kernel/trace/trace_nop.c

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