Re: [PATCH net-next v6 2/4] net: add AF_PACKET multicast dumps
flat view
From: Nicolas Dichtel <hidden>
Date: 2026-09-22 07:20:52
Also in:
linux-kselftest, lkml
Le 22/09/2026 à 01:59, 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 next to
the dev->mc helpers in dev_addr_lists.c 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.
Requests are always validated, there are no legacy users: prefixlen,
flags and scope must be zero, ifa_index selects one device and
IFA_TARGET_NETNSID is the only attribute accepted. The dump runs under
RCU and netif_addr_lock_bh() without RTNL, and stamps cb->seq from
dev_base_seq so a device added or removed between dump rounds sets
NLM_F_DUMP_INTR.
Signed-off-by: Yuyang Huang <redacted>
Reviewed-by: Nicolas Dichtel <redacted>
---[snip]
quoted hunk ↗ jump to hunk
+static int dev_mc_dump_dev(struct net_device *dev, struct sk_buff *skb, + struct netlink_callback *cb, int *s_addr_idx, + unsigned int flags, int netnsid) +{ + struct netdev_hw_addr *ha; + int addr_idx = 0; + int err = 0; + + netif_addr_lock_bh(dev); + netdev_for_each_mc_addr(ha, dev) { + if (addr_idx < *s_addr_idx) { + addr_idx++; + continue; + } + err = dev_mc_fill_addr(skb, dev, ha, NETLINK_CB(cb->skb).portid, + cb->nlh->nlmsg_seq, flags, netnsid); + if (err < 0) + break; + nl_dump_check_consistent(cb, nlmsg_hdr(skb)); + addr_idx++; + } + netif_addr_unlock_bh(dev); + + *s_addr_idx = err < 0 ? addr_idx : 0; + + return err; +}
[snip]
quoted hunk ↗ jump to hunk
+int dev_mc_dump(struct sk_buff *skb, struct netlink_callback *cb) +{ + struct dev_mc_dump_filter filter = { + .tgt_net = sock_net(skb->sk), + .netnsid = -1, + }; + unsigned int flags = NLM_F_MULTI; + struct { + unsigned long ifindex; + int addr_idx; + } *ctx = (void *)cb->ctx; + unsigned long s_ifindex; + struct net_device *dev; + int err; + + err = dev_mc_valid_dump_req(cb->nlh, skb->sk, &filter, cb->extack); + if (err < 0) + return err; + + cb->seq = READ_ONCE(filter.tgt_net->dev_base_seq);
dev_base_seq only indicates whether the netdevice list has changed, not whether the addr list has changed. It's only a partial consistency check. See inet_base_seq()/inet6_base_seq(). I don't see an equivalent of dev_addr_genid for the L2 mcaddr list; it should probably be added.