Re: [PATCH net-next v5 0/4] rtnetlink: dump link-layer multicast addresses

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.