; i < c->addr_count; i++)
+		if (!inany_v4(&c->addrs[i].addr))
+			count++;
+	return count;
+}
+
+/**
+ * _next_addr_idx() - Find next address index matching family filter
+ * @c:		Pointer to struct ctx
+ * @i:		Starting index
+ * @af:		Address family filter: AF_INET, AF_INET6, or 0 for all
+ *
+ * Return: next matching index, or addr_count if none found
+ */
+static inline int _next_addr_idx(const struct ctx *c, int i, int af)
+{
+	while (i < c->addr_count) {
+		if (!af || ((af == AF_INET) == !!inany_v4(&c->addrs[i].addr)))
+			return i;
+		i++;
+	}
+	return i;
+}
+
 void proto_update_l2_buf(const unsigned char *eth_d);
 
 #endif /* PASST_H */
diff --git a/pasta.c b/pasta.c
index c307b8a..08f35f4 100644
--- a/pasta.c
+++ b/pasta.c
@@ -338,10 +338,12 @@ void pasta_ns_conf(struct ctx *c)
 
 		if (c->ifi4) {
 			if (c->ip4.no_copy_addrs) {
+				struct inany_addr_entry *e = first_v4(c);
+
 				rc = nl_addr_set(nl_sock_ns, c->pasta_ifi,
 						 AF_INET,
-						 &c->ip4.addr,
-						 c->ip4.prefix_len);
+						 inany_v4(&e->addr),
+						 e->prefix_len);
 			} else {
 				rc = nl_addr_dup(nl_sock, c->ifi4,
 						 nl_sock_ns, c->pasta_ifi,
@@ -387,10 +389,13 @@ void pasta_ns_conf(struct ctx *c)
 					  0, IFF_NOARP);
 
 			if (c->ip6.no_copy_addrs) {
-				if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr)) {
+				struct inany_addr_entry *e = first_v6(c);
+
+				if (e && !IN6_IS_ADDR_UNSPECIFIED(&e->addr.a6)) {
 					rc = nl_addr_set(nl_sock_ns,
-							 c->pasta_ifi, AF_INET6,
-							 &c->ip6.addr, 64);
+							 c->pasta_ifi,
+							 AF_INET6,
+							 &e->addr.a6, 64);
 				}
 			} else {
 				rc = nl_addr_dup(nl_sock, c->ifi6,
diff --git a/tap.c b/tap.c
index 9d1344b..f3073c6 100644
--- a/tap.c
+++ b/tap.c
@@ -951,8 +951,9 @@ resume:
 				c->ip6.addr_seen = *saddr;
 			}
 
-			if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr))
-				c->ip6.addr = *saddr;
+			if (first_v6(c) &&
+			    IN6_IS_ADDR_UNSPECIFIED(&first_v6(c)->addr.a6))
+				first_v6(c)->addr.a6 = *saddr;
 		} else if (!IN6_IS_ADDR_UNSPECIFIED(saddr)){
 			c->ip6.addr_seen = *saddr;
 		}
-- 
2.52.0