commit 1153f73f038205dc17303e6e6c455bbbb56191f7
Author: ABC <abc@openwall.com>
Date:   Wed Oct 14 15:35:57 2020 +0300

    gen_compat_def: Check for vlan_dev_priv instead of version if

diff --git a/gen_compat_def b/gen_compat_def
index c0f20f6..3965e94 100755
--- a/gen_compat_def
+++ b/gen_compat_def
@@ -85,6 +85,8 @@ kbuild_test_struct proc_ops linux/proc_fs.h
 kbuild_test_struct proc_ops linux/proc_fs.h
 # No since v5.1, but present in CentOS-8's 4.18.0-227
 kbuild_test_symbol synchronize_sched linux/rcupdate.h
+# Stumbled on 5.9
+kbuild_test_struct vlan_dev_priv linux/if_vlan.h
 
 echo "// End of compat_def.h"
 
diff --git a/ipt_NETFLOW.c b/ipt_NETFLOW.c
index 01055df..6f95166 100644
--- a/ipt_NETFLOW.c
+++ b/ipt_NETFLOW.c
@@ -4874,7 +4874,7 @@ static void parse_l2_header(const struct sk_buff *skb, struct ipt_netflow_tuple
 		tuple->tag[tag_num++] = htons(vlan_tx_tag_get(skb));
 	else if (skb->dev && is_vlan_dev(skb->dev)) {
 		struct net_device *vlan_dev = skb->dev;
-# if LINUX_VERSION_CODE >= KERNEL_VERSION(3,2,0)
+# ifdef HAVE_VLAN_DEV_PRIV
 		struct vlan_dev_priv *vlan = vlan_dev_priv(vlan_dev);
 
 		/* `if` condition is `#if`ed intentionally, and this is