"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 fixes the type of target-netnsid in the rt-addr spec. Patch 2 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 a new IFA_F_GLOBAL flag in IFA_FLAGS marks entries added explicitly, which is the "static" column /proc/net/dev_mcast has and "ip maddr" prints. A non-zero ifa_index limits the dump to one device and IFA_TARGET_NETNSID selects another netns, like the IPv4 and IPv6 dumps. Patch 3 updates the rt-addr spec and patch 4 adds a selftest that checks the filter, the user count, the global flag and target-netnsid. 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. Changes in v3: - Report the static bit as a new IFA_F_GLOBAL flag in IFA_FLAGS instead of IFA_F_PERMANENT - Support IFA_TARGET_NETNSID and test it - Describe global_use accurately, it is also set by dev_mc_add_excl() - Fix the target-netnsid type in the rt-addr spec, as its own patch Changes in v2: - Always validate the request header, not only with strict checking - Use a single "with" statement in the selftest (ruff) Yuyang Huang (4): netlink: specs: rt-addr: fix the type of target-netnsid 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 | 17 ++- include/uapi/linux/if_addr.h | 1 + net/core/rtnetlink.c | 165 +++++++++++++++++++++++ tools/testing/selftests/net/rtnetlink.py | 71 +++++++++- 4 files changed, 248 insertions(+), 6 deletions(-) -- 2.43.0
