LXR linux/samples/bpf/tracex3

   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 <linux/version.h>
  10#include <uapi/linux/bpf.h>
  11#include "bpf_helpers.h"
  12
  13struct bpf_map_def SEC("maps") my_map = {
  14        .type = BPF_MAP_TYPE_HASH,
  15        .key_size = sizeof(long),
  16        .value_size = sizeof(u64),
  17        .max_entries = 4096,
  18};
  19
  20/* kprobe is NOT a stable ABI. If kernel internals change this bpf+kprobe
  21 * example will no longer be meaningful
  22 */
  23SEC("kprobe/blk_start_request")
  24int bpf_prog1(struct pt_regs *ctx)
  25{
  26        long rq = PT_REGS_PARM1(ctx);
  27        u64 val = bpf_ktime_get_ns();
  28
  29        bpf_map_update_elem(&my_map, &rq, &val, BPF_ANY);
  30        return 0;
  31}
  32
  33static unsigned int log2l(unsigned long long n)
  34{
  35#define S(k) if (n >= (1ull << k)) { i += k; n >>= k; }
  36        int i = -(n == 0);
  37        S(32); S(16); S(8); S(4); S(2); S(1);
  38        return i;
  39#undef S
  40}
  41
  42#define SLOTS 100
  43
  44struct bpf_map_def SEC("maps") lat_map = {
  45        .type = BPF_MAP_TYPE_PERCPU_ARRAY,
  46        .key_size = sizeof(u32),
  47        .value_size = sizeof(u64),
  48        .max_entries = SLOTS,
  49};
  50
  51SEC("kprobe/blk_account_io_completion")
  52int bpf_prog2(struct pt_regs *ctx)
  53{
  54        long rq = PT_REGS_PARM1(ctx);
  55        u64 *value, l, base;
  56        u32 index;
  57
  58        value = bpf_map_lookup_elem(&my_map, &rq);
  59        if (!value)
  60                return 0;
  61
  62        u64 cur_time = bpf_ktime_get_ns();
  63        u64 delta = cur_time - *value;
  64
  65        bpf_map_delete_elem(&my_map, &rq);
  66
  67        /* the lines below are computing index = log10(delta)*10
  68         * using integer arithmetic
  69         * index = 29 ~ 1 usec
  70         * index = 59 ~ 1 msec
  71         * index = 89 ~ 1 sec
  72         * index = 99 ~ 10sec or more
  73         * log10(x)*10 = log2(x)*10/log2(10) = log2(x)*3
  74         */
  75        l = log2l(delta);
  76        base = 1ll << l;
  77        index = (l * 64 + (delta - base) * 64 / base) * 3 / 64;
  78
  79        if (index >= SLOTS)
  80                index = SLOTS - 1;
  81
  82        value = bpf_map_lookup_elem(&lat_map, &index);
  83        if (value)
  84                *value += 1;
  85
  86        return 0;
  87}
  88char _license[] SEC("license") = "GPL";
  89u32 _version SEC("version") = LINUX_VERSION_CODE;
  90