samples/bpf/tracex1_kern.c

   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  */
  26 SEC("kprobe/__netif_receive_skb_core")
  27 int bpf_prog1(struct pt_regs *ctx)
  28 {
  29         /* attaches to kprobe netif_receive_skb,
  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         skb = (struct sk_buff *) 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
  53 char _license[] SEC("license") = "GPL";
  54 u32 _version SEC("version") = LINUX_VERSION_CODE;