Re: [PATCH net-next v4 2/4] rtnetlink: add AF_PACKET multicast dumps

Le 11/09/2026 à 12:51, Yuyang Huang a écrit :

RTM_GETMULTICAST dumps IPv4 and IPv6 multicast group memberships, but
the device multicast list (dev->mc) is only available through
/proc/net/dev_mcast, so "ip maddr show" still has to parse procfs for
its link-layer entries.

Handle RTM_GETMULTICAST dumps with ifa_family set to AF_PACKET and
report every entry of dev->mc in the existing ifaddrmsg format:

  - IFA_MULTICAST carries the raw link-layer address
  - IFA_MC_USERS carries the entry reference count
  - IFA_F_GLOBAL in IFA_FLAGS reports netdev_hw_addr::global_use, set
    by dev_mc_add_global() (SIOCADDMULTI) and dev_mc_add_excl()
    ("bridge fdb add ... self"), i.e. entries added explicitly rather
    than by a protocol join. This is the static column of
    /proc/net/dev_mcast
  - ifa_scope is RT_SCOPE_LINK

This covers every column of /proc/net/dev_mcast. AF_PACKET is the
family iproute2 already uses for link-layer addresses ("ip -0").

The default FDB dump also walks dev->mc, but only for Ethernet devices
without an ndo_fdb_dump of their own, so bridge, vxlan or macvlan
devices never show their multicast filter there, and it has no users
count or global_use bit. Extending it would change "bridge fdb show"
output and add NDA_* attributes.

There are no legacy users of AF_PACKET requests, so they are always
validated: prefixlen, flags and scope must be zero and a non-zero
ifa_index restricts the dump to that device. IFA_TARGET_NETNSID selects
another netns like the IPv4 and IPv6 dumps and is the only attribute
accepted. The dump runs under RCU and netif_addr_lock_bh() and does not
need RTNL.

Signed-off-by: Yuyang Huang <redacted>

Reviewed-by: Nicolas Dichtel <redacted>