kernel/trace/trace_nop.c

   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 */
  15 enum {
  16         TRACE_NOP_OPT_ACCEPT = 0x1,
  17         TRACE_NOP_OPT_REFUSE = 0x2
  18 };
  19
  20 /* Options for the tracer (see trace_options file) */
  21 static 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
  29 static 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
  35 static struct trace_array       *ctx_trace;
  36
  37 static void start_nop_trace(struct trace_array *tr)
  38 {
  39         /* Nothing to do! */
  40 }
  41
  42 static void stop_nop_trace(struct trace_array *tr)
  43 {
  44         /* Nothing to do! */
  45 }
  46
  47 static int nop_trace_init(struct trace_array *tr)
  48 {
  49         ctx_trace = tr;
  50         start_nop_trace(tr);
  51         return 0;
  52 }
  53
  54 static 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  */
  64 static 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
  88 struct 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 };
 100