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/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;
  55