Re: [PATCH v8 02/14] passt, pasta: Introduce unified multi-address data structures

[Jon Maloy <jmaloy@redhat.com>]

On 2026-07-09 00:05, David Gibson wrote:
> On Thu, Jun 25, 2026 at 10:45:07PM -0400, Jon Maloy wrote:
>> 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.
>>
>> Despite some code refactoring, there are only two real functional
>> changes:
>> - The indicated IPv6 prefix length is now properly stored, instead
>>    of being ignored and overridden with the hardcoded value 64, 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].
>>
>> In conf_ip6(), the explicit IN6_IS_ADDR_UNSPECIFIED() check on the
>> address at the end of the function is no longer needed: for
>> host-discovered addresses, it is now checked inside the if (!a) block
>> before calling fwd_set_addr(); for user-provided addresses (via -a),
>> validation already rejects unspecified addresses at parse time.
>>
>> 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
>>
>> v4: -Updated according to changes in previous commits
>>      -Updated according to feedback from David G.
>>      -Squashed IP4_MASK macro commit into this one
>>
>> v6: -Renamed and moved some definitions
>>      -Introduced fwd_set_addr() and fwd_get_addr() already in this commit
>>      -Eliminated first_v4/v6() functions, replaced with fwd_get_addr()
>>      -Some other changes as suggested by David G.
>>      -I kept the flag CONF_ADDR_LINKLOCAL, since it will be
>>       needed later in an address selection function.
>>
>> v7: -Introduced CONF_ADDR_GENERATED flag
>>      -Other fixes based on feedback from David and Stefano.
>>      -I changed signature of inany_prefix_len(), but I did not change
>>       its semantics, since the premise of David's comment is wrong: the
>>       caller does *not* explicitly know he is dealing with an IPv4 address.
>>       In fact, there are examples later in this series where it may be an
>>       IPv6 address, and the caller just trusts he gets the return value in
>>       the appropriate format.
>>      -Intoduced the inverse of inany_prefix_len(), called inany_prefix_len6()
>>       which always returns the prefix in IPv6 or mapped IPv4 format.
>>       The name of the function isn't great, but any alternative I came up
>>       with became too long to be practical.
>>
>> v8: -Added inany_prefix_v4() (David G.) to extract IPv4 address and
>>       prefix length simultaneously, replacing inany_prefix_len().
>>      -Removed both inany_prefix_len() and inany_prefix_len6()
>>       auto-detecting functions. Prefix length attached to an inany is
>>       now always stored in IPv6 format (96-128 for IPv4-mapped).
>>      -fwd_set_addr() now requires prefix_len in IPv6 format; callers
>>       updated to pass prefix_len + 96 for IPv4 addresses.
>>      -Fixed -n option to store prefix_len in IPv6 format.
>>      -Fixed addr_seen regression: when address was set via -a,
>>       addr_seen was not initialised in conf_ip4().
>>      -Replaced assert() with graceful no-op in dhcp.c and ndp.c when
>>       no address is configured (David G.).
>>      -Note: addr_seen is still initialised both at conf_ip*() time
>>       and at DHCP/DHCPv6 send time (David's concern). This
>>       inconsistency will be addressed in a follow-up.
>>      -Introduced a new CONF_ADDR_ANY macro tobe used for address
>>       selection, as suggested by Stefano.
>>      -Deferred introduction of an explicit scope field (replacing
>>       CONF_ADDR_LINKLOCAL flag) to a later commit or series.
>> ---
>>   arp.c    |  12 ++++-
>>   conf.c   | 142 +++++++++++++++++++++++++++++++------------------------
>>   dhcp.c   |  19 ++++++--
>>   dhcpv6.c |  15 ++++--
>>   fwd.c    | 111 +++++++++++++++++++++++++++++++++++--------
>>   fwd.h    |   4 ++
>>   inany.h  |  28 +++++++++++
>>   ip.h     |   2 +
>>   ndp.c    |  19 ++++++--
>>   passt.h  |  66 +++++++++++++++++++++++---
>>   pasta.c  |  26 ++++++----
>>   tap.c    |   8 +++-
>>   12 files changed, 342 insertions(+), 110 deletions(-)
>>
>> diff --git a/arp.c b/arp.c
>> index bb042e95..0392861d 100644
>> --- a/arp.c
>> +++ b/arp.c
>> @@ -41,6 +41,8 @@
>>   static bool ignore_arp(const struct ctx *c,
>>   		       const struct arphdr *ah, const struct arpmsg *am)
>>   {
>> +	const struct guest_addr *a;
>> +
>>   	if (ah->ar_hrd != htons(ARPHRD_ETHER)	||
>>   	    ah->ar_pro != htons(ETH_P_IP)	||
>>   	    ah->ar_hln != ETH_ALEN		||
>> @@ -54,7 +56,8 @@ 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)))
>> +	a = fwd_get_addr(c, AF_INET, CONF_ADDR_ANY, 0);
>> +	if (a && !memcmp(am->tip, inany_v4(&a->addr), sizeof(am->tip)))
>>   		return true;
>>   
>>   	return false;
>> @@ -123,12 +126,17 @@ int arp(const struct ctx *c, struct iov_tail *data)
>>    */
>>   void arp_send_init_req(const struct ctx *c)
>>   {
>> +	const struct guest_addr *a;
>>   	struct {
>>   		struct ethhdr eh;
>>   		struct arphdr ah;
>>   		struct arpmsg am;
>>   	} __attribute__((__packed__)) req;
>>   
>> +	a = fwd_get_addr(c, AF_INET, CONF_ADDR_ANY, 0);
>> +	if (!a)
>> +		return;
>> +
>>   	/* Ethernet header */
>>   	req.eh.h_proto = htons(ETH_P_ARP);
>>   	memcpy(req.eh.h_dest, MAC_BROADCAST, sizeof(req.eh.h_dest));
>> @@ -145,7 +153,7 @@ 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(&a->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 4755a9f4..ac8facc8 100644
>> --- a/conf.c
>> +++ b/conf.c
>> @@ -373,13 +373,16 @@ static int conf_ip4_prefix(const char *arg)
>>   
>>   /**
>>    * conf_ip4() - Verify or detect IPv4 support, get relevant addresses
>> + * @c:		Execution context
>>    * @ifi:	Host interface to attempt (0 to determine one)
>> - * @ip4:	IPv4 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(struct ctx *c, unsigned int ifi)
>>   {
>> +	const struct guest_addr *a = fwd_get_addr(c, AF_INET, CONF_ADDR_ANY, 0);
>> +	struct ip4_ctx *ip4 = &c->ip4;
>> +
>>   	if (!ifi)
>>   		ifi = nl_get_ext_if(nl_sock, AF_INET);
>>   
>> @@ -398,60 +401,58 @@ static unsigned int conf_ip4(unsigned int ifi, struct ip4_ctx *ip4)
>>   		}
>>   	}
>>   
>> -	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->addr)) {
>> +	if (!a) {
>> +		struct in_addr addr;
>> +		int prefix_len;
>>   		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;
> 
> Nit: If we get here, the netlink probe succeeded, and the host
> apparently has an address of 0.0.0.0.  That's pretty strange, and
> probably warrants a warn().

ok.

> 
>>   
>> -	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;
>> +		fwd_set_addr(c, &inany_from_v4(addr), CONF_ADDR_HOST,
>> +			     prefix_len + 96);
>>   	}
>>   
>> -	ip4->addr_seen = ip4->addr;
>> -
>> +	a = fwd_get_addr(c, AF_INET, CONF_ADDR_ANY, 0);
> 
> Nit: maybe assert(a), since I doubt static checkers will be able to
> reason that the fwd_set_addr() above means this fwd_get_addr() can't
> fail.  Also, I think that go inside the if block, since the other case
> means we already have a perfectly good a.

I think my conclusion was that the static checker ignores assert() as a
conditonal test, but I can try it.

> 
>> +	ip4->addr_seen = *inany_v4(&a->addr);
>>   	ip4->our_tap_addr = ip4->guest_gw;
>>   
>> -	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->addr))
>> -		return 0;
>> -
>>   	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;
>> +	struct ip4_ctx *ip4 = &c->ip4;
>>   
>> +	ip4->addr_seen = IP4_LL_GUEST_ADDR;
>> +	ip4->our_tap_addr = ip4->guest_gw = IP4_LL_GUEST_GW;
>>   	ip4->no_copy_addrs = ip4->no_copy_routes = true;
>> +	fwd_set_addr(c, &inany_from_v4(IP4_LL_GUEST_ADDR),
>> +		     CONF_ADDR_GENERATED | CONF_ADDR_LINKLOCAL,
>> +		     IP4_LL_PREFIX_LEN + 96);
>>   }
>>   
>>   /**
>>    * conf_ip6() - Verify or detect IPv6 support, get relevant addresses
>> + * @c:		Execution context
>>    * @ifi:	Host interface to attempt (0 to determine one)
>> - * @ip6:	IPv6 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(struct ctx *c, unsigned int ifi)
>>   {
>> +	struct ip6_ctx *ip6 = &c->ip6;
>> +	const struct guest_addr *a;
>> +	union inany_addr addr;
>>   	int prefix_len = 0;
>>   	int rc;
>>   
>> @@ -472,21 +473,28 @@ 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,
>> +	rc = nl_addr_get(nl_sock, ifi, AF_INET6, &addr.a6,
>>   			 &prefix_len, &ip6->our_tap_ll);
>>   	if (rc < 0) {
>>   		debug("Couldn't discover IPv6 address: %s", strerror_(-rc));
>>   		return 0;
>>   	}
>>   
>> -	ip6->addr_seen = ip6->addr;
>> +	a = fwd_get_addr(c, AF_INET6, CONF_ADDR_ANY, 0);
>> +	if (!a) {
>> +		if (IN6_IS_ADDR_UNSPECIFIED(&addr))
>> +			return 0;
>> +
>> +		fwd_set_addr(c, &addr, CONF_ADDR_HOST, prefix_len);
>> +		ip6->addr_seen = addr.a6;
>> +	} else {
>> +		ip6->addr_seen = a->addr.a6;
>> +	}
>>   
>>   	if (IN6_IS_ADDR_LINKLOCAL(&ip6->guest_gw))
>>   		ip6->our_tap_ll = ip6->guest_gw;
>>   
>> -	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->addr) ||
>> -	    IN6_IS_ADDR_UNSPECIFIED(&ip6->our_tap_ll))
>> +	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->our_tap_ll))
>>   		return 0;
>>   
>>   	return ifi;
>> @@ -494,13 +502,13 @@ 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;
>>   }
>>   
>>   /**
>> @@ -784,6 +792,7 @@ enum passt_modes conf_mode(int argc, char *argv[])
>>   static void conf_print(const struct ctx *c)
>>   {
>>   	char buf[INANY_ADDRSTRLEN];
>> +	const struct guest_addr *a;
>>   	int i;
>>   
>>   	if (c->fd_control_listen >= 0)
>> @@ -831,16 +840,19 @@ static void conf_print(const struct ctx *c)
>>   			     inet_ntop(AF_INET, &c->ip4.map_host_loopback,
>>   				       buf, sizeof(buf)));
>>   
>> -		if (!c->no_dhcp) {
>> +		a = fwd_get_addr(c, AF_INET, CONF_ADDR_ANY, 0);
>> +		if (a && !c->no_dhcp) {
>>   			uint32_t mask;
>> +			int plen = 0;
>>   
>> -			mask = htonl(0xffffffff << (32 - c->ip4.prefix_len));
>> +			inany_prefix_v4(&a->addr, a->prefix_len, &plen);
>> +			mask = IN4_MASK(plen);
>>   
>>   			info("DHCP:");
>>   			info("    assign: %s",
>> -			     inet_ntop(AF_INET, &c->ip4.addr, buf, sizeof(buf)));
>> +			     inany_ntop(&a->addr, buf, sizeof(buf)));
>>   			info("    mask: %s",
>> -			     inet_ntop(AF_INET, &mask,        buf, sizeof(buf)));
>> +			     inet_ntop(AF_INET, &mask, buf, sizeof(buf)));
>>   			info("    router: %s",
>>   			     inet_ntop(AF_INET, &c->ip4.guest_gw,
>>   				       buf, sizeof(buf)));
>> @@ -851,8 +863,8 @@ static void conf_print(const struct ctx *c)
>>   				break;
>>   			if (!i)
>>   				info("DNS:");
>> -			inet_ntop(AF_INET, &c->ip4.dns[i], buf, sizeof(buf));
>> -			info("    %s", buf);
>> +			info("    %s", inet_ntop(AF_INET, &c->ip4.dns[i],
>> +						 buf, sizeof(buf)));
>>   		}
>>   
>>   		for (i = 0; *c->dns_search[i].n; i++) {
>> @@ -877,13 +889,15 @@ static void conf_print(const struct ctx *c)
>>   		else
>>   			goto dns6;
>>   
>> -		info("    assign: %s",
>> -		     inet_ntop(AF_INET6, &c->ip6.addr, buf, sizeof(buf)));
>> +		a = fwd_get_addr(c, AF_INET6, CONF_ADDR_ANY,
>> +				 CONF_ADDR_LINKLOCAL);
>> +		if (a)
>> +			info("    assign: %s",
>> +			     inany_ntop(&a->addr, buf, sizeof(buf)));
>>   		info("    router: %s",
>>   		     inet_ntop(AF_INET6, &c->ip6.guest_gw, buf, sizeof(buf)));
>>   		info("    our link-local: %s",
>> -		     inet_ntop(AF_INET6, &c->ip6.our_tap_ll,
>> -			       buf, sizeof(buf)));
>> +		     inet_ntop(AF_INET6, &c->ip6.our_tap_ll, buf, sizeof(buf)));
>>   
>>   dns6:
>>   		for (i = 0; i < ARRAY_SIZE(c->ip6.dns); i++) {
>> @@ -891,8 +905,10 @@ dns6:
>>   			    break;
>>   			if (!i)
>>   				info("DNS:");
>> -			inet_ntop(AF_INET6, &c->ip6.dns[i], buf, sizeof(buf));
>> -			info("    %s", buf);
>> +			info("    %s",
>> +			     inet_ntop(AF_INET6, &c->ip6.dns[i],
>> +				       buf, sizeof(buf)));
>> +
>>   		}
>>   
>>   		for (i = 0; *c->dns_search[i].n; i++) {
>> @@ -1580,21 +1596,19 @@ void conf(struct ctx *c, int argc, char **argv)
>>   			    IN6_IS_ADDR_V4COMPAT(&addr.a6))
>>   				die("Invalid address: %s", optarg);
>>   
>> +			/* Legacy behaviour: replace existing address if any */
>> +			fwd_set_addr(c, &addr, CONF_ADDR_USER, prefix_len);
>>   			if (inany_v4(&addr)) {
>> -				c->ip4.addr = *inany_v4(&addr);
>> -				c->ip4.prefix_len = prefix_len - 96;
>> +				c->ip4.no_copy_addrs = true;
>>   				c->ip4.addr_fixed = true;
>> -				if (c->mode == MODE_PASTA)
>> -					c->ip4.no_copy_addrs = true;
>>   			} else {
>> -				c->ip6.addr = addr.a6;
>> +				c->ip6.no_copy_addrs = true;
>>   				c->ip6.addr_fixed = true;
>> -				if (c->mode == MODE_PASTA)
>> -					c->ip6.no_copy_addrs = true;
>>   			}
>>   			break;
>>   		}
>>   		case 'n': {
>> +			struct guest_addr *a;
>>   			int plen;
>>   
>>   			if (addr_has_prefix_len)
>> @@ -1604,8 +1618,12 @@ void conf(struct ctx *c, int argc, char **argv)
>>   			if (plen < 0)
>>   				die("Invalid prefix length: %s", optarg);
>>   
>> -			prefix_len_from_opt = plen + 96;
>> -			c->ip4.prefix_len = plen;
>> +			prefix_len_from_opt = plen;
> 
> Two problems here.  First it will need a rebase, because I renamed
> prefix_len_from_opt to opt_n.  More importantly, you're changing the
> encoding of the variable from v6 style to v4-style.  Which is
> fine... except you don't also change the other place that it's used
> (where -n is parsed before -a).  TBH, if you want to change the
> encoding of this variable, I'd put it in a separate patch, so it
> doesn't get lost in this large one.
>

ok.


>> +
>> +			for_each_addr(a, c->addrs, c->addr_count, AF_INET) {
>> +				a->prefix_len = plen + 96;
>> +				break;
>> +			}
>>   			break;
>>   		}
>>   		case 'M':
>> @@ -1801,9 +1819,9 @@ void conf(struct ctx *c, int argc, char **argv)
>>   
>>   	nl_sock_init(c, false);
>>   	if (!v6_only && !c->splice_only)
>> -		c->ifi4 = conf_ip4(ifi4, &c->ip4);
>> +		c->ifi4 = conf_ip4(c, ifi4);
>>   	if (!v4_only && !c->splice_only)
>> -		c->ifi6 = conf_ip6(ifi6, &c->ip6);
>> +		c->ifi6 = conf_ip6(c, ifi6);
>>   
>>   	if (c->ifi4 && c->mtu < IPV4_MIN_MTU) {
>>   		warn("MTU %"PRIu16" is too small for IPv4 (minimum %u)",
>> @@ -1826,7 +1844,7 @@ void conf(struct ctx *c, int argc, char **argv)
>>   	if (!c->ifi4 && !v6_only) {
>>   		if (!c->splice_only) {
>>   			info("IPv4: no external interface as template, use local mode");
>> -			conf_ip4_local(&c->ip4);
>> +			conf_ip4_local(c);
>>   		}
>>   		c->ifi4 = -1;
>>   	}
>> @@ -1834,7 +1852,7 @@ void conf(struct ctx *c, int argc, char **argv)
>>   	if (!c->ifi6 && !v4_only) {
>>   		if (!c->splice_only) {
>>   			info("IPv6: no external interface as template, use local mode");
>> -			conf_ip6_local(&c->ip6);
>> +			conf_ip6_local(c);
>>   		}
>>   		c->ifi6 = -1;
>>   	}
>> @@ -1905,7 +1923,7 @@ 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 (!fwd_get_addr(c, AF_INET6, CONF_ADDR_ANY, 0)) {
>>   		c->no_dhcpv6 = 1;
>>   	}
>>   
>> diff --git a/dhcp.c b/dhcp.c
>> index 1ff8cba9..727485f7 100644
>> --- a/dhcp.c
>> +++ b/dhcp.c
>> @@ -303,6 +303,7 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len)
>>   int dhcp(const struct ctx *c, struct iov_tail *data)
>>   {
>>   	char macstr[ETH_ADDRSTRLEN];
>> +	const struct guest_addr *a;
>>   	size_t mlen, dlen, opt_len;
>>   	struct in_addr mask, dst;
>>   	struct ethhdr eh_storage;
>> @@ -313,8 +314,10 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
>>   	const struct udphdr *uh;
>>   	struct msg m_storage;
>>   	struct msg const *m;
>> +	struct in_addr addr;
>>   	struct msg reply;
>>   	unsigned int i;
>> +	int plen;
>>   
>>   	eh = IOV_REMOVE_HEADER(data, eh_storage);
>>   	iph = IOV_PEEK_HEADER(data, iph_storage);
>> @@ -344,6 +347,14 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
>>   	    m->op != BOOTREQUEST)
>>   		return -1;
>>   
>> +	a = fwd_get_addr(c, AF_INET, CONF_ADDR_USER, 0);
>> +	if (!a)
>> +		a = fwd_get_addr(c, AF_INET, CONF_ADDR_ANY, 0);
>> +	if (!a)
>> +		return -1;
>> +
>> +	addr = *inany_prefix_v4(&a->addr, a->prefix_len, &plen);
>> +
> 
> I think an assert that inany_prefix_v4() returns non-NULL is probably
> a good idea.  I doubt that static checkers will be able to reason that
> calling with AF_INET above means it must succeed here.

Same comment as above.

> 
>>   	reply.op		= BOOTREPLY;
>>   	reply.htype		= m->htype;
>>   	reply.hlen		= m->hlen;
>> @@ -352,7 +363,7 @@ 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		= addr;
>>   	reply.siaddr		= 0;
>>   	reply.giaddr		= m->giaddr;
>>   	memcpy(&reply.chaddr,	m->chaddr,	sizeof(reply.chaddr));
>> @@ -404,7 +415,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
>>   
>>   	info("    from %s", eth_ntop(m->chaddr, macstr, sizeof(macstr)));
>>   
>> -	mask.s_addr = htonl(0xffffffff << (32 - c->ip4.prefix_len));
>> +	mask.s_addr = IN4_MASK(plen);
>>   	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 +423,7 @@ 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 ((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;
>> @@ -471,7 +482,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
>>   	if (m->flags & FLAG_BROADCAST)
>>   		dst = in4addr_broadcast;
>>   	else
>> -		dst = c->ip4.addr;
>> +		dst = addr;
>>   
>>   	tap_udp4_send(c, c->ip4.our_tap_addr, 67, dst, 68, &reply, dlen);
>>   
>> diff --git a/dhcpv6.c b/dhcpv6.c
>> index 29c7e320..f64cbc24 100644
>> --- a/dhcpv6.c
>> +++ b/dhcpv6.c
>> @@ -318,7 +318,7 @@ static bool dhcpv6_opt(struct iov_tail *data, uint16_t type)
>>    *         false otherwise and @data is unmodified
>>    */
>>   static bool dhcpv6_ia_notonlink(struct iov_tail *data,
>> -				struct in6_addr *la)
>> +				const struct in6_addr *la)
>>   {
>>   	int ia_types[2] = { OPT_IA_NA, OPT_IA_TA };
>>   	struct opt_ia_addr opt_addr_storage;
>> @@ -567,6 +567,7 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
>>   	struct opt_hdr client_id_storage;
>>   	/* cppcheck-suppress [variableScope,unmatchedSuppression] */
>>   	struct opt_ia_na ia_storage;
>> +	const struct guest_addr *a;
>>   	const struct in6_addr *src;
>>   	struct msg_hdr mh_storage;
>>   	const struct msg_hdr *mh;
>> @@ -574,6 +575,8 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
>>   	const struct udphdr *uh;
>>   	size_t mlen, n;
>>   
>> +	a = fwd_get_addr(c, AF_INET6, 0, CONF_ADDR_LINKLOCAL);
>> +
>>   	uh = IOV_REMOVE_HEADER(data, uh_storage);
>>   	if (!uh)
>>   		return -1;
>> @@ -627,7 +630,7 @@ 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 (a && dhcpv6_ia_notonlink(data, &a->addr.a6)) {
>>   
>>   			dhcpv6_send_ia_notonlink(c, saddr, data,
>>   						 &client_id_base,
>> @@ -682,7 +685,8 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
>>   	resp.hdr.xid = mh->xid;
>>   
>>   	tap_udp6_send(c, src, 547, saddr, 546, mh->xid, &resp, n);
>> -	c->ip6.addr_seen = c->ip6.addr;
>> +	if (a)
>> +		c->ip6.addr_seen = a->addr.a6;
>>   
>>   	return 1;
>>   }
>> @@ -694,6 +698,7 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
>>   void dhcpv6_init(const struct ctx *c)
>>   {
>>   	time_t y2k = 946684800; /* Epoch to 2000-01-01T00:00:00Z, no mktime() */
>> +	const struct guest_addr *a;
>>   	uint32_t duid_time;
>>   
>>   	duid_time = htonl(difftime(time(NULL), y2k));
>> @@ -706,5 +711,7 @@ 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;
>> +	a = fwd_get_addr(c, AF_INET6, 0, CONF_ADDR_LINKLOCAL);
>> +	if (a)
>> +		resp.ia_addr.addr = a->addr.a6;
>>   }
>> diff --git a/fwd.c b/fwd.c
>> index 042158cf..f2ca34c2 100644
>> --- a/fwd.c
>> +++ b/fwd.c
>> @@ -243,6 +243,61 @@ void fwd_neigh_table_init(const struct ctx *c)
>>   		fwd_neigh_table_update(c, &mga, c->our_tap_mac, true);
>>   }
>>   
>> +/**
>> + * fwd_set_addr() - Add or update an address in the unified address array
>> + * @c:		Execution context
>> + * @addr:	Address to add (IPv4-mapped or IPv6)
>> + * @flags:	CONF_ADDR_* flags for this address
>> + * @prefix_len:	Prefix length in IPv6 format (96-128 for IPv4-mapped)
>> + *
>> + * Find the first existing entry of the same address family and
>> + * overwrite it, or create a new one if none exists
>> + */
>> +void fwd_set_addr(struct ctx *c, const union inany_addr *addr,
>> +		  uint8_t flags, int prefix_len)
>> +{
>> +	struct guest_addr *a;
>> +
>> +	for_each_addr(a, c->addrs, c->addr_count, inany_af(addr)) {
>> +		goto found;
>> +	}
>> +
>> +	if (c->addr_count >= MAX_GUEST_ADDRS)
>> +		return;
>> +
>> +	a = &c->addrs[c->addr_count++];
>> +
>> +found:
>> +	a->addr = *addr;
>> +	a->prefix_len = prefix_len;
>> +	a->flags = flags;
>> +}
>> +
>> +/**
>> + * fwd_get_addr() - Get guest address entry matching criteria
>> + * @c:		Execution context
>> + * @af:		Address family (AF_INET, AF_INET6, or AF_UNSPEC for any)
>> + * @incl:	Required flags (any-match), CONF_ADDR_ANY for any
>> + * @excl:	Flags that must not be present
>> + *
>> + * Return: first address entry matching criteria, or NULL
>> + */
>> +const struct guest_addr *fwd_get_addr(const struct ctx *c, sa_family_t af,
>> +				      uint8_t incl, uint8_t excl)
>> +{
>> +	const struct guest_addr *a;
>> +
>> +	for_each_addr(a, c->addrs, c->addr_count, af) {
>> +		if (!(a->flags & incl))
>> +			continue;
>> +		if (a->flags & excl)
>> +			continue;
>> +		return a;
>> +	}
>> +
>> +	return NULL;
>> +}
>> +
>>   /* Forwarding table storage, generally accessed via pointers in struct ctx */
>>   static struct fwd_table fwd_in;
>>   static struct fwd_table fwd_out;
>> @@ -794,8 +849,10 @@ static bool is_dns_flow(uint8_t proto, const struct flowside *ini)
>>    *         translation, false otherwise
>>    */
>>   static bool fwd_guest_accessible4(const struct ctx *c,
>> -				    const struct in_addr *addr)
>> +				  const struct in_addr *addr)
>>   {
>> +	const struct guest_addr *a;
>> +
>>   	if (IN4_IS_ADDR_LOOPBACK(addr))
>>   		return false;
>>   
>> @@ -810,7 +867,8 @@ 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) ||
>> +	a = fwd_get_addr(c, AF_INET, CONF_ADDR_ANY, 0);
>> +	if ((a && IN4_ARE_ADDR_EQUAL(addr, inany_v4(&a->addr))) ||
>>   	    IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr_seen))
>>   		return false;
>>   
>> @@ -828,10 +886,13 @@ static bool fwd_guest_accessible4(const struct ctx *c,
>>   static bool fwd_guest_accessible6(const struct ctx *c,
>>   				  const struct in6_addr *addr)
>>   {
>> +	const struct guest_addr *a;
>> +
>>   	if (IN6_IS_ADDR_LOOPBACK(addr))
>>   		return false;
>>   
>> -	if (IN6_ARE_ADDR_EQUAL(addr, &c->ip6.addr))
>> +	a = fwd_get_addr(c, AF_INET6, CONF_ADDR_ANY, 0);
>> +	if (a && IN6_ARE_ADDR_EQUAL(addr, &a->addr.a6))
>>   		return false;
>>   
>>   	/* For IPv6, addr_seen starts unspecified, because we don't know what LL
>> @@ -876,16 +937,21 @@ static bool fwd_guest_accessible(const struct ctx *c,
>>   static void nat_outbound(const struct ctx *c, const union inany_addr *addr,
>>   			 union inany_addr *translated)
>>   {
>> -	if (inany_equals4(addr, &c->ip4.map_host_loopback))
>> +	const struct guest_addr *ga;
>> +
>> +	if (inany_equals4(addr, &c->ip4.map_host_loopback)) {
>>   		*translated = inany_loopback4;
>> -	else if (inany_equals6(addr, &c->ip6.map_host_loopback))
>> +	} 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
>> +	} else if (inany_equals4(addr, &c->ip4.map_guest_addr)) {
>> +		ga = fwd_get_addr(c, AF_INET, CONF_ADDR_ANY, 0);
>> +		*translated = ga ? ga->addr : inany_any4;
>> +	} else if (inany_equals6(addr, &c->ip6.map_guest_addr)) {
>> +		ga = fwd_get_addr(c, AF_INET6, CONF_ADDR_ANY, 0);
>> +		translated->a6 = ga ? ga->addr.a6 : in6addr_any;
>> +	} else {
>>   		*translated = *addr;
>> +	}
>>   }
>>   
>>   /**
>> @@ -990,16 +1056,23 @@ bool nat_inbound(const struct ctx *c, const union inany_addr *addr,
>>   	} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.map_host_loopback) &&
>>   		   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)) {
>> -		*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)) {
>> -		translated->a6 = c->ip6.map_guest_addr;
>> -	} else if (fwd_guest_accessible(c, addr)) {
>> -		*translated = *addr;
>>   	} else {
>> -		return false;
>> +		const struct guest_addr *ga4, *ga6;
>> +
>> +		ga4 = fwd_get_addr(c, AF_INET, CONF_ADDR_ANY, 0);
>> +		ga6 = fwd_get_addr(c, AF_INET6, CONF_ADDR_ANY, 0);
>> +
>> +		if (!IN4_IS_ADDR_UNSPECIFIED(&c->ip4.map_guest_addr) &&
>> +		    ga4 && inany_equals(addr, &ga4->addr)) {
>> +			*translated = inany_from_v4(c->ip4.map_guest_addr);
>> +		} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.map_guest_addr) &&
>> +			   ga6 && inany_equals(addr, &ga6->addr)) {
>> +			translated->a6 = c->ip6.map_guest_addr;
>> +		} else if (fwd_guest_accessible(c, addr)) {
>> +			*translated = *addr;
>> +		} else {
>> +			return false;
>> +		}
>>   	}
>>   
>>   	return true;
>> diff --git a/fwd.h b/fwd.h
>> index b60697d9..d677440f 100644
>> --- a/fwd.h
>> +++ b/fwd.h
>> @@ -79,5 +79,9 @@ void fwd_neigh_table_free(const struct ctx *c,
>>   void fwd_neigh_mac_get(const struct ctx *c, const union inany_addr *addr,
>>   		       uint8_t *mac);
>>   void fwd_neigh_table_init(const struct ctx *c);
>> +void fwd_set_addr(struct ctx *c, const union inany_addr *addr,
>> +		  uint8_t flags, int prefix_len);
>> +const struct guest_addr *fwd_get_addr(const struct ctx *c, sa_family_t af,
>> +				      uint8_t incl, uint8_t excl);
>>   
>>   #endif /* FWD_H */
>> diff --git a/inany.h b/inany.h
>> index 6bf3ecaa..95756eb8 100644
>> --- a/inany.h
>> +++ b/inany.h
>> @@ -102,6 +102,34 @@ static inline struct in_addr *inany_v4(const union inany_addr *addr)
>>   	return (struct in_addr *)&addr->v4mapped.a4;
>>   }
>>   
>> +/** inany_prefix_v4() - Extract IPv4 address and prefix length from inany
>> + * @addr:	IPv4 (as mapped) or IPv6 address
>> + * @prefix_len:	Prefix length in IPv6 format (96-128 for IPv4)
>> + * @v4_plen:	Set to IPv4 prefix length (0-32) on success
>> + *
>> + * Return: IPv4 address if @addr is IPv4, NULL otherwise
>> + */
>> +static inline struct in_addr *inany_prefix_v4(const union inany_addr *addr,
>> +					      int prefix_len, int *v4_plen)
>> +{
>> +	struct in_addr *v4 = inany_v4(addr);
>> +
>> +	if (!v4)
>> +		return NULL;
>> +	*v4_plen = prefix_len - 96;
>> +	return v4;
>> +}
>> +
>> +/** inany_af - Get address family of IPv[46] address
>> + * @addr:	IPv4 or IPv6 address
>> + *
>> + * Return: AF_INET for IPv4, AF_INET6 for IPv6
>> + */
>> +static inline sa_family_t inany_af(const union inany_addr *addr)
>> +{
>> +	return inany_v4(addr) ? AF_INET : AF_INET6;
>> +}
>> +
>>   /** inany_default_prefix_len() - Get default prefix length for address
>>    * @addr:	IPv4 or iPv6 address
>>    *
>> diff --git a/ip.h b/ip.h
>> index aab9b86a..ac93c543 100644
>> --- a/ip.h
>> +++ b/ip.h
>> @@ -19,6 +19,8 @@
>>   	(ntohl(((struct in_addr *)(a))->s_addr) >> IN_CLASSA_NSHIFT == IN_LOOPBACKNET)
>>   #define IN4_IS_ADDR_MULTICAST(a) \
>>   	(IN_MULTICAST(ntohl(((struct in_addr *)(a))->s_addr)))
>> +#define IN4_MASK(prefix) \
>> +	((prefix) <= 0 ? 0 : htonl(0xffffffff << (32 - (prefix))))
>>   #define IN4_ARE_ADDR_EQUAL(a, b) \
>>   	(((struct in_addr *)(a))->s_addr == ((struct in_addr *)b)->s_addr)
>>   #define IN4ADDR_LOOPBACK_INIT \
>> diff --git a/ndp.c b/ndp.c
>> index 1f2bcb0c..a6a79055 100644
>> --- a/ndp.c
>> +++ b/ndp.c
>> @@ -257,7 +257,6 @@ static void ndp_ra(const struct ctx *c, const struct in6_addr *dst)
>>   			.valid_lifetime		= ~0U,
>>   			.pref_lifetime		= ~0U,
>>   		},
>> -		.prefix = c->ip6.addr,
>>   		.source_ll = {
>>   			.header = {
>>   				.type		= OPT_SRC_L2_ADDR,
>> @@ -265,8 +264,15 @@ static void ndp_ra(const struct ctx *c, const struct in6_addr *dst)
>>   			},
>>   		},
>>   	};
>> +	const struct guest_addr *a;
>>   	unsigned char *ptr = NULL;
>>   
>> +	a = fwd_get_addr(c, AF_INET6, CONF_ADDR_ANY, 0);
> 
> Don't you need to exclude link local addresses?

Yes.

> 
>> +	if (!a)
>> +		return;
>> +
>> +	ra.prefix = a->addr.a6;
>> +
>>   	ptr = &ra.var[0];
>>   
>>   	if (c->mtu) {
>> @@ -460,6 +466,7 @@ first:
>>    */
>>   void ndp_send_init_req(const struct ctx *c)
>>   {
>> +	const struct guest_addr *a;
>>   	struct ndp_ns ns = {
>>   		.ih = {
>>   			.icmp6_type		= NS,
>> @@ -468,8 +475,14 @@ void ndp_send_init_req(const struct ctx *c)
>>   			.icmp6_solicited	= 0, /* Reserved */
>>   			.icmp6_override		= 0, /* Reserved */
>>   		},
>> -		.target_addr = c->ip6.addr
>> +		.target_addr = IN6ADDR_ANY_INIT
>>   	};
>> +
>> +	a = fwd_get_addr(c, AF_INET6, CONF_ADDR_ANY, 0);
> 
> Again, don't you need to exclude linklocal, as the old code implicitly did?
> 
>> +	if (!a)
>> +		return;
>> +
>> +	ns.target_addr = a->addr.a6;
>>   	debug("Sending initial NDP NS request for guest MAC address");
>> -	ndp_send(c, &c->ip6.addr, &ns, sizeof(ns));
>> +	ndp_send(c, &a->addr.a6, &ns, sizeof(ns));
>>   }
>> diff --git a/passt.h b/passt.h
>> index 16506dcd..cafa35ea 100644
>> --- a/passt.h
>> +++ b/passt.h
>> @@ -64,11 +64,29 @@ enum passt_modes {
>>   	MODE_VU,
>>   };
>>   
>> +/* Maximum number of addresses in context address array */
>> +#define MAX_GUEST_ADDRS		32
>> +
>> +/**
>> + * struct guest_addr - 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:	CONF_ADDR_* flags
>> + */
>> +struct guest_addr {
>> +	union inany_addr addr;
>> +	uint8_t prefix_len;
>> +	uint8_t flags;
>> +#define CONF_ADDR_USER		BIT(0)		/* User set via -a */
>> +#define CONF_ADDR_HOST		BIT(1)		/* From host interface */
>> +#define CONF_ADDR_GENERATED	BIT(2)		/* Generated by PASST/PASTA */
>> +#define CONF_ADDR_LINKLOCAL	BIT(3)		/* Link-local address */
>> +#define CONF_ADDR_ANY		0xff		/* Match any flag */
> 
> In general I like CONF_ADDR_ANY instead of 0 being special-cased.  But
> with LINKLOCAL in the mix it doesn't quite work.  ANY meaning "USER or
> HOST or GENERATED" makes sense.  ANY meaning "USER or HOST or
> GENERATED or LINKLOCAL" is nonsense.  I suggest you move LINKLOCAL
> into a different field, as Stefano has suggested to handle this (maybe
> "provenance" for USER/HOST/GENERATED and "flags" for LINKLOCAL?).  Or
> you could remove the LINKLOCAL flag from the structure entirely: the
> information is already present in the address itself.

I was hoping to postpone this to a commit after this series, but I see 
your point. I can try with a 'scope' field, as suggested earlier, or 
just skip it altogheter and using an is_link_local() function.

> 
>> +};
>> +
>>   /**
>>    * 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
>> @@ -87,9 +105,7 @@ enum passt_modes {
>>    */
>>   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;
>> @@ -110,7 +126,6 @@ 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
>> @@ -131,7 +146,6 @@ struct ip4_ctx {
>>    */
>>   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;
>> @@ -190,6 +204,8 @@ struct ip6_ctx {
>>    * @fqdn:		Guest FQDN
>>    * @ifi6:		Template interface for IPv6, -1: none, 0: IPv6 disabled
>>    * @ip6:		IPv6 configuration
>> + * @addrs:		Unified address array for both IPv4 (mapped) and IPv6
>> + * @addr_count:		Number of active entries in @addrs array
>>    * @pasta_ifn:		Name of namespace interface for pasta
>>    * @pasta_ifi:		Index of namespace interface for pasta
>>    * @pasta_conf_ns:	Configure namespace after creating it
>> @@ -273,6 +289,9 @@ struct ctx {
>>   	int ifi6;
>>   	struct ip6_ctx ip6;
>>   
>> +	struct guest_addr addrs[MAX_GUEST_ADDRS];
>> +	int addr_count;
>> +
>>   	char pasta_ifn[IF_NAMESIZE];
>>   	unsigned int pasta_ifi;
>>   	int pasta_conf_ns;
>> @@ -317,6 +336,41 @@ struct ctx {
>>   
>>   extern struct ctx passt_ctx;
>>   
>> +/**
>> + * next_addr_idx_() - Find next address index matching family filter
>> + * @addrs:	Array of guest addresses
>> + * @count:	Number of addresses in array
>> + * @i:		Starting index
>> + * @af:		Address family filter: AF_INET, AF_INET6, or AF_UNSPEC for all
>> + *
>> + * Return: next matching index, or count if none found
>> + */
>> +static inline int next_addr_idx_(const struct guest_addr *addrs, int count,
>> +				 int i, sa_family_t af)
>> +{
>> +	for (; i < count; i++) {
>> +		sa_family_t entry_af;
>> +
>> +		entry_af = inany_v4(&addrs[i].addr) ? AF_INET : AF_INET6;
> 
> You can reuse inany_af() here.
Ok.

> 
>> +
>> +		if (af == AF_UNSPEC || af == entry_af)
>> +			return i;
>> +	}
>> +	return i;
>> +}
>> +
>> +/**
>> + * for_each_addr() - Iterate over addresses in array
>> + * @a:		Pointer variable for current entry (struct guest_addr *)
>> + * @addrs:	Array of guest addresses (e.g., c->addrs)
>> + * @count:	Number of addresses (e.g., c->addr_count)
>> + * @af:		Address family filter: AF_INET, AF_INET6, or 0 for all
>> + */
>> +#define for_each_addr(a, addrs, count, af)				\
>> +	for (int i_ = next_addr_idx_((addrs), (count), 0, (af));	\
>> +	     i_ < (count) && ((a) = &(addrs)[i_], true);		\
>> +	     i_ = next_addr_idx_((addrs), (count), i_ + 1, (af)))
>> +
>>   void proto_update_l2_buf(const unsigned char *eth_d);
>>   
>>   #endif /* PASST_H */
>> diff --git a/pasta.c b/pasta.c
>> index 4e7ee542..9ef3ac00 100644
>> --- a/pasta.c
>> +++ b/pasta.c
>> @@ -330,6 +330,8 @@ void pasta_ns_conf(struct ctx *c)
>>   
>>   	if (c->pasta_conf_ns) {
>>   		unsigned int flags = IFF_UP;
>> +		const struct guest_addr *a;
>> +		int plen = 0;
>>   
>>   		if (c->mtu)
>>   			nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
>> @@ -341,10 +343,17 @@ void pasta_ns_conf(struct ctx *c)
>>   
>>   		if (c->ifi4) {
> 
> Nit: I think you can reduce the very deep nesting here, by moving the
> fwd_get_addr() and changing the if below to..

This is already done in a later patch, by introducing two subfuntions.
However, this has caused lot of trouble at each rebase, so I think I 
will move it to a separate, standalone patch before this series.

/jon


> 
> 
>>   			if (c->ip4.no_copy_addrs) {
> 
> .. if (no_copy_addrs && a && (v4 = inany_v4(a...)))
> 
> It means the address search will happen even when we don't need it,
> but it's once per startup, so we don't really care.
> 
>> -				rc = nl_addr_set(nl_sock_ns, c->pasta_ifi,
>> -						 AF_INET,
>> -						 &c->ip4.addr,
>> -						 c->ip4.prefix_len);
>> +				a = fwd_get_addr(c, AF_INET, CONF_ADDR_ANY, 0);
>> +				if (a) {
>> +					const struct in_addr *v4;
>> +
>> +					v4 = inany_prefix_v4(&a->addr,
>> +							     a->prefix_len,
>> +							     &plen);
>> +					rc = nl_addr_set(nl_sock_ns,
>> +							 c->pasta_ifi, AF_INET,
>> +							 v4, plen);
>> +				}
> 
> 
> 
>>   			} else {
>>   				rc = nl_addr_dup(nl_sock, c->ifi4,
>>   						 nl_sock_ns, c->pasta_ifi,
>> @@ -397,11 +406,12 @@ ipv4_done:
>>   					  0, IFF_NOARP);
>>   
>>   			if (c->ip6.no_copy_addrs) {
> 
> I think a similar transformation should be possible here.
> 
> 
>> -				if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr)) {
>> +				a = fwd_get_addr(c, AF_INET6, CONF_ADDR_ANY, 0);
>> +				if (a)
>>   					rc = nl_addr_set(nl_sock_ns,
>> -							 c->pasta_ifi, AF_INET6,
>> -							 &c->ip6.addr, 64);
>> -				}
>> +							 c->pasta_ifi,
>> +							 AF_INET6, &a->addr.a6,
>> +							 a->prefix_len);
>>   			} else {
>>   				rc = nl_addr_dup(nl_sock, c->ifi6,
>>   						 nl_sock_ns, c->pasta_ifi,
>> diff --git a/tap.c b/tap.c
>> index d4189617..12630f58 100644
>> --- a/tap.c
>> +++ b/tap.c
>> @@ -1005,8 +1005,12 @@ resume:
>>   				c->ip6.addr_seen = *saddr;
>>   			}
>>   
>> -			if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr))
>> -				c->ip6.addr = *saddr;
>> +			if (!c->ip6.addr_fixed &&
> 
> This addr_fixed check is unnnecessary - addr_fixed can only be set if
> an address is specified, so the fwd_get_addr() below can't fail.
> 
>> +			    !fwd_get_addr(c, AF_INET6, CONF_ADDR_ANY, 0)) {
>> +				union inany_addr addr = { .a6 = *saddr };
>> +
>> +				fwd_set_addr(c, &addr, CONF_ADDR_LINKLOCAL, 64);
>> +			}
>>   		} else if (!c->ip6.addr_fixed &&
>>   			   !IN6_IS_ADDR_UNSPECIFIED(saddr)) {
>>   			c->ip6.addr_seen = *saddr;
>> -- 
>> 2.52.0
>>
>