Line data    Source code

       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           0 : static void start_nop_trace(struct trace_array *tr)
      38             : {
      39             :         /* Nothing to do! */
      40           0 : }
      41             : 
      42           0 : static void stop_nop_trace(struct trace_array *tr)
      43             : {
      44             :         /* Nothing to do! */
      45           0 : }
      46             : 
      47           0 : static int nop_trace_init(struct trace_array *tr)
      48             : {
      49           0 :         ctx_trace = tr;
      50           0 :         start_nop_trace(tr);
      51           0 :         return 0;
      52             : }
      53             : 
      54           0 : static void nop_trace_reset(struct trace_array *tr)
      55             : {
      56           0 :         stop_nop_trace(tr);
      57           0 : }
      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           0 : 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           0 :         if (bit == TRACE_NOP_OPT_ACCEPT) {
      71           0 :                 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           0 :                 return 0;
      75             :         }
      76             : 
      77           0 :         if (bit == TRACE_NOP_OPT_REFUSE) {
      78           0 :                 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           0 :                 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             :