| 1 | tracelog(3) |
| 2 | =========== |
| 3 | :object-type: macro |
| 4 | |
| 5 | |
| 6 | NAME |
| 7 | ---- |
| 8 | tracelog - LTTng-UST printf(3)-like interface with a log level |
| 9 | |
| 10 | |
| 11 | SYNOPSIS |
| 12 | -------- |
| 13 | [verse] |
| 14 | *#include <lttng/tracelog.h>* |
| 15 | |
| 16 | [verse] |
| 17 | #define *tracelog*('level', 'fmt', ...) |
| 18 | |
| 19 | Link with `-llttng-ust`. |
| 20 | |
| 21 | |
| 22 | DESCRIPTION |
| 23 | ----------- |
| 24 | The LTTng-UST `tracelog()` API allows you to trace your application with |
| 25 | the help of a simple man:printf(3)-like macro, with an additional |
| 26 | parameter for the desired log level. The 'fmt' argument is passed |
| 27 | directly to the 'fmt' parameter of man:vasprintf(3), as well as |
| 28 | the optional parameters following 'fmt'. |
| 29 | |
| 30 | The purpose of `tracelog()` is to ease the migration from logging to |
| 31 | tracing. |
| 32 | |
| 33 | The available values for the 'level' parameter are: |
| 34 | |
| 35 | include::log-levels.txt[] |
| 36 | |
| 37 | To use `tracelog()`, include `<lttng/tracelog.h>` where you need it, and |
| 38 | link your application with `liblttng-ust`. See the <<example,EXAMPLE>> |
| 39 | section below for a complete usage example. |
| 40 | |
| 41 | Once your application is instrumented with `tracelog()` calls and |
| 42 | ready to run, use man:lttng-enable-event(1) to enable the |
| 43 | `lttng_ust_tracelog:*` event. You can isolate specific log levels with |
| 44 | the nloption:--loglevel and nloption:--loglevel-only options of this |
| 45 | command. |
| 46 | |
| 47 | The `tracelog()` events contain the following fields: |
| 48 | |
| 49 | [options="header"] |
| 50 | |=== |
| 51 | |Field name |Description |
| 52 | |
| 53 | |`line` |
| 54 | |Line in source file where `tracelog()` was called. |
| 55 | |
| 56 | |`file` |
| 57 | |Source file from which `tracelog()` was called. |
| 58 | |
| 59 | |`func` |
| 60 | |Function name from which `tracelog()` was called. |
| 61 | |
| 62 | |`msg` |
| 63 | |Formatted string output. |
| 64 | |=== |
| 65 | |
| 66 | If you do not need to attach a specific log level to a `tracelog()` |
| 67 | call, use man:tracef(3) instead. |
| 68 | |
| 69 | See also the <<limitations,LIMITATIONS>> section below for important |
| 70 | limitations to consider when using `tracelog()`. |
| 71 | |
| 72 | |
| 73 | [[example]] |
| 74 | EXAMPLE |
| 75 | ------- |
| 76 | Here's a usage example of `tracelog()`: |
| 77 | |
| 78 | ------------------------------------------------------------------- |
| 79 | #include <stdlib.h> |
| 80 | #include <lttng/tracelog.h> |
| 81 | |
| 82 | int main(int argc, char *argv[]) |
| 83 | { |
| 84 | int i; |
| 85 | |
| 86 | if (argc < 2) { |
| 87 | tracelog(TRACE_CRIT, "Not enough arguments: %d", argc); |
| 88 | return EXIT_FAILURE; |
| 89 | } |
| 90 | |
| 91 | tracelog(TRACE_INFO, "Starting app with %d arguments", argc); |
| 92 | |
| 93 | for (i = 0; i < argc; i++) { |
| 94 | tracelog(TRACE_DEBUG, "Argument %d: %s", i, argv[i]); |
| 95 | } |
| 96 | |
| 97 | tracelog(TRACE_INFO, "Exiting app"); |
| 98 | |
| 99 | return EXIT_SUCCESS; |
| 100 | } |
| 101 | ------------------------------------------------------------------- |
| 102 | |
| 103 | This C source file, saved as `app.c`, can be compiled into a program |
| 104 | like this: |
| 105 | |
| 106 | [role="term"] |
| 107 | --------------------------- |
| 108 | cc -o app app.c -llttng-ust |
| 109 | --------------------------- |
| 110 | |
| 111 | You can create an LTTng tracing session, enable all the `tracelog()` |
| 112 | events, and start the created tracing session like this: |
| 113 | |
| 114 | [role="term"] |
| 115 | --------------------------------------------------- |
| 116 | lttng create my-session |
| 117 | lttng enable-event --userspace 'lttng_ust_tracelog:*' |
| 118 | lttng start |
| 119 | --------------------------------------------------- |
| 120 | |
| 121 | Or you can enable `tracelog()` events matching a log level at least |
| 122 | as severe as a given log level: |
| 123 | |
| 124 | [role="term"] |
| 125 | ------------------------------------------------------- |
| 126 | lttng enable-event --userspace 'lttng_ust_tracelog:*' \ |
| 127 | --loglevel=TRACE_INFO |
| 128 | ------------------------------------------------------- |
| 129 | |
| 130 | Next, start the program to be traced: |
| 131 | |
| 132 | [role="term"] |
| 133 | ------------------------------------------------ |
| 134 | ./app a few arguments passed to this application |
| 135 | ------------------------------------------------ |
| 136 | |
| 137 | Finally, stop the tracing session, and inspect the recorded events: |
| 138 | |
| 139 | [role="term"] |
| 140 | ---------- |
| 141 | lttng stop |
| 142 | lttng view |
| 143 | ---------- |
| 144 | |
| 145 | |
| 146 | [[limitations]] |
| 147 | LIMITATIONS |
| 148 | ----------- |
| 149 | :macro-name: tracelog |
| 150 | |
| 151 | include::tracef-tracelog-limitations.txt[] |
| 152 | |
| 153 | |
| 154 | include::common-footer.txt[] |
| 155 | |
| 156 | include::common-copyrights.txt[] |
| 157 | |
| 158 | include::common-authors.txt[] |
| 159 | |
| 160 | |
| 161 | SEE ALSO |
| 162 | -------- |
| 163 | man:tracef(3), |
| 164 | man:lttng-ust(3), |
| 165 | man:lttng(1), |
| 166 | man:printf(3) |