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net: ipv4: report multicast group user count

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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 <sigefriedhyy@gmail.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260630110207.37841-2-sigefriedhyy@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Yuyang Huang 2026-06-30 20:02:05 +09:00 committed by Paolo Abeni
parent 2ed8d5c724
commit 7cb8198761
3 changed files with 7 additions and 0 deletions
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4
Documentation/netlink/specs/rt-addr.yaml
View File

@ -123,6 +123,9 @@ attribute-sets:
- -
name: proto name: proto
type: u8 type: u8
-
name: mc-users
type: u32
operations: operations:
@ -176,6 +179,7 @@ operations:
value: 58 value: 58
attributes: &mcaddr-attrs attributes: &mcaddr-attrs
- multicast - multicast
- mc-users
- cacheinfo - cacheinfo
dump: dump:
request: request:

1
include/uapi/linux/if_addr.h
View File

@ -36,6 +36,7 @@ enum {
IFA_RT_PRIORITY, /* u32, priority/metric for prefix route */ IFA_RT_PRIORITY, /* u32, priority/metric for prefix route */
IFA_TARGET_NETNSID, IFA_TARGET_NETNSID,
IFA_PROTO, /* u8, address protocol */ IFA_PROTO, /* u8, address protocol */
IFA_MC_USERS, /* u32, multicast group users */
__IFA_MAX, __IFA_MAX,
}; };

2
net/ipv4/igmp.c
View File

@ -1473,6 +1473,7 @@ int inet_fill_ifmcaddr(struct sk_buff *skb, struct net_device *dev,
ci.ifa_valid = INFINITY_LIFE_TIME; ci.ifa_valid = INFINITY_LIFE_TIME;
if (nla_put_in_addr(skb, IFA_MULTICAST, im->multiaddr) < 0 || 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) { nla_put(skb, IFA_CACHEINFO, sizeof(ci), &ci) < 0) {
nlmsg_cancel(skb, nlh); nlmsg_cancel(skb, nlh);
return -EMSGSIZE; return -EMSGSIZE;
@ -1494,6 +1495,7 @@ static void inet_ifmcaddr_notify(struct net_device *dev,
skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct ifaddrmsg)) + skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct ifaddrmsg)) +
nla_total_size(sizeof(__be32)) + nla_total_size(sizeof(__be32)) +
nla_total_size(sizeof(u32)) +
nla_total_size(sizeof(struct ifa_cacheinfo)), nla_total_size(sizeof(struct ifa_cacheinfo)),
GFP_KERNEL); GFP_KERNEL);
if (!skb) if (!skb)