+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2018 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <linux/bpf.h>
+#include <linux/if_ether.h>
+#include <bpf/bpf_helpers.h>
+
+int _version SEC("version") = 1;
+
+SEC("xdp_adjust_tail_shrink")
+int _xdp_adjust_tail_shrink(struct xdp_md *xdp)
+{
+ void *data_end = (void *)(long)xdp->data_end;
+ void *data = (void *)(long)xdp->data;
+ int offset = 0;
+
+ if (data_end - data == 54) /* sizeof(pkt_v4) */
+ offset = 256; /* shrink too much */
+ else
+ offset = 20;
+ if (bpf_xdp_adjust_tail(xdp, 0 - offset))
+ return XDP_DROP;
+ return XDP_TX;
+}
+
+char _license[] SEC("license") = "GPL";