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/bpf_helpers.h>
12#include <bpf/bpf_tracing.h>
13
14#define _(P)                                                                   \
15	({                                                                     \
16		typeof(P) val = 0;                                             \
17		bpf_probe_read_kernel(&val, sizeof(val), &(P));                \
18		val;                                                           \
19	})
20
21/* kprobe is NOT a stable ABI
22 * kernel functions can be removed, renamed or completely change semantics.
23 * Number of arguments and their positions can change, etc.
24 * In such case this bpf+kprobe example will no longer be meaningful
25 */
26SEC("kprobe/__netif_receive_skb_core")
27int bpf_prog1(struct pt_regs *ctx)
28{
29	/* attaches to kprobe __netif_receive_skb_core,
30	 * looks for packets on loobpack device and prints them
31	 */
32	char devname[IFNAMSIZ];
33	struct net_device *dev;
34	struct sk_buff *skb;
35	int len;
36
37	/* non-portable! works for the given kernel only */
38	bpf_probe_read_kernel(&skb, sizeof(skb), (void *)PT_REGS_PARM1(ctx));
39	dev = _(skb->dev);
40	len = _(skb->len);
41
42	bpf_probe_read_kernel(devname, sizeof(devname), dev->name);
43
44	if (devname[0] == 'l' && devname[1] == 'o') {
45		char fmt[] = "skb %p len %d\n";
46		/* using bpf_trace_printk() for DEBUG ONLY */
47		bpf_trace_printk(fmt, sizeof(fmt), skb, len);
48	}
49
50	return 0;
51}
52
53char _license[] SEC("license") = "GPL";
54u32 _version SEC("version") = LINUX_VERSION_CODE;