lib: introduce bt_message_iterator_class
[babeltrace.git] / CONTRIBUTING.adoc
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1// Render with Asciidoctor
2
3= Babeltrace contributor's guide
f9ded0e0 4Jérémie Galarneau, Philippe Proulx
cd4aac1e 5v0.2, 19 June 2019
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6:toc:
7:toclevels: 5
8
beb0fb75 9
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10This is a partial contributor's guide for the
11http://diamon.org/babeltrace[Babeltrace] project. If you have any
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12questions that are not answered by this guide, please post them on
13https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev[Babeltrace's
14mailing list].
15
beb0fb75 16
cd4aac1e 17== Babeltrace library
f9ded0e0 18
cd4aac1e 19=== Object reference counting and lifetime
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20
21This section covers the rationale behind the design of Babeltrace's
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22object lifetime management. This applies to the Babeltrace library, as
23well as to the CTF writer library (although the public reference
24counting functions are not named the same way).
f9ded0e0 25
cd4aac1e 26Starting from Babeltrace 2.0, all publicly exposed objects inherit a
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27common base: `bt_object`. This base provides a number of facilities to
28all objects, chief amongst which are lifetime management functions.
29
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30The lifetime of some public objects is managed by reference counting. In
31this case, the API offers the `+bt_*_get_ref()+` and `+bt_*_put_ref()+`
32functions which respectively increment and decrement an object's
33reference count.
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34
35As far as lifetime management in concerned, Babeltrace makes a clear
36distinction between regular objects, which have a single parent, and
37root objects, which don't.
38
39
cd4aac1e 40==== The problem
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41
42Let us consider a problematic case to illustrate the need for this
43distinction.
44
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45A user of the Babeltrace library creates a trace class, which _has_ a
46stream class (the class of a stream) and that stream class, in turn,
47_has_ an event class (the class of an event).
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48
49Nothing prevents this user from releasing his reference on any one of
50these objects in any order. However, all objects in the
51__trace--stream class--event class__ hierarchy can be retrieved
52from any other.
53
54For instance, the user could discard his reference on both the event
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55class and the stream class, only keeping a reference on the trace class.
56From this trace class reference, stream classes can be enumerated,
57providing the user with a new reference to the stream class he discarded
58earlier. Event classes can also be enumerated from stream classes,
59providing the user with references to the individual event classes.
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60
61Conversely, the user could also hold a reference to an event class and
cd4aac1e 62retrieve its parent stream class. The trace class, in turn, can then be
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63retrieved from the stream class.
64
65This example illustrates what could be interpreted as a circular
66reference dependency existing between these objects. Of course, if the
67objects in such a scenario were to hold references to each other (in
68both directions), we would be in presence of a circular ownership
69resulting in a leak of both objects as their reference counts would
70never reach zero.
71
72Nonetheless, the API must offer the guarantee that holding a node to any
73node of the graph keeps all other reachable nodes alive.
74
75
cd4aac1e 76==== The solution
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77
78The scheme employed in Babeltrace to break this cycle consists in the
cd4aac1e 79"children" holding _reverse component references_ to their parents. That
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80is, in the context of the trace IR, that event classes hold a reference
81to their parent stream class and stream classes hold a reference to
cd4aac1e 82their parent trace class.
f9ded0e0 83
cd4aac1e 84On the other hand, parents hold _claiming aggregation references_ to
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85their children. A claiming aggregation reference means that the object
86being referenced should not be deleted as long as the reference still
87exists. In this respect, it can be said that parents truly hold the
88ownership of their children, since they control their lifetime.
89Conversely, the reference counting mechanism is leveraged by children to
90notify parents that no other child indirectly exposes the parent.
91
92When a parented object's reference count reaches zero, it invokes
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93`+bt_*_put_ref()+` on its parent and does _not_ free itself. However,
94from that point, the object depends on its parent to signal the moment
95when it can be safely reclaimed.
96
97The invocation of `+bt_*_put_ref()+` by the last children holding a
98reference to its parent might trigger a cascade of `+bt_*_put_ref()+`
99from child to parent. Eventually, a **root** object is reached. At that
100point, if this orphaned object's reference count reaches zero, the
101object invokes the destructor method defined by everyone of its children
102as part of their base `struct bt_object`. The key point here is that the
103cascade of destructor will necessarily originate from the root and
104propagate in preorder to the children. These children will propagate the
105destruction to their own children before reclaiming their own memory.
106This ensures that a node's pointer to its parent is _always_ valid since
107the parent has the responsibility of tearing-down their children before
108cleaning themselves up.
109
110Assuming a reference to an object is _acquired_ by calling
111`+bt_*_get_ref()+` while its reference count is zero, the object
112acquires, in turn, a reference on its parent using `+bt_*_get_ref()+`.
113At that point, the child can be thought of as having converted its weak
114reference to its parent into a regular reference. That is why this
115reference is referred to as a _claiming_ aggregation reference.
116
117
118==== Caveats
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119
120This scheme imposes a number of strict rules defining the relation
121between objects:
122
123* Objects may only have one parent.
124* Objects, beside the root, are only retrievable from their direct
125 parent or children.
126
127
cd4aac1e 128==== Example
f9ded0e0 129
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130The initial situation is rather simple: **User{nbsp}A** is holding a
131reference to a trace class, **TC1**. As per the rules previously
132enounced, stream classes **SC1** and **SC2** don't hold a reference to
133**TC1** since their own reference counts are zero. The same holds true
134for **EC1**, **EC2** and **EC3** with respect to **SC1** and **SC2**.
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135
136image::doc/contributing-images/bt-ref01.png[]
137
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138In this second step, we can see that **User{nbsp}A** has acquired a
139reference on **SC2** through the trace class, **TC1**.
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140
141The stream class's reference count transitions from zero to one,
142triggering the acquisition of a strong reference on **TC1** from
143**SC2**.
144
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145Hence, at this point, the trace class's ownership is shared by
146**User{nbsp}A** and **SC2**.
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147
148image::doc/contributing-images/bt-ref02.png[]
149
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150Next, **User{nbsp}A** acquires a reference on the **EC3** event class
151through its parent stream class, **SC2**. Again, the transition of an
152object's reference count from 0 to 1 triggers the acquisition of a
153reference on its parent.
f9ded0e0 154
cd4aac1e 155Note that SC2's reference count was incremented to 2. The trace class's
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156reference count remains unchanged.
157
158image::doc/contributing-images/bt-ref03.png[]
159
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160**User{nbsp}A** decides to drop its reference on **SC2**. **SC2**'s
161reference count returns back to 1, everything else remaining unchanged.
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162
163image::doc/contributing-images/bt-ref04.png[]
164
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165**User{nbsp}A** can then decide to drop its reference on the trace
166class. This results in a reversal of the initial situation:
167**User{nbsp}A** now owns an event, **EC3**, which is keeping everything
168else alive and reachable.
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169
170image::doc/contributing-images/bt-ref05.png[]
171
cd4aac1e 172If another object, **User{nbsp}B**, enters the picture and acquires a
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173reference on the **SC1** stream class, we see that **SC1**'s reference
174count transitioned from 0 to 1, triggering the acquisition of a
175reference on **TC1**.
176
177image::doc/contributing-images/bt-ref06.png[]
178
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179**User{nbsp}B** hands off a reference to **EC1**, acquired through
180**SC1**, to another object, **User{nbsp}C**. The acquisition of a
181reference on **EC1**, which transitions from 0 to 1, triggers the
182acquisition of a reference on its parent, **SC1**.
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183
184image::doc/contributing-images/bt-ref07.png[]
185
cd4aac1e 186At some point, **User{nbsp}A** releases its reference on **EC3**. Since
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187**EC3**'s reference count transitions to zero, it releases its reference
188on **SC2**. **SC2**'s reference count, in turn, reaches zero and it
189releases its reference to **TC1**.
190
191**TC1**'s reference count is now 1 and no further action is taken.
192
193image::doc/contributing-images/bt-ref08.png[]
194
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195**User{nbsp}B** releases its reference on **SC1**. **User{nbsp}C**
196becomes the sole owner of the whole hierarchy through his ownership of
197**EC1**.
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198
199image::doc/contributing-images/bt-ref09.png[]
200
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201Finally, **User{nbsp}C** releases his ownership of **EC1**, triggering
202the release of the whole hierarchy. Let's walk through the reclamation
203of the whole graph.
f9ded0e0 204
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205Mirroring what happened when **User{nbsp}A** released its last reference
206on **EC3**, the release of **EC1** by **User{nbsp}C** causes its
207reference count to fall to zero.
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208
209This transition to zero causes **EC1** to release its reference on
210**SC1**. **SC1**'s reference count reaching zero causes it to release
211its reference on **TC1**.
212
213image::doc/contributing-images/bt-ref10.png[]
214
215Since the reference count of **TC1**, a root object, has reached zero,
216it invokes the destructor method on its children. This method is
217recursive and causes the stream classes to call the destructor method on
218their event classes.
219
220The event classes are reached and, having no children of their own, are
221reclaimed.
222
223image::doc/contributing-images/bt-ref11.png[]
224
225The stream classes having destroyed their children, are then reclaimed
cd4aac1e 226by the trace class.
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227
228image::doc/contributing-images/bt-ref12.png[]
229
230Finally, the stream classes having been reclaimed, **TC1** is reclaimed.
231
232image::doc/contributing-images/bt-ref13.png[]
233
234
f9ded0e0 235== Logging
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236
237Logging is a great instrument for a developer to be able to collect
238information about a running software.
239
240Babeltrace is a complex software with many layers. When a Babeltrace
241graph fails to run, what caused the failure? It could be caused by any
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242component, any message iterator, and any deeply nested validation of a
243CTF IR object (within the `ctf` plugin), for example. With the
244appropriate logging statements manually placed in the source code, we
245can find the cause of a bug faster.
beb0fb75 246
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247While <<choose-a-log-level,care must be taken>> when placing _DEBUG_ to
248_FATAL_ logging statements, you should liberally instrument your
ef267d12 249Babeltrace module with _TRACE_ logging statements to help future you
cd4aac1e 250and other developers understand what's happening at run time.
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251
252
f9ded0e0 253=== Logging API
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254
255The Babeltrace logging API is internal: it is not exposed to the users
cd4aac1e 256of the library; only to their developers. The only thing that a library
4a41523d 257user can control is the current log level of the library itself with
beb0fb75 258`bt_logging_set_global_level()` and the initial library's log level with
cd4aac1e 259the `LIBBABELTRACE2_INIT_LOG_LEVEL` environment variable.
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260
261This API is based on https://github.com/wonder-mice/zf_log[zf_log], a
262lightweight, yet featureful, MIT-licensed core logging library for C and
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263pass:[C++]. The zf_log source files were modified to have the `BT_` and
264`bt_` prefixes, and other small changes, like color support and using
265the project's `BT_DEBUG_MODE` definition instead of the standard
266`NDEBUG`.
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267
268The logging functions are implemented in the logging convenience
cd4aac1e 269library (`src/logging` directory).
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270
271
cd4aac1e 272[[logging-headers]]
f9ded0e0 273==== Headers
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274
275The logging API headers are:
276
3fadfbc0 277`<babeltrace2/logging.h>`::
cd4aac1e 278 Public header which a library user can use to set and get
a12f3d62 279 libbabeltrace2's current log level.
beb0fb75 280
cd4aac1e 281`"logging/log.h"`::
beb0fb75 282 Internal, generic logging API which you can use in any Babeltrace
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283 module. This is the translation of `zf_log.h`.
284+
285This header offers the <<gen-logging-statements,generic logging
286statement macros>>.
beb0fb75 287
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288`"lib/logging.h"`::
289 Specific internal header to use within the library.
290+
291This header defines `BT_LOG_OUTPUT_LEVEL` to a custom, library-wide
292hidden symbol which is the library's current log level before including
293`"logging/log.h"`.
294+
295This header offers the <<lib-logging-statements,library-specific logging
296statement macros>>.
beb0fb75 297
d9c39b0a 298`"logging/comp-logging.h"`::
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299 Specific internal header to use within a component class.
300+
301This header offers the <<comp-logging-statements,component-specific
302logging statement macros>>.
beb0fb75 303
b4b9064d 304
cd4aac1e 305[[log-levels]]
f9ded0e0 306==== Log levels
beb0fb75 307
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308The internal logging API offers the following log levels, in ascending
309order of severity:
beb0fb75 310
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311[options="header,autowidth",cols="4"]
312|===
313|Log level name
314|Log level short name
315|Internal API enumerator
316|Public API enumerator
317
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318|_TRACE_
319|`T`
320|`BT_LOG_TRACE`
321|`BT_LOGGING_LEVEL_TRACE`
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322
323|_DEBUG_
324|`D`
325|`BT_LOG_DEBUG`
326|`BT_LOGGING_LEVEL_DEBUG`
327
328|_INFO_
329|`I`
330|`BT_LOG_INFO`
331|`BT_LOGGING_LEVEL_INFO`
332
770538dd 333|_WARNING_
cd4aac1e 334|`W`
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335|`BT_LOG_WARNING`
336|`BT_LOGGING_LEVEL_WARNING`
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337
338|_ERROR_
339|`E`
340|`BT_LOG_ERROR`
341|`BT_LOGGING_LEVEL_ERROR`
342
343|_FATAL_
344|`F`
345|`BT_LOG_FATAL`
346|`BT_LOGGING_LEVEL_FATAL`
347
348|_NONE_
349|`N`
350|`BT_LOG_NONE`
351|`BT_LOGGING_LEVEL_NONE`
352|===
353
354The short name is accepted by the log level environment variables and by
355the CLI's `--log-level` options.
beb0fb75 356
cd4aac1e 357See <<choose-a-log-level,how to decide which one to use>> below.
beb0fb75 358
cd4aac1e 359There are two important log level expressions:
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360
361[[build-time-log-level]]Build-time, minimal log level::
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362 The minimal log level, or build-time log level, is set at build time
363 and determines the minimal log level of the logging statements which
364 can be executed. This applies to all the modules (CLI, library,
365 plugins, bindings, etc.).
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366+
367All the logging statements with a level below this level are **not built
368at all**. All the logging statements with a level equal to or greater
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369than this level _can_ be executed, depending on the
370<<run-time-log-level,run-time log level>>.
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371+
372You can set this level at configuration time with the
373`BABELTRACE_MINIMAL_LOG_LEVEL` environment variable, for example:
374+
375--
376----
770538dd 377$ BABELTRACE_MINIMAL_LOG_LEVEL=INFO ./configure
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378----
379--
380+
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381The default build-time log level is `DEBUG`. For optimal performance,
382set it to `INFO`, which effectively disables all fast path logging in
770538dd 383all the Babeltrace modules. You can't set it to `WARNING`, `ERROR`,
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384`FATAL`, or `NONE` because the impact on performance is minuscule
385starting from the _INFO_ log level anyway and we want any Babeltrace
386build to always be able to print _INFO_-level logs.
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387+
388The library's public API provides `bt_logging_get_minimal_level()` to
389get the configured minimal log level.
390
391[[run-time-log-level]]Run-time, dynamic log level::
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392 The dynamic log level is set at run time and determines the current,
393 _active_ log level. All the logging statements with a level below
394 this level are not executed, **but they still evaluate the
395 condition**. All the logging statements with a level equal to or
396 greater than this level are executed, provided that their level is
397 also <<build-time-log-level,enabled at build time>>.
beb0fb75 398+
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399`zf_log` has a concept of a global run-time log level which uses the
400`_bt_log_global_output_lvl` symbol. In practice, we never use this
401symbol, and always make sure that `BT_LOG_OUTPUT_LEVEL` is defined to a
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402module-wise expression before including `"logging/log.h"`.
403+
404In the library, `"lib/logging.h"` defines its own
405`BT_LOG_OUTPUT_LEVEL` to the library's log level symbol before it
406includes `"logging/log.h"` itself.
beb0fb75 407+
a12f3d62 408In libbabeltrace2, the user can set the current run-time log level with
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409the `bt_logging_set_global_level()` function, for example:
410+
411--
412[source,c]
413----
414bt_logging_set_global_level(BT_LOGGING_LEVEL_INFO);
415----
416--
417+
418The library's initial run-time log level is defined by the
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419`LIBBABELTRACE2_INIT_LOG_LEVEL` environment variable, or set to _NONE_
420if this environment variable is undefined.
421+
422Other modules have their own way of setting their run-time log level.
423+
424For example, the CLI uses the `BABELTRACE_CLI_LOG_LEVEL` environment
425variable, as well as its global `--log-level` option:
426+
427----
428$ babeltrace2 --log-level=I ...
429----
430+
431The components use their own log level (as returned by
432`bt_component_get_logging_level()`). With the CLI, you can set a
433specific component's log level with its own, position-dependent
434`--log-level` option:
435+
436----
437$ babeltrace2 /path/to/trace -c sink.ctf.fs --log-level=D
438----
439+
440Code which is common to the whole project, for example `src/common`
441and `src/compat`, use function parameters to get its run-time log
442level, for example:
443+
444[source,c]
445----
446BT_HIDDEN
447char *bt_common_get_home_plugin_path(int log_level);
448----
beb0fb75 449+
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450Typically, when a logging-enabled module calls such a function, it
451passes its own log level expression directly (`BT_LOG_OUTPUT_LEVEL`):
beb0fb75 452+
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453[source,c]
454----
455path = bt_common_get_home_plugin_path(BT_LOG_OUTPUT_LEVEL);
456----
457+
458Otherwise, just pass `BT_LOG_NONE`:
459+
460----
461path = bt_common_get_home_plugin_path(BT_LOG_NONE);
462----
463
464
465[[gen-logging-statements]]
466==== Generic logging statement macros
467
468The Babeltrace logging statement macros work just like `printf()`
469(except the `+BT_LOG*_STR()+` ones) and contain their <<log-levels,log
470level>> (short name) in their name.
beb0fb75 471
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472Each of the following macros evaluate the
473<<build-time-log-level,build-time log level>> definition and
474<<run-time-log-level,run-time log level>> expression (as defined by
475`BT_LOG_OUTPUT_LEVEL`) to log conditionally.
beb0fb75 476
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477See <<logging-instrument-c-file-gen,Instrument a C source file
478(generic)>> and <<logging-instrument-h-file-gen,Instrument a C header
479file (generic)>> to learn how to be able to use the following macros.
beb0fb75 480
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481`+BT_LOGT("format string", ...)+`::
482 Generic trace logging statement.
beb0fb75 483
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484`+BT_LOGD("format string", ...)+`::
485 Generic debug logging statement.
beb0fb75 486
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487`+BT_LOGI("format string", ...)+`::
488 Generic info logging statement.
beb0fb75 489
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490`+BT_LOGW("format string", ...)+`::
491 Generic warning logging statement.
beb0fb75 492
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493`+BT_LOGE("format string", ...)+`::
494 Generic error logging statement.
beb0fb75 495
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496`+BT_LOGF("format string", ...)+`::
497 Generic fatal logging statement.
beb0fb75 498
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499`+BT_LOGT_STR("preformatted string")+`::
500 Generic preformatted string trace logging statement.
beb0fb75 501
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502`+BT_LOGD_STR("preformatted string")+`::
503 Generic preformatted string debug logging statement.
beb0fb75 504
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505`+BT_LOGI_STR("preformatted string")+`::
506 Generic preformatted string info logging statement.
beb0fb75 507
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508`+BT_LOGW_STR("preformatted string")+`::
509 Generic preformatted string warning logging statement.
beb0fb75 510
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511`+BT_LOGE_STR("preformatted string")+`::
512 Generic preformatted string error logging statement.
beb0fb75 513
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514`+BT_LOGF_STR("preformatted string")+`::
515 Generic preformatted string fatal logging statement.
beb0fb75 516
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517`+BT_LOGT_MEM(data_ptr, data_size, "format string", ...)+`::
518 Generic memory trace logging statement.
beb0fb75 519
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520`+BT_LOGD_MEM(data_ptr, data_size, "format string", ...)+`::
521 Generic memory debug logging statement.
b81626f9 522
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523`+BT_LOGI_MEM(data_ptr, data_size, "format string", ...)+`::
524 Generic memory info logging statement.
b81626f9 525
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526`+BT_LOGW_MEM(data_ptr, data_size, "format string", ...)+`::
527 Generic memory warning logging statement.
b81626f9 528
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529`+BT_LOGE_MEM(data_ptr, data_size, "format string", ...)+`::
530 Generic memory error logging statement.
b81626f9 531
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532`+BT_LOGF_MEM(data_ptr, data_size, "format string", ...)+`::
533 Generic memory fatal logging statement.
b81626f9 534
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535`+BT_LOGT_ERRNO("initial message", "format string", ...)+`::
536 Generic `errno` string trace logging statement.
b81626f9 537
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538`+BT_LOGD_ERRNO("initial message", "format string", ...)+`::
539 Generic `errno` string debug logging statement.
beb0fb75 540
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541`+BT_LOGI_ERRNO("initial message", "format string", ...)+`::
542 Generic `errno` string info logging statement.
beb0fb75 543
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544`+BT_LOGW_ERRNO("initial message", "format string", ...)+`::
545 Generic `errno` string warning logging statement.
beb0fb75 546
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547`+BT_LOGE_ERRNO("initial message", "format string", ...)+`::
548 Generic `errno` string error logging statement.
beb0fb75 549
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550`+BT_LOGF_ERRNO("initial message", "format string", ...)+`::
551 Generic `errno` string fatal logging statement.
beb0fb75 552
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553
554[[lib-logging-statements]]
555==== Library-specific logging statement macros
556
557The Babeltrace library contains an internal logging API based on the
558generic logging framework. You can use it to log known Babeltrace
559objects without having to manually log each member.
560
561See <<logging-instrument-c-file-lib,Instrument a library C source file>>
562and <<logging-instrument-h-file-lib,Instrument a library C header file>> to
563learn how to be able to use the following macros.
564
565The library logging statement macros are named `+BT_LIB_LOG*()+` instead
566of `+BT_LOG*()+`:
567
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568`+BT_LIB_LOGT("format string", ...)+`::
569 Library trace logging statement.
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570
571`+BT_LIB_LOGD("format string", ...)+`::
572 Library debug logging statement.
573
574`+BT_LIB_LOGI("format string", ...)+`::
575 Library info logging statement.
576
577`+BT_LIB_LOGW("format string", ...)+`::
578 Library warning logging statement.
579
580`+BT_LIB_LOGE("format string", ...)+`::
581 Library error logging statement.
582
583`+BT_LIB_LOGF("format string", ...)+`::
584 Library fatal logging statement.
585
3cd4c495
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586`+BT_LIB_LOGW_APPEND_CAUSE("format string", ...)+`::
587 Library warning logging statement, and unconditional error cause
588 appending.
589
590`+BT_LIB_LOGE_APPEND_CAUSE("format string", ...)+`::
591 Library error logging statement, and unconditional error cause
592 appending.
593
594`+BT_LIB_LOGF_APPEND_CAUSE("format string", ...)+`::
595 Library fatal logging statement, and unconditional error cause
596 appending.
597
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598The macros above accept the typical `printf()` conversion specifiers
599with the following limitations:
600
601* The `+*+` width specifier is not accepted.
602* The `+*+` precision specifier is not accepted.
603* The `j` and `t` length modifiers are not accepted.
604* The `n` format specifier is not accepted.
605* The format specifiers defined in `<inttypes.h>` are not accepted,
606 except for `PRId64`, `PRIu64`, `PRIx64`, `PRIX64`, `PRIo64`, and
607 `PRIi64`.
608
609The Babeltrace library custom conversion specifier is accepted. Its
610syntax is either `%!u` to format a UUID (`bt_uuid` type), or:
611
612. Introductory `%!` sequence.
613
614. **Optional**: `[` followed by a custom prefix for the printed fields
615 of this specifier, followed by `]`. The standard form is to end this
616 prefix with `-` so that, for example, with the prefix `tc-`, the
617 complete field name becomes `tc-addr`.
618
619. **Optional**: `pass:[+]` to print extended object members. This
620 depends on the provided format specifier.
621
622. Format specifier (see below).
623
624The available format specifiers are:
625
626[options="header,autowidth",cols="3"]
627|===
628|Specifier
629|Object
630|Expected C type
631
632|`F`
633|Trace IR field class
6769570a 634|`+const struct bt_field_class *+`
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635
636|`f`
637|Trace IR field
6769570a 638|`+const struct bt_field *+`
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639
640|`P`
641|Trace IR field path
6769570a 642|`+const struct bt_field_path *+`
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643
644|`E`
645|Trace IR event class
6769570a 646|`+const struct bt_event_class *+`
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647
648|`e`
649|Trace IR event
6769570a 650|`+const struct bt_event *+`
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651
652|`S`
653|Trace IR stream class.
6769570a 654|`+const struct bt_stream_class *+`
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655
656|`s`
657|Trace IR stream
6769570a 658|`+const struct bt_stream *+`
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659
660|`a`
661|Trace IR packet
6769570a 662|`+const struct bt_packet *+`
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663
664|`T`
665|Trace IR trace class
6769570a 666|`+const struct bt_trace_class *+`
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667
668|`t`
669|Trace IR trace
6769570a 670|`+const struct bt_trace *+`
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671
672|`K`
673|Trace IR clock class
6769570a 674|`+const struct bt_clock_class *+`
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675
676|`k`
677|Trace IR clock snapshot
6769570a 678|`+const struct bt_clock_snapshot *+`
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679
680|`v`
681|Value object
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682|`+const struct bt_value *+`
683
684|`R`
685|Integer range set
686|`const struct bt_integer_range_set *`
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687
688|`n`
689|Message
6769570a 690|`+const struct bt_message *+`
cd4aac1e 691
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692|`I`
693|Message iterator class
694|`struct bt_message_iterator_class *`
695
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696|`i`
697|Message iterator
698|`struct bt_message_iterator *`
699
700|`C`
701|Component class
702|`struct bt_component_class *`
703
704|`c`
705|Component
6769570a 706|`+const struct bt_component *+`
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707
708|`p`
709|Port
6769570a 710|`+const struct bt_port *+`
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711
712|`x`
713|Connection
6769570a 714|`+const struct bt_connection *+`
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715
716|`g`
717|Graph
6769570a 718|`+const struct bt_graph *+`
cd4aac1e 719
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720|`z`
721|Interrupter
722|`+struct bt_interrupter *+`
723
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724|`l`
725|Plugin
6769570a 726|`+const struct bt_plugin *+`
cd4aac1e 727
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728|`r`
729|Error cause
6769570a 730|`+const struct bt_error_cause *+`
553c4bab 731
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732|`o`
733|Object pool
6769570a 734|`+const struct bt_object_pool *+`
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735
736|`O`
737|Object
6769570a 738|`+const struct bt_object *+`
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739|===
740
741Conversion specifier examples:
742
743* `%!f`
744* `%![my-event-]+e`
745* `%!t`
746* `%!+F`
747
748The ``, `` string (comma and space) is printed between individual
749fields, but **not after the last one**. Therefore, you must put this
750separator in the format string between two conversion specifiers, for
751example:
752
753[source,c]
754----
755BT_LIB_LOGW("Message: count=%u, %!E, %!+K", count, event_class, clock_class);
756----
757
758Example with a custom prefix:
759
760[source,c]
761----
762BT_LIB_LOGI("Some message: %![ec-a-]e, %![ec-b-]+e", ec_a, ec_b);
763----
764
765It is safe to pass `NULL` as any Babeltrace object parameter: the macros
766only print its null address.
767
768WARNING: Build-time `printf()` format checks are disabled for the
769`+BT_LIB_LOG*()+` macros because there are custom conversion specifiers,
770so make sure to test your logging statements.
771
772
773[[comp-logging-statements]]
774==== Component-specific logging statement macros
775
776There are available logging macros for components. They prepend a prefix
777including the component's name to the logging message.
778
779See <<logging-instrument-c-file-compcls,Instrument a component class C
780source file>> and <<logging-instrument-h-file-compcls,Instrument a
781component class C header file>> to learn how to be able to use the
782following macros.
783
784The component logging statement macros are named `+BT_COMP_LOG*()+`
785instead of `+BT_LOG*()+`:
786
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787`+BT_COMP_LOGT("format string", ...)+`::
788 Component trace logging statement.
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789
790`+BT_COMP_LOGD("format string", ...)+`::
791 Component debug logging statement.
792
793`+BT_COMP_LOGI("format string", ...)+`::
794 Component info logging statement.
795
796`+BT_COMP_LOGW("format string", ...)+`::
797 Component warning logging statement.
798
799`+BT_COMP_LOGE("format string", ...)+`::
800 Component error logging statement.
801
802`+BT_COMP_LOGF("format string", ...)+`::
803 Component fatal logging statement.
804
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805`+BT_COMP_LOGT_STR("preformatted string")+`::
806 Component preformatted string trace logging statement.
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807
808`+BT_COMP_LOGD_STR("preformatted string")+`::
809 Component preformatted string debug logging statement.
810
811`+BT_COMP_LOGI_STR("preformatted string")+`::
812 Component preformatted string info logging statement.
813
814`+BT_COMP_LOGW_STR("preformatted string")+`::
815 Component preformatted string warning logging statement.
816
817`+BT_COMP_LOGE_STR("preformatted string")+`::
818 Component preformatted string error logging statement.
819
820`+BT_COMP_LOGF_STR("preformatted string")+`::
821 Component preformatted string fatal logging statement.
822
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823`+BT_COMP_LOGT_ERRNO("initial message", "format string", ...)+`::
824 Component `errno` string trace logging statement.
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825
826`+BT_COMP_LOGD_ERRNO("initial message", "format string", ...)+`::
827 Component `errno` string debug logging statement.
828
829`+BT_COMP_LOGI_ERRNO("initial message", "format string", ...)+`::
830 Component `errno` string info logging statement.
831
832`+BT_COMP_LOGW_ERRNO("initial message", "format string", ...)+`::
833 Component `errno` string warning logging statement.
834
835`+BT_COMP_LOGE_ERRNO("initial message", "format string", ...)+`::
836 Component `errno` string error logging statement.
837
838`+BT_COMP_LOGF_ERRNO("initial message", "format string", ...)+`::
839 Component `errno` string fatal logging statement.
840
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841`+BT_COMP_LOGT_MEM(data_ptr, data_size, "format string", ...)+`::
842 Component memory trace logging statement.
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843
844`+BT_COMP_LOGD_MEM(data_ptr, data_size, "format string", ...)+`::
845 Component memory debug logging statement.
846
847`+BT_COMP_LOGI_MEM(data_ptr, data_size, "format string", ...)+`::
848 Component memory info logging statement.
849
850`+BT_COMP_LOGW_MEM(data_ptr, data_size, "format string", ...)+`::
851 Component memory warning logging statement.
852
853`+BT_COMP_LOGE_MEM(data_ptr, data_size, "format string", ...)+`::
854 Component memory error logging statement.
855
856`+BT_COMP_LOGF_MEM(data_ptr, data_size, "format string", ...)+`::
857 Component memory fatal logging statement.
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858
859
f9ded0e0 860==== Conditional logging
beb0fb75 861
cd4aac1e 862`+BT_LOG_IF(cond, statement)+`::
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863 Execute `statement` only if `cond` is true.
864+
865Example:
866+
867--
868[source,c]
869----
870BT_LOG_IF(i < count / 2, BT_LOGD("Log this: i=%d", i));
871----
872--
873
874To check the <<build-time-log-level,build-time log level>>:
875
876[source,c]
877----
878#if BT_LOG_ENABLED_DEBUG
879...
880#endif
881----
882
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883This tests if the _DEBUG_ level was enabled at build time. This means
884that the current, <<run-time-log-level,run-time log level>> _could_ be
f9ded0e0
PP
885_DEBUG_, but it could also be higher. The rule of thumb is to use only
886logging statements at the same level in a `BT_LOG_ENABLED_*` conditional
887block.
beb0fb75
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888
889The available definitions for build-time conditions are:
890
ef267d12 891* `BT_LOG_ENABLED_TRACE`
beb0fb75
PP
892* `BT_LOG_ENABLED_DEBUG`
893* `BT_LOG_ENABLED_INFO`
770538dd 894* `BT_LOG_ENABLED_WARNING`
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895* `BT_LOG_ENABLED_ERROR`
896* `BT_LOG_ENABLED_FATAL`
897
898To check the current, <<run-time-log-level,run-time log level>>:
899
900[source,c]
901----
902if (BT_LOG_ON_DEBUG) {
903 ...
904}
905----
906
907This tests if the _DEBUG_ log level is dynamically turned on
cd4aac1e 908(implies that it's also enabled at build time). This check could have a
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PP
909noticeable impact on performance.
910
911The available definitions for run-time conditions are:
912
ef267d12 913* `BT_LOG_ON_TRACE`
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PP
914* `BT_LOG_ON_DEBUG`
915* `BT_LOG_ON_INFO`
770538dd 916* `BT_LOG_ON_WARNING`
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917* `BT_LOG_ON_ERROR`
918* `BT_LOG_ON_FATAL`
919
cd4aac1e
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920Those macros check the module-specific log level symbol (defined by
921`BT_LOG_OUTPUT_LEVEL`).
beb0fb75
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922
923Never, ever write code which would be executed only to compute the
924fields of a logging statement outside a conditional logging scope,
925for example:
926
927[source,c]
928----
929int number = get_number_of_event_classes_with_property_x(...);
930BT_LOGD("Bla bla: number=%d", number);
931----
932
933Do this instead:
934
935[source,c]
936----
937if (BT_LOG_ON_DEBUG) {
938 int number = get_number_of_event_classes_with_property_x(...);
939 BT_LOGD("Bla bla: number=%d", number);
940}
941----
942
943Or even this:
944
945[source,c]
946----
947BT_LOGD("Bla bla: number=%d", get_number_of_event_classes_with_property_x(...));
948----
949
950
cd4aac1e 951=== Guides
beb0fb75 952
cd4aac1e
PP
953[[logging-instrument-c-file-gen]]
954==== Instrument a C source file (generic)
beb0fb75 955
cd4aac1e
PP
956To instrument a C source file (`.c`):
957
958. At the top of the file, before the first `#include` line (if any),
959 define your file's <<choose-a-logging-tag,logging tag>> name:
4a41523d
PP
960+
961--
962[source,c]
963----
cd4aac1e 964#define BT_LOG_TAG "SUBSYS/MY-MODULE/MY-FILE"
4a41523d
PP
965----
966--
cd4aac1e
PP
967
968. Below the line above, define the source file's log level expression,
969 `BT_LOG_OUTPUT_LEVEL`. This expression is evaluated for each
970 <<gen-logging-statements,logging statement>> to know the current
971 <<run-time-log-level,run-time log level>>.
972+
973Examples:
974+
975[source,c]
976----
977/* Global log level variable */
978#define BT_LOG_OUTPUT_LEVEL module_global_log_level
979----
4a41523d 980+
cd4aac1e
PP
981[source,c]
982----
983/* Local log level variable; must exist where you use BT_LOG*() */
984#define BT_LOG_OUTPUT_LEVEL log_level
985----
986+
987[source,c]
988----
989/* Object's log level; `obj` must exist where you use BT_LOG*() */
990#define BT_LOG_OUTPUT_LEVEL (obj->log_level)
991----
4a41523d 992
cd4aac1e 993. Include `"logging/log.h"`:
4a41523d 994+
beb0fb75
PP
995[source,c]
996----
578e048b 997#include "logging/log.h"
cd4aac1e 998----
4a41523d 999
cd4aac1e
PP
1000. In the file, instrument your code with the
1001 <<gen-logging-statements,generic logging statement macros>>.
4a41523d 1002
cd4aac1e
PP
1003
1004[[logging-instrument-h-file-gen]]
1005==== Instrument a C header file (generic)
1006
1007To instrument a C header file (`.h`), if you have `static inline`
1008functions in it:
1009
1010. Do not include `"logging/log.h"`!
1011
1012. Do one of:
1013
1014.. In the file, instrument your code with the
1015 <<gen-logging-statements,generic logging statement macros>>, making
1016 each of them conditional to the existence of the macro you're using:
4a41523d 1017+
cd4aac1e
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1018[source,c]
1019----
1020static inline
1021int some_function(int x)
1022{
1023 /* ... */
4a41523d 1024
ef267d12
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1025#ifdef BT_LOGT
1026 BT_LOGT(...);
cd4aac1e 1027#endif
beb0fb75 1028
cd4aac1e 1029 /* ... */
6470c171 1030
cd4aac1e
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1031#ifdef BT_LOGW_STR
1032 BT_LOGW_STR(...);
1033#endif
f9ded0e0 1034
cd4aac1e
PP
1035 /* ... */
1036}
1037----
1038+
1039The C source files which include this header file determine if logging
1040is enabled or not for them, and if so, what is their
1041<<choose-a-logging-tag,logging tag>> and <<run-time-log-level,run-time
1042log level>> expression.
f9ded0e0 1043
cd4aac1e
PP
1044.. Require that logging be enabled:
1045+
1046[source,c]
1047----
1048/* Protection: this file uses BT_LOG*() macros directly */
1049#ifndef BT_LOG_SUPPORTED
1050# error Please include "logging/log.h" before including this file.
1051#endif
1052----
1053+
1054Then, in the file, instrument your code with the
1055<<gen-logging-statements,generic logging statement macros>>.
1056
1057
1058[[logging-instrument-c-file-lib]]
1059==== Instrument a library C source file
1060
1061To instrument a library C source file (`.c`):
4a41523d
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1062
1063. At the top of the file, before the first `#include` line (if any),
cd4aac1e
PP
1064 define your file's <<choose-a-logging-tag,logging tag>> name (this
1065 tag must start with `LIB/`):
4a41523d
PP
1066+
1067--
1068[source,c]
1069----
cd4aac1e 1070#define BT_LOG_TAG "LIB/THE-FILE"
4a41523d
PP
1071----
1072--
cd4aac1e
PP
1073
1074. Include `"lib/logging.h"`:
4a41523d 1075+
cd4aac1e
PP
1076[source,c]
1077----
1078#include "lib/logging.h"
1079----
4a41523d 1080
cd4aac1e
PP
1081. In the file, instrument your code with the
1082 <<lib-logging-statements,library logging statement macros>> or with
1083 the <<gen-logging-statements,generic logging statement macros>>.
4a41523d 1084
f9ded0e0 1085
cd4aac1e
PP
1086[[logging-instrument-h-file-lib]]
1087==== Instrument a library C header file
1088
1089To instrument a library C header file (`.h`), if you have `static
1090inline` functions in it:
1091
1092. Do not include `"lib/logging.h"`!
1093
1094. Require that library logging be enabled:
1095+
1096[source,c]
1097----
1098/* Protection: this file uses BT_LIB_LOG*() macros directly */
1099#ifndef BT_LIB_LOG_SUPPORTED
1100# error Please include "lib/logging.h" before including this file.
1101#endif
1102----
1103
1104. In the file, instrument your code with the
1105 <<lib-logging-statements,library logging statement macros>> or with
1106 the <<gen-logging-statements,generic logging statement macros>>.
f9ded0e0 1107
4a41523d 1108
cd4aac1e
PP
1109[[logging-instrument-c-file-compcls]]
1110==== Instrument a component class C source file
1111
1112To instrument a component class C source file (`.c`):
1113
1114. At the top of the file, before the first `#include` line (if any),
1115 define your file's <<choose-a-logging-tag,logging tag>> name (this tag
1116 must start with `PLUGIN/` followed by the component class identifier):
4a41523d
PP
1117+
1118--
1119[source,c]
1120----
cd4aac1e
PP
1121#define BT_LOG_TAG "PLUGIN/SRC.MY-PLUGIN.MY-SRC"
1122----
1123--
4a41523d 1124
cd4aac1e
PP
1125. Below the line above, define the source file's log level expression,
1126 `BT_LOG_OUTPUT_LEVEL`. This expression is evaluated for each
1127 <<comp-logging-statements,logging statement>> to know the current
1128 <<run-time-log-level,run-time log level>>.
1129+
1130For a component class file, it is usually a member of a local component
1131private structure variable:
1132+
1133[source,c]
1134----
1135#define BT_LOG_OUTPUT_LEVEL (my_comp->log_level)
1136----
4a41523d 1137
cd4aac1e
PP
1138. Below the line above, define `BT_COMP_LOG_SELF_COMP` to an expression
1139 which, evaluated in the context of the
1140 <<comp-logging-statements,logging statements>>, evaluates to the self
1141 component address (`+bt_self_component *+`) of the component.
1142+
1143This is usually a member of a local component private structure
1144variable:
1145+
1146[source,c]
1147----
1148#define BT_COMP_LOG_SELF_COMP (my_comp->self_comp)
1149----
1150
d9c39b0a 1151. Include `"logging/comp-logging.h"`:
cd4aac1e
PP
1152+
1153[source,c]
1154----
d9c39b0a 1155#include "logging/comp-logging.h"
cd4aac1e
PP
1156----
1157
1158. In the component initialization method, make sure to set the
1159 component private structure's log level member to the initial
1160 component's log level:
1161+
1162[source,c]
1163----
1164struct my_comp {
1165 bt_logging_level log_level;
4a41523d 1166 /* ... */
cd4aac1e 1167};
4a41523d 1168
cd4aac1e
PP
1169BT_HIDDEN
1170bt_self_component_status my_comp_init(
1171 bt_self_component_source *self_comp_src,
1172 bt_value *params, void *init_method_data)
1173{
1174 struct my_comp *my_comp = g_new0(struct my_comp, 1);
1175 bt_self_component *self_comp =
1176 bt_self_component_source_as_self_component(self_comp_src);
1177 const bt_component *comp = bt_self_component_as_component(self_comp);
1178
1179 BT_ASSERT(my_comp);
1180 my_comp->log_level = bt_component_get_logging_level(comp);
4a41523d
PP
1181
1182 /* ... */
1183}
1184----
cd4aac1e
PP
1185
1186. In the file, instrument your code with the
1187 <<comp-logging-statements,component logging statement macros>>.
1188
1189
1190[[logging-instrument-h-file-compcls]]
1191==== Instrument a component class C header file
1192
1193To instrument a component class C header file (`.h`), if you have
1194`static inline` functions in it:
1195
d9c39b0a 1196. Do not include `"logging/comp-logging.h"`!
cd4aac1e
PP
1197
1198. Require that component logging be enabled:
4a41523d 1199+
cd4aac1e
PP
1200[source,c]
1201----
1202/* Protection: this file uses BT_COMP_LOG*() macros directly */
1203#ifndef BT_COMP_LOG_SUPPORTED
d9c39b0a 1204# error Please include "logging/comp-logging.h" before including this file.
cd4aac1e
PP
1205#endif
1206----
1207
1208. In the file, instrument your code with the
1209 <<comp-logging-statements,component logging statement macros>>.
1210
1211
1212[[choose-a-logging-tag]]
1213==== Choose a logging tag
beb0fb75 1214
cd4aac1e
PP
1215Each logging-enabled C source file must define `BT_LOG_TAG` to a logging
1216tag. A logging tag is a namespace to identify the logging messages of
1217this specific source file.
beb0fb75 1218
cd4aac1e
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1219In general, a logging tag name _must_ be only uppercase letters, digits,
1220and the `-`, `.`, and `/` characters.
beb0fb75 1221
cd4aac1e
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1222Use `/` to show the subsystem to source file hierarchy.
1223
1224For the Babeltrace library, start with `LIB/`.
1225
1226For the CTF writer library, start with `CTF-WRITER/`.
1227
1228For component classes, use:
beb0fb75 1229
93841983 1230[verse]
cd4aac1e
PP
1231`PLUGIN/__CCTYPE__.__PNAME__.__CCNAME__[/__FILE__]`
1232
1233With:
1234
1235`__CCTYPE__`::
1236 Component class's type (`SRC`, `FLT`, or `SINK`).
beb0fb75 1237
cd4aac1e 1238`__PNAME__`::
93841983 1239 Plugin's name.
beb0fb75 1240
cd4aac1e 1241`__CCNAME__`::
93841983 1242 Component class's name.
beb0fb75 1243
cd4aac1e 1244`__FILE__`::
93841983 1245 Additional information to specify the source file name or module.
beb0fb75 1246
cd4aac1e 1247For plugins (files common to many component classes), use:
beb0fb75 1248
cd4aac1e
PP
1249[verse]
1250`PLUGIN/__PNAME__[/__FILE__]`
beb0fb75 1251
cd4aac1e 1252With:
beb0fb75 1253
cd4aac1e
PP
1254`__PNAME__`::
1255 Plugin's name.
1256
1257`__FILE__`::
1258 Additional information to specify the source file name or module.
1259
1260
1261[[choose-a-log-level]]
1262==== Choose a log level
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1263
1264Choosing the appropriate level for your logging statement is very
1265important.
1266
cd4aac1e 1267[options="header,autowidth",cols="1,2,3a,4"]
beb0fb75 1268|===
cd4aac1e 1269|Log level |Description |Use cases |Expected impact on performance
beb0fb75
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1270
1271|_FATAL_
cd4aac1e
PP
1272|
1273The program, library, or plugin cannot continue to work in this
beb0fb75
PP
1274condition: it must be terminated immediately.
1275
b4b9064d 1276A _FATAL_-level logging statement should always be followed by
4a41523d 1277`abort()`.
beb0fb75
PP
1278|
1279* Unexpected return values from system calls.
4a41523d
PP
1280* Logic error in internal code, for example an unexpected value in a
1281 `switch` statement.
cd4aac1e 1282* Failed assertion (within `BT_ASSERT()`).
bdb288b3
PP
1283* Unsatisfied library precondition (within `BT_ASSERT_PRE()` or
1284 `BT_ASSERT_PRE_DEV()`).
1285* Unsatisfied library postcondition (within `BT_ASSERT_POST()` or
1286 `BT_ASSERT_POST_DEV()`).
dd22a91f 1287|Almost none: always enabled.
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PP
1288
1289|_ERROR_
cd4aac1e
PP
1290|
1291An important error which is somewhat not fatal, that is, the program,
beb0fb75
PP
1292library, or plugin can continue to work after this, but you judge that
1293it should be reported to the user.
1294
1295Usually, the program cannot recover from such an error, but it can at
1296least exit cleanly.
1297|
1298* Memory allocation errors.
cd4aac1e
PP
1299* Wrong component initialization parameters.
1300* Corrupted, unrecoverable trace data.
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1301* Failed to perform an operation which should work considering the
1302 implementation and the satisfied preconditions. For example, the
1303 failure to create an empty object (no parameters): most probably
1304 failed internally because of an allocation error.
93841983 1305* Almost any error in terminal elements: CLI and plugins.
dd22a91f 1306|Almost none: always enabled.
beb0fb75 1307
770538dd 1308|_WARNING_
cd4aac1e
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1309|
1310An error which still allows the execution to continue, but you judge
1311that it should be reported to the user.
6c1b33a8 1312
770538dd
PP
1313_WARNING_-level logging statements are for any error or weird action
1314that is directly or indirectly caused by the user, often through some
1315bad input data. For example, not having enough memory is considered
1316beyond the user's control, so we always log memory errors with an
1317_ERROR_ level (not _FATAL_ because we usually don't abort in this
1318condition).
beb0fb75 1319|
cd4aac1e
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1320* Missing data within something that is expected to have it, but there's
1321 an alternative.
1322* Invalid file, but recoverable/fixable.
dd22a91f 1323|Almost none: always enabled.
beb0fb75
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1324
1325|_INFO_
beb0fb75 1326|
cd4aac1e
PP
1327Any useful information which a non-developer user would possibly
1328understand.
1329
1330Anything logged with this level must _not_ happen repetitively on the
1331fast path, that is, nothing related to each message, for example. This
1332level is used for sporadic and one-shot events.
1333|
1334* CLI or component configuration report.
1335* Successful plugin, component, or message iterator initialization.
1336* In the library: anything related to plugins, graphs, component
1337 classes, components, message iterators, connections, and ports which
1338 is not on the fast path.
beb0fb75 1339* Successful connection to or disconnection from another system.
4a41523d 1340* An _optional_ subsystem cannot be loaded.
cd4aac1e
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1341* An _optional_ field/datum cannot be found.
1342|
dd22a91f 1343Very little: always enabled.
beb0fb75
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1344
1345|_DEBUG_
beb0fb75 1346|
cd4aac1e
PP
1347Something that only Babeltrace developers would be interested into,
1348which can occur on the fast path, but not more often than once per
1349message.
1350
1351The _DEBUG_ level is the default <<build-time-log-level,build-time log
1352level>> as, since it's not _too_ verbose, the performance is similar to
1353an _INFO_ build.
1354|
1355* Object construction and destruction.
1356* Object recycling (except fields).
1357* Object copying (except fields and values).
1358* Object freezing (whatever the type, as freezing only occurs in
1359 developer mode).
9b4f9b42 1360* Object interruption.
cd4aac1e
PP
1361* Calling user methods and logging the result.
1362* Setting object properties (except fields and values).
1363|
ef267d12 1364Noticeable, but not as much as the _TRACE_ level: could be executed
cd4aac1e
PP
1365in production if you're going to need a thorough log for support
1366tickets without having to rebuild the project.
beb0fb75 1367
ef267d12 1368|_TRACE_
cd4aac1e
PP
1369|
1370Low-level debugging context information (anything that does not fit the
1371other log levels). More appropriate for tracing in general.
beb0fb75
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1372|
1373* Reference count change.
cd4aac1e 1374* Fast path, low level state machine's state change.
beb0fb75
PP
1375* Get or set an object's property.
1376* Object comparison's intermediate results.
1377|Huge: not executed in production.
1378|===
1379
cd4aac1e
PP
1380[IMPORTANT]
1381--
770538dd 1382Make sure not to use a _WARNING_ (or higher) log level when the
cd4aac1e
PP
1383condition leading to the logging statement can occur under normal
1384circumstances.
1385
1386For example, a public function to get some object or
1387property from an object by name or key that fails to find the value is
1388not a warning scenario: the user could legitimately use this function to
1389check if the name/key exists in the object. In this case, use the
ef267d12 1390_TRACE_ level (or do not log at all).
cd4aac1e 1391--
b4b9064d 1392
beb0fb75 1393
b4b9064d 1394[[message]]
cd4aac1e 1395==== Write an appropriate message
beb0fb75
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1396
1397Follow those rules when you write a logging statement's message:
1398
cd4aac1e
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1399* Use an English sentence which starts with a capital letter.
1400
1401* Start the sentence with the appropriate verb tense depending on the
1402 context. For example:
beb0fb75
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1403+
1404--
b4b9064d
PP
1405** Beginning of operation (present continuous): _Creating ..._,
1406 _Copying ..._, _Serializing ..._, _Freezing ..._, _Destroying ..._
1407** End of operation (simple past): _Created ..._, _Successfully created ..._,
1408 _Failed to create ..._, _Set ..._ (simple past of _to set_ which is
1409 also _set_)
beb0fb75
PP
1410--
1411+
1412For warning and error messages, you can start the message with _Cannot_
b4b9064d 1413or _Failed to_ followed by a verb if it's appropriate.
beb0fb75
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1414
1415* Do not include the log level in the message itself. For example,
1416 do not start the message with _Error while_ or _Warning:_.
1417
cd4aac1e
PP
1418* Do not put newlines, tabs, or other special characters in the message,
1419 unless you want to log a string with such characters. Note that
1420 multiline logging messages can be hard to parse, analyze, and filter,
1421 however, so prefer multiple logging statements over a single statement
1422 with newlines.
beb0fb75
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1423
1424* **If there are fields that your logging statement must record**,
1425 follow the message with `:` followed by a space, then with the list of
1426 fields (more about this below). If there are no fields, end the
1427 sentence with a period.
1428
1429The statement's fields _must_ be a comma-separated list of
cd4aac1e
PP
1430`__name__=__value__` tokens. Keep `__name__` as simple as possible; use
1431kebab case if possible. If `__value__` is a non-alphanumeric string, put
1432it between double quotes (`"%s"` specifier). Always use the `PRId64` and
1433`PRIu64` specifiers to log an `int64_t` or an `uint64_t` value. Use `%d`
1434to log a boolean value.
beb0fb75
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1435
1436Example:
1437
cd4aac1e
PP
1438 "Cannot read stream data for indexing: path=\"%s\", name=\"%s\", "
1439 "stream-id=%" PRIu64 ", stream-fd=%d, "
1440 "index=%" PRIu64 ", status=%s, is-mapped=%d"
beb0fb75 1441
cd4aac1e
PP
1442By following a standard format for the statement fields, it is easier to
1443use tools like https://www.elastic.co/products/logstash[Logstash] or
1444even https://www.splunk.com/[Splunk] to split fields and analyze logs.
beb0fb75
PP
1445
1446Prefer the following suffixes in field names:
1447
1448[options="header,autowidth"]
1449|===
1450|Field name suffix |Description |Format specifier
1451
1452|`-addr` |Memory address |`%p`
1453|`-fd` |File descriptor |`%d`
cd4aac1e
PP
1454|`-fp` |File stream (`+FILE *+`) |`%p`
1455|`-id` |Object's ID |`%" PRIu64 "`
1456|`-index` |Index |`%" PRIu64 "`
beb0fb75 1457|`-name` |Object's name |`\"%s\"`
beb0fb75
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1458|===
1459
1460
f9ded0e0 1461=== Output
beb0fb75
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1462
1463The log is printed to the standard error stream. A log line contains the
cd4aac1e
PP
1464time, the process and thread IDs, the <<log-levels,log level>>, the
1465<<choose-a-logging-tag,logging tag>>, the source's function name, file
1466name and line number, and the <<message,message>>.
beb0fb75 1467
f9ded0e0
PP
1468When Babeltrace supports terminal color codes (depends on the
1469`BABELTRACE_TERM_COLOR` environment variable's value and what the
1470standard output and error streams are plugged into), _INFO_-level lines
770538dd 1471are blue, _WARNING_-level lines are yellow, and _ERROR_-level and
f9ded0e0
PP
1472_FATAL_-level lines are red.
1473
1474Log line example:
beb0fb75 1475
cd4aac1e
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1476----
147705-11 00:58:03.691 23402 23402 D VALUES bt_value_destroy@values.c:498 Destroying value: addr=0xb9c3eb0
1478----
beb0fb75 1479
cd4aac1e
PP
1480You can easily filter the log with `grep` or `ag`. For example, to keep
1481only the _DEBUG_-level logging messages that the `FIELD-CLASS` module
beb0fb75
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1482generates:
1483
cd4aac1e
PP
1484----
1485$ babeltrace2 --log-level=D /path/to/trace |& ag 'D FIELD-CLASS'
1486----
1487
1488
1489== Valgrind
1490
1491To use Valgrind on an application (for example, the CLI or a test) which
1492loads libbabeltrace2, use:
1493
1494----
1495$ G_SLICE=always-malloc G_DEBUG=gc-friendly PYTHONMALLOC=malloc \
916d0d91 1496 LIBBABELTRACE2_NO_DLCLOSE=1 valgrind --leak-check=full app
cd4aac1e
PP
1497----
1498
1499`G_SLICE=always-malloc` and `G_DEBUG=gc-friendly` is for GLib and
1500`PYTHONMALLOC=malloc` is for the Python interpreter, if it is used by
1501the Python plugin provider (Valgrind will probably show a lot of errors
1502which originate from the Python interpreter anyway).
1503
16b7b5e7 1504`LIBBABELTRACE2_NO_DLCLOSE=1` makes libbabeltrace2 not close the shared
cd4aac1e
PP
1505libraries (plugins) which it loads. You need this to see the appropriate
1506backtrace when Valgrind shows errors.
c637d729
FD
1507
1508== Testing
1509
800400d8
PP
1510[[test-env]]
1511=== Environment
c637d729 1512
800400d8
PP
1513`tests/utils/utils.sh` sets the environment variables for any Babeltrace
1514test script.
1515
1516`utils.sh` only needs to know the path to the `tests` directory within
1517the source and the build directories. By default, `utils.sh` assumes the
1518build is in tree, that is, you ran `./configure` from the source's root
1519directory, and sets the `BT_TESTS_SRCDIR` and `BT_TESTS_BUILDDIR`
1520environment variables accordingly. You can override those variables, for
1521example if you build out of tree.
1522
1523All test scripts eventually do something like this to source `utils.sh`,
1524according to where they are located relative to the `tests` directory:
1525
1526[source,bash]
1527----
1528if [ "x${BT_TESTS_SRCDIR:-}" != "x" ]; then
1529 UTILSSH="$BT_TESTS_SRCDIR/utils/utils.sh"
1530else
1531 UTILSSH="$(dirname "$0")/../utils/utils.sh"
1532fi
1533----
1534
1535==== Python
1536
1537You can use the `tests/utils/run_python_bt2` script to run any command
1538within an environment making the build's `bt2` Python package available.
1539
1540`run_python_bt2` uses <<test-env,`utils.sh`>> which needs to know the
1541build directory, so make sure you set the `BT_TESTS_BUILDDIR`
1542environment variable correctly _if you build out of tree_, for example:
1543
1544----
1545$ export BT_TESTS_BUILDDIR=/path/to/build/babeltrace/tests
1546----
1547
1548You can run any command which needs the `bt2` Python package through
1549`run_python_bt2`, for example:
c637d729
FD
1550
1551----
800400d8 1552$ ./tests/utils/run_python_bt2 ipython3
c637d729
FD
1553----
1554
800400d8
PP
1555=== Report format
1556
1557All test scripts output the test results following the
1558https://testanything.org/[Test Anything Protocol] (TAP) format.
1559
1560The TAP format has two mechanisms to print additional information about
1561a test:
1562
1563* Print a line starting with `#` to the standard output.
1564+
1565This is usually done with the `diag()` C function or the `diag` shell
1566function.
1567
1568* Print to the standard error.
1569
1570
1571=== Python bindings
1572
1573The `bt2` Python package tests are located in
1574`tests/bindings/python/bt2`.
1575
1576
1577==== Python test runner
1578
1579`tests/utils/python/testrunner.py` is Babeltrace's Python test runner
1580which loads Python files containing unit tests, finds all the test
1581cases, and runs the tests, producing a TAP report.
1582
1583You can see the test runner command's help with:
c637d729
FD
1584
1585----
800400d8 1586$ python3 ./tests/utils/python/testrunner.py --help
c637d729
FD
1587----
1588
800400d8
PP
1589By default, the test runner reports failing tests (TAP's `not{nbsp}ok`
1590line), but continues to run other tests. You can use the `--failfast`
1591option to make the test runner fail as soon as a test fails.
c637d729 1592
800400d8
PP
1593
1594==== Guides
1595
1596To run all the `bt2` Python package tests:
1597
1598* Run:
1599+
1600----
1601$ ./tests/utils/run_python_bt2 ./tests/bindings/python/bt2/test_python_bt2
1602----
1603+
1604or:
1605+
1606----
1607$ ./tests/utils/run_python_bt2 python3 ./tests/utils/python/testrunner.py \
1608 ./tests/bindings/python/bt2/ -p '*.py'
1609----
1610
1611To run **all the tests** in a test module (for example,
1612`test_value.py`):
1613
1614* Run:
1615+
1616----
1617$ ./tests/utils/run_python_bt2 python3 ./tests/utils/python/testrunner.py \
1618 ./tests/bindings/python/bt2 -t test_value
1619----
1620
1621To run a **specific test case** (for example, `RealValueTestCase` within
1622`test_value.py`):
1623
1624* Run:
1625+
1626----
1627$ ./tests/utils/run_python_bt2 python3 ./tests/utils/python/testrunner.py \
1628 ./tests/bindings/python/bt2/ -t test_value.RealValueTestCase
1629----
1630
1631To run a **specific test** (for example,
1632`RealValueTestCase.test_assign_pos_int` within `test_value.py`):
1633
1634* Run:
1635+
c637d729 1636----
800400d8
PP
1637$ ./tests/utils/run_python_bt2 python3 ./tests/utils/python/testrunner.py \
1638 ./tests/bindings/python/bt2/ -t test_value.RealValueTestCase.test_assign_pos_int
c637d729 1639----
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