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")
_xdp_adjust_tail_shrink(struct xdp_md * xdp)13 int _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 
52 char _license[] SEC("license") = "GPL";
53