"ip maddr show" prints three kinds of entries: link-layer, IPv4 and
IPv6. The IPv4 and IPv6 ones can be read over netlink today: IPv6 has
had RTM_GETMULTICAST for a long time and IPv4 got it in eb4e17a1d915
("netlink: support dumping IPv4 multicast addresses"), with IFA_MC_USERS
added later so the user count no longer has to come from procfs.The link-layer list is the missing piece. dev->mc, the addresses programmed into the device filter, is only exported via /proc/net/dev_mcast, so iproute2 still carries a procfs parser just for that. This series closes the gap so that "ip maddr show" can be served from rtnetlink alone. Patch 1 handles RTM_GETMULTICAST dumps with ifa_family set to AF_PACKET and walks dev->mc under netif_addr_lock_bh(), no RTNL. The reply reuses the ifaddrmsg format of the IPv4 and IPv6 dumps: IFA_MULTICAST carries the raw link-layer address, IFA_MC_USERS the reference count, and IFA_F_PERMANENT is set for entries added with SIOCADDMULTI, which is the "static" column /proc/net/dev_mcast has and "ip maddr" prints. A non-zero ifa_index in a strict request limits the dump to one device. Patch 2 updates the rt-addr spec and patch 3 adds a selftest that checks the filter, the user count and the permanent flag on a dummy device. Nothing changes for other families. AF_PACKET dumps returned -EOPNOTSUPP before, so iproute2 can keep the procfs fallback for older kernels. I have the iproute2 side ready and will post it once this is in; with it, "ip maddr show" does not open /proc/net at all. Yuyang Huang (3): rtnetlink: add AF_PACKET multicast dumps netlink: specs: rt-addr: document AF_PACKET multicast dumps selftests: net: test AF_PACKET multicast dumps Documentation/netlink/specs/rt-addr.yaml | 7 +- net/core/rtnetlink.c | 132 +++++++++++++++++++++++ tools/testing/selftests/net/rtnetlink.py | 58 +++++++++- 3 files changed, 193 insertions(+), 4 deletions(-) -- 2.43.0
