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/fs.h>
  10 #include <linux/debugfs.h>
  11 #include <linux/ftrace.h>
  12
  13 #include "trace.h"
  14
  15 /* Our two options */
  16 enum {
  17         TRACE_NOP_OPT_ACCEPT = 0x1,
  18         TRACE_NOP_OPT_REFUSE = 0x2
  19 };
  20
  21 /* Options for the tracer (see trace_options file) */
  22 static 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
  30 static 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
  36 static struct trace_array       *ctx_trace;
  37
  38 static void start_nop_trace(struct trace_array *tr)
  39 {
  40         /* Nothing to do! */
  41 }
  42
  43 static void stop_nop_trace(struct trace_array *tr)
  44 {
  45         /* Nothing to do! */
  46 }
  47
  48 static int nop_trace_init(struct trace_array *tr)
  49 {
  50         ctx_trace = tr;
  51         start_nop_trace(tr);
  52         return 0;
  53 }
  54
  55 static 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  */
  65 static int nop_set_flag(struct trace_array *tr, 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
  89 struct tracer nop_trace __read_mostly =
  90 {
  91         .name           = "nop",
  92         .init           = nop_trace_init,
  93         .reset          = nop_trace_reset,
  94 #ifdef CONFIG_FTRACE_SELFTEST
  95         .selftest       = trace_selftest_startup_nop,
  96 #endif
  97         .flags          = &nop_flags,
  98         .set_flag       = nop_set_flag,
  99         .allow_instances = true,
 100 };
 101