Re: [PATCH v2 net 3/4] neighbour: Don't render blackhole_netdev via RTM_GETNEIGHTBL.

On Tue, Sep 08, 2026 at 09:12:47PM +0000, Kuniyuki Iwashima wrote:

The cited commits started to initialise blackhole_netdev with
neigh_parms_alloc().

This is visible in init_net as the ifindex==0 entries via
RTM_GETNEIGHTBL:

  # ynl --family rt-neigh --dump getneightbl --output-json \
    | jq '.[] | select(.parms.ifindex == 0)
              | {name: .name, ifindex: .parms.ifindex}'
  {
    "name": "arp_cache",
    "ifindex": 0
  }
  {
    "name": "ndisc_cache",
    "ifindex": 0
  }

For RTM_SETNEIGHTBL, ifindex being 0 means wildcard.

Let's skip blackhole_netdev's parms in neightbl_dump_info().

Note that lookup_neigh_parms() does not need the same change
because the default parms is always the first entry and matches
with ifindex == 0.

Fixes: e5f80fcf869a ("ipv6: give an IPv6 dev to blackhole_netdev")
Fixes: 22600596b675 ("ipv4: give an IPv4 dev to blackhole_netdev")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>