LXR linux/kernel/trace/trace

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * nop tracer
   4 *
   5 * Copyright (C) 2008 Steven Noonan <steven@uplinklabs.net>
   6 *
   7 */
   8
   9#include <linux/module.h>
  10#include <linux/ftrace.h>
  11
  12#include "trace.h"
  13
  14/* Our two options */
  15enum {
  16        TRACE_NOP_OPT_ACCEPT = 0x1,
  17        TRACE_NOP_OPT_REFUSE = 0x2
  18};
  19
  20/* Options for the tracer (see trace_options file) */
  21static struct tracer_opt nop_opts[] = {
  22        /* Option that will be accepted by set_flag callback */
  23        { TRACER_OPT(test_nop_accept, TRACE_NOP_OPT_ACCEPT) },
  24        /* Option that will be refused by set_flag callback */
  25        { TRACER_OPT(test_nop_refuse, TRACE_NOP_OPT_REFUSE) },
  26        { } /* Always set a last empty entry */
  27};
  28
  29static struct tracer_flags nop_flags = {
  30        /* You can check your flags value here when you want. */
  31        .val = 0, /* By default: all flags disabled */
  32        .opts = nop_opts
  33};
  34
  35static struct trace_array       *ctx_trace;
  36
  37static void start_nop_trace(struct trace_array *tr)
  38{
  39        /* Nothing to do! */
  40}
  41
  42static void stop_nop_trace(struct trace_array *tr)
  43{
  44        /* Nothing to do! */
  45}
  46
  47static int nop_trace_init(struct trace_array *tr)
  48{
  49        ctx_trace = tr;
  50        start_nop_trace(tr);
  51        return 0;
  52}
  53
  54static void nop_trace_reset(struct trace_array *tr)
  55{
  56        stop_nop_trace(tr);
  57}
  58
  59/* It only serves as a signal handler and a callback to
  60 * accept or refuse the setting of a flag.
  61 * If you don't implement it, then the flag setting will be
  62 * automatically accepted.
  63 */
  64static int nop_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
  65{
  66        /*
  67         * Note that you don't need to update nop_flags.val yourself.
  68         * The tracing Api will do it automatically if you return 0
  69         */
  70        if (bit == TRACE_NOP_OPT_ACCEPT) {
  71                printk(KERN_DEBUG "nop_test_accept flag set to %d: we accept."
  72                        " Now cat trace_options to see the result\n",
  73                        set);
  74                return 0;
  75        }
  76
  77        if (bit == TRACE_NOP_OPT_REFUSE) {
  78                printk(KERN_DEBUG "nop_test_refuse flag set to %d: we refuse."
  79                        " Now cat trace_options to see the result\n",
  80                        set);
  81                return -EINVAL;
  82        }
  83
  84        return 0;
  85}
  86
  87
  88struct tracer nop_trace __read_mostly =
  89{
  90        .name           = "nop",
  91        .init           = nop_trace_init,
  92        .reset          = nop_trace_reset,
  93#ifdef CONFIG_FTRACE_SELFTEST
  94        .selftest       = trace_selftest_startup_nop,
  95#endif
  96        .flags          = &nop_flags,
  97        .set_flag       = nop_set_flag,
  98        .allow_instances = true,
  99};
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