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

On Sat, 21 Mar 2026 20:43:26 -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 --- 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).

Skips IPv6 link-local addresses...

+ * + * 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,

I only reviewed up to 8/13, 7/13 looks good to me (minus comments from David), and I plan to finish reviewing the rest soon, but I thought I'd start sharing the comments I have so far, meanwhile. -- Stefano