netlink: add IPv6 anycast join/leave notifications

JIRA: https://issues.redhat.com/browse/RHEL-84540

commit 33d97a0
Author: Yuyang Huang <yuyanghuang@google.com>
Date:   Tue Jan 7 20:43:55 2025 +0900

    netlink: add IPv6 anycast join/leave notifications

    This change introduces a mechanism for notifying userspace
    applications about changes to IPv6 anycast addresses via netlink. It
    includes:

    * Addition and deletion of IPv6 anycast addresses are reported using
      RTM_NEWANYCAST and RTM_DELANYCAST.
    * A new netlink group (RTNLGRP_IPV6_ACADDR) for subscribing to these
      notifications.

    This enables user space applications(e.g. ip monitor) to efficiently
    track anycast addresses through netlink messages, improving metrics
    collection and system monitoring. It also unlocks the potential for
    advanced anycast management in user space, such as hardware offload
    control and fine grained network control.

    Cc: Maciej Żenczykowski <maze@google.com>
    Cc: Lorenzo Colitti <lorenzo@google.com>
    Signed-off-by: Yuyang Huang <yuyanghuang@google.com>
    Reviewed-by: David Ahern <dsahern@kernel.org>
    Link: https://patch.msgid.link/20250107114355.1766086-1-yuyanghuang@google.com
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

include/net/addrconf.h

@@ -546,4 +546,7 @@ int inet6_fill_ifmcaddr(struct sk_buff *skb,
 			const struct ifmcaddr6 *ifmca,
 			struct inet6_fill_args *args);
 
+int inet6_fill_ifacaddr(struct sk_buff *skb,
+			const struct ifacaddr6 *ifaca,
+			struct inet6_fill_args *args);
 #endif

include/uapi/linux/rtnetlink.h

@@ -100,7 +100,11 @@ enum {
 	RTM_GETMULTICAST,
 #define RTM_GETMULTICAST RTM_GETMULTICAST
 
-	RTM_GETANYCAST	= 62,
+	RTM_NEWANYCAST	= 60,
+#define RTM_NEWANYCAST RTM_NEWANYCAST
+	RTM_DELANYCAST,
+#define RTM_DELANYCAST RTM_DELANYCAST
+	RTM_GETANYCAST,
 #define RTM_GETANYCAST	RTM_GETANYCAST
 
 	RTM_NEWNEIGHTBL	= 64,
@@ -782,6 +786,8 @@ enum rtnetlink_groups {
 #define RTNLGRP_IPV4_MCADDR	RTNLGRP_IPV4_MCADDR
 	RTNLGRP_IPV6_MCADDR,
 #define RTNLGRP_IPV6_MCADDR	RTNLGRP_IPV6_MCADDR
+	RTNLGRP_IPV6_ACADDR,
+#define RTNLGRP_IPV6_ACADDR	RTNLGRP_IPV6_ACADDR
 	__RTNLGRP_MAX
 };
 #define RTNLGRP_MAX	(__RTNLGRP_MAX - 1)

net/ipv6/addrconf.c

@@ -5243,9 +5243,9 @@ int inet6_fill_ifmcaddr(struct sk_buff *skb,
 	return 0;
 }
 
-static int inet6_fill_ifacaddr(struct sk_buff *skb,
-			       const struct ifacaddr6 *ifaca,
-			       struct inet6_fill_args *args)
+int inet6_fill_ifacaddr(struct sk_buff *skb,
+			const struct ifacaddr6 *ifaca,
+			struct inet6_fill_args *args)
 {
 	struct net_device *dev = fib6_info_nh_dev(ifaca->aca_rt);
 	int ifindex = dev ? dev->ifindex : 1;

net/ipv6/anycast.c

@@ -278,6 +278,37 @@ static struct ifacaddr6 *aca_alloc(struct fib6_info *f6i,
 	return aca;
 }
 
+static void inet6_ifacaddr_notify(struct net_device *dev,
+				  const struct ifacaddr6 *ifaca, int event)
+{
+	struct inet6_fill_args fillargs = {
+		.event = event,
+		.netnsid = -1,
+	};
+	struct net *net = dev_net(dev);
+	struct sk_buff *skb;
+	int err = -ENOMEM;
+
+	skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct ifaddrmsg)) +
+			nla_total_size(sizeof(struct in6_addr)) +
+			nla_total_size(sizeof(struct ifa_cacheinfo)),
+			GFP_KERNEL);
+	if (!skb)
+		goto error;
+
+	err = inet6_fill_ifacaddr(skb, ifaca, &fillargs);
+	if (err < 0) {
+		pr_err("Failed to fill in anycast addresses (err %d)\n", err);
+		nlmsg_free(skb);
+		goto error;
+	}
+
+	rtnl_notify(skb, net, 0, RTNLGRP_IPV6_ACADDR, NULL, GFP_KERNEL);
+	return;
+error:
+	rtnl_set_sk_err(net, RTNLGRP_IPV6_ACADDR, err);
+}
+
 /*
  *	device anycast group inc (add if not found)
  */
@@ -333,6 +364,8 @@ int __ipv6_dev_ac_inc(struct inet6_dev *idev, const struct in6_addr *addr)
 
 	addrconf_join_solict(idev->dev, &aca->aca_addr);
 
+	inet6_ifacaddr_notify(idev->dev, aca, RTM_NEWANYCAST);
+
 	aca_put(aca);
 	return 0;
 out:
@@ -375,6 +408,8 @@ int __ipv6_dev_ac_dec(struct inet6_dev *idev, const struct in6_addr *addr)
 
 	ip6_del_rt(dev_net(idev->dev), aca->aca_rt, false);
 
+	inet6_ifacaddr_notify(idev->dev, aca, RTM_DELANYCAST);
+
 	aca_put(aca);
 	return 0;
 }