linux/kernel/trace/trace_nop.c
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   1/*
   2 * nop tracer
   3 *
   4 * Copyright (C) 2008 Steven Noonan <steven@uplinklabs.net>
   5 *
   6 */
   7
   8#include <linux/module.h>
   9#include <linux/fs.h>
  10#include <linux/debugfs.h>
  11#include <linux/ftrace.h>
  12
  13#include "trace.h"
  14
  15/* Our two options */
  16enum {
  17        TRACE_NOP_OPT_ACCEPT = 0x1,
  18        TRACE_NOP_OPT_REFUSE = 0x2
  19};
  20
  21/* Options for the tracer (see trace_options file) */
  22static struct tracer_opt nop_opts[] = {
  23        /* Option that will be accepted by set_flag callback */
  24        { TRACER_OPT(test_nop_accept, TRACE_NOP_OPT_ACCEPT) },
  25        /* Option that will be refused by set_flag callback */
  26        { TRACER_OPT(test_nop_refuse, TRACE_NOP_OPT_REFUSE) },
  27        { } /* Always set a last empty entry */
  28};
  29
  30static struct tracer_flags nop_flags = {
  31        /* You can check your flags value here when you want. */
  32        .val = 0, /* By default: all flags disabled */
  33        .opts = nop_opts
  34};
  35
  36static struct trace_array       *ctx_trace;
  37
  38static void start_nop_trace(struct trace_array *tr)
  39{
  40        /* Nothing to do! */
  41}
  42
  43static void stop_nop_trace(struct trace_array *tr)
  44{
  45        /* Nothing to do! */
  46}
  47
  48static int nop_trace_init(struct trace_array *tr)
  49{
  50        ctx_trace = tr;
  51        start_nop_trace(tr);
  52        return 0;
  53}
  54
  55static void nop_trace_reset(struct trace_array *tr)
  56{
  57        stop_nop_trace(tr);
  58}
  59
  60/* It only serves as a signal handler and a callback to
  61 * accept or refuse tthe setting of a flag.
  62 * If you don't implement it, then the flag setting will be
  63 * automatically accepted.
  64 */
  65static int nop_set_flag(u32 old_flags, u32 bit, int set)
  66{
  67        /*
  68         * Note that you don't need to update nop_flags.val yourself.
  69         * The tracing Api will do it automatically if you return 0
  70         */
  71        if (bit == TRACE_NOP_OPT_ACCEPT) {
  72                printk(KERN_DEBUG "nop_test_accept flag set to %d: we accept."
  73                        " Now cat trace_options to see the result\n",
  74                        set);
  75                return 0;
  76        }
  77
  78        if (bit == TRACE_NOP_OPT_REFUSE) {
  79                printk(KERN_DEBUG "nop_test_refuse flag set to %d: we refuse."
  80                        "Now cat trace_options to see the result\n",
  81                        set);
  82                return -EINVAL;
  83        }
  84
  85        return 0;
  86}
  87
  88
  89struct tracer nop_trace __read_mostly =
  90{
  91        .name           = "nop",
  92        .init           = nop_trace_init,
  93        .reset          = nop_trace_reset,
  94        .wait_pipe      = poll_wait_pipe,
  95#ifdef CONFIG_FTRACE_SELFTEST
  96        .selftest       = trace_selftest_startup_nop,
  97#endif
  98        .flags          = &nop_flags,
  99        .set_flag       = nop_set_flag
 100};
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