Re: [PATCH v6 06/13] netlink, conf: Read all addresses from template interface at startup

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

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On Sat, Mar 21, 2026 at 08:43:26PM -0400, Jon Maloy wrote:
> Add nl_addr_get_all() to read all addresses from the template interface
> into c->addrs[] array, rather than just selecting the "best" one.
> 
> This allows multi-address configurations where the template interface
> has multiple IPv4 or IPv6 addresses assigned to it, all of which
> will now be copied to the guest namespace when using --config-net.
> 
> For IPv6, the function also captures the link-local address into
> c->ip6.our_tap_ll as a side effect.
> 
> Update conf_ip4() and conf_ip6() to use nl_addr_get_all() when no
> user-specified addresses are present.
> 
> Signed-off-by: Jon Maloy <jmaloy@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  conf.c    | 51 ++++++++++++++++++++++++++++-----------------------
>  netlink.c | 53 +++++++++++++++++++++++++++++------------------------
>  netlink.h |  3 +--
>  3 files changed, 58 insertions(+), 49 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index 95f09cb..70435d3 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -736,6 +736,7 @@ static int conf_ip4_prefix(const char *arg)
>  static unsigned int conf_ip4(struct ctx *c, unsigned int ifi)
>  {
>  	struct ip4_ctx *ip4 = &c->ip4;
> +	const struct guest_addr *a;
>  
>  	if (!ifi)
>  		ifi = nl_get_ext_if(nl_sock, AF_INET);
> @@ -755,24 +756,24 @@ static unsigned int conf_ip4(struct ctx *c, unsigned int ifi)
>  		}
>  	}
>  
> -	if (!fwd_get_addr(c, AF_INET, 0, 0)) {
> -		struct in_addr addr;
> -		int prefix_len;
> -		int rc = nl_addr_get(nl_sock, ifi, AF_INET,
> -				     &addr, &prefix_len, NULL);
> +	a = fwd_get_addr(c, AF_INET, CONF_ADDR_USER, 0);
> +	if (!a) {
> +		int rc = nl_addr_get_all(c, nl_sock, ifi, AF_INET);
> +
>  		if (rc < 0) {
> -			debug("Couldn't discover IPv4 address: %s",
> +			debug("Couldn't discover IPv4 addresses: %s",
>  			      strerror_(-rc));
>  			return 0;
>  		}
> -		if (IN4_IS_ADDR_UNSPECIFIED(&addr))
> +		if (!rc || !fwd_get_addr(c, AF_INET, 0, 0))
>  			return 0;
>  
> -		fwd_set_addr(c, &inany_from_v4(addr), CONF_ADDR_HOST,
> -			     prefix_len + 96);
> -		ip4->addr_seen = addr;
> +		a = fwd_get_addr(c, AF_INET, CONF_ADDR_HOST, 0);
>  	}
>  
> +	if (a)
> +		ip4->addr_seen = *inany_v4(&a->addr);
> +
>  	ip4->our_tap_addr = ip4->guest_gw;
>  
>  	return ifi;
> @@ -803,10 +804,8 @@ static void conf_ip4_local(struct ctx *c)
>   */
>  static unsigned int conf_ip6(struct ctx *c, unsigned int ifi)
>  {
> -	const struct guest_addr *a = fwd_get_addr(c, AF_INET6, 0, 0);
>  	struct ip6_ctx *ip6 = &c->ip6;
> -	union inany_addr addr;
> -	int prefix_len = 0;
> +	const struct guest_addr *a;
>  	int rc;
>  
>  	if (!ifi)
> @@ -826,20 +825,26 @@ static unsigned int conf_ip6(struct ctx *c, unsigned int ifi)
>  		}
>  	}
>  
> -	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;
> -	}
> -
> +	a = fwd_get_addr(c, AF_INET6, CONF_ADDR_USER, 0);
>  	if (!a) {
> -		fwd_set_addr(c, &addr, CONF_ADDR_HOST, prefix_len);
> -		ip6->addr_seen = addr.a6;
> +		rc = nl_addr_get_all(c, nl_sock, ifi, AF_INET6);
> +		if (rc < 0) {
> +			debug("Couldn't discover IPv6 addresses: %s",
> +			      strerror_(-rc));
> +			return 0;
> +		}
> +		a = fwd_get_addr(c, AF_INET6, CONF_ADDR_HOST, 0);
>  	} else {
> -		ip6->addr_seen = a->addr.a6;
> +		rc = nl_addr_get_ll(nl_sock, ifi, &ip6->our_tap_ll);
> +		if (rc < 0) {
> +			debug("Couldn't get link-local address: %s",
> +			      strerror_(-rc));
> +		}
>  	}
>  
> +	if (a)
> +		ip6->addr_seen = a->addr.a6;
> +
>  	if (IN6_IS_ADDR_LINKLOCAL(&ip6->guest_gw))
>  		ip6->our_tap_ll = ip6->guest_gw;
>  
> diff --git a/netlink.c b/netlink.c
> index e07b47f..2727eec 100644
> --- a/netlink.c
> +++ b/netlink.c
> @@ -747,20 +747,20 @@ int nl_addr_set_ll_nodad(int s, unsigned int ifi)
>  }
>  
>  /**
> - * nl_addr_get() - Get most specific global address, given interface and family
> + * nl_addr_get_all() - Get all addresses for a given interface into ctx
> + * @c:		Execution context
>   * @s:		Netlink socket
> - * @ifi:	Interface index in outer network namespace
> - * @af:		Address family
> - * @addr:	Global address to fill
> - * @prefix_len:	Mask or prefix length, to fill
> - * @addr_l:	Link-scoped address to fill (for IPv6)
> + * @ifi:	Interface index
> + * @af:		Address family (AF_INET or AF_INET6)
>   *
> - * Return: 0 on success, negative error code on failure
> + * Populates c->addrs[] with all non-deprecated addresses from the interface.
> + * For IPv6, also captures link-local address in c->ip6.our_tap_ll.
> + * Skips link-local addresses for the main array (kernel auto-configures them).
> + *
> + * Return: number of addresses added, or negative error code on failure
>   */
> -int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
> -		void *addr, int *prefix_len, void *addr_l)
> +int nl_addr_get_all(struct ctx *c, int s, unsigned int ifi, sa_family_t af)
>  {
> -	uint8_t prefix_max = 0, prefix_max_ll = 0;
>  	struct req_t {
>  		struct nlmsghdr nlh;
>  		struct ifaddrmsg ifa;
> @@ -771,6 +771,7 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
>  	struct nlmsghdr *nh;
>  	char buf[NLBUFSIZ];
>  	ssize_t status;
> +	int count = 0;
>  	uint32_t seq;
>  
>  	seq = nl_send(s, &req, RTM_GETADDR, NLM_F_DUMP, sizeof(req));
> @@ -784,27 +785,31 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
>  
>  		for (rta = IFA_RTA(ifa), na = IFA_PAYLOAD(nh); RTA_OK(rta, na);
>  		     rta = RTA_NEXT(rta, na)) {
> -			if ((af == AF_INET  && rta->rta_type != IFA_LOCAL) ||
> -			    (af == AF_INET6 && rta->rta_type != IFA_ADDRESS))
> -				continue;
> +			union inany_addr addr;
> +			int prefix_len;
>  
> -			if (ifa->ifa_prefixlen > prefix_max && addr &&
> -			    (af == AF_INET || ifa->ifa_scope < RT_SCOPE_LINK)) {
> -				memcpy(addr, RTA_DATA(rta), RTA_PAYLOAD(rta));
> +			if (af == AF_INET && rta->rta_type != IFA_LOCAL)
> +				continue;
> +			if (af == AF_INET6 && rta->rta_type != IFA_ADDRESS)
> +				continue;
>  
> -				prefix_max = *prefix_len = ifa->ifa_prefixlen;
> +			if (af == AF_INET6 &&
> +			    ifa->ifa_scope == RT_SCOPE_LINK) {
> +				memcpy(&c->ip6.our_tap_ll, RTA_DATA(rta),
> +				       sizeof(c->ip6.our_tap_ll));
> +				continue;
>  			}
>  
> -			if (addr_l &&
> -			    af == AF_INET6 && ifa->ifa_scope == RT_SCOPE_LINK &&
> -			    ifa->ifa_prefixlen > prefix_max_ll) {
> -				memcpy(addr_l, RTA_DATA(rta), RTA_PAYLOAD(rta));
> +			inany_from_af(&addr, af, RTA_DATA(rta));
> +			prefix_len = ifa->ifa_prefixlen +
> +				     (af == AF_INET ? 96 : 0);
>  
> -				prefix_max_ll = ifa->ifa_prefixlen;
> -			}
> +			fwd_set_addr(c, &addr, CONF_ADDR_HOST, prefix_len);
> +			count++;
>  		}
>  	}
> -	return status;
> +
> +	return status < 0 ? status : count;
>  }
>  
>  /**
> diff --git a/netlink.h b/netlink.h
> index b22f485..3af6d58 100644
> --- a/netlink.h
> +++ b/netlink.h
> @@ -19,8 +19,7 @@ int nl_route_get_def(int s, unsigned int ifi, sa_family_t af, void *gw);
>  int nl_route_set_def(int s, unsigned int ifi, sa_family_t af, const void *gw);
>  int nl_route_dup(int s_src, unsigned int ifi_src,
>  		 int s_dst, unsigned int ifi_dst, sa_family_t af);
> -int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
> -		void *addr, int *prefix_len, void *addr_l);
> +int nl_addr_get_all(struct ctx *c, int s, unsigned int ifi, sa_family_t af);
>  bool nl_neigh_mac_get(int s, const union inany_addr *addr, int ifi,
>  		      unsigned char *mac);
>  int nl_addr_set(int s, unsigned int ifi, sa_family_t af,
> -- 
> 2.52.0
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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