doc/examples/clock-override/lttng-ust-clock-override-example.c

   1 /*
   2  * lttng-clock-override-example.c
   3  *
   4  * Copyright (c) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 #include <stdlib.h>
  26 #include <time.h>
  27 #include <string.h>
  28 #include <stdio.h>
  29 #include <lttng/ust-clock.h>
  30
  31 static
  32 uint64_t plugin_read64(void)
  33 {
  34         struct timespec ts;
  35
  36         clock_gettime(CLOCK_MONOTONIC, &ts);
  37         /*
  38          * This is a rather dumb example, but it illustrates the plugin
  39          * mechanism: we take the monotonic clock, and transform it into
  40          * a very coarse clock, which increment only at 1KHz frequency.
  41          */
  42         return ((uint64_t) ts.tv_sec * 1000ULL) + (ts.tv_nsec / 1000000ULL);
  43 }
  44
  45 static
  46 uint64_t plugin_freq(void)
  47 {
  48         return 1000;    /* 1KHz clock (very coarse!) */
  49 }
  50
  51 static
  52 int plugin_uuid(char *uuid)
  53 {
  54         const char myuuid[] = "123456789012345678901234567890123456";
  55
  56         /*
  57          * Should read some unique identifier for this clock shared
  58          * across all components of the system using this clock for
  59          * tracing.
  60          */
  61         memcpy(uuid, myuuid, LTTNG_UST_UUID_STR_LEN);
  62         return 0;
  63 }
  64
  65 static
  66 const char *plugin_name(void)
  67 {
  68         return "my_example_clock";
  69 }
  70
  71 static
  72 const char *plugin_description(void)
  73 {
  74         return "Coarse monotonic clock at 1KHz";
  75 }
  76
  77 void lttng_ust_clock_plugin_init(void)
  78 {
  79         int ret;
  80
  81         ret = lttng_ust_trace_clock_set_read64_cb(plugin_read64);
  82         if (ret) {
  83                 fprintf(stderr, "Error setting clock override read64 callback: %s\n",
  84                         strerror(-ret));
  85                 goto error;
  86         }
  87         ret = lttng_ust_trace_clock_set_freq_cb(plugin_freq);
  88         if (ret) {
  89                 fprintf(stderr, "Error setting clock override freq callback: %s\n",
  90                         strerror(-ret));
  91                 goto error;
  92         }
  93         ret = lttng_ust_trace_clock_set_uuid_cb(plugin_uuid);
  94         if (ret) {
  95                 fprintf(stderr, "Error setting clock override uuid callback: %s\n",
  96                         strerror(-ret));
  97                 goto error;
  98         }
  99
 100         ret = lttng_ust_trace_clock_set_name_cb(plugin_name);
 101         if (ret) {
 102                 fprintf(stderr, "Error setting clock override name callback: %s\n",
 103                         strerror(-ret));
 104                 goto error;
 105         }
 106
 107         ret = lttng_ust_trace_clock_set_description_cb(plugin_description);
 108         if (ret) {
 109                 fprintf(stderr, "Error setting clock override description callback: %s\n",
 110                         strerror(-ret));
 111                 goto error;
 112         }
 113
 114         ret = lttng_ust_enable_trace_clock_override();
 115         if (ret) {
 116                 fprintf(stderr, "Error enabling clock override: %s\n",
 117                         strerror(-ret));
 118                 goto error;
 119         }
 120
 121         return;
 122
 123 error:
 124         exit(EXIT_FAILURE);
 125 }