/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of version 2 of the GNU General Public
   * License as published by the Free Software Foundation.
   */
  #include <linux/skbuff.h>
  #include <linux/netdevice.h>
  #include <uapi/linux/bpf.h>
  #include <linux/version.h>
  #include "bpf_helpers.h"
  
  #define _(P) ({typeof(P) val = 0; bpf_probe_read(&val, sizeof(val), &P); val;})
  
  /* kprobe is NOT a stable ABI
   * kernel functions can be removed, renamed or completely change semantics.
   * Number of arguments and their positions can change, etc.
   * In such case this bpf+kprobe example will no longer be meaningful
   */
  SEC("kprobe/__netif_receive_skb_core")
  int bpf_prog1(struct pt_regs *ctx)
  {
  	/* attaches to kprobe netif_receive_skb,
  	 * looks for packets on loobpack device and prints them
  	 */

  	char devname[IFNAMSIZ];

  	struct net_device *dev;
  	struct sk_buff *skb;
  	int len;
  
  	/* non-portable! works for the given kernel only */

  	skb = (struct sk_buff *) PT_REGS_PARM1(ctx);

  	dev = _(skb->dev);

  	len = _(skb->len);
  
  	bpf_probe_read(devname, sizeof(devname), dev->name);
  
  	if (devname[0] == 'l' && devname[1] == 'o') {
  		char fmt[] = "skb %p len %d
  ";
  		/* using bpf_trace_printk() for DEBUG ONLY */
  		bpf_trace_printk(fmt, sizeof(fmt), skb, len);
  	}
  
  	return 0;
  }
  
  char _license[] SEC("license") = "GPL";
  u32 _version SEC("version") = LINUX_VERSION_CODE;