[PATCH 5/6] net: Change CONFIG_INET to CONFIG_LEGACY_IP for IPv4-only code

David Woodhouse
2026-04-01T07:45:44Z

From: David Woodhouse <dwmw@amazon.co.uk>

Several functions guarded by CONFIG_INET are actually IPv4-specific
and should be gated by CONFIG_LEGACY_IP instead:

- bpf_out_neigh_v4(): BPF IPv4 neighbour output helper
- bpf_ipv4_fib_lookup(): BPF IPv4 FIB lookup
- case AF_INET in bpf_xdp_fib_lookup/bpf_skb_fib_lookup switch
- br_arp_send(): bridge ARP proxy (ARP is IPv4-only)

This allows the compiler to eliminate these functions when
LEGACY_IP=n.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
net/bridge/br_arp_nd_proxy.c | 2 +-
net/bridge/br_private.h | 8 ++++++++
net/core/filter.c | 10 +++++-----
net/core/sock.c | 2 +-
net/mac80211/main.c | 10 +++++-----
net/netfilter/nfnetlink_queue.c | 2 +-
6 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/net/bridge/br_arp_nd_proxy.c b/net/bridge/br_arp_nd_proxy.c
index 1e2b51769eec..e056fa0cd1fe 100644
--- a/net/bridge/br_arp_nd_proxy.c
+++ b/net/bridge/br_arp_nd_proxy.c
@@ -39,7 +39,7 @@ void br_recalculate_neigh_suppress_enabled(struct net_bridge *br)
br_opt_toggle(br, BROPT_NEIGH_SUPPRESS_ENABLED, neigh_suppress);
}

-#if IS_ENABLED(CONFIG_INET)
+#if IS_ENABLED(CONFIG_LEGACY_IP)
static void br_arp_send(struct net_bridge *br, struct net_bridge_port *p,
struct net_device *dev, __be32 dest_ip, __be32 src_ip,
const unsigned char *dest_hw,
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 9b55d38ea9ed..28131fa0a7c5 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -2347,8 +2347,16 @@ static inline void br_switchdev_init(struct net_bridge *br)

/* br_arp_nd_proxy.c */
void br_recalculate_neigh_suppress_enabled(struct net_bridge *br);
+#if IS_ENABLED(CONFIG_LEGACY_IP)
void br_do_proxy_suppress_arp(struct sk_buff *skb, struct net_bridge *br,
u16 vid, struct net_bridge_port *p);
+#else
+static inline void br_do_proxy_suppress_arp(struct sk_buff *skb,
+ struct net_bridge *br,
+ u16 vid, struct net_bridge_port *p)
+{
+}
+#endif
void br_do_suppress_nd(struct sk_buff *skb, struct net_bridge *br,
u16 vid, struct net_bridge_port *p, struct nd_msg *msg);
struct nd_msg *br_is_nd_neigh_msg(const struct sk_buff *skb, struct nd_msg *m);
diff --git a/net/core/filter.c b/net/core/filter.c
index ad71ceefcb5e..ef99bd9fddd6 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2310,7 +2310,7 @@ static int __bpf_redirect_neigh_v6(struct sk_buff *skb, struct net_device *dev,
}
#endif /* CONFIG_IPV6 */

-#if IS_ENABLED(CONFIG_INET)
+#if IS_ENABLED(CONFIG_LEGACY_IP)
static int bpf_out_neigh_v4(struct net *net, struct sk_buff *skb,
struct net_device *dev, struct bpf_nh_params *nh)
{
@@ -2419,7 +2419,7 @@ static int __bpf_redirect_neigh_v4(struct sk_buff *skb, struct net_device *dev,
kfree_skb(skb);
return NET_XMIT_DROP;
}
-#endif /* CONFIG_INET */
+#endif /* CONFIG_LEGACY_IP */

static int __bpf_redirect_neigh(struct sk_buff *skb, struct net_device *dev,
struct bpf_nh_params *nh)
@@ -6095,7 +6095,7 @@ static int bpf_fib_set_fwd_params(struct bpf_fib_lookup *params, u32 mtu)
}
#endif

-#if IS_ENABLED(CONFIG_INET)
+#if IS_ENABLED(CONFIG_LEGACY_IP)
static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
u32 flags, bool check_mtu)
{
@@ -6390,7 +6390,7 @@ BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx,
return -EINVAL;

switch (params->family) {
-#if IS_ENABLED(CONFIG_INET)
+#if IS_ENABLED(CONFIG_LEGACY_IP)
case AF_INET:
return bpf_ipv4_fib_lookup(dev_net(ctx->rxq->dev), params,
flags, true);
@@ -6431,7 +6431,7 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb,
check_mtu = true;

switch (params->family) {
-#if IS_ENABLED(CONFIG_INET)
+#if IS_ENABLED(CONFIG_LEGACY_IP)
case AF_INET:
rc = bpf_ipv4_fib_lookup(net, params, flags, check_mtu);
break;
diff --git a/net/core/sock.c b/net/core/sock.c
index 5976100a9d55..6b2914702a38 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -4267,7 +4267,7 @@ int sock_load_diag_module(int family, int protocol)
NETLINK_SOCK_DIAG, family);
}

-#ifdef CONFIG_INET
+#ifdef CONFIG_LEGACY_IP
if (family == AF_INET &&
protocol != IPPROTO_RAW &&
protocol < MAX_INET_PROTOS &&
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index 616f86b1a7e4..7c1bbbb2c5c7 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -558,7 +558,7 @@ void ieee80211_restart_hw(struct ieee80211_hw *hw)
}
EXPORT_SYMBOL(ieee80211_restart_hw);

-#ifdef CONFIG_INET
+#ifdef CONFIG_LEGACY_IP
static int ieee80211_ifa_changed(struct notifier_block *nb,
unsigned long data, void *arg)
{
@@ -1624,7 +1624,7 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
wiphy_unlock(hw->wiphy);
rtnl_unlock();

-#ifdef CONFIG_INET
+#ifdef CONFIG_LEGACY_IP
local->ifa_notifier.notifier_call = ieee80211_ifa_changed;
result = register_inetaddr_notifier(&local->ifa_notifier);
if (result)
@@ -1642,11 +1642,11 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)

#if IS_ENABLED(CONFIG_IPV6)
fail_ifa6:
-#ifdef CONFIG_INET
+#ifdef CONFIG_LEGACY_IP
unregister_inetaddr_notifier(&local->ifa_notifier);
#endif
#endif
-#if defined(CONFIG_INET) || defined(CONFIG_IPV6)
+#if defined(CONFIG_LEGACY_IP) || defined(CONFIG_IPV6)
fail_ifa:
#endif
wiphy_unregister(local->hw.wiphy);
@@ -1673,7 +1673,7 @@ void ieee80211_unregister_hw(struct ieee80211_hw *hw)
tasklet_kill(&local->tx_pending_tasklet);
tasklet_kill(&local->tasklet);

-#ifdef CONFIG_INET
+#ifdef CONFIG_LEGACY_IP
unregister_inetaddr_notifier(&local->ifa_notifier);
#endif
#if IS_ENABLED(CONFIG_IPV6)
diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
index 47f7f62906e2..e453fdb2254c 100644
--- a/net/netfilter/nfnetlink_queue.c
+++ b/net/netfilter/nfnetlink_queue.c
@@ -339,7 +339,7 @@ static struct nf_hook_entries *nf_hook_entries_head(const struct net *net, u8 pf

static int nf_ip_reroute(struct sk_buff *skb, const struct nf_queue_entry *entry)
{
-#ifdef CONFIG_INET
+#ifdef CONFIG_LEGACY_IP
const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);

if (entry->state.hook == NF_INET_LOCAL_OUT) {
--
2.51.0