1 // SPDX-License-Identifier: GPL-2.0
2 /* Copyright (c) 2018 Facebook
3  *
4  * This program is free software; you can redistribute it and/or
5  * modify it under the terms of version 2 of the GNU General Public
6  * License as published by the Free Software Foundation.
7  */
8 #include <linux/bpf.h>
9 #include <linux/if_ether.h>
10 #include <bpf/bpf_helpers.h>
11 
12 SEC("xdp")
13 int _xdp_adjust_tail_shrink(struct xdp_md *xdp)
14 {
15 	void *data_end = (void *)(long)xdp->data_end;
16 	void *data = (void *)(long)xdp->data;
17 	int offset = 0;
18 
19 	if (data_end - data == 54) /* sizeof(pkt_v4) */
20 		offset = 256; /* shrink too much */
21 	else
22 		offset = 20;
23 	if (bpf_xdp_adjust_tail(xdp, 0 - offset))
24 		return XDP_DROP;
25 	return XDP_TX;
26 }
27 
28 char _license[] SEC("license") = "GPL";
29