net: vlan: Make is_vlan_dev() a stub when VLAN is not configured

Add a stub implementation of is_vlan_dev() that returns false when
VLAN support is not compiled in (CONFIG_VLAN_8021Q=n).

This allows us to compile-out VLAN-dependent dead code when it is not
needed.

This also resolves the following compilation error when:
* CONFIG_VLAN_8021Q=n
* CONFIG_OBJTOOL=y
* CONFIG_OBJTOOL_WERROR=y

drivers/net/ethernet/mellanox/mlx5/core/mlx5_core.o: error: objtool: parse_mirred.isra.0+0x370: mlx5e_tc_act_vlan_add_push_action() missing __noreturn in .c/.h or NORETURN() in noreturns.h

The error occurs because objtool cannot determine that unreachable BUG()
(which doesn't return) calls in VLAN code paths are actually dead code
when VLAN support is disabled.

Signed-off-by: Gal Pressman <gal@nvidia.com>
Link: https://patch.msgid.link/20250616132626.1749331-2-gal@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 38456b42cdb5566b69291071d4e438c66009e86b..618a973ff8ee1f1e6b8b28d50be3a662ef2ddc7d 100644 (file)
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -79,11 +79,6 @@ static inline struct vlan_ethhdr *skb_vlan_eth_hdr(const struct sk_buff *skb)
 /* found in socket.c */
 extern void vlan_ioctl_set(int (*hook)(struct net *, void __user *));
 
-static inline bool is_vlan_dev(const struct net_device *dev)
-{
-        return dev->priv_flags & IFF_802_1Q_VLAN;
-}
-
 #define skb_vlan_tag_present(__skb)    (!!(__skb)->vlan_all)
 #define skb_vlan_tag_get(__skb)                ((__skb)->vlan_tci)
 #define skb_vlan_tag_get_id(__skb)     ((__skb)->vlan_tci & VLAN_VID_MASK)
@@ -200,6 +195,11 @@ struct vlan_dev_priv {
 #endif
 };
 
+static inline bool is_vlan_dev(const struct net_device *dev)
+{
+       return dev->priv_flags & IFF_802_1Q_VLAN;
+}
+
 static inline struct vlan_dev_priv *vlan_dev_priv(const struct net_device *dev)
 {
        return netdev_priv(dev);
@@ -237,6 +237,11 @@ extern void vlan_vids_del_by_dev(struct net_device *dev,
 extern bool vlan_uses_dev(const struct net_device *dev);
 
 #else
+static inline bool is_vlan_dev(const struct net_device *dev)
+{
+       return false;
+}
+
 static inline struct net_device *
 __vlan_find_dev_deep_rcu(struct net_device *real_dev,
                     __be16 vlan_proto, u16 vlan_id)