1/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
2 *
3 * This program is free software; you can redistribute it and/or
4 * modify it under the terms of version 2 of the GNU General Public
5 * License as published by the Free Software Foundation.
6 */
7#include <linux/skbuff.h>
8#include <linux/netdevice.h>
9#include <uapi/linux/bpf.h>
10#include <linux/version.h>
11#include "bpf_helpers.h"
12
13#define _(P) ({typeof(P) val = 0; bpf_probe_read(&val, sizeof(val), &P); val;})
14
15/* kprobe is NOT a stable ABI
16 * kernel functions can be removed, renamed or completely change semantics.
17 * Number of arguments and their positions can change, etc.
18 * In such case this bpf+kprobe example will no longer be meaningful
19 */
20SEC("kprobe/__netif_receive_skb_core")
21int bpf_prog1(struct pt_regs *ctx)
22{
23	/* attaches to kprobe netif_receive_skb,
24	 * looks for packets on loobpack device and prints them
25	 */
26	char devname[IFNAMSIZ] = {};
27	struct net_device *dev;
28	struct sk_buff *skb;
29	int len;
30
31	/* non-portable! works for the given kernel only */
32	skb = (struct sk_buff *) ctx->di;
33
34	dev = _(skb->dev);
35
36	len = _(skb->len);
37
38	bpf_probe_read(devname, sizeof(devname), dev->name);
39
40	if (devname[0] == 'l' && devname[1] == 'o') {
41		char fmt[] = "skb %p len %d\n";
42		/* using bpf_trace_printk() for DEBUG ONLY */
43		bpf_trace_printk(fmt, sizeof(fmt), skb, len);
44	}
45
46	return 0;
47}
48
49char _license[] SEC("license") = "GPL";
50u32 _version SEC("version") = LINUX_VERSION_CODE;
51