On Mon, 14 Sep 2026 10:45:35 +0900 Yuyang Huang wrote:
> "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.You compare the situation to IP but for L2 the UC addresses are not exposed via RTM_GETADDR. Are you going to add it? > 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. Is that the only justification? To avoid reading proc? Are you planning to extend this interface with new features? > 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.
