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_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  */
  20 SEC("kprobe/__netif_receive_skb_core")
  21 int 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         dev = _(skb->dev);
  34         len = _(skb->len);
  35
  36         bpf_probe_read(devname, sizeof(devname), dev->name);
  37
  38         if (devname[0] == 'l' && devname[1] == 'o') {
  39                 char fmt[] = "skb %p len %d\n";
  40                 /* using bpf_trace_printk() for DEBUG ONLY */
  41                 bpf_trace_printk(fmt, sizeof(fmt), skb, len);
  42         }
  43
  44         return 0;
  45 }
  46
  47 char _license[] SEC("license") = "GPL";
  48 u32 _version SEC("version") = LINUX_VERSION_CODE;