[PATCH iproute2-next 0/2] ipmaddr: read link-layer multicast addresses via netlink

[Yuyang Huang <yuyanghuang@google.com>]

"ip maddr show" gets the IPv4 and IPv6 multicast addresses from
RTM_GETMULTICAST dumps, but it still parses /proc/net/dev_mcast for the
link-layer addresses. The kernel now also supports RTM_GETMULTICAST
dumps with ifa_family AF_PACKET, which report the device multicast list
with every column of /proc/net/dev_mcast. Patch 2 uses this dump. The
output does not change. Older kernels reject the AF_PACKET dump with
EOPNOTSUPP, and "ip maddr" then reads /proc/net/dev_mcast as before.

Patch 1 adds IFA_F_GLOBAL to include/uapi/linux/if_addr.h. It is only
there so that the series builds, and it should not be merged: the uapi
headers are synced into iproute2-next regularly, and the next sync
brings in IFA_F_GLOBAL.

The kernel side is the net-next series "rtnetlink: dump link-layer
multicast addresses":
https://patch.msgid.link/20261012011707.3378-1-sigefriedhyy@gmail.com

Testing:
- net-next kernel in vng: "ip maddr show" output is byte-identical to
  the current code for plain, -0/-4/-6, -o, -j, dev and -n <netns>, and
  /proc/net/dev_mcast is not read. This includes a multi-part dump with
  2000 entries on one device.
- 7.1 kernel without AF_PACKET support: falls back to
  /proc/net/dev_mcast, with the same output.

Yuyang Huang (2):
  uapi: update if_addr.h
  ipmaddr: read link-layer multicast addresses via netlink

 include/uapi/linux/if_addr.h |  1 +
 ip/ipmaddr.c                 | 10 ++++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

-- 
2.56.0.455.g6c5a503b38-goog