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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>