samples/bpf/lwt_len_hist.bpf.c

   1 /* Copyright (c) 2016 Thomas Graf <tgraf@tgraf.ch>
   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  * This program is distributed in the hope that it will be useful, but
   8  * WITHOUT ANY WARRANTY; without even the implied warranty of
   9  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  10  * General Public License for more details.
  11  */
  12
  13 #include "vmlinux.h"
  14 #include <bpf/bpf_helpers.h>
  15
  16 struct {
  17         __uint(type, BPF_MAP_TYPE_PERCPU_HASH);
  18         __type(key, u64);
  19         __type(value, u64);
  20         __uint(pinning, LIBBPF_PIN_BY_NAME);
  21         __uint(max_entries, 1024);
  22 } lwt_len_hist_map SEC(".maps");
  23
  24 static unsigned int log2(unsigned int v)
  25 {
  26         unsigned int r;
  27         unsigned int shift;
  28
  29         r = (v > 0xFFFF) << 4; v >>= r;
  30         shift = (v > 0xFF) << 3; v >>= shift; r |= shift;
  31         shift = (v > 0xF) << 2; v >>= shift; r |= shift;
  32         shift = (v > 0x3) << 1; v >>= shift; r |= shift;
  33         r |= (v >> 1);
  34         return r;
  35 }
  36
  37 static unsigned int log2l(unsigned long v)
  38 {
  39         unsigned int hi = v >> 32;
  40         if (hi)
  41                 return log2(hi) + 32;
  42         else
  43                 return log2(v);
  44 }
  45
  46 SEC("len_hist")
  47 int do_len_hist(struct __sk_buff *skb)
  48 {
  49         __u64 *value, key, init_val = 1;
  50
  51         key = log2l(skb->len);
  52
  53         value = bpf_map_lookup_elem(&lwt_len_hist_map, &key);
  54         if (value)
  55                 __sync_fetch_and_add(value, 1);
  56         else
  57                 bpf_map_update_elem(&lwt_len_hist_map, &key, &init_val, BPF_ANY);
  58
  59         return BPF_OK;
  60 }
  61
  62 char _license[] SEC("license") = "GPL";