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Linux/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;
 49 

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