/*
* lttng-clock-override-example.c
*
* Copyright (c) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <stdio.h>
#include <lttng/ust-clock.h>
/*
* For sake of example, transform time into a coarse clock (freq: 1KHz).
* Note that division can be slow on some architectures. Should be
* avoided. Use shift and multiplication instead. e.g.:
*
* Operation: / 1000000ULL
* 1/1000000ULL = .000001
* 2^19 < 1000000 < 2^20
* Add a 10 bits shift to increase accuracy:
* 2^(19+10) = 536870912
* x * 1 / 2^(19+10) ~= .000001
* 537 * 1 / 2^29 = .00000100024044513702
* 537 (multiplication factor) is between 2^9 and 2^10.
*
* In order not to overflow, first right shift by 10, multiply, and right
* shift by 19.
*/
#define DIV_CLOCK_SHIFT1 10
#define DIV_CLOCK_MUL 537
#define DIV_CLOCK_SHIFT2 19
static
uint64_t plugin_read64(void)
{
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
/*
* This is a rather dumb example, but it illustrates the plugin
* mechanism: we take the monotonic clock, and transform it into
* a very coarse clock, which increment only at 1KHz frequency.
*/
return ((uint64_t) ts.tv_sec * 1000ULL)
+ ((DIV_CLOCK_MUL * ((uint64_t) ts.tv_nsec >> DIV_CLOCK_SHIFT1))
>> DIV_CLOCK_SHIFT2);
}
static
uint64_t plugin_freq(void)
{
return 1000; /* 1KHz clock (very coarse!) */
}
static
int plugin_uuid(char *uuid)
{
const char myuuid[] = "123456789012345678901234567890123456";
/*
* Should read some unique identifier for this clock shared
* across all components of the system using this clock for
* tracing.
*/
memcpy(uuid, myuuid, LTTNG_UST_UUID_STR_LEN);
return 0;
}
static
const char *plugin_name(void)
{
return "my_example_clock";
}
static
const char *plugin_description(void)
{
return "Coarse monotonic clock at 1KHz";
}
void lttng_ust_clock_plugin_init(void)
{
int ret;
ret = lttng_ust_trace_clock_set_read64_cb(plugin_read64);
if (ret) {
fprintf(stderr, "Error setting clock override read64 callback: %s\n",
strerror(-ret));
goto error;
}
ret = lttng_ust_trace_clock_set_freq_cb(plugin_freq);
if (ret) {
fprintf(stderr, "Error setting clock override freq callback: %s\n",
strerror(-ret));
goto error;
}
ret = lttng_ust_trace_clock_set_uuid_cb(plugin_uuid);
if (ret) {
fprintf(stderr, "Error setting clock override uuid callback: %s\n",
strerror(-ret));
goto error;
}
ret = lttng_ust_trace_clock_set_name_cb(plugin_name);
if (ret) {
fprintf(stderr, "Error setting clock override name callback: %s\n",
strerror(-ret));
goto error;
}
ret = lttng_ust_trace_clock_set_description_cb(plugin_description);
if (ret) {
fprintf(stderr, "Error setting clock override description callback: %s\n",
strerror(-ret));
goto error;
}
ret = lttng_ust_enable_trace_clock_override();
if (ret) {
fprintf(stderr, "Error enabling clock override: %s\n",
strerror(-ret));
goto error;
}
return;
error:
exit(EXIT_FAILURE);
}