doc/man/lttng-ust.3.txt

   1 lttng-ust(3)
   2 ============
   3 :object-type: library
   4
   5
   6 NAME
   7 ----
   8 lttng-ust - LTTng user space tracing
   9
  10
  11 SYNOPSIS
  12 --------
  13 [verse]
  14 *#include <lttng/tracepoint.h>*
  15
  16 [verse]
  17 #define *TRACEPOINT_ENUM*('prov_name', 'enum_name', 'mappings')
  18 #define *TRACEPOINT_EVENT*('prov_name', 't_name', 'args', 'fields')
  19 #define *TRACEPOINT_EVENT_CLASS*('prov_name', 'class_name', 'args', 'fields')
  20 #define *TRACEPOINT_EVENT_INSTANCE*('prov_name', 'class_name', 't_name', 'args')
  21 #define *TRACEPOINT_LOGLEVEL*('prov_name', 't_name', 'level')
  22 #define *ctf_array*('int_type', 'field_name', 'expr', 'count')
  23 #define *ctf_array_nowrite*('int_type', 'field_name', 'expr', 'count')
  24 #define *ctf_array_hex*('int_type', 'field_name', 'expr', 'count')
  25 #define *ctf_array_nowrite_hex*('int_type', 'field_name', 'expr', 'count')
  26 #define *ctf_array_network*('int_type', 'field_name', 'expr', 'count')
  27 #define *ctf_array_network_nowrite*('int_type', 'field_name', 'expr', 'count')
  28 #define *ctf_array_network_hex*('int_type', 'field_name', 'expr', 'count')
  29 #define *ctf_array_network_nowrite_hex*('int_type', 'field_name', 'expr', 'count')
  30 #define *ctf_array_text*(char, 'field_name', 'expr', 'count')
  31 #define *ctf_array_text_nowrite*(char, 'field_name', 'expr', 'count')
  32 #define *ctf_enum*('prov_name', 'enum_name', 'int_type', 'field_name', 'expr')
  33 #define *ctf_enum_nowrite*('prov_name', 'enum_name', 'int_type', 'field_name',
  34                          'expr')
  35 #define *ctf_enum_value*('label', 'value')
  36 #define *ctf_enum_range*('label', 'start', 'end')
  37 #define *ctf_float*('float_type', 'field_name', 'expr')
  38 #define *ctf_float_nowrite*('float_type', 'field_name', 'expr')
  39 #define *ctf_integer*('int_type', 'field_name', 'expr')
  40 #define *ctf_integer_hex*('int_type', 'field_name', 'expr')
  41 #define *ctf_integer_network*('int_type', 'field_name', 'expr')
  42 #define *ctf_integer_network_hex*('int_type', 'field_name', 'expr')
  43 #define *ctf_integer_nowrite*('int_type', 'field_name', 'expr')
  44 #define *ctf_sequence*('int_type', 'field_name', 'expr', 'len_type', 'len_expr')
  45 #define *ctf_sequence_nowrite*('int_type', 'field_name', 'expr', 'len_type',
  46                              'len_expr')
  47 #define *ctf_sequence_hex*('int_type', 'field_name', 'expr', 'len_type',
  48                          'len_expr')
  49 #define *ctf_sequence_nowrite_hex*('int_type', 'field_name', 'expr', 'len_type',
  50                                  'len_expr')
  51 #define *ctf_sequence_network*('int_type', 'field_name', 'expr', 'len_type',
  52                              'len_expr')
  53 #define *ctf_sequence_network_nowrite*('int_type', 'field_name', 'expr',
  54                                      'len_type', 'len_expr')
  55 #define *ctf_sequence_network_hex*('int_type', 'field_name', 'expr', 'len_type',
  56                                  'len_expr')
  57 #define *ctf_sequence_network_nowrite_hex*('int_type', 'field_name', 'expr',
  58                                          'len_type', 'len_expr')
  59 #define *ctf_sequence_text*(char, 'field_name', 'expr', 'len_type', 'len_expr')
  60 #define *ctf_sequence_text_nowrite*(char, 'field_name', 'expr', 'len_type',
  61                                   'len_expr')
  62 #define *ctf_string*('field_name', 'expr')
  63 #define *ctf_string_nowrite*('field_name', 'expr')
  64 #define *do_tracepoint*('prov_name', 't_name', ...)
  65 #define *tracepoint*('prov_name', 't_name', ...)
  66 #define *tracepoint_enabled*('prov_name', 't_name')
  67
  68 Link with `-llttng-ust -ldl`, following this man page.
  69
  70
  71 DESCRIPTION
  72 -----------
  73 The http://lttng.org/[_Linux Trace Toolkit: next generation_] is an open
  74 source software package used for correlated tracing of the Linux kernel,
  75 user applications, and user libraries.
  76
  77 LTTng-UST is the user space tracing component of the LTTng project. It
  78 is a port to user space of the low-overhead tracing capabilities of the
  79 LTTng Linux kernel tracer. The `liblttng-ust` library is used to trace
  80 user applications and libraries.
  81
  82 NOTE: This man page is about the `liblttng-ust` library. The LTTng-UST
  83 project also provides Java and Python packages to trace applications
  84 written in those languages. How to instrument and trace Java and Python
  85 applications is documented in
  86 http://lttng.org/docs/[the online LTTng documentation].
  87
  88 There are three ways to use `liblttng-ust`:
  89
  90   * Using the man:tracef(3) API, which is similar to man:printf(3).
  91   * Using the man:tracelog(3) API, which is man:tracef(3) with
  92     a log level parameter.
  93   * Defining your own tracepoints. See the
  94     <<creating-tp,Creating a tracepoint provider>> section below.
  95
  96
  97 [[creating-tp]]
  98 Creating a tracepoint provider
  99 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 100 Creating a tracepoint provider is the first step of using
 101 `liblttng-ust`. The next steps are:
 102
 103   * <<tracepoint,Instrumenting your application with `tracepoint()` calls>>
 104   * Building your application with LTTng-UST support, either
 105     <<build-static,statically>> or <<build-dynamic,dynamically>>.
 106
 107 A *tracepoint provider* is a compiled object containing the event
 108 probes corresponding to your custom tracepoint definitions. A tracepoint
 109 provider contains the code to get the size of an event and to serialize
 110 it, amongst other things.
 111
 112 To create a tracepoint provider, start with the following
 113 _tracepoint provider header_ template:
 114
 115 ------------------------------------------------------------------------
 116 #undef TRACEPOINT_PROVIDER
 117 #define TRACEPOINT_PROVIDER my_provider
 118
 119 #undef TRACEPOINT_INCLUDE
 120 #define TRACEPOINT_INCLUDE "./tp.h"
 121
 122 #if !defined(_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ)
 123 #define _TP_H
 124
 125 #include <lttng/tracepoint.h>
 126
 127 /*
 128  * TRACEPOINT_EVENT(), TRACEPOINT_EVENT_CLASS(),
 129  * TRACEPOINT_EVENT_INSTANCE(), TRACEPOINT_LOGLEVEL(),
 130  * and `TRACEPOINT_ENUM()` are used here.
 131  */
 132
 133 #endif /* _TP_H */
 134
 135 #include <lttng/tracepoint-event.h>
 136 ------------------------------------------------------------------------
 137
 138 In this template, the tracepoint provider is named `my_provider`
 139 (`TRACEPOINT_PROVIDER` definition). The file needs to bear the
 140 name of the `TRACEPOINT_INCLUDE` definition (`tp.h` in this case).
 141 Between `#include <lttng/tracepoint.h>` and `#endif` go
 142 the invocations of the <<tracepoint-event,`TRACEPOINT_EVENT()`>>,
 143 <<tracepoint-event-class,`TRACEPOINT_EVENT_CLASS()`>>,
 144 <<tracepoint-event-class,`TRACEPOINT_EVENT_INSTANCE()`>>,
 145 <<tracepoint-loglevel,`TRACEPOINT_LOGLEVEL()`>>, and
 146 <<tracepoint-enum,`TRACEPOINT_ENUM()`>> macros.
 147
 148 NOTE: You can avoid writing the prologue and epilogue boilerplate in the
 149 template file above by using the man:lttng-gen-tp(1) tool shipped with
 150 LTTng-UST.
 151
 152 The tracepoint provider header file needs to be included in a source
 153 file which looks like this:
 154
 155 ------------------------------------------------------------------------
 156 #define TRACEPOINT_CREATE_PROBES
 157
 158 #include "tp.h"
 159 ------------------------------------------------------------------------
 160
 161 Together, those two files (let's call them `tp.h` and `tp.c`) form the
 162 tracepoint provider sources, ready to be compiled.
 163
 164 You can create multiple tracepoint providers to be used in a single
 165 application, but each one must have its own header file.
 166
 167 The <<tracepoint-event,`TRACEPOINT_EVENT()` usage>> section below
 168 shows how to use the `TRACEPOINT_EVENT()` macro to define the actual
 169 tracepoints in the tracepoint provider header file.
 170
 171 See the <<example,EXAMPLE>> section below for a complete example.
 172
 173
 174 [[tracepoint-event]]
 175 `TRACEPOINT_EVENT()` usage
 176 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 177 The `TRACEPOINT_EVENT()` macro is used in a template provider
 178 header file (see the <<creating-tp,Creating a tracepoint provider>>
 179 section above) to define LTTng-UST tracepoints.
 180
 181 The `TRACEPOINT_EVENT()` usage template is as follows:
 182
 183 ------------------------------------------------------------------------
 184 TRACEPOINT_EVENT(
 185     /* Tracepoint provider name */
 186     my_provider,
 187
 188     /* Tracepoint/event name */
 189     my_tracepoint,
 190
 191     /* List of tracepoint arguments (input) */
 192     TP_ARGS(
 193         ...
 194     ),
 195
 196     /* List of fields of eventual event (output) */
 197     TP_FIELDS(
 198         ...
 199     )
 200 )
 201 ------------------------------------------------------------------------
 202
 203 The `TP_ARGS()` macro contains the input arguments of the tracepoint.
 204 Those arguments can be used in the argument expressions of the output
 205 fields defined in `TP_FIELDS()`.
 206
 207 The format of the `TP_ARGS()` parameters is: C type, then argument name;
 208 repeat as needed, up to ten times. For example:
 209
 210 ------------------------------------------------------------------------
 211 TP_ARGS(
 212     int, my_int,
 213     const char *, my_string,
 214     FILE *, my_file,
 215     double, my_float,
 216     struct my_data *, my_data
 217 )
 218 ------------------------------------------------------------------------
 219
 220 The `TP_FIELDS()` macro contains the output fields of the tracepoint,
 221 that is, the actual data that can be recorded in the payload of an
 222 event emitted by this tracepoint.
 223
 224 The `TP_FIELDS()` macro contains a list of `ctf_*()` macros
 225 :not: separated by commas. The available macros are documented in the
 226 <<ctf-macros,Available `ctf_*()` field type macros>> section below.
 227
 228
 229 [[ctf-macros]]
 230 Available `ctf_*()` field type macros
 231 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 232 This section documents the available `ctf_*()` macros that can be
 233 inserted in the `TP_FIELDS()` macro of the
 234 <<tracepoint-event,`TRACEPOINT_EVENT()` macro>>.
 235
 236 Standard integer, displayed in base 10:
 237
 238 [verse]
 239 *ctf_integer*('int_type', 'field_name', 'expr')
 240 *ctf_integer_nowrite*('int_type', 'field_name', 'expr')
 241
 242 Standard integer, displayed in base 16:
 243
 244 [verse]
 245 *ctf_integer_hex*('int_type', 'field_name', 'expr')
 246
 247 Integer in network byte order (big endian), displayed in base 10:
 248
 249 [verse]
 250 *ctf_integer_network*('int_type', 'field_name', 'expr')
 251
 252 Integer in network byte order, displayed in base 16:
 253
 254 [verse]
 255 *ctf_integer_network_hex*('int_type', 'field_name', 'expr')
 256
 257 Floating point number:
 258
 259 [verse]
 260 *ctf_float*('float_type', 'field_name', 'expr')
 261 *ctf_float_nowrite*('float_type', 'field_name', 'expr')
 262
 263 Null-terminated string:
 264
 265 [verse]
 266 *ctf_string*('field_name', 'expr')
 267 *ctf_string_nowrite*('field_name', 'expr')
 268
 269 Statically-sized array of integers (`_hex` versions displayed in
 270 hexadecimal, `_network` versions in network byte order):
 271
 272 [verse]
 273 *ctf_array*('int_type', 'field_name', 'expr', 'count')
 274 *ctf_array_nowrite*('int_type', 'field_name', 'expr', 'count')
 275 *ctf_array_hex*('int_type', 'field_name', 'expr', 'count')
 276 *ctf_array_nowrite_hex*('int_type', 'field_name', 'expr', 'count')
 277 *ctf_array_network*('int_type', 'field_name', 'expr', 'count')
 278 *ctf_array_network_nowrite*('int_type', 'field_name', 'expr', 'count')
 279 *ctf_array_network_hex*('int_type', 'field_name', 'expr', 'count')
 280 *ctf_array_network_nowrite_hex*('int_type', 'field_name', 'expr', 'count')
 281
 282 Statically-sized array, printed as text; no need to be null-terminated:
 283
 284 [verse]
 285 *ctf_array_text*(char, 'field_name', 'expr', 'count')
 286 *ctf_array_text_nowrite*(char, 'field_name', 'expr', 'count')
 287
 288 Dynamically-sized array of integers (`_hex` versions displayed in
 289 hexadecimal, `_network` versions in network byte order):
 290
 291 [verse]
 292 *ctf_sequence*('int_type', 'field_name', 'expr', 'len_type', 'len_expr')
 293 *ctf_sequence_nowrite*('int_type', 'field_name', 'expr', 'len_type', 'len_expr')
 294 *ctf_sequence_hex*('int_type', 'field_name', 'expr', 'len_type', 'len_expr')
 295 *ctf_sequence_nowrite_hex*('int_type', 'field_name', 'expr', 'len_type',
 296                          'len_expr')
 297 *ctf_sequence_network*('int_type', 'field_name', 'expr', 'len_type', 'len_expr')
 298 *ctf_sequence_network_nowrite*('int_type', 'field_name', 'expr', 'len_type',
 299                              'len_expr')
 300 *ctf_sequence_network_hex*('int_type', 'field_name', 'expr', 'len_type',
 301                          'len_expr')
 302 *ctf_sequence_network_nowrite_hex*('int_type', 'field_name', 'expr',
 303                                  'len_type', 'len_expr')
 304
 305 Dynamically-sized array, displayed as text; no need to be null-terminated:
 306
 307 [verse]
 308 *ctf_sequence_text*(char, 'field_name', 'expr', 'len_type', 'len_expr')
 309 *ctf_sequence_text_nowrite*(char, 'field_name', 'expr', 'len_type', 'len_expr')
 310
 311 Enumeration. The enumeration field must be defined before using this
 312 macro with the `TRACEPOINT_ENUM()` macro. See the
 313 <<tracepoint-enum,`TRACEPOINT_ENUM()` usage>> section for more
 314 information.
 315
 316 [verse]
 317 *ctf_enum*('prov_name', 'enum_name', 'int_type', 'field_name', 'expr')
 318 *ctf_enum_nowrite*('prov_name', 'enum_name', 'int_type', 'field_name', 'expr')
 319
 320 The parameters are:
 321
 322 'count'::
 323     Number of elements in array/sequence. This must be known at
 324     compile time.
 325
 326 'enum_name'::
 327     Name of an enumeration field previously defined with the
 328     `TRACEPOINT_ENUM()` macro. See the
 329     <<tracepoint-enum,`TRACEPOINT_ENUM()` usage>> section for more
 330     information.
 331
 332 'expr'::
 333     C expression resulting in the field's value. This expression can
 334     use one or more arguments passed to the tracepoint. The arguments
 335     of a given tracepoint are defined in the `TP_ARGS()` macro (see
 336     the <<creating-tp,Creating a tracepoint provider>> section above).
 337
 338 'field_name'::
 339     Event field name (C identifier syntax, :not: a literal string).
 340
 341 'float_type'::
 342     Float C type (`float` or `double`). The size of this type determines
 343     the size of the floating point number field.
 344
 345 'int_type'::
 346     Integer C type. The size of this type determines the size of the
 347     integer/enumeration field.
 348
 349 'len_expr'::
 350     C expression resulting in the sequence's length. This expression
 351     can use one or more arguments passed to the tracepoint.
 352
 353 'len_type'::
 354     Unsigned integer C type of sequence's length.
 355
 356 'prov_name'::
 357     Tracepoint provider name. This must be the same as the tracepoint
 358     provider name used in a previous field definition.
 359
 360 The `_nowrite` versions omit themselves from the recorded trace, but are
 361 otherwise identical. Their primary purpose is to make some of the
 362 event context available to the event filters without having to commit
 363 the data to sub-buffers. See man:lttng-enable-event(1) to learn more
 364 about dynamic event filtering.
 365
 366 See the <<example,EXAMPLE>> section below for a complete example.
 367
 368
 369 [[tracepoint-enum]]
 370 `TRACEPOINT_ENUM()` usage
 371 ~~~~~~~~~~~~~~~~~~~~~~~~~
 372 An enumeration field is a list of mappings between an integers, or a
 373 range of integers, and strings (sometimes called _labels_ or
 374 _enumerators_). Enumeration fields can be used to have a more compact
 375 trace when the possible values for a field are limited.
 376
 377 An enumeration field is defined with the `TRACEPOINT_ENUM()` macro:
 378
 379 ------------------------------------------------------------------------
 380 TRACEPOINT_ENUM(
 381     /* Tracepoint provider name */
 382     my_provider,
 383
 384     /* Enumeration name (unique in the whole tracepoint provider) */
 385     my_enum,
 386
 387     /* Enumeration mappings */
 388     TP_ENUM_VALUES(
 389         ...
 390     )
 391 )
 392 ------------------------------------------------------------------------
 393
 394 `TP_ENUM_VALUES()` contains a list of enumeration mappings, :not:
 395 separated by commas. Two macros can be used in the `TP_ENUM_VALUES()`:
 396 `ctf_enum_value()` and `ctf_enum_range()`.
 397
 398 `ctf_enum_value()` is a single value mapping:
 399
 400 [verse]
 401 *ctf_enum_value*('label', 'value')
 402
 403 This macro maps the given 'label' string to the value 'value'.
 404
 405 `ctf_enum_range()` is a range mapping:
 406
 407 [verse]
 408 *ctf_enum_range*('label', 'start', 'end')
 409
 410 This macro maps the given 'label' string to the range of integers from
 411 'start' to 'end', inclusively. Range mappings may overlap, but the
 412 behaviour is implementation-defined: each trace reader handles
 413 overlapping ranges as it wishes.
 414
 415 See the <<example,EXAMPLE>> section below for a complete example.
 416
 417
 418 [[tracepoint-event-class]]
 419 `TRACEPOINT_EVENT_CLASS()` usage
 420 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 421 A *tracepoint class* is a class of tracepoints sharing the
 422 same field types and names. A tracepoint instance is one instance of
 423 such a declared tracepoint class, with its own event name.
 424
 425 LTTng-UST creates one event serialization function per tracepoint
 426 class. Using `TRACEPOINT_EVENT()` creates one tracepoint class per
 427 tracepoint definition, whereas using `TRACEPOINT_EVENT_CLASS()` and
 428 `TRACEPOINT_EVENT_INSTANCE()` creates one tracepoint class, and one or
 429 more tracepoint instances of this class. In other words, many
 430 tracepoints can reuse the same serialization code. Reusing the same
 431 code, when possible, can reduce cache pollution, thus improve
 432 performance.
 433
 434 The `TRACEPOINT_EVENT_CLASS()` macro accepts the same parameters as
 435 the `TRACEPOINT_EVENT()` macro, except that instead of an event name,
 436 its second parameter is the _tracepoint class name_:
 437
 438 ------------------------------------------------------------------------
 439 TRACEPOINT_EVENT_CLASS(
 440     /* Tracepoint provider name */
 441     my_provider,
 442
 443     /* Tracepoint class name */
 444     my_tracepoint_class,
 445
 446     /* List of tracepoint arguments (input) */
 447     TP_ARGS(
 448         ...
 449     ),
 450
 451     /* List of fields of eventual event (output) */
 452     TP_FIELDS(
 453         ...
 454     )
 455 )
 456 ------------------------------------------------------------------------
 457
 458 Once the tracepoint class is defined, you can create as many tracepoint
 459 instances as needed:
 460
 461 -------------------------------------------------------------------------
 462 TRACEPOINT_EVENT_INSTANCE(
 463     /* Tracepoint provider name */
 464     my_provider,
 465
 466     /* Tracepoint class name */
 467     my_tracepoint_class,
 468
 469     /* Tracepoint/event name */
 470     my_tracepoint,
 471
 472     /* List of tracepoint arguments (input) */
 473     TP_ARGS(
 474         ...
 475     )
 476 )
 477 ------------------------------------------------------------------------
 478
 479 As you can see, the `TRACEPOINT_EVENT_INSTANCE()` does not contain
 480 the `TP_FIELDS()` macro, because they are defined at the
 481 `TRACEPOINT_EVENT_CLASS()` level.
 482
 483 See the <<example,EXAMPLE>> section below for a complete example.
 484
 485
 486 [[tracepoint-loglevel]]
 487 `TRACEPOINT_LOGLEVEL()` usage
 488 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 489 Optionally, a *log level* can be assigned to a defined tracepoint.
 490 Assigning different levels of severity to tracepoints can be useful:
 491 when controlling tracing sessions, you can choose to only enable
 492 events falling into a specific log level range using the
 493 nloption:--loglevel and nloption:--loglevel-only options of the
 494 man:lttng-enable-event(1) command.
 495
 496 Log levels are assigned to tracepoints that are already defined using
 497 the `TRACEPOINT_LOGLEVEL()` macro. The latter must be used after having
 498 used `TRACEPOINT_EVENT()` or `TRACEPOINT_EVENT_INSTANCE()` for a given
 499 tracepoint. The `TRACEPOINT_LOGLEVEL()` macro is used as follows:
 500
 501 ------------------------------------------------------------------------
 502 TRACEPOINT_LOGLEVEL(
 503     /* Tracepoint provider name */
 504     my_provider,
 505
 506     /* Tracepoint/event name */
 507     my_tracepoint,
 508
 509     /* Log level */
 510     TRACE_INFO
 511 )
 512 ------------------------------------------------------------------------
 513
 514 The available log level definitions are:
 515
 516 include::log-levels.txt[]
 517
 518 See the <<example,EXAMPLE>> section below for a complete example.
 519
 520
 521 [[tracepoint]]
 522 Instrumenting your application
 523 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 524 Once the tracepoint provider is created (see the
 525 <<creating-tp,Creating a tracepoint provider>> section above), you can
 526 instrument your application with the defined tracepoints thanks to the
 527 `tracepoint()` macro:
 528
 529 [verse]
 530 #define *tracepoint*('prov_name', 't_name', ...)
 531
 532 With:
 533
 534 'prov_name'::
 535     Tracepoint provider name.
 536
 537 't_name'::
 538     Tracepoint/event name.
 539
 540 `...`::
 541     Tracepoint arguments, if any.
 542
 543 Make sure to include the tracepoint provider header file anywhere you
 544 use `tracepoint()` for this provider.
 545
 546 NOTE: Even though LTTng-UST supports `tracepoint()` call site duplicates
 547 having the same provider and tracepoint names, it is recommended to use
 548 a provider/tracepoint name pair only once within the application source
 549 code to help map events back to their call sites when analyzing the
 550 trace.
 551
 552 Sometimes, arguments to the tracepoint are expensive to compute (take
 553 call stack, for example). To avoid the computation when the tracepoint
 554 is disabled, you can use the `tracepoint_enabled()` and
 555 `do_tracepoint()` macros:
 556
 557 [verse]
 558 #define *tracepoint_enabled*('prov_name', 't_name')
 559 #define *do_tracepoint*('prov_name', 't_name', ...)
 560
 561 `tracepoint_enabled()` returns a non-zero value if the tracepoint
 562 named 't_name' from the provider named 'prov_name' is enabled at
 563 run time.
 564
 565 `do_tracepoint()` is like `tracepoint()`, except that it doesn't check
 566 if the tracepoint is enabled. Using `tracepoint()` with
 567 `tracepoint_enabled()` is dangerous since `tracepoint()` also contains
 568 the `tracepoint_enabled()` check, thus a race condition is possible
 569 in this situation:
 570
 571 ------------------------------------------------------------------------
 572 if (tracepoint_enabled(my_provider, my_tracepoint)) {
 573     stuff = prepare_stuff();
 574 }
 575
 576 tracepoint(my_provider, my_tracepoint, stuff);
 577 ------------------------------------------------------------------------
 578
 579 If the tracepoint is enabled after the condition, then `stuff` is not
 580 prepared: the emitted event will either contain wrong data, or the
 581 whole application could crash (segmentation fault, for example).
 582
 583 NOTE: Neither `tracepoint_enabled()` nor `do_tracepoint()` have
 584 a `STAP_PROBEV()` call, so if you need it, you should emit this call
 585 yourself.
 586
 587
 588 [[build-static]]
 589 Statically linking the tracepoint provider
 590 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 591 With the static linking method, compiled tracepoint providers are copied
 592 into the target application.
 593
 594 Define `TRACEPOINT_DEFINE` definition below the
 595 `TRACEPOINT_CREATE_PROBES` definition in the tracepoint provider
 596 source:
 597
 598 ------------------------------------------------------------------------
 599 #define TRACEPOINT_CREATE_PROBES
 600 #define TRACEPOINT_DEFINE
 601
 602 #include "tp.h"
 603 ------------------------------------------------------------------------
 604
 605 Create the tracepoint provider object file:
 606
 607 [role="term"]
 608 --------------
 609 cc -c -I. tp.c
 610 --------------
 611
 612 NOTE: Although an application instrumented with LTTng-UST tracepoints
 613 can be compiled with a C++ compiler, tracepoint probes should be
 614 compiled with a C compiler.
 615
 616 At this point, you _can_ archive this tracepoint provider object file,
 617 possibly with other object files of your application or with other
 618 tracepoint provider object files, as a static library:
 619
 620 [role="term"]
 621 ---------------
 622 ar rc tp.a tp.o
 623 ---------------
 624
 625 Using a static library does have the advantage of centralising the
 626 tracepoint providers objects so they can be shared between multiple
 627 applications. This way, when the tracepoint provider is modified, the
 628 source code changes don't have to be patched into each application's
 629 source code tree. The applications need to be relinked after each
 630 change, but need not to be otherwise recompiled (unless the tracepoint
 631 provider's API changes).
 632
 633 Then, link your application with this object file (or with the static
 634 library containing it) and with `liblttng-ust` and `libdl`
 635 (`libc` on a BSD system):
 636
 637 [role="term"]
 638 -------------------------------------
 639 cc -o app tp.o app.o -llttng-ust -ldl
 640 -------------------------------------
 641
 642
 643 [[build-dynamic]]
 644 Dynamically loading the tracepoint provider
 645 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 646 The second approach to package the tracepoint provider is to use the
 647 dynamic loader: the library and its member functions are explicitly
 648 sought, loaded at run time.
 649
 650 In this scenario, the tracepoint provider is compiled as a shared
 651 object.
 652
 653 The process to create the tracepoint provider shared object is pretty
 654 much the same as the <<build-static,static linking method>>, except
 655 that:
 656
 657   * Since the tracepoint provider is not part of the application,
 658     `TRACEPOINT_DEFINE` must be defined, for each tracepoint
 659     provider, in exactly one source file of the
 660     _application_
 661   * `TRACEPOINT_PROBE_DYNAMIC_LINKAGE` must be defined next
 662     to `TRACEPOINT_DEFINE`
 663
 664 Regarding `TRACEPOINT_DEFINE` and `TRACEPOINT_PROBE_DYNAMIC_LINKAGE`,
 665 the recommended practice is to use a separate C source file in your
 666 application to define them, then include the tracepoint provider header
 667 files afterwards. For example, as `tp-define.c`:
 668
 669 ------------------------------------------------------------------------
 670 #define TRACEPOINT_DEFINE
 671 #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE
 672
 673 #include "tp.h"
 674 ------------------------------------------------------------------------
 675
 676 The tracepoint provider object file used to create the shared library is
 677 built like it is using the static linking method, but with the
 678 nloption:-fpic option:
 679
 680 [role="term"]
 681 --------------------
 682 cc -c -fpic -I. tp.c
 683 --------------------
 684
 685 It is then linked as a shared library like this:
 686
 687 [role="term"]
 688 -------------------------------------------------------
 689 cc -shared -Wl,--no-as-needed -o tp.so tp.o -llttng-ust
 690 -------------------------------------------------------
 691
 692 This tracepoint provider shared object isn't linked with the user
 693 application: it must be loaded manually. This is why the application is
 694 built with no mention of this tracepoint provider, but still needs
 695 libdl:
 696
 697 [role="term"]
 698 --------------------------------
 699 cc -o app app.o tp-define.o -ldl
 700 --------------------------------
 701
 702 There are two ways to dynamically load the tracepoint provider shared
 703 object:
 704
 705   * Load it manually from the application using man:dlopen(3)
 706   * Make the dynamic loader load it with the `LD_PRELOAD`
 707     environment variable (see man:ld.so(8))
 708
 709 If the application does not dynamically load the tracepoint provider
 710 shared object using one of the methods above, tracing is disabled for
 711 this application, and the events are not listed in the output of
 712 man:lttng-list(1).
 713
 714 Note that it is not safe to use man:dlclose(3) on a tracepoint provider
 715 shared object that is being actively used for tracing, due to a lack of
 716 reference counting from LTTng-UST to the shared object.
 717
 718 For example, statically linking a tracepoint provider to a shared object
 719 which is to be dynamically loaded by an application (a plugin, for
 720 example) is not safe: the shared object, which contains the tracepoint
 721 provider, could be dynamically closed (man:dlclose(3)) at any time by
 722 the application.
 723
 724 To instrument a shared object, either:
 725
 726   * Statically link the tracepoint provider to the application, or
 727   * Build the tracepoint provider as a shared object (following the
 728     procedure shown in this section), and preload it when tracing is
 729     needed using the `LD_PRELOAD` environment variable.
 730
 731
 732 Using LTTng-UST with daemons
 733 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 734 Some extra care is needed when using `liblttng-ust` with daemon
 735 applications that call man:fork(2), man:clone(2), or BSD's man:rfork(2)
 736 without a following man:exec(3) family system call. The library
 737 `liblttng-ust-fork.so` needs to be preloaded before starting the
 738 application with the `LD_PRELOAD` environment variable (see
 739 man:ld.so(8)).
 740
 741
 742 Context information
 743 ~~~~~~~~~~~~~~~~~~~
 744 Context information can be prepended by the LTTng-UST tracer before
 745 each event, or before specific events.
 746
 747 Context fields can be added to specific channels using
 748 man:lttng-add-context(1).
 749
 750 The following context fields are supported by LTTng-UST:
 751
 752 `cpu_id`::
 753     CPU ID.
 754 +
 755 NOTE: This context field is always enabled, and it cannot be added
 756 with man:lttng-add-context(1). Its main purpose is to be used for
 757 dynamic event filtering. See man:lttng-enable-event(1) for more
 758 information about event filtering.
 759
 760 `ip`::
 761     Instruction pointer: enables recording the exact address from which
 762     an event was emitted. This context field can be used to
 763     reverse-lookup the source location that caused the event
 764     to be emitted.
 765
 766 +perf:thread:COUNTER+::
 767     perf counter named 'COUNTER'. Use `lttng add-context --list` to
 768     list the available perf counters.
 769 +
 770 Only available on IA-32 and x86-64 architectures.
 771
 772 `pthread_id`::
 773     POSIX thread identifier. Can be used on architectures where
 774     `pthread_t` maps nicely to an `unsigned long` type.
 775
 776 `procname`::
 777     Thread name, as set by man:exec(3) or man:prctl(2). It is
 778     recommended that programs set their thread name with man:prctl(2)
 779     before hitting the first tracepoint for that thread.
 780
 781 `vpid`::
 782     Virtual process ID: process ID as seen from the point of view of
 783     the process namespace.
 784
 785 `vtid`::
 786     Virtual thread ID: thread ID as seen from the point of view of
 787     the process namespace.
 788
 789
 790 [[state-dump]]
 791 LTTng-UST state dump
 792 ~~~~~~~~~~~~~~~~~~~~
 793 If an application that uses `liblttng-ust` becomes part of a tracing
 794 session, information about its currently loaded shared objects, their
 795 build IDs, and their debug link information are emitted as events
 796 by the tracer.
 797
 798 The following LTTng-UST state dump events exist and must be enabled
 799 to record application state dumps.
 800
 801 `lttng_ust_statedump:start`::
 802     Emitted when the state dump begins.
 803 +
 804 This event has no fields.
 805
 806 `lttng_ust_statedump:end`::
 807     Emitted when the state dump ends. Once this event is emitted, it
 808     is guaranteed that, for a given process, the state dump is
 809     complete.
 810 +
 811 This event has no fields.
 812
 813 `lttng_ust_statedump:bin_info`::
 814     Emitted when information about a currently loaded executable or
 815     shared object is found.
 816 +
 817 Fields:
 818 +
 819 [options="header"]
 820 |==================================================================
 821 | Field name                 | Description
 822 | `baddr`                    | Base address of loaded executable
 823 | `memsz`                    | Size of loaded executable in memory
 824 | `path`                     | Path to loaded executable file
 825 | `is_pic`                   | Whether the executable is
 826                                position-independent code
 827 |==================================================================
 828
 829 `lttng_ust_statedump:build_id`::
 830     Emitted when a build ID is found in a currently loaded shared
 831     library. See
 832     https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html[Debugging Information in Separate Files]
 833     for more information about build IDs.
 834 +
 835 Fields:
 836 +
 837 [options="header"]
 838 |==============================================================
 839 | Field name                 | Description
 840 | `baddr`                    | Base address of loaded library
 841 | `build_id`                 | Build ID
 842 |==============================================================
 843
 844 `lttng_ust_statedump:debug_link`::
 845     Emitted when debug link information is found in a currently loaded
 846     shared library. See
 847     https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html[Debugging Information in Separate Files]
 848     for more information about debug links.
 849 +
 850 Fields:
 851 +
 852 [options="header"]
 853 |==============================================================
 854 | Field name                 | Description
 855 | `baddr`                    | Base address of loaded library
 856 | `crc`                      | Debug link file's CRC
 857 | `filename`                 | Debug link file name
 858 |==============================================================
 859
 860
 861 [[example]]
 862 EXAMPLE
 863 -------
 864 NOTE: A few examples are available in the
 865 https://github.com/lttng/lttng-ust/tree/master/doc/examples[`doc/examples`]
 866 directory of LTTng-UST's source tree.
 867
 868 This example shows all the features documented in the previous
 869 sections. The <<build-static,static linking>> method is chosen here
 870 to link the application with the tracepoint provider.
 871
 872 You can compile the source files and link them together statically
 873 like this:
 874
 875 [role="term"]
 876 -------------------------------------
 877 cc -c -I. tp.c
 878 cc -c app.c
 879 cc -o app tp.o app.o -llttng-ust -ldl
 880 -------------------------------------
 881
 882 Using the man:lttng(1) tool, create an LTTng tracing session, enable
 883 all the events of this tracepoint provider, and start tracing:
 884
 885 [role="term"]
 886 ----------------------------------------------
 887 lttng create my-session
 888 lttng enable-event --userspace 'my_provider:*'
 889 lttng start
 890 ----------------------------------------------
 891
 892 You may also enable specific events:
 893
 894 [role="term"]
 895 ----------------------------------------------------------
 896 lttng enable-event --userspace my_provider:big_event
 897 lttng enable-event --userspace my_provider:event_instance2
 898 ----------------------------------------------------------
 899
 900 Run the application:
 901
 902 [role="term"]
 903 --------------------
 904 ./app some arguments
 905 --------------------
 906
 907 Stop the current tracing session and inspect the recorded events:
 908
 909 [role="term"]
 910 ----------
 911 lttng stop
 912 lttng view
 913 ----------
 914
 915
 916 Tracepoint provider header file
 917 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 918 `tp.h`:
 919
 920 ------------------------------------------------------------------------
 921 #undef TRACEPOINT_PROVIDER
 922 #define TRACEPOINT_PROVIDER my_provider
 923
 924 #undef TRACEPOINT_INCLUDE
 925 #define TRACEPOINT_INCLUDE "./tp.h"
 926
 927 #if !defined(_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ)
 928 #define _TP_H
 929
 930 #include <lttng/tracepoint.h>
 931 #include <stdio.h>
 932
 933 #include "app.h"
 934
 935 TRACEPOINT_EVENT(
 936     my_provider,
 937     simple_event,
 938     TP_ARGS(
 939         int, my_integer_arg,
 940         const char *, my_string_arg
 941     ),
 942     TP_FIELDS(
 943         ctf_string(argc, my_string_arg)
 944         ctf_integer(int, argv, my_integer_arg)
 945     )
 946 )
 947
 948 TRACEPOINT_ENUM(
 949     my_provider,
 950     my_enum,
 951     TP_ENUM_VALUES(
 952         ctf_enum_value("ZERO", 0)
 953         ctf_enum_value("ONE", 1)
 954         ctf_enum_value("TWO", 2)
 955         ctf_enum_range("A RANGE", 52, 125)
 956         ctf_enum_value("ONE THOUSAND", 1000)
 957     )
 958 )
 959
 960 TRACEPOINT_EVENT(
 961     my_provider,
 962     big_event,
 963     TP_ARGS(
 964         int, my_integer_arg,
 965         const char *, my_string_arg,
 966         FILE *, stream,
 967         double, flt_arg,
 968         int *, array_arg
 969     ),
 970     TP_FIELDS(
 971         ctf_integer(int, int_field1, my_integer_arg * 2)
 972         ctf_integer_hex(long int, stream_pos, ftell(stream))
 973         ctf_float(double, float_field, flt_arg)
 974         ctf_string(string_field, my_string_arg)
 975         ctf_array(int, array_field, array_arg, 7)
 976         ctf_array_text(char, array_text_field, array_arg, 5)
 977         ctf_sequence(int, seq_field, array_arg, int,
 978                      my_integer_arg / 10)
 979         ctf_sequence_text(char, seq_text_field, array_arg,
 980                           int, my_integer_arg / 5)
 981         ctf_enum(my_provider, my_enum, int,
 982                  enum_field, array_arg[1])
 983     )
 984 )
 985
 986 TRACEPOINT_LOGLEVEL(my_provider, big_event, TRACE_WARNING)
 987
 988 TRACEPOINT_EVENT_CLASS(
 989     my_provider,
 990     my_tracepoint_class,
 991     TP_ARGS(
 992         int, my_integer_arg,
 993         struct app_struct *, app_struct_arg
 994     ),
 995     TP_FIELDS(
 996         ctf_integer(int, a, my_integer_arg)
 997         ctf_integer(unsigned long, b, app_struct_arg->b)
 998         ctf_string(c, app_struct_arg->c)
 999     )
1000 )
1001
1002 TRACEPOINT_EVENT_INSTANCE(
1003     my_provider,
1004     my_tracepoint_class,
1005     event_instance1,
1006     TP_ARGS(
1007         int, my_integer_arg,
1008         struct app_struct *, app_struct_arg
1009     )
1010 )
1011
1012 TRACEPOINT_EVENT_INSTANCE(
1013     my_provider,
1014     my_tracepoint_class,
1015     event_instance2,
1016     TP_ARGS(
1017         int, my_integer_arg,
1018         struct app_struct *, app_struct_arg
1019     )
1020 )
1021
1022 TRACEPOINT_LOGLEVEL(my_provider, event_instance2, TRACE_INFO)
1023
1024 TRACEPOINT_EVENT_INSTANCE(
1025     my_provider,
1026     my_tracepoint_class,
1027     event_instance3,
1028     TP_ARGS(
1029         int, my_integer_arg,
1030         struct app_struct *, app_struct_arg
1031     )
1032 )
1033
1034 #endif /* _TP_H */
1035
1036 #include <lttng/tracepoint-event.h>
1037 ------------------------------------------------------------------------
1038
1039
1040 Tracepoint provider source file
1041 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1042 `tp.c`:
1043
1044 ------------------------------------------------------------------------
1045 #define TRACEPOINT_CREATE_PROBES
1046 #define TRACEPOINT_DEFINE
1047
1048 #include "tp.h"
1049 ------------------------------------------------------------------------
1050
1051
1052 Application header file
1053 ~~~~~~~~~~~~~~~~~~~~~~~
1054 `app.h`:
1055
1056 ------------------------------------------------------------------------
1057 #ifndef _APP_H
1058 #define _APP_H
1059
1060 struct app_struct {
1061     unsigned long b;
1062     const char *c;
1063     double d;
1064 };
1065
1066 #endif /* _APP_H */
1067 ------------------------------------------------------------------------
1068
1069
1070 Application source file
1071 ~~~~~~~~~~~~~~~~~~~~~~~
1072 `app.c`:
1073
1074 ------------------------------------------------------------------------
1075 #include <stdlib.h>
1076 #include <stdio.h>
1077
1078 #include "tp.h"
1079 #include "app.h"
1080
1081 static int array_of_ints[] = {
1082     100, -35, 1, 23, 14, -6, 28, 1001, -3000,
1083 };
1084
1085 int main(int argc, char* argv[])
1086 {
1087     FILE *stream;
1088     struct app_struct app_struct;
1089
1090     tracepoint(my_provider, simple_event, argc, argv[0]);
1091     stream = fopen("/tmp/app.txt", "w");
1092
1093     if (!stream) {
1094         fprintf(stderr,
1095                 "Error: Cannot open /tmp/app.txt for writing\n");
1096         return EXIT_FAILURE;
1097     }
1098
1099     if (fprintf(stream, "0123456789") != 10) {
1100         fclose(stream);
1101         fprintf(stderr, "Error: Cannot write to /tmp/app.txt\n");
1102         return EXIT_FAILURE;
1103     }
1104
1105     tracepoint(my_provider, big_event, 35, "hello tracepoint",
1106                stream, -3.14, array_of_ints);
1107     fclose(stream);
1108     app_struct.b = argc;
1109     app_struct.c = "[the string]";
1110     tracepoint(my_provider, event_instance1, 23, &app_struct);
1111     app_struct.b = argc * 5;
1112     app_struct.c = "[other string]";
1113     tracepoint(my_provider, event_instance2, 17, &app_struct);
1114     app_struct.b = 23;
1115     app_struct.c = "nothing";
1116     tracepoint(my_provider, event_instance3, -52, &app_struct);
1117
1118     return EXIT_SUCCESS;
1119 }
1120 ------------------------------------------------------------------------
1121
1122
1123 ENVIRONMENT VARIABLES
1124 ---------------------
1125 `LTTNG_HOME`::
1126     Alternative user's home directory. This variable is useful when the
1127     user running the instrumented application has a non-writable home
1128     directory.
1129 +
1130 Unix sockets used for the communication between `liblttng-ust` and the
1131 LTTng session and consumer daemons (part of the LTTng-tools project)
1132 are located in a specific directory under `$LTTNG_HOME` (or `$HOME` if
1133 `$LTTNG_HOME` is not set).
1134
1135 `LTTNG_UST_BLOCKING_RETRY_TIMEOUT`::
1136     Maximum duration (milliseconds) to retry event tracing when
1137     there's no space left for the event record in the sub-buffer.
1138 +
1139 --
1140 `0` (default)::
1141     Never block the application.
1142
1143 Positive value::
1144     Block the application for the specified number of milliseconds. If
1145     there's no space left after this duration, discard the event
1146     record.
1147
1148 Negative value::
1149     Block the application until there's space left for the event record.
1150 --
1151 +
1152 This option can be useful in workloads generating very large trace data
1153 throughput, where blocking the application is an acceptable trade-off to
1154 prevent discarding event records.
1155 +
1156 WARNING: Setting this environment variable to a non-zero value may
1157 significantly affect application timings.
1158
1159 `LTTNG_UST_CLOCK_PLUGIN`::
1160     Path to the shared object which acts as the clock override plugin.
1161     An example of such a plugin can be found in the LTTng-UST
1162     documentation under
1163     https://github.com/lttng/lttng-ust/tree/master/doc/examples/clock-override[`examples/clock-override`].
1164
1165 `LTTNG_UST_DEBUG`::
1166     Activates `liblttng-ust`'s debug and error output if set to `1`.
1167
1168 `LTTNG_UST_GETCPU_PLUGIN`::
1169     Path to the shared object which acts as the `getcpu()` override
1170     plugin. An example of such a plugin can be found in the LTTng-UST
1171     documentation under
1172     https://github.com/lttng/lttng-ust/tree/master/doc/examples/getcpu-override[`examples/getcpu-override`].
1173
1174 `LTTNG_UST_REGISTER_TIMEOUT`::
1175     Waiting time for the _registration done_ session daemon command
1176     before proceeding to execute the main program (milliseconds).
1177 +
1178 The value `0` means _do not wait_. The value `-1` means _wait forever_.
1179 Setting this environment variable to `0` is recommended for applications
1180 with time constraints on the process startup time.
1181 +
1182 Default: {lttng_ust_register_timeout}.
1183
1184 `LTTNG_UST_BLOCKING_RETRY_TIMEOUT`::
1185     Maximum time during which event tracing retry is attempted on buffer
1186     full condition (millliseconds). Setting this environment to non-zero
1187     value effectively blocks the application on buffer full condition.
1188     Setting this environment variable to non-zero values may
1189     significantly affect application timings. Setting this to a negative
1190     value may block the application indefinitely if there is no consumer
1191     emptying the ring buffer. The delay between retry attempts is the
1192     minimum between the specified timeout value and 100ms. This option
1193     can be useful in workloads generating very large trace data
1194     throughput, where blocking the application is an acceptable
1195     trade-off to not discard events. _Use with caution_.
1196 +
1197 The value `0` means _do not retry_. The value `-1` means _retry forever_.
1198 Value > `0` means a maximum timeout of the given value.
1199 +
1200 Default: {lttng_ust_blocking_retry_timeout}.
1201
1202 `LTTNG_UST_WITHOUT_BADDR_STATEDUMP`::
1203     Prevents `liblttng-ust` from performing a base address state dump
1204     (see the <<state-dump,LTTng-UST state dump>> section above) if
1205     set to `1`.
1206
1207
1208 include::common-footer.txt[]
1209
1210 include::common-copyrights.txt[]
1211
1212 include::common-authors.txt[]
1213
1214
1215 SEE ALSO
1216 --------
1217 man:tracef(3),
1218 man:tracelog(3),
1219 man:lttng-gen-tp(1),
1220 man:lttng-ust-dl(3),
1221 man:lttng-ust-cyg-profile(3),
1222 man:lttng(1),
1223 man:lttng-enable-event(1),
1224 man:lttng-list(1),
1225 man:lttng-add-context(1),
1226 man:babeltrace(1),
1227 man:dlopen(3),
1228 man:ld.so(8)