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