| 1 | /* |
| 2 | * SPDX-License-Identifier: MIT |
| 3 | * |
| 4 | * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 5 | */ |
| 6 | |
| 7 | #include <stdlib.h> |
| 8 | #include <stdint.h> |
| 9 | #include <time.h> |
| 10 | #include <string.h> |
| 11 | #include <stdio.h> |
| 12 | #include <lttng/ust-clock.h> |
| 13 | |
| 14 | /* |
| 15 | * For sake of example, transform time into a coarse clock (freq: 1KHz). |
| 16 | * Note that division can be slow on some architectures. Should be |
| 17 | * avoided. Use shift and multiplication instead. e.g.: |
| 18 | * |
| 19 | * Operation: / 1000000ULL |
| 20 | * 1/1000000ULL = .000001 |
| 21 | * 2^19 < 1000000 < 2^20 |
| 22 | * Add a 10 bits shift to increase accuracy: |
| 23 | * 2^(19+10) = 536870912 |
| 24 | * x * 1 / 2^(19+10) ~= .000001 |
| 25 | * 537 * 1 / 2^29 = .00000100024044513702 |
| 26 | * 537 (multiplication factor) is between 2^9 and 2^10. |
| 27 | * |
| 28 | * In order not to overflow, first right shift by 10, multiply, and right |
| 29 | * shift by 19. |
| 30 | */ |
| 31 | #define DIV_CLOCK_SHIFT1 10 |
| 32 | #define DIV_CLOCK_MUL 537 |
| 33 | #define DIV_CLOCK_SHIFT2 19 |
| 34 | |
| 35 | static |
| 36 | uint64_t plugin_read64(void) |
| 37 | { |
| 38 | struct timespec ts; |
| 39 | |
| 40 | clock_gettime(CLOCK_MONOTONIC, &ts); |
| 41 | /* |
| 42 | * This is a rather dumb example, but it illustrates the plugin |
| 43 | * mechanism: we take the monotonic clock, and transform it into |
| 44 | * a very coarse clock, which increment only at 1KHz frequency. |
| 45 | */ |
| 46 | return ((uint64_t) ts.tv_sec * 1000ULL) |
| 47 | + ((DIV_CLOCK_MUL * ((uint64_t) ts.tv_nsec >> DIV_CLOCK_SHIFT1)) |
| 48 | >> DIV_CLOCK_SHIFT2); |
| 49 | } |
| 50 | |
| 51 | static |
| 52 | uint64_t plugin_freq(void) |
| 53 | { |
| 54 | return 1000; /* 1KHz clock (very coarse!) */ |
| 55 | } |
| 56 | |
| 57 | static |
| 58 | int plugin_uuid(char *uuid) |
| 59 | { |
| 60 | const char myuuid[] = "123456789012345678901234567890123456"; |
| 61 | |
| 62 | /* |
| 63 | * Should read some unique identifier for this clock shared |
| 64 | * across all components of the system using this clock for |
| 65 | * tracing. |
| 66 | */ |
| 67 | memcpy(uuid, myuuid, LTTNG_UST_UUID_STR_LEN); |
| 68 | return 0; |
| 69 | } |
| 70 | |
| 71 | static |
| 72 | const char *plugin_name(void) |
| 73 | { |
| 74 | return "my_example_clock"; |
| 75 | } |
| 76 | |
| 77 | static |
| 78 | const char *plugin_description(void) |
| 79 | { |
| 80 | return "Coarse monotonic clock at 1KHz"; |
| 81 | } |
| 82 | |
| 83 | /* |
| 84 | * Entry-point called by liblttng-ust through dlsym(); |
| 85 | */ |
| 86 | void lttng_ust_clock_plugin_init(void); |
| 87 | void lttng_ust_clock_plugin_init(void) |
| 88 | { |
| 89 | int ret; |
| 90 | |
| 91 | ret = lttng_ust_trace_clock_set_read64_cb(plugin_read64); |
| 92 | if (ret) { |
| 93 | fprintf(stderr, "Error setting clock override read64 callback: %s\n", |
| 94 | strerror(-ret)); |
| 95 | goto error; |
| 96 | } |
| 97 | ret = lttng_ust_trace_clock_set_freq_cb(plugin_freq); |
| 98 | if (ret) { |
| 99 | fprintf(stderr, "Error setting clock override freq callback: %s\n", |
| 100 | strerror(-ret)); |
| 101 | goto error; |
| 102 | } |
| 103 | ret = lttng_ust_trace_clock_set_uuid_cb(plugin_uuid); |
| 104 | if (ret) { |
| 105 | fprintf(stderr, "Error setting clock override uuid callback: %s\n", |
| 106 | strerror(-ret)); |
| 107 | goto error; |
| 108 | } |
| 109 | |
| 110 | ret = lttng_ust_trace_clock_set_name_cb(plugin_name); |
| 111 | if (ret) { |
| 112 | fprintf(stderr, "Error setting clock override name callback: %s\n", |
| 113 | strerror(-ret)); |
| 114 | goto error; |
| 115 | } |
| 116 | |
| 117 | ret = lttng_ust_trace_clock_set_description_cb(plugin_description); |
| 118 | if (ret) { |
| 119 | fprintf(stderr, "Error setting clock override description callback: %s\n", |
| 120 | strerror(-ret)); |
| 121 | goto error; |
| 122 | } |
| 123 | |
| 124 | ret = lttng_ust_enable_trace_clock_override(); |
| 125 | if (ret) { |
| 126 | fprintf(stderr, "Error enabling clock override: %s\n", |
| 127 | strerror(-ret)); |
| 128 | goto error; |
| 129 | } |
| 130 | |
| 131 | return; |
| 132 | |
| 133 | error: |
| 134 | exit(EXIT_FAILURE); |
| 135 | } |