| 1 | lttng_ust_tracelog(3) |
| 2 | ===================== |
| 3 | :object-type: macro |
| 4 | |
| 5 | |
| 6 | NAME |
| 7 | ---- |
| 8 | lttng_ust_tracelog, lttng_ust_vtracelog - 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 *lttng_ust_tracelog*('level', 'fmt', ...) |
| 18 | #define *lttng_ust_vtracelog*('level', 'fmt', 'ap') |
| 19 | |
| 20 | Link with `-llttng-ust -llttng-ust-common`. |
| 21 | |
| 22 | |
| 23 | DESCRIPTION |
| 24 | ----------- |
| 25 | The LTTng-UST `lttng_ust_tracelog()` and `lttng_ust_vtracelog()` API |
| 26 | allows you to trace your application with the help of simple |
| 27 | man:printf(3)-like and man:vprintf(3)-like macros, with an additional |
| 28 | parameter for the desired log level. |
| 29 | |
| 30 | The 'fmt' argument is passed directly as the 'fmt' parameter of |
| 31 | man:vasprintf(3), as well as: |
| 32 | |
| 33 | For `lttng_ust_tracelog()`:: |
| 34 | The optional parameters following 'fmt'. |
| 35 | |
| 36 | For `lttng_ust_vtracelog()`:: |
| 37 | The 'ap' parameter as the 'ap' parameter of man:vasprintf(3) |
| 38 | (`va_list` type). |
| 39 | |
| 40 | The purpose of `lttng_ust_tracelog()` and `lttng_ust_vtracelog()` is to |
| 41 | ease the migration from logging to tracing. |
| 42 | |
| 43 | The available values for the 'level' parameter are: |
| 44 | |
| 45 | include::log-levels.txt[] |
| 46 | |
| 47 | To use `lttng_ust_tracelog()` or `lttng_ust_vtracelog()`, include |
| 48 | `<lttng/tracelog.h>` where you need it, and link your application with |
| 49 | `liblttng-ust` and `liblttng-ust-common`. See the <<example,EXAMPLE>> |
| 50 | section below for a complete usage example. |
| 51 | |
| 52 | Once your application is instrumented with `lttng_ust_tracelog()` and/or |
| 53 | `lttng_ust_vtracelog()` calls and ready to run, use |
| 54 | man:lttng-enable-event(1) to enable the `lttng_ust_tracelog:*` event. |
| 55 | You can isolate specific log levels with the nloption:--loglevel and |
| 56 | nloption:--loglevel-only options of this command. |
| 57 | |
| 58 | The `lttng_ust_tracelog()` and `lttng_ust_vtracelog()` events contain |
| 59 | the following fields: |
| 60 | |
| 61 | [options="header"] |
| 62 | |=== |
| 63 | |Field name |Description |
| 64 | |
| 65 | |`line` |
| 66 | |Line in source file where `lttng_ust_tracelog()` was called. |
| 67 | |
| 68 | |`file` |
| 69 | |Source file from which `lttng_ust_tracelog()` was called. |
| 70 | |
| 71 | |`func` |
| 72 | |Function name from which `lttng_ust_tracelog()` was called. |
| 73 | |
| 74 | |`msg` |
| 75 | |Formatted string output. |
| 76 | |=== |
| 77 | |
| 78 | If you do not need to attach a specific log level to a |
| 79 | `lttng_ust_tracelog()`/`lttng_ust_vtracelog()` call, use |
| 80 | man:lttng_ust_tracef(3) instead. |
| 81 | |
| 82 | See also the <<limitations,LIMITATIONS>> section below for important |
| 83 | limitations to consider when using `lttng_ust_tracelog()` or |
| 84 | `lttng_ust_vtracelog()`. |
| 85 | |
| 86 | |
| 87 | [[example]] |
| 88 | EXAMPLE |
| 89 | ------- |
| 90 | Here's a usage example of `lttng_ust_tracelog()`: |
| 91 | |
| 92 | ------------------------------------------------------------------- |
| 93 | #include <stdlib.h> |
| 94 | #include <lttng/tracelog.h> |
| 95 | |
| 96 | int main(int argc, char *argv[]) |
| 97 | { |
| 98 | int i; |
| 99 | |
| 100 | if (argc < 2) { |
| 101 | lttng_ust_tracelog(LTTNG_UST_TRACEPOINT_LOGLEVEL_CRIT, |
| 102 | "Not enough arguments: %d", argc); |
| 103 | return EXIT_FAILURE; |
| 104 | } |
| 105 | |
| 106 | lttng_ust_tracelog(LTTNG_UST_TRACEPOINT_LOGLEVEL_INFO, |
| 107 | "Starting app with %d arguments", argc); |
| 108 | |
| 109 | for (i = 0; i < argc; i++) { |
| 110 | lttng_ust_tracelog(LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG, |
| 111 | "Argument %d: %s", i, argv[i]); |
| 112 | } |
| 113 | |
| 114 | lttng_ust_tracelog(LTTNG_UST_TRACEPOINT_LOGLEVEL_INFO, |
| 115 | "Exiting app"); |
| 116 | return EXIT_SUCCESS; |
| 117 | } |
| 118 | ------------------------------------------------------------------- |
| 119 | |
| 120 | This C source file, saved as `app.c`, can be compiled into a program |
| 121 | like this: |
| 122 | |
| 123 | [role="term"] |
| 124 | ---- |
| 125 | $ cc -o app app.c -llttng-ust -llttng-ust-common |
| 126 | ---- |
| 127 | |
| 128 | You can create an LTTng tracing session, enable all the |
| 129 | `lttng_ust_tracelog()` events, and start the created tracing session |
| 130 | like this: |
| 131 | |
| 132 | [role="term"] |
| 133 | ---- |
| 134 | $ lttng create my-session |
| 135 | $ lttng enable-event --userspace 'lttng_ust_tracelog:*' |
| 136 | $ lttng start |
| 137 | ---- |
| 138 | |
| 139 | Or you can enable `lttng_ust_tracelog()` events matching a log level at |
| 140 | least as severe as a given log level: |
| 141 | |
| 142 | [role="term"] |
| 143 | ---- |
| 144 | $ lttng enable-event --userspace 'lttng_ust_tracelog:*' \ |
| 145 | --loglevel=INFO |
| 146 | ---- |
| 147 | |
| 148 | Next, start the program to be traced: |
| 149 | |
| 150 | [role="term"] |
| 151 | ---- |
| 152 | $ ./app a few arguments passed to this application |
| 153 | ---- |
| 154 | |
| 155 | Finally, stop the tracing session, and inspect the recorded events: |
| 156 | |
| 157 | [role="term"] |
| 158 | ---- |
| 159 | $ lttng stop |
| 160 | $ lttng view |
| 161 | ---- |
| 162 | |
| 163 | |
| 164 | [[limitations]] |
| 165 | LIMITATIONS |
| 166 | ----------- |
| 167 | :macro-suffix: tracelog |
| 168 | |
| 169 | include::tracef-tracelog-limitations.txt[] |
| 170 | |
| 171 | |
| 172 | include::common-footer.txt[] |
| 173 | |
| 174 | include::common-copyrights.txt[] |
| 175 | |
| 176 | include::common-authors.txt[] |
| 177 | |
| 178 | |
| 179 | SEE ALSO |
| 180 | -------- |
| 181 | man:lttng_ust_tracef(3), |
| 182 | man:lttng_ust_vtracef(3), |
| 183 | man:lttng-ust(3), |
| 184 | man:lttng(1), |
| 185 | man:printf(3) |