LXR linux/samples/bpf/tracex1

   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 *) PT_REGS_PARM1(ctx);
  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