[PATCH net-next 2/3] net: ipv6: report multicast group user count

[Yuyang Huang <sigefriedhyy@gmail.com>]

The previous patch added IFA_MC_USERS and emits it for IPv4 multicast
groups. Add the same snapshot attribute to IPv6 RTM_GETMULTICAST
replies and entry-lifecycle notifications, carrying
ifmcaddr6::mca_users.

This makes the multicast rtnetlink ABI symmetric across IPv4 and IPv6
and gives userspace the same user count that /proc/net/igmp6 exposes.

Signed-off-by: Yuyang Huang <sigefriedhyy@gmail.com>
---
 net/ipv6/addrconf.c | 1 +
 net/ipv6/mcast.c    | 1 +
 2 files changed, 2 insertions(+)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index cbe681de3818..f1fe9ede1edb 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5264,6 +5264,7 @@ int inet6_fill_ifmcaddr(struct sk_buff *skb,
 
 	put_ifaddrmsg(nlh, 128, IFA_F_PERMANENT, scope, ifindex);
 	if (nla_put_in6_addr(skb, IFA_MULTICAST, &ifmca->mca_addr) < 0 ||
+	    nla_put_u32(skb, IFA_MC_USERS, READ_ONCE(ifmca->mca_users)) < 0 ||
 	    put_cacheinfo(skb, ifmca->mca_cstamp, READ_ONCE(ifmca->mca_tstamp),
 			  INFINITY_LIFE_TIME, INFINITY_LIFE_TIME) < 0) {
 		nlmsg_cancel(skb, nlh);
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 04b811b3be97..774f4c72a6fa 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -908,6 +908,7 @@ static void inet6_ifmcaddr_notify(struct net_device *dev,
 
 	skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct ifaddrmsg)) +
 			nla_total_size(sizeof(struct in6_addr)) +
+			nla_total_size(sizeof(u32)) +
 			nla_total_size(sizeof(struct ifa_cacheinfo)),
 			GFP_KERNEL);
 	if (!skb)
-- 
2.43.0