[PATCH net-next 1/3] net: ipv4: report multicast group user count
From: Yuyang Huang <hidden>
Date: 2026-06-30 11:02:20
Also in:
linux-kselftest, lkml
Subsystem:
networking drivers, networking [general], networking [ipv4/ipv6], the rest, yaml netlink (ynl) · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds, Donald Hunter
RTM_GETMULTICAST has been part of the rtnetlink ABI for a long time and already reports IPv4 multicast group membership through IFA_MULTICAST and IFA_CACHEINFO. It does not report how many consumers hold each membership, so userspace still has to parse /proc/net/igmp to get the Users column. Add IFA_MC_USERS as a u32 attribute carrying ip_mc_list::users in RTM_GETMULTICAST replies and entry-lifecycle notifications. This gives iproute2 enough information to migrate the IPv4 part of "ip maddr show" from procfs parsing to rtnetlink. Signed-off-by: Yuyang Huang <redacted> --- Documentation/netlink/specs/rt-addr.yaml | 4 ++++ include/uapi/linux/if_addr.h | 1 + net/ipv4/igmp.c | 2 ++ 3 files changed, 7 insertions(+)
diff --git a/Documentation/netlink/specs/rt-addr.yaml b/Documentation/netlink/specs/rt-addr.yaml
index 163a106c41bb..0ecbd24c890c 100644
--- a/Documentation/netlink/specs/rt-addr.yaml
+++ b/Documentation/netlink/specs/rt-addr.yaml@@ -123,6 +123,9 @@ attribute-sets: - name: proto type: u8 + - + name: mc-users + type: u32 operations:
@@ -176,6 +179,7 @@ operations: value: 58 attributes: &mcaddr-attrs - multicast + - mc-users - cacheinfo dump: request:
diff --git a/include/uapi/linux/if_addr.h b/include/uapi/linux/if_addr.h
index aa7958b4e41d..7fb630b7fe31 100644
--- a/include/uapi/linux/if_addr.h
+++ b/include/uapi/linux/if_addr.h@@ -36,6 +36,7 @@ enum { IFA_RT_PRIORITY, /* u32, priority/metric for prefix route */ IFA_TARGET_NETNSID, IFA_PROTO, /* u8, address protocol */ + IFA_MC_USERS, /* u32, multicast group users */ __IFA_MAX, };
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index b6337a47c141..116ce7cec80e 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c@@ -1473,6 +1473,7 @@ int inet_fill_ifmcaddr(struct sk_buff *skb, struct net_device *dev, ci.ifa_valid = INFINITY_LIFE_TIME; if (nla_put_in_addr(skb, IFA_MULTICAST, im->multiaddr) < 0 || + nla_put_u32(skb, IFA_MC_USERS, READ_ONCE(im->users)) < 0 || nla_put(skb, IFA_CACHEINFO, sizeof(ci), &ci) < 0) { nlmsg_cancel(skb, nlh); return -EMSGSIZE;
@@ -1494,6 +1495,7 @@ static void inet_ifmcaddr_notify(struct net_device *dev, skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct ifaddrmsg)) + nla_total_size(sizeof(__be32)) + + nla_total_size(sizeof(u32)) + nla_total_size(sizeof(struct ifa_cacheinfo)), GFP_KERNEL); if (!skb)
--
2.43.0