RTM_GETMULTICAST reports IPv4 and IPv6 multicast group membership, but
does not include the per-group user count. Userspace therefore still has
to parse /proc/net/igmp and /proc/net/igmp6 to obtain the Users column.
In particular, this prevents iproute2 from moving "ip maddr show"
entirely from procfs to rtnetlink.

Add IFA_MC_USERS to carry the user count in RTM_GETMULTICAST dumps and
RTM_NEWMULTICAST / RTM_DELMULTICAST notifications for both address
families. Update the rt-addr YNL specification and extend the rtnetlink
selftest to verify that two joins increase the reported count by two.

Yuyang Huang (3):
  net: ipv4: report multicast group user count
  net: ipv6: report multicast group user count
  selftests: net: check multicast group user count

 Documentation/netlink/specs/rt-addr.yaml |   4 +
 include/uapi/linux/if_addr.h             |   1 +
 net/ipv4/igmp.c                          |   2 +
 net/ipv6/addrconf.c                      |   1 +
 net/ipv6/mcast.c                         |   1 +
 tools/testing/selftests/net/rtnetlink.py | 101 ++++++++++++++++++++---
 6 files changed, 99 insertions(+), 11 deletions(-)

-- 
2.43.0