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
12SEC("xdp")
13int _xdp_adjust_tail_shrink(struct xdp_md *xdp)
14{
15	__u8 *data_end = (void *)(long)xdp->data_end;
16	__u8 *data = (void *)(long)xdp->data;
17	int offset = 0;
18
19	switch (bpf_xdp_get_buff_len(xdp)) {
20	case 54:
21		/* sizeof(pkt_v4) */
22		offset = 256; /* shrink too much */
23		break;
24	case 9000:
25		/* non-linear buff test cases */
26		if (data + 1 > data_end)
27			return XDP_DROP;
28
29		switch (data[0]) {
30		case 0:
31			offset = 10;
32			break;
33		case 1:
34			offset = 4100;
35			break;
36		case 2:
37			offset = 8200;
38			break;
39		default:
40			return XDP_DROP;
41		}
42		break;
43	default:
44		offset = 20;
45		break;
46	}
47	if (bpf_xdp_adjust_tail(xdp, 0 - offset))
48		return XDP_DROP;
49	return XDP_TX;
50}
51
52char _license[] SEC("license") = "GPL";
53