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7adf7ee2 PP |
1 | The LTTng Documentation |
2 | ======================= | |
3 | Philippe Proulx <pproulx@efficios.com> | |
c0468840 | 4 | v2.8, 24 July 2017 |
7adf7ee2 PP |
5 | |
6 | ||
7 | include::../common/copyright.txt[] | |
8 | ||
9 | ||
85c29972 PP |
10 | include::../common/warning-not-maintained.txt[] |
11 | ||
12 | ||
7adf7ee2 PP |
13 | include::../common/welcome.txt[] |
14 | ||
15 | ||
16 | include::../common/audience.txt[] | |
17 | ||
18 | ||
19 | [[chapters]] | |
20 | === What's in this documentation? | |
21 | ||
22 | The LTTng Documentation is divided into the following sections: | |
23 | ||
24 | * **<<nuts-and-bolts,Nuts and bolts>>** explains the | |
25 | rudiments of software tracing and the rationale behind the | |
26 | LTTng project. | |
27 | + | |
28 | You can skip this section if you’re familiar with software tracing and | |
29 | with the LTTng project. | |
30 | ||
31 | * **<<installing-lttng,Installation>>** describes the steps to | |
32 | install the LTTng packages on common Linux distributions and from | |
33 | their sources. | |
34 | + | |
35 | You can skip this section if you already properly installed LTTng on | |
36 | your target system. | |
37 | ||
38 | * **<<getting-started,Quick start>>** is a concise guide to | |
39 | getting started quickly with LTTng kernel and user space tracing. | |
40 | + | |
41 | We recommend this section if you're new to LTTng or to software tracing | |
42 | in general. | |
43 | + | |
44 | You can skip this section if you're not new to LTTng. | |
45 | ||
46 | * **<<core-concepts,Core concepts>>** explains the concepts at | |
47 | the heart of LTTng. | |
48 | + | |
49 | It's a good idea to become familiar with the core concepts | |
50 | before attempting to use the toolkit. | |
51 | ||
52 | * **<<plumbing,Components of LTTng>>** describes the various components | |
53 | of the LTTng machinery, like the daemons, the libraries, and the | |
54 | command-line interface. | |
55 | * **<<instrumenting,Instrumentation>>** shows different ways to | |
56 | instrument user applications and the Linux kernel. | |
57 | + | |
58 | Instrumenting source code is essential to provide a meaningful | |
59 | source of events. | |
60 | + | |
61 | You can skip this section if you do not have a programming background. | |
62 | ||
63 | * **<<controlling-tracing,Tracing control>>** is divided into topics | |
64 | which demonstrate how to use the vast array of features that | |
65 | LTTng{nbsp}{revision} offers. | |
66 | * **<<reference,Reference>>** contains reference tables. | |
67 | * **<<glossary,Glossary>>** is a specialized dictionary of terms related | |
68 | to LTTng or to the field of software tracing. | |
69 | ||
70 | ||
71 | include::../common/convention.txt[] | |
72 | ||
73 | ||
74 | include::../common/acknowledgements.txt[] | |
75 | ||
76 | ||
77 | [[whats-new]] | |
78 | == What's new in LTTng {revision}? | |
79 | ||
78ca092c PP |
80 | LTTng{nbsp}{revision} bears the name _Isseki Nicho_. The result of a |
81 | collaboration between http://www.dieuduciel.com/[Dieu du Ciel!] and | |
82 | Nagano-based Shiga Kogen, | |
83 | https://www.beeradvocate.com/beer/profile/1141/53111/[_**Isseki | |
84 | Nicho**_] is a strong Imperial Dark Saison offering a rich roasted malt | |
85 | flavor combined with a complex fruity finish typical of Saison yeasts. | |
86 | ||
87 | New features and changes in LTTng{nbsp}{revision}: | |
88 | ||
7adf7ee2 PP |
89 | * **Tracing control**: |
90 | ** You can attach <<java-application-context,Java application-specific | |
91 | context fields>> to a <<channel,channel>> with the | |
92 | man:lttng-add-context(1) command: | |
93 | + | |
94 | -- | |
95 | [role="term"] | |
96 | ---- | |
ded02698 | 97 | $ lttng add-context --jul --type='$app.retriever:cur_msg_id' |
7adf7ee2 PP |
98 | ---- |
99 | -- | |
100 | + | |
101 | Here, `$app` is the prefix of all application-specific context fields, | |
102 | `retriever` names a _context information retriever_ defined at the | |
103 | application level, and `cur_msg_id` names a context field read from this | |
104 | retriever. | |
105 | + | |
106 | Both the `java.util.logging` and Apache log4j <<domain,tracing domains>> | |
107 | are supported. | |
108 | ||
109 | ** You can use Java application-specific <<adding-context,context>> | |
110 | fields in the <<enabling-disabling-events,filter expression>> of an | |
111 | <<event,event rule>>: | |
112 | + | |
113 | -- | |
114 | [role="term"] | |
115 | ---- | |
ded02698 | 116 | $ lttng enable-event --log4j my_logger \ |
7adf7ee2 PP |
117 | --filter='$app.retriever:cur_msg_id == 23' |
118 | ---- | |
119 | -- | |
120 | ||
121 | ** New `lttng status` command which is the equivalent of +lttng list | |
122 | __CUR__+, where +__CUR__+ is the name of the current | |
123 | <<tracing-session,tracing session>>. | |
124 | + | |
125 | See man:lttng-status(1). | |
126 | ||
837c451d PP |
127 | ** New `lttng metadata regenerate` command to |
128 | <<metadata-regenerate,regenerate the metadata file of an LTTng | |
129 | trace>> at any moment. This command is meant to be used to resample | |
130 | the wall time following a major | |
7adf7ee2 PP |
131 | https://en.wikipedia.org/wiki/Network_Time_Protocol[NTP] correction |
132 | so that a system which boots with an incorrect wall time can be | |
133 | traced before its wall time is NTP-corrected. | |
134 | + | |
135 | See man:lttng-metadata(1). | |
136 | ||
137 | ** New command-line interface warnings when <<event,event records>> or | |
138 | whole sub-buffers are | |
139 | <<channel-overwrite-mode-vs-discard-mode,lost>>. The warning messages | |
140 | are printed when a <<tracing-session,tracing session>> is | |
141 | <<basic-tracing-session-control,stopped>> (man:lttng-stop(1) | |
142 | command). | |
143 | ||
144 | * **User space tracing**: | |
145 | ** Shared object base address dump in order to map <<event,event | |
146 | records>> to original source location (file and line number). | |
147 | + | |
148 | If you attach the `ip` and `vpid` <<adding-context,context fields>> to a | |
149 | user space <<channel,channel>> and if you use the | |
150 | <<liblttng-ust-dl,path:{liblttng-ust-dl.so} helper>>, you can retrieve | |
151 | the source location where a given event record was generated. | |
152 | + | |
153 | The http://diamon.org/babeltrace/[Babeltrace] trace viewer supports this | |
154 | state dump and those context fields since version 1.4 to print the | |
155 | source location of a given event record. http://tracecompass.org/[Trace | |
156 | Compass] also supports this since version 2.0. | |
157 | ||
158 | ** A <<java-application,Java application>> which uses | |
159 | `java.util.logging` now adds an LTTng-UST log handler to the desired | |
160 | JUL loggers. | |
161 | + | |
162 | The previous workflow was to initialize the LTTng-UST Java agent | |
163 | by calling `LTTngAgent.getLTTngAgent()`. This had the effect of adding | |
164 | an LTTng-UST log handler to the root loggers. | |
165 | ||
166 | ** A <<java-application,Java application>> which uses Apache log4j now | |
167 | adds an LTTng-UST log appender to the desired log4j loggers. | |
168 | + | |
169 | The previous workflow was to initialize the LTTng-UST Java agent | |
170 | by calling `LTTngAgent.getLTTngAgent()`. This had the effect of adding | |
171 | an LTTng-UST appender to the root loggers. | |
172 | ||
173 | ** Any <<java-application,Java application>> can provide | |
174 | <<java-application-context,dynamic context fields>> while running | |
175 | thanks to a new API provided by the <<lttng-ust-agents,LTTng-UST Java | |
176 | agent>>. You can require LTTng to record specific context fields in | |
177 | event records, and you can use them in the filter expression of | |
178 | <<event,event rules>>. | |
179 | ||
180 | * **Linux kernel tracing**: | |
181 | ** The LTTng kernel modules can now be built into a Linux kernel image, | |
182 | that is, not as loadable modules. | |
183 | + | |
184 | Follow the project's | |
185 | https://github.com/lttng/lttng-modules/blob/stable-{revision}/README.md#kernel-built-in-support[`README.md`] | |
186 | file to learn how. | |
187 | ||
188 | ** New instrumentation: | |
189 | *** ARM64 architecture support. | |
190 | *** x86 page faults. | |
191 | *** x86 `irq_vectors`. | |
192 | ** New <<adding-context,context fields>>: | |
193 | *** `interruptible` | |
194 | *** `preemptible` | |
195 | *** `need_reschedule` | |
196 | *** `migratable` (specific to RT-Preempt) | |
197 | ** Clock source plugin support for advanced cases where a custom source | |
198 | of time is needed to timestamp LTTng event records. | |
199 | + | |
200 | See https://github.com/lttng/lttng-modules/blob/stable-{revision}/lttng-clock.h[`lttng-clock.h`] | |
201 | for an overview of the small API. | |
202 | ||
203 | * **Documentation**: | |
204 | ** The link:/man[man pages] of the man:lttng(1) command-line tool are | |
205 | split into one man page per command (à la Git), for example: | |
206 | + | |
207 | -- | |
208 | [role="term"] | |
209 | ---- | |
ded02698 | 210 | $ man lttng-enable-event |
7adf7ee2 PP |
211 | ---- |
212 | -- | |
213 | + | |
214 | You can also use the `--help` option of any man:lttng(1) command to | |
215 | open its man page. | |
216 | + | |
217 | The content and formatting of all the LTTng man pages has improved | |
218 | dramatically. | |
219 | ||
220 | ||
221 | [[nuts-and-bolts]] | |
222 | == Nuts and bolts | |
223 | ||
224 | What is LTTng? As its name suggests, the _Linux Trace Toolkit: next | |
225 | generation_ is a modern toolkit for tracing Linux systems and | |
226 | applications. So your first question might be: | |
227 | **what is tracing?** | |
228 | ||
229 | ||
230 | [[what-is-tracing]] | |
231 | === What is tracing? | |
232 | ||
233 | As the history of software engineering progressed and led to what | |
234 | we now take for granted--complex, numerous and | |
235 | interdependent software applications running in parallel on | |
236 | sophisticated operating systems like Linux--the authors of such | |
237 | components, software developers, began feeling a natural | |
238 | urge to have tools that would ensure the robustness and good performance | |
239 | of their masterpieces. | |
240 | ||
241 | One major achievement in this field is, inarguably, the | |
242 | https://www.gnu.org/software/gdb/[GNU debugger (GDB)], | |
243 | an essential tool for developers to find and fix bugs. But even the best | |
244 | debugger won't help make your software run faster, and nowadays, faster | |
245 | software means either more work done by the same hardware, or cheaper | |
246 | hardware for the same work. | |
247 | ||
248 | A _profiler_ is often the tool of choice to identify performance | |
249 | bottlenecks. Profiling is suitable to identify _where_ performance is | |
250 | lost in a given software. The profiler outputs a profile, a statistical | |
251 | summary of observed events, which you may use to discover which | |
252 | functions took the most time to execute. However, a profiler won't | |
253 | report _why_ some identified functions are the bottleneck. Bottlenecks | |
254 | might only occur when specific conditions are met, conditions that are | |
255 | sometimes impossible to capture by a statistical profiler, or impossible | |
256 | to reproduce with an application altered by the overhead of an | |
257 | event-based profiler. For a thorough investigation of software | |
258 | performance issues, a history of execution is essential, with the | |
259 | recorded values of variables and context fields you choose, and | |
260 | with as little influence as possible on the instrumented software. This | |
261 | is where tracing comes in handy. | |
262 | ||
263 | _Tracing_ is a technique used to understand what goes on in a running | |
264 | software system. The software used for tracing is called a _tracer_, | |
265 | which is conceptually similar to a tape recorder. When recording, | |
266 | specific instrumentation points placed in the software source code | |
267 | generate events that are saved on a giant tape: a _trace_ file. You | |
268 | can trace user applications and the operating system at the same time, | |
269 | opening the possibility of resolving a wide range of problems that would | |
270 | otherwise be extremely challenging. | |
271 | ||
272 | Tracing is often compared to _logging_. However, tracers and loggers are | |
273 | two different tools, serving two different purposes. Tracers are | |
274 | designed to record much lower-level events that occur much more | |
275 | frequently than log messages, often in the range of thousands per | |
276 | second, with very little execution overhead. Logging is more appropriate | |
277 | for a very high-level analysis of less frequent events: user accesses, | |
278 | exceptional conditions (errors and warnings, for example), database | |
279 | transactions, instant messaging communications, and such. Simply put, | |
280 | logging is one of the many use cases that can be satisfied with tracing. | |
281 | ||
282 | The list of recorded events inside a trace file can be read manually | |
283 | like a log file for the maximum level of detail, but it is generally | |
284 | much more interesting to perform application-specific analyses to | |
285 | produce reduced statistics and graphs that are useful to resolve a | |
286 | given problem. Trace viewers and analyzers are specialized tools | |
287 | designed to do this. | |
288 | ||
289 | In the end, this is what LTTng is: a powerful, open source set of | |
290 | tools to trace the Linux kernel and user applications at the same time. | |
291 | LTTng is composed of several components actively maintained and | |
292 | developed by its link:/community/#where[community]. | |
293 | ||
294 | ||
295 | [[lttng-alternatives]] | |
296 | === Alternatives to noch:{LTTng} | |
297 | ||
298 | Excluding proprietary solutions, a few competing software tracers | |
299 | exist for Linux: | |
300 | ||
301 | * https://github.com/dtrace4linux/linux[dtrace4linux] is a port of | |
302 | Sun Microsystems's DTrace to Linux. The cmd:dtrace tool interprets | |
303 | user scripts and is responsible for loading code into the | |
304 | Linux kernel for further execution and collecting the outputted data. | |
305 | * https://en.wikipedia.org/wiki/Berkeley_Packet_Filter[eBPF] is a | |
306 | subsystem in the Linux kernel in which a virtual machine can execute | |
307 | programs passed from the user space to the kernel. You can attach | |
308 | such programs to tracepoints and KProbes thanks to a system call, and | |
309 | they can output data to the user space when executed thanks to | |
310 | different mechanisms (pipe, VM register values, and eBPF maps, to name | |
311 | a few). | |
312 | * https://www.kernel.org/doc/Documentation/trace/ftrace.txt[ftrace] | |
313 | is the de facto function tracer of the Linux kernel. Its user | |
314 | interface is a set of special files in sysfs. | |
315 | * https://perf.wiki.kernel.org/[perf] is | |
316 | a performance analyzing tool for Linux which supports hardware | |
317 | performance counters, tracepoints, as well as other counters and | |
318 | types of probes. perf's controlling utility is the cmd:perf command | |
319 | line/curses tool. | |
320 | * http://linux.die.net/man/1/strace[strace] | |
321 | is a command-line utility which records system calls made by a | |
322 | user process, as well as signal deliveries and changes of process | |
323 | state. strace makes use of https://en.wikipedia.org/wiki/Ptrace[ptrace] | |
324 | to fulfill its function. | |
325 | * http://www.sysdig.org/[sysdig], like SystemTap, uses scripts to | |
326 | analyze Linux kernel events. You write scripts, or _chisels_ in | |
327 | sysdig's jargon, in Lua and sysdig executes them while the system is | |
328 | being traced or afterwards. sysdig's interface is the cmd:sysdig | |
329 | command-line tool as well as the curses-based cmd:csysdig tool. | |
330 | * https://sourceware.org/systemtap/[SystemTap] is a Linux kernel and | |
331 | user space tracer which uses custom user scripts to produce plain text | |
332 | traces. SystemTap converts the scripts to the C language, and then | |
333 | compiles them as Linux kernel modules which are loaded to produce | |
334 | trace data. SystemTap's primary user interface is the cmd:stap | |
335 | command-line tool. | |
336 | ||
337 | The main distinctive features of LTTng is that it produces correlated | |
338 | kernel and user space traces, as well as doing so with the lowest | |
339 | overhead amongst other solutions. It produces trace files in the | |
340 | http://diamon.org/ctf[CTF] format, a file format optimized | |
341 | for the production and analyses of multi-gigabyte data. | |
342 | ||
343 | LTTng is the result of more than 10 years of active open source | |
344 | development by a community of passionate developers. | |
345 | LTTng{nbsp}{revision} is currently available on major desktop and server | |
346 | Linux distributions. | |
347 | ||
348 | The main interface for tracing control is a single command-line tool | |
349 | named cmd:lttng. The latter can create several tracing sessions, enable | |
350 | and disable events on the fly, filter events efficiently with custom | |
351 | user expressions, start and stop tracing, and much more. LTTng can | |
352 | record the traces on the file system or send them over the network, and | |
353 | keep them totally or partially. You can view the traces once tracing | |
354 | becomes inactive or in real-time. | |
355 | ||
356 | <<installing-lttng,Install LTTng now>> and | |
357 | <<getting-started,start tracing>>! | |
358 | ||
359 | ||
360 | [[installing-lttng]] | |
361 | == Installation | |
362 | ||
4234ccdd | 363 | include::../common/warning-no-installation.txt[] |
85c29972 | 364 | |
7adf7ee2 PP |
365 | **LTTng** is a set of software <<plumbing,components>> which interact to |
366 | <<instrumenting,instrument>> the Linux kernel and user applications, and | |
367 | to <<controlling-tracing,control tracing>> (start and stop | |
368 | tracing, enable and disable event rules, and the rest). Those | |
369 | components are bundled into the following packages: | |
370 | ||
371 | * **LTTng-tools**: Libraries and command-line interface to | |
372 | control tracing. | |
373 | * **LTTng-modules**: Linux kernel modules to instrument and | |
374 | trace the kernel. | |
375 | * **LTTng-UST**: Libraries and Java/Python packages to instrument and | |
376 | trace user applications. | |
377 | ||
378 | Most distributions mark the LTTng-modules and LTTng-UST packages as | |
4234ccdd PP |
379 | optional when installing LTTng-tools (which is always required). Note |
380 | that: | |
7adf7ee2 PP |
381 | |
382 | * You only need to install LTTng-modules if you intend to trace the | |
383 | Linux kernel. | |
384 | * You only need to install LTTng-UST if you intend to trace user | |
385 | applications. | |
386 | ||
7adf7ee2 | 387 | |
7adf7ee2 PP |
388 | [[building-from-source]] |
389 | === Build from source | |
390 | ||
391 | To build and install LTTng{nbsp}{revision} from source: | |
392 | ||
393 | . Using your distribution's package manager, or from source, install | |
394 | the following dependencies of LTTng-tools and LTTng-UST: | |
395 | + | |
396 | -- | |
397 | * https://sourceforge.net/projects/libuuid/[libuuid] | |
398 | * http://directory.fsf.org/wiki/Popt[popt] | |
399 | * http://liburcu.org/[Userspace RCU] | |
400 | * http://www.xmlsoft.org/[libxml2] | |
401 | -- | |
402 | ||
403 | . Download, build, and install the latest LTTng-modules{nbsp}{revision}: | |
404 | + | |
405 | -- | |
406 | [role="term"] | |
407 | ---- | |
ded02698 | 408 | $ cd $(mktemp -d) && |
7adf7ee2 PP |
409 | wget http://lttng.org/files/lttng-modules/lttng-modules-latest-2.8.tar.bz2 && |
410 | tar -xf lttng-modules-latest-2.8.tar.bz2 && | |
411 | cd lttng-modules-2.8.* && | |
412 | make && | |
413 | sudo make modules_install && | |
414 | sudo depmod -a | |
415 | ---- | |
416 | -- | |
417 | ||
418 | . Download, build, and install the latest LTTng-UST{nbsp}{revision}: | |
419 | + | |
420 | -- | |
421 | [role="term"] | |
422 | ---- | |
ded02698 | 423 | $ cd $(mktemp -d) && |
7adf7ee2 PP |
424 | wget http://lttng.org/files/lttng-ust/lttng-ust-latest-2.8.tar.bz2 && |
425 | tar -xf lttng-ust-latest-2.8.tar.bz2 && | |
426 | cd lttng-ust-2.8.* && | |
427 | ./configure && | |
428 | make && | |
429 | sudo make install && | |
430 | sudo ldconfig | |
431 | ---- | |
432 | -- | |
433 | + | |
434 | -- | |
435 | [IMPORTANT] | |
436 | .Java and Python application tracing | |
437 | ==== | |
438 | If you need to instrument and trace <<java-application,Java | |
439 | applications>>, pass the `--enable-java-agent-jul`, | |
440 | `--enable-java-agent-log4j`, or `--enable-java-agent-all` options to the | |
441 | `configure` script, depending on which Java logging framework you use. | |
442 | ||
443 | If you need to instrument and trace <<python-application,Python | |
444 | applications>>, pass the `--enable-python-agent` option to the | |
445 | `configure` script. You can set the `PYTHON` environment variable to the | |
446 | path to the Python interpreter for which to install the LTTng-UST Python | |
447 | agent package. | |
448 | ==== | |
449 | -- | |
450 | + | |
451 | -- | |
452 | [NOTE] | |
453 | ==== | |
454 | By default, LTTng-UST libraries are installed to | |
455 | dir:{/usr/local/lib}, which is the de facto directory in which to | |
456 | keep self-compiled and third-party libraries. | |
457 | ||
458 | When <<building-tracepoint-providers-and-user-application,linking an | |
459 | instrumented user application with `liblttng-ust`>>: | |
460 | ||
461 | * Append `/usr/local/lib` to the env:LD_LIBRARY_PATH environment | |
462 | variable. | |
463 | * Pass the `-L/usr/local/lib` and `-Wl,-rpath,/usr/local/lib` options to | |
464 | man:gcc(1), man:g++(1), or man:clang(1). | |
465 | ==== | |
466 | -- | |
467 | ||
468 | . Download, build, and install the latest LTTng-tools{nbsp}{revision}: | |
469 | + | |
470 | -- | |
471 | [role="term"] | |
472 | ---- | |
ded02698 | 473 | $ cd $(mktemp -d) && |
7adf7ee2 PP |
474 | wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.8.tar.bz2 && |
475 | tar -xf lttng-tools-latest-2.8.tar.bz2 && | |
476 | cd lttng-tools-2.8.* && | |
477 | ./configure && | |
478 | make && | |
479 | sudo make install && | |
480 | sudo ldconfig | |
481 | ---- | |
482 | -- | |
483 | ||
484 | TIP: The https://github.com/eepp/vlttng[vlttng tool] can do all the | |
485 | previous steps automatically for a given version of LTTng and confine | |
486 | the installed files in a specific directory. This can be useful to test | |
487 | LTTng without installing it on your system. | |
488 | ||
489 | ||
490 | [[getting-started]] | |
491 | == Quick start | |
492 | ||
493 | This is a short guide to get started quickly with LTTng kernel and user | |
494 | space tracing. | |
495 | ||
496 | Before you follow this guide, make sure to <<installing-lttng,install>> | |
497 | LTTng. | |
498 | ||
499 | This tutorial walks you through the steps to: | |
500 | ||
501 | . <<tracing-the-linux-kernel,Trace the Linux kernel>>. | |
502 | . <<tracing-your-own-user-application,Trace a user application>> written | |
503 | in C. | |
504 | . <<viewing-and-analyzing-your-traces,View and analyze the | |
505 | recorded events>>. | |
506 | ||
507 | ||
508 | [[tracing-the-linux-kernel]] | |
509 | === Trace the Linux kernel | |
510 | ||
ded02698 PP |
511 | The following command lines start with the `#` prompt because you need |
512 | root privileges to trace the Linux kernel. You can also trace the kernel | |
513 | as a regular user if your Unix user is a member of the | |
514 | <<tracing-group,tracing group>>. | |
7adf7ee2 | 515 | |
cdd6b153 PP |
516 | . Create a <<tracing-session,tracing session>> which writes its traces |
517 | to dir:{/tmp/my-kernel-trace}: | |
7adf7ee2 PP |
518 | + |
519 | -- | |
520 | [role="term"] | |
521 | ---- | |
ded02698 | 522 | # lttng create my-kernel-session --output=/tmp/my-kernel-trace |
7adf7ee2 PP |
523 | ---- |
524 | -- | |
525 | ||
526 | . List the available kernel tracepoints and system calls: | |
527 | + | |
528 | -- | |
529 | [role="term"] | |
530 | ---- | |
ded02698 PP |
531 | # lttng list --kernel |
532 | # lttng list --kernel --syscall | |
7adf7ee2 PP |
533 | ---- |
534 | -- | |
535 | ||
cdd6b153 PP |
536 | . Create <<event,event rules>> which match the desired instrumentation |
537 | point names, for example the `sched_switch` and `sched_process_fork` | |
538 | tracepoints, and the man:open(2) and man:close(2) system calls: | |
7adf7ee2 PP |
539 | + |
540 | -- | |
541 | [role="term"] | |
542 | ---- | |
ded02698 PP |
543 | # lttng enable-event --kernel sched_switch,sched_process_fork |
544 | # lttng enable-event --kernel --syscall open,close | |
7adf7ee2 PP |
545 | ---- |
546 | -- | |
547 | + | |
cdd6b153 | 548 | You can also create an event rule which matches _all_ the Linux kernel |
7adf7ee2 PP |
549 | tracepoints (this will generate a lot of data when tracing): |
550 | + | |
551 | -- | |
552 | [role="term"] | |
553 | ---- | |
ded02698 | 554 | # lttng enable-event --kernel --all |
7adf7ee2 PP |
555 | ---- |
556 | -- | |
557 | ||
cdd6b153 | 558 | . <<basic-tracing-session-control,Start tracing>>: |
7adf7ee2 PP |
559 | + |
560 | -- | |
561 | [role="term"] | |
562 | ---- | |
ded02698 | 563 | # lttng start |
7adf7ee2 PP |
564 | ---- |
565 | -- | |
566 | ||
567 | . Do some operation on your system for a few seconds. For example, | |
568 | load a website, or list the files of a directory. | |
cdd6b153 PP |
569 | . <<basic-tracing-session-control,Stop tracing>> and destroy the |
570 | tracing session: | |
7adf7ee2 PP |
571 | + |
572 | -- | |
573 | [role="term"] | |
574 | ---- | |
575 | sudo lttng stop | |
576 | sudo lttng destroy | |
577 | ---- | |
578 | -- | |
579 | + | |
580 | The man:lttng-destroy(1) command does not destroy the trace data; it | |
581 | only destroys the state of the tracing session. | |
582 | ||
cdd6b153 PP |
583 | . For the sake of this example, make the recorded trace accessible to |
584 | the non-root users: | |
585 | + | |
586 | -- | |
587 | [role="term"] | |
588 | ---- | |
589 | sudo chown -R $(whoami) /tmp/my-kernel-trace | |
590 | ---- | |
591 | -- | |
7adf7ee2 PP |
592 | |
593 | See <<viewing-and-analyzing-your-traces,View and analyze the | |
594 | recorded events>> to view the recorded events. | |
595 | ||
596 | ||
597 | [[tracing-your-own-user-application]] | |
598 | === Trace a user application | |
599 | ||
600 | This section steps you through a simple example to trace a | |
601 | _Hello world_ program written in C. | |
602 | ||
603 | To create the traceable user application: | |
604 | ||
605 | . Create the tracepoint provider header file, which defines the | |
606 | tracepoints and the events they can generate: | |
607 | + | |
608 | -- | |
609 | [source,c] | |
610 | .path:{hello-tp.h} | |
611 | ---- | |
612 | #undef TRACEPOINT_PROVIDER | |
613 | #define TRACEPOINT_PROVIDER hello_world | |
614 | ||
615 | #undef TRACEPOINT_INCLUDE | |
616 | #define TRACEPOINT_INCLUDE "./hello-tp.h" | |
617 | ||
618 | #if !defined(_HELLO_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ) | |
619 | #define _HELLO_TP_H | |
620 | ||
621 | #include <lttng/tracepoint.h> | |
622 | ||
623 | TRACEPOINT_EVENT( | |
624 | hello_world, | |
625 | my_first_tracepoint, | |
626 | TP_ARGS( | |
627 | int, my_integer_arg, | |
628 | char*, my_string_arg | |
629 | ), | |
630 | TP_FIELDS( | |
631 | ctf_string(my_string_field, my_string_arg) | |
632 | ctf_integer(int, my_integer_field, my_integer_arg) | |
633 | ) | |
634 | ) | |
635 | ||
636 | #endif /* _HELLO_TP_H */ | |
637 | ||
638 | #include <lttng/tracepoint-event.h> | |
639 | ---- | |
640 | -- | |
641 | ||
642 | . Create the tracepoint provider package source file: | |
643 | + | |
644 | -- | |
645 | [source,c] | |
646 | .path:{hello-tp.c} | |
647 | ---- | |
648 | #define TRACEPOINT_CREATE_PROBES | |
649 | #define TRACEPOINT_DEFINE | |
650 | ||
651 | #include "hello-tp.h" | |
652 | ---- | |
653 | -- | |
654 | ||
655 | . Build the tracepoint provider package: | |
656 | + | |
657 | -- | |
658 | [role="term"] | |
659 | ---- | |
ded02698 | 660 | $ gcc -c -I. hello-tp.c |
7adf7ee2 PP |
661 | ---- |
662 | -- | |
663 | ||
664 | . Create the _Hello World_ application source file: | |
665 | + | |
666 | -- | |
667 | [source,c] | |
668 | .path:{hello.c} | |
669 | ---- | |
670 | #include <stdio.h> | |
671 | #include "hello-tp.h" | |
672 | ||
673 | int main(int argc, char *argv[]) | |
674 | { | |
675 | int x; | |
676 | ||
677 | puts("Hello, World!\nPress Enter to continue..."); | |
678 | ||
679 | /* | |
680 | * The following getchar() call is only placed here for the purpose | |
681 | * of this demonstration, to pause the application in order for | |
682 | * you to have time to list its tracepoints. It is not | |
683 | * needed otherwise. | |
684 | */ | |
685 | getchar(); | |
686 | ||
687 | /* | |
688 | * A tracepoint() call. | |
689 | * | |
690 | * Arguments, as defined in hello-tp.h: | |
691 | * | |
692 | * 1. Tracepoint provider name (required) | |
693 | * 2. Tracepoint name (required) | |
694 | * 3. my_integer_arg (first user-defined argument) | |
695 | * 4. my_string_arg (second user-defined argument) | |
696 | * | |
697 | * Notice the tracepoint provider and tracepoint names are | |
698 | * NOT strings: they are in fact parts of variables that the | |
699 | * macros in hello-tp.h create. | |
700 | */ | |
701 | tracepoint(hello_world, my_first_tracepoint, 23, "hi there!"); | |
702 | ||
703 | for (x = 0; x < argc; ++x) { | |
704 | tracepoint(hello_world, my_first_tracepoint, x, argv[x]); | |
705 | } | |
706 | ||
707 | puts("Quitting now!"); | |
708 | tracepoint(hello_world, my_first_tracepoint, x * x, "x^2"); | |
709 | ||
710 | return 0; | |
711 | } | |
712 | ---- | |
713 | -- | |
714 | ||
715 | . Build the application: | |
716 | + | |
717 | -- | |
718 | [role="term"] | |
719 | ---- | |
ded02698 | 720 | $ gcc -c hello.c |
7adf7ee2 PP |
721 | ---- |
722 | -- | |
723 | ||
724 | . Link the application with the tracepoint provider package, | |
725 | `liblttng-ust`, and `libdl`: | |
726 | + | |
727 | -- | |
728 | [role="term"] | |
729 | ---- | |
ded02698 | 730 | $ gcc -o hello hello.o hello-tp.o -llttng-ust -ldl |
7adf7ee2 PP |
731 | ---- |
732 | -- | |
733 | ||
734 | Here's the whole build process: | |
735 | ||
736 | [role="img-100"] | |
737 | .User space tracing tutorial's build steps. | |
738 | image::ust-flow.png[] | |
739 | ||
740 | To trace the user application: | |
741 | ||
742 | . Run the application with a few arguments: | |
743 | + | |
744 | -- | |
745 | [role="term"] | |
746 | ---- | |
ded02698 | 747 | $ ./hello world and beyond |
7adf7ee2 PP |
748 | ---- |
749 | -- | |
750 | + | |
751 | You see: | |
752 | + | |
753 | -- | |
754 | ---- | |
755 | Hello, World! | |
756 | Press Enter to continue... | |
757 | ---- | |
758 | -- | |
759 | ||
760 | . Start an LTTng <<lttng-sessiond,session daemon>>: | |
761 | + | |
762 | -- | |
763 | [role="term"] | |
764 | ---- | |
ded02698 | 765 | $ lttng-sessiond --daemonize |
7adf7ee2 PP |
766 | ---- |
767 | -- | |
768 | + | |
769 | Note that a session daemon might already be running, for example as | |
770 | a service that the distribution's service manager started. | |
771 | ||
772 | . List the available user space tracepoints: | |
773 | + | |
774 | -- | |
775 | [role="term"] | |
776 | ---- | |
ded02698 | 777 | $ lttng list --userspace |
7adf7ee2 PP |
778 | ---- |
779 | -- | |
780 | + | |
781 | You see the `hello_world:my_first_tracepoint` tracepoint listed | |
782 | under the `./hello` process. | |
783 | ||
784 | . Create a <<tracing-session,tracing session>>: | |
785 | + | |
786 | -- | |
787 | [role="term"] | |
788 | ---- | |
ded02698 | 789 | $ lttng create my-user-space-session |
7adf7ee2 PP |
790 | ---- |
791 | -- | |
792 | ||
793 | . Create an <<event,event rule>> which matches the | |
794 | `hello_world:my_first_tracepoint` event name: | |
795 | + | |
796 | -- | |
797 | [role="term"] | |
798 | ---- | |
ded02698 | 799 | $ lttng enable-event --userspace hello_world:my_first_tracepoint |
7adf7ee2 PP |
800 | ---- |
801 | -- | |
802 | ||
cdd6b153 | 803 | . <<basic-tracing-session-control,Start tracing>>: |
7adf7ee2 PP |
804 | + |
805 | -- | |
806 | [role="term"] | |
807 | ---- | |
ded02698 | 808 | $ lttng start |
7adf7ee2 PP |
809 | ---- |
810 | -- | |
811 | ||
812 | . Go back to the running `hello` application and press Enter. The | |
813 | program executes all `tracepoint()` instrumentation points and exits. | |
cdd6b153 PP |
814 | . <<basic-tracing-session-control,Stop tracing>> and destroy the |
815 | tracing session: | |
7adf7ee2 PP |
816 | + |
817 | -- | |
818 | [role="term"] | |
819 | ---- | |
ded02698 PP |
820 | $ lttng stop |
821 | $ lttng destroy | |
7adf7ee2 PP |
822 | ---- |
823 | -- | |
824 | + | |
825 | The man:lttng-destroy(1) command does not destroy the trace data; it | |
826 | only destroys the state of the tracing session. | |
827 | ||
828 | By default, LTTng saves the traces in | |
829 | +$LTTNG_HOME/lttng-traces/__name__-__date__-__time__+, | |
cdd6b153 | 830 | where +__name__+ is the tracing session name. The |
7adf7ee2 PP |
831 | env:LTTNG_HOME environment variable defaults to `$HOME` if not set. |
832 | ||
833 | See <<viewing-and-analyzing-your-traces,View and analyze the | |
834 | recorded events>> to view the recorded events. | |
835 | ||
836 | ||
837 | [[viewing-and-analyzing-your-traces]] | |
838 | === View and analyze the recorded events | |
839 | ||
840 | Once you have completed the <<tracing-the-linux-kernel,Trace the Linux | |
841 | kernel>> and <<tracing-your-own-user-application,Trace a user | |
842 | application>> tutorials, you can inspect the recorded events. | |
843 | ||
844 | Many tools are available to read LTTng traces: | |
845 | ||
846 | * **cmd:babeltrace** is a command-line utility which converts trace | |
847 | formats; it supports the format that LTTng produces, CTF, as well as a | |
848 | basic text output which can be ++grep++ed. The cmd:babeltrace command | |
849 | is part of the http://diamon.org/babeltrace[Babeltrace] project. | |
850 | * Babeltrace also includes | |
851 | **https://www.python.org/[Python] bindings** so | |
852 | that you can easily open and read an LTTng trace with your own script, | |
853 | benefiting from the power of Python. | |
854 | * http://tracecompass.org/[**Trace Compass**] | |
855 | is a graphical user interface for viewing and analyzing any type of | |
856 | logs or traces, including LTTng's. | |
857 | * https://github.com/lttng/lttng-analyses[**LTTng analyses**] is a | |
858 | project which includes many high-level analyses of LTTng kernel | |
859 | traces, like scheduling statistics, interrupt frequency distribution, | |
860 | top CPU usage, and more. | |
861 | ||
862 | NOTE: This section assumes that the traces recorded during the previous | |
863 | tutorials were saved to their default location, in the | |
cdd6b153 | 864 | dir:{$LTTNG_HOME/lttng-traces} directory. The env:LTTNG_HOME |
7adf7ee2 PP |
865 | environment variable defaults to `$HOME` if not set. |
866 | ||
867 | ||
868 | [[viewing-and-analyzing-your-traces-bt]] | |
869 | ==== Use the cmd:babeltrace command-line tool | |
870 | ||
871 | The simplest way to list all the recorded events of a trace is to pass | |
872 | its path to cmd:babeltrace with no options: | |
873 | ||
874 | [role="term"] | |
875 | ---- | |
ded02698 | 876 | $ babeltrace ~/lttng-traces/my-user-space-session* |
7adf7ee2 PP |
877 | ---- |
878 | ||
879 | cmd:babeltrace finds all traces recursively within the given path and | |
880 | prints all their events, merging them in chronological order. | |
881 | ||
882 | You can pipe the output of cmd:babeltrace into a tool like man:grep(1) for | |
883 | further filtering: | |
884 | ||
885 | [role="term"] | |
886 | ---- | |
ded02698 | 887 | $ babeltrace /tmp/my-kernel-trace | grep _switch |
7adf7ee2 PP |
888 | ---- |
889 | ||
890 | You can pipe the output of cmd:babeltrace into a tool like man:wc(1) to | |
891 | count the recorded events: | |
892 | ||
893 | [role="term"] | |
894 | ---- | |
ded02698 | 895 | $ babeltrace /tmp/my-kernel-trace | grep _open | wc --lines |
7adf7ee2 PP |
896 | ---- |
897 | ||
898 | ||
899 | [[viewing-and-analyzing-your-traces-bt-python]] | |
900 | ==== Use the Babeltrace Python bindings | |
901 | ||
902 | The <<viewing-and-analyzing-your-traces-bt,text output of cmd:babeltrace>> | |
903 | is useful to isolate events by simple matching using man:grep(1) and | |
904 | similar utilities. However, more elaborate filters, such as keeping only | |
905 | event records with a field value falling within a specific range, are | |
906 | not trivial to write using a shell. Moreover, reductions and even the | |
907 | most basic computations involving multiple event records are virtually | |
908 | impossible to implement. | |
909 | ||
910 | Fortunately, Babeltrace ships with Python 3 bindings which makes it easy | |
911 | to read the event records of an LTTng trace sequentially and compute the | |
912 | desired information. | |
913 | ||
914 | The following script accepts an LTTng Linux kernel trace path as its | |
915 | first argument and prints the short names of the top 5 running processes | |
916 | on CPU 0 during the whole trace: | |
917 | ||
918 | [source,python] | |
919 | .path:{top5proc.py} | |
920 | ---- | |
921 | from collections import Counter | |
922 | import babeltrace | |
923 | import sys | |
924 | ||
925 | ||
926 | def top5proc(): | |
927 | if len(sys.argv) != 2: | |
928 | msg = 'Usage: python3 {} TRACEPATH'.format(sys.argv[0]) | |
929 | print(msg, file=sys.stderr) | |
930 | return False | |
931 | ||
932 | # A trace collection contains one or more traces | |
933 | col = babeltrace.TraceCollection() | |
934 | ||
935 | # Add the trace provided by the user (LTTng traces always have | |
936 | # the 'ctf' format) | |
937 | if col.add_trace(sys.argv[1], 'ctf') is None: | |
938 | raise RuntimeError('Cannot add trace') | |
939 | ||
940 | # This counter dict contains execution times: | |
941 | # | |
942 | # task command name -> total execution time (ns) | |
943 | exec_times = Counter() | |
944 | ||
945 | # This contains the last `sched_switch` timestamp | |
946 | last_ts = None | |
947 | ||
948 | # Iterate on events | |
949 | for event in col.events: | |
950 | # Keep only `sched_switch` events | |
951 | if event.name != 'sched_switch': | |
952 | continue | |
953 | ||
954 | # Keep only events which happened on CPU 0 | |
955 | if event['cpu_id'] != 0: | |
956 | continue | |
957 | ||
958 | # Event timestamp | |
959 | cur_ts = event.timestamp | |
960 | ||
961 | if last_ts is None: | |
962 | # We start here | |
963 | last_ts = cur_ts | |
964 | ||
965 | # Previous task command (short) name | |
966 | prev_comm = event['prev_comm'] | |
967 | ||
968 | # Initialize entry in our dict if not yet done | |
969 | if prev_comm not in exec_times: | |
970 | exec_times[prev_comm] = 0 | |
971 | ||
972 | # Compute previous command execution time | |
973 | diff = cur_ts - last_ts | |
974 | ||
975 | # Update execution time of this command | |
976 | exec_times[prev_comm] += diff | |
977 | ||
978 | # Update last timestamp | |
979 | last_ts = cur_ts | |
980 | ||
981 | # Display top 5 | |
982 | for name, ns in exec_times.most_common(5): | |
983 | s = ns / 1000000000 | |
984 | print('{:20}{} s'.format(name, s)) | |
985 | ||
986 | return True | |
987 | ||
988 | ||
989 | if __name__ == '__main__': | |
990 | sys.exit(0 if top5proc() else 1) | |
991 | ---- | |
992 | ||
993 | Run this script: | |
994 | ||
995 | [role="term"] | |
996 | ---- | |
ded02698 | 997 | $ python3 top5proc.py /tmp/my-kernel-trace/kernel |
7adf7ee2 PP |
998 | ---- |
999 | ||
1000 | Output example: | |
1001 | ||
1002 | ---- | |
1003 | swapper/0 48.607245889 s | |
1004 | chromium 7.192738188 s | |
1005 | pavucontrol 0.709894415 s | |
1006 | Compositor 0.660867933 s | |
1007 | Xorg.bin 0.616753786 s | |
1008 | ---- | |
1009 | ||
1010 | Note that `swapper/0` is the "idle" process of CPU 0 on Linux; since we | |
1011 | weren't using the CPU that much when tracing, its first position in the | |
1012 | list makes sense. | |
1013 | ||
1014 | ||
1015 | [[core-concepts]] | |
1016 | == [[understanding-lttng]]Core concepts | |
1017 | ||
1018 | From a user's perspective, the LTTng system is built on a few concepts, | |
1019 | or objects, on which the <<lttng-cli,cmd:lttng command-line tool>> | |
1020 | operates by sending commands to the <<lttng-sessiond,session daemon>>. | |
1021 | Understanding how those objects relate to eachother is key in mastering | |
1022 | the toolkit. | |
1023 | ||
1024 | The core concepts are: | |
1025 | ||
1026 | * <<tracing-session,Tracing session>> | |
1027 | * <<domain,Tracing domain>> | |
1028 | * <<channel,Channel and ring buffer>> | |
1029 | * <<"event","Instrumentation point, event rule, event, and event record">> | |
1030 | ||
1031 | ||
1032 | [[tracing-session]] | |
1033 | === Tracing session | |
1034 | ||
1035 | A _tracing session_ is a stateful dialogue between you and | |
1036 | a <<lttng-sessiond,session daemon>>. You can | |
1037 | <<creating-destroying-tracing-sessions,create a new tracing | |
1038 | session>> with the `lttng create` command. | |
1039 | ||
1040 | Anything that you do when you control LTTng tracers happens within a | |
1041 | tracing session. In particular, a tracing session: | |
1042 | ||
1043 | * Has its own name. | |
1044 | * Has its own set of trace files. | |
1045 | * Has its own state of activity (started or stopped). | |
1046 | * Has its own <<tracing-session-mode,mode>> (local, network streaming, | |
1047 | snapshot, or live). | |
1048 | * Has its own <<channel,channels>> which have their own | |
1049 | <<event,event rules>>. | |
1050 | ||
1051 | [role="img-100"] | |
1052 | .A _tracing session_ contains <<channel,channels>> that are members of <<domain,tracing domains>> and contain <<event,event rules>>. | |
1053 | image::concepts.png[] | |
1054 | ||
1055 | Those attributes and objects are completely isolated between different | |
1056 | tracing sessions. | |
1057 | ||
1058 | A tracing session is analogous to a cash machine session: | |
1059 | the operations you do on the banking system through the cash machine do | |
1060 | not alter the data of other users of the same system. In the case of | |
1061 | the cash machine, a session lasts as long as your bank card is inside. | |
1062 | In the case of LTTng, a tracing session lasts from the `lttng create` | |
1063 | command to the `lttng destroy` command. | |
1064 | ||
1065 | [role="img-100"] | |
1066 | .Each Unix user has its own set of tracing sessions. | |
1067 | image::many-sessions.png[] | |
1068 | ||
1069 | ||
1070 | [[tracing-session-mode]] | |
1071 | ==== Tracing session mode | |
1072 | ||
1073 | LTTng can send the generated trace data to different locations. The | |
1074 | _tracing session mode_ dictates where to send it. The following modes | |
1075 | are available in LTTng{nbsp}{revision}: | |
1076 | ||
1077 | Local mode:: | |
1078 | LTTng writes the traces to the file system of the machine being traced | |
1079 | (target system). | |
1080 | ||
1081 | Network streaming mode:: | |
1082 | LTTng sends the traces over the network to a | |
1083 | <<lttng-relayd,relay daemon>> running on a remote system. | |
1084 | ||
1085 | Snapshot mode:: | |
1086 | LTTng does not write the traces by default. Instead, you can request | |
1087 | LTTng to <<taking-a-snapshot,take a snapshot>>, that is, a copy of the | |
1088 | current tracing buffers, and to write it to the target's file system | |
1089 | or to send it over the network to a <<lttng-relayd,relay daemon>> | |
1090 | running on a remote system. | |
1091 | ||
1092 | Live mode:: | |
1093 | This mode is similar to the network streaming mode, but a live | |
1094 | trace viewer can connect to the distant relay daemon to | |
1095 | <<lttng-live,view event records as LTTng generates them>> by | |
1096 | the tracers. | |
1097 | ||
1098 | ||
1099 | [[domain]] | |
1100 | === Tracing domain | |
1101 | ||
1102 | A _tracing domain_ is a namespace for event sources. A tracing domain | |
1103 | has its own properties and features. | |
1104 | ||
1105 | There are currently five available tracing domains: | |
1106 | ||
1107 | * Linux kernel | |
1108 | * User space | |
1109 | * `java.util.logging` (JUL) | |
1110 | * log4j | |
1111 | * Python | |
1112 | ||
1113 | You must specify a tracing domain when using some commands to avoid | |
1114 | ambiguity. For example, since all the domains support named tracepoints | |
1115 | as event sources (instrumentation points that you manually insert in the | |
1116 | source code), you need to specify a tracing domain when | |
1117 | <<enabling-disabling-events,creating an event rule>> because all the | |
1118 | tracing domains could have tracepoints with the same names. | |
1119 | ||
1120 | Some features are reserved to specific tracing domains. Dynamic function | |
1121 | entry and return instrumentation points, for example, are currently only | |
1122 | supported in the Linux kernel tracing domain, but support for other | |
1123 | tracing domains could be added in the future. | |
1124 | ||
1125 | You can create <<channel,channels>> in the Linux kernel and user space | |
1126 | tracing domains. The other tracing domains have a single default | |
1127 | channel. | |
1128 | ||
1129 | ||
1130 | [[channel]] | |
1131 | === Channel and ring buffer | |
1132 | ||
1133 | A _channel_ is an object which is responsible for a set of ring buffers. | |
1134 | Each ring buffer is divided into multiple sub-buffers. When an LTTng | |
1135 | tracer emits an event, it can record it to one or more | |
1136 | sub-buffers. The attributes of a channel determine what to do when | |
1137 | there's no space left for a new event record because all sub-buffers | |
1138 | are full, where to send a full sub-buffer, and other behaviours. | |
1139 | ||
1140 | A channel is always associated to a <<domain,tracing domain>>. The | |
1141 | `java.util.logging` (JUL), log4j, and Python tracing domains each have | |
1142 | a default channel which you cannot configure. | |
1143 | ||
1144 | A channel also owns <<event,event rules>>. When an LTTng tracer emits | |
1145 | an event, it records it to the sub-buffers of all | |
1146 | the enabled channels with a satisfied event rule, as long as those | |
1147 | channels are part of active <<tracing-session,tracing sessions>>. | |
1148 | ||
1149 | ||
1150 | [[channel-buffering-schemes]] | |
1151 | ==== Per-user vs. per-process buffering schemes | |
1152 | ||
1153 | A channel has at least one ring buffer _per CPU_. LTTng always | |
1154 | records an event to the ring buffer associated to the CPU on which it | |
1155 | occurred. | |
1156 | ||
1157 | Two _buffering schemes_ are available when you | |
1158 | <<enabling-disabling-channels,create a channel>> in the | |
1159 | user space <<domain,tracing domain>>: | |
1160 | ||
1161 | Per-user buffering:: | |
1162 | Allocate one set of ring buffers--one per CPU--shared by all the | |
1163 | instrumented processes of each Unix user. | |
1164 | + | |
1165 | -- | |
1166 | [role="img-100"] | |
1167 | .Per-user buffering scheme. | |
1168 | image::per-user-buffering.png[] | |
1169 | -- | |
1170 | ||
1171 | Per-process buffering:: | |
1172 | Allocate one set of ring buffers--one per CPU--for each | |
1173 | instrumented process. | |
1174 | + | |
1175 | -- | |
1176 | [role="img-100"] | |
1177 | .Per-process buffering scheme. | |
1178 | image::per-process-buffering.png[] | |
1179 | -- | |
1180 | + | |
1181 | The per-process buffering scheme tends to consume more memory than the | |
1182 | per-user option because systems generally have more instrumented | |
1183 | processes than Unix users running instrumented processes. However, the | |
1184 | per-process buffering scheme ensures that one process having a high | |
1185 | event throughput won't fill all the shared sub-buffers of the same | |
1186 | user, only its own. | |
1187 | ||
1188 | The Linux kernel tracing domain has only one available buffering scheme | |
1189 | which is to allocate a single set of ring buffers for the whole system. | |
1190 | This scheme is similar to the per-user option, but with a single, global | |
1191 | user "running" the kernel. | |
1192 | ||
1193 | ||
1194 | [[channel-overwrite-mode-vs-discard-mode]] | |
1195 | ==== Overwrite vs. discard event loss modes | |
1196 | ||
1197 | When an event occurs, LTTng records it to a specific sub-buffer (yellow | |
1198 | arc in the following animation) of a specific channel's ring buffer. | |
1199 | When there's no space left in a sub-buffer, the tracer marks it as | |
1200 | consumable (red) and another, empty sub-buffer starts receiving the | |
1201 | following event records. A <<lttng-consumerd,consumer daemon>> | |
1202 | eventually consumes the marked sub-buffer (returns to white). | |
1203 | ||
1204 | [NOTE] | |
1205 | [role="docsvg-channel-subbuf-anim"] | |
1206 | ==== | |
1207 | {note-no-anim} | |
1208 | ==== | |
1209 | ||
1210 | In an ideal world, sub-buffers are consumed faster than they are filled, | |
1211 | as is the case in the previous animation. In the real world, | |
1212 | however, all sub-buffers can be full at some point, leaving no space to | |
1213 | record the following events. | |
1214 | ||
1215 | By design, LTTng is a _non-blocking_ tracer: when no empty sub-buffer is | |
1216 | available, it is acceptable to lose event records when the alternative | |
1217 | would be to cause substantial delays in the instrumented application's | |
1218 | execution. LTTng privileges performance over integrity; it aims at | |
1219 | perturbing the traced system as little as possible in order to make | |
1220 | tracing of subtle race conditions and rare interrupt cascades possible. | |
1221 | ||
1222 | When it comes to losing event records because no empty sub-buffer is | |
1223 | available, the channel's _event loss mode_ determines what to do. The | |
1224 | available event loss modes are: | |
1225 | ||
1226 | Discard mode:: | |
1227 | Drop the newest event records until a the tracer | |
1228 | releases a sub-buffer. | |
1229 | ||
1230 | Overwrite mode:: | |
1231 | Clear the sub-buffer containing the oldest event records and start | |
1232 | writing the newest event records there. | |
1233 | + | |
1234 | This mode is sometimes called _flight recorder mode_ because it's | |
1235 | similar to a | |
1236 | https://en.wikipedia.org/wiki/Flight_recorder[flight recorder]: | |
1237 | always keep a fixed amount of the latest data. | |
1238 | ||
1239 | Which mechanism you should choose depends on your context: prioritize | |
1240 | the newest or the oldest event records in the ring buffer? | |
1241 | ||
1242 | Beware that, in overwrite mode, the tracer abandons a whole sub-buffer | |
1243 | as soon as a there's no space left for a new event record, whereas in | |
1244 | discard mode, the tracer only discards the event record that doesn't | |
1245 | fit. | |
1246 | ||
4089946d PP |
1247 | In discard mode, LTTng increments a count of lost event records when an |
1248 | event record is lost and saves this count to the trace. In overwrite | |
1249 | mode, since LTTng 2.8, LTTng increments a count of lost sub-buffers when | |
1250 | a sub-buffer is lost and saves this count to the trace. In this mode, | |
1251 | the exact number of lost event records in those lost sub-buffers is not | |
1252 | saved to the trace. Trace analyses can use the trace's saved discarded | |
1253 | event record and sub-buffer counts to decide whether or not to perform | |
1254 | the analyses even if trace data is known to be missing. | |
7adf7ee2 PP |
1255 | |
1256 | There are a few ways to decrease your probability of losing event | |
1257 | records. | |
1258 | <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>> shows | |
1259 | how you can fine-une the sub-buffer count and size of a channel to | |
1260 | virtually stop losing event records, though at the cost of greater | |
1261 | memory usage. | |
1262 | ||
1263 | ||
1264 | [[channel-subbuf-size-vs-subbuf-count]] | |
1265 | ==== Sub-buffer count and size | |
1266 | ||
1267 | When you <<enabling-disabling-channels,create a channel>>, you can | |
1268 | set its number of sub-buffers and their size. | |
1269 | ||
1270 | Note that there is noticeable CPU overhead introduced when | |
1271 | switching sub-buffers (marking a full one as consumable and switching | |
1272 | to an empty one for the following events to be recorded). Knowing this, | |
1273 | the following list presents a few practical situations along with how | |
1274 | to configure the sub-buffer count and size for them: | |
1275 | ||
1276 | * **High event throughput**: In general, prefer bigger sub-buffers to | |
1277 | lower the risk of losing event records. | |
1278 | + | |
4ef3b81e PP |
1279 | Having bigger sub-buffers also ensures a lower |
1280 | <<channel-switch-timer,sub-buffer switching frequency>>. | |
7adf7ee2 PP |
1281 | + |
1282 | The number of sub-buffers is only meaningful if you create the channel | |
1283 | in overwrite mode: in this case, if a sub-buffer overwrite happens, the | |
1284 | other sub-buffers are left unaltered. | |
1285 | ||
1286 | * **Low event throughput**: In general, prefer smaller sub-buffers | |
1287 | since the risk of losing event records is low. | |
1288 | + | |
1289 | Because events occur less frequently, the sub-buffer switching frequency | |
1290 | should remain low and thus the tracer's overhead should not be a | |
1291 | problem. | |
1292 | ||
1293 | * **Low memory system**: If your target system has a low memory | |
1294 | limit, prefer fewer first, then smaller sub-buffers. | |
1295 | + | |
1296 | Even if the system is limited in memory, you want to keep the | |
1297 | sub-buffers as big as possible to avoid a high sub-buffer switching | |
1298 | frequency. | |
1299 | ||
1300 | Note that LTTng uses http://diamon.org/ctf/[CTF] as its trace format, | |
1301 | which means event data is very compact. For example, the average | |
1302 | LTTng kernel event record weights about 32{nbsp}bytes. Thus, a | |
1303 | sub-buffer size of 1{nbsp}MiB is considered big. | |
1304 | ||
1305 | The previous situations highlight the major trade-off between a few big | |
1306 | sub-buffers and more, smaller sub-buffers: sub-buffer switching | |
1307 | frequency vs. how much data is lost in overwrite mode. Assuming a | |
1308 | constant event throughput and using the overwrite mode, the two | |
1309 | following configurations have the same ring buffer total size: | |
1310 | ||
1311 | [NOTE] | |
1312 | [role="docsvg-channel-subbuf-size-vs-count-anim"] | |
1313 | ==== | |
1314 | {note-no-anim} | |
1315 | ==== | |
1316 | ||
1317 | * **2 sub-buffers of 4{nbsp}MiB each**: Expect a very low sub-buffer | |
1318 | switching frequency, but if a sub-buffer overwrite happens, half of | |
1319 | the event records so far (4{nbsp}MiB) are definitely lost. | |
1320 | * **8 sub-buffers of 1{nbsp}MiB each**: Expect 4{nbsp}times the tracer's | |
1321 | overhead as the previous configuration, but if a sub-buffer | |
1322 | overwrite happens, only the eighth of event records so far are | |
1323 | definitely lost. | |
1324 | ||
1325 | In discard mode, the sub-buffers count parameter is pointless: use two | |
1326 | sub-buffers and set their size according to the requirements of your | |
1327 | situation. | |
1328 | ||
1329 | ||
1330 | [[channel-switch-timer]] | |
1331 | ==== Switch timer period | |
1332 | ||
1333 | The _switch timer period_ is an important configurable attribute of | |
1334 | a channel to ensure periodic sub-buffer flushing. | |
1335 | ||
1336 | When the _switch timer_ expires, a sub-buffer switch happens. You can | |
1337 | set the switch timer period attribute when you | |
1338 | <<enabling-disabling-channels,create a channel>> to ensure that event | |
1339 | data is consumed and committed to trace files or to a distant relay | |
1340 | daemon periodically in case of a low event throughput. | |
1341 | ||
1342 | [NOTE] | |
1343 | [role="docsvg-channel-switch-timer"] | |
1344 | ==== | |
1345 | {note-no-anim} | |
1346 | ==== | |
1347 | ||
1348 | This attribute is also convenient when you use big sub-buffers to cope | |
1349 | with a sporadic high event throughput, even if the throughput is | |
1350 | normally low. | |
1351 | ||
1352 | ||
1353 | [[channel-read-timer]] | |
1354 | ==== Read timer period | |
1355 | ||
1356 | By default, the LTTng tracers use a notification mechanism to signal a | |
1357 | full sub-buffer so that a consumer daemon can consume it. When such | |
1358 | notifications must be avoided, for example in real-time applications, | |
1359 | you can use the channel's _read timer_ instead. When the read timer | |
1360 | fires, the <<lttng-consumerd,consumer daemon>> checks for full, | |
1361 | consumable sub-buffers. | |
1362 | ||
1363 | ||
1364 | [[tracefile-rotation]] | |
1365 | ==== Trace file count and size | |
1366 | ||
1367 | By default, trace files can grow as large as needed. You can set the | |
1368 | maximum size of each trace file that a channel writes when you | |
1369 | <<enabling-disabling-channels,create a channel>>. When the size of | |
1370 | a trace file reaches the channel's fixed maximum size, LTTng creates | |
1371 | another file to contain the next event records. LTTng appends a file | |
1372 | count to each trace file name in this case. | |
1373 | ||
1374 | If you set the trace file size attribute when you create a channel, the | |
1375 | maximum number of trace files that LTTng creates is _unlimited_ by | |
1376 | default. To limit them, you can also set a maximum number of trace | |
1377 | files. When the number of trace files reaches the channel's fixed | |
1378 | maximum count, the oldest trace file is overwritten. This mechanism is | |
1379 | called _trace file rotation_. | |
1380 | ||
1381 | ||
1382 | [[event]] | |
1383 | === Instrumentation point, event rule, event, and event record | |
1384 | ||
1385 | An _event rule_ is a set of conditions which must be **all** satisfied | |
1386 | for LTTng to record an occuring event. | |
1387 | ||
1388 | You set the conditions when you <<enabling-disabling-events,create | |
1389 | an event rule>>. | |
1390 | ||
1391 | You always attach an event rule to <<channel,channel>> when you create | |
1392 | it. | |
1393 | ||
1394 | When an event passes the conditions of an event rule, LTTng records it | |
1395 | in one of the attached channel's sub-buffers. | |
1396 | ||
1397 | The available conditions, as of LTTng{nbsp}{revision}, are: | |
1398 | ||
1399 | * The event rule _is enabled_. | |
1400 | * The instrumentation point's type _is{nbsp}T_. | |
1401 | * The instrumentation point's name (sometimes called _event name_) | |
1402 | _matches{nbsp}N_, but _is not{nbsp}E_. | |
1403 | * The instrumentation point's log level _is as severe as{nbsp}L_, or | |
1404 | _is exactly{nbsp}L_. | |
1405 | * The fields of the event's payload _satisfy_ a filter | |
1406 | expression{nbsp}__F__. | |
1407 | ||
1408 | As you can see, all the conditions but the dynamic filter are related to | |
1409 | the event rule's status or to the instrumentation point, not to the | |
1410 | occurring events. This is why, without a filter, checking if an event | |
1411 | passes an event rule is not a dynamic task: when you create or modify an | |
1412 | event rule, all the tracers of its tracing domain enable or disable the | |
1413 | instrumentation points themselves once. This is possible because the | |
1414 | attributes of an instrumentation point (type, name, and log level) are | |
1415 | defined statically. In other words, without a dynamic filter, the tracer | |
1416 | _does not evaluate_ the arguments of an instrumentation point unless it | |
1417 | matches an enabled event rule. | |
1418 | ||
1419 | Note that, for LTTng to record an event, the <<channel,channel>> to | |
1420 | which a matching event rule is attached must also be enabled, and the | |
1421 | tracing session owning this channel must be active. | |
1422 | ||
1423 | [role="img-100"] | |
1424 | .Logical path from an instrumentation point to an event record. | |
1425 | image::event-rule.png[] | |
1426 | ||
1427 | .Event, event record, or event rule? | |
1428 | **** | |
1429 | With so many similar terms, it's easy to get confused. | |
1430 | ||
1431 | An **event** is the consequence of the execution of an _instrumentation | |
1432 | point_, like a tracepoint that you manually place in some source code, | |
1433 | or a Linux kernel KProbe. An event is said to _occur_ at a specific | |
310431f4 | 1434 | time. Different actions can be taken upon the occurrence of an event, |
7adf7ee2 PP |
1435 | like record the event's payload to a buffer. |
1436 | ||
1437 | An **event record** is the representation of an event in a sub-buffer. A | |
1438 | tracer is responsible for capturing the payload of an event, current | |
1439 | context variables, the event's ID, and the event's timestamp. LTTng | |
1440 | can append this sub-buffer to a trace file. | |
1441 | ||
1442 | An **event rule** is a set of conditions which must all be satisfied for | |
1443 | LTTng to record an occuring event. Events still occur without | |
1444 | satisfying event rules, but LTTng does not record them. | |
1445 | **** | |
1446 | ||
1447 | ||
1448 | [[plumbing]] | |
1449 | == Components of noch:{LTTng} | |
1450 | ||
1451 | The second _T_ in _LTTng_ stands for _toolkit_: it would be wrong | |
1452 | to call LTTng a simple _tool_ since it is composed of multiple | |
1453 | interacting components. This section describes those components, | |
1454 | explains their respective roles, and shows how they connect together to | |
1455 | form the LTTng ecosystem. | |
1456 | ||
1457 | The following diagram shows how the most important components of LTTng | |
1458 | interact with user applications, the Linux kernel, and you: | |
1459 | ||
1460 | [role="img-100"] | |
1461 | .Control and trace data paths between LTTng components. | |
1462 | image::plumbing.png[] | |
1463 | ||
1464 | The LTTng project incorporates: | |
1465 | ||
1466 | * **LTTng-tools**: Libraries and command-line interface to | |
1467 | control tracing sessions. | |
1468 | ** <<lttng-sessiond,Session daemon>> (man:lttng-sessiond(8)). | |
a9f3997c | 1469 | ** <<lttng-consumerd,Consumer daemon>> (cmd:lttng-consumerd). |
7adf7ee2 PP |
1470 | ** <<lttng-relayd,Relay daemon>> (man:lttng-relayd(8)). |
1471 | ** <<liblttng-ctl-lttng,Tracing control library>> (`liblttng-ctl`). | |
1472 | ** <<lttng-cli,Tracing control command-line tool>> (man:lttng(1)). | |
1473 | * **LTTng-UST**: Libraries and Java/Python packages to trace user | |
1474 | applications. | |
1475 | ** <<lttng-ust,User space tracing library>> (`liblttng-ust`) and its | |
1476 | headers to instrument and trace any native user application. | |
1477 | ** <<prebuilt-ust-helpers,Preloadable user space tracing helpers>>: | |
1478 | *** `liblttng-ust-libc-wrapper` | |
1479 | *** `liblttng-ust-pthread-wrapper` | |
1480 | *** `liblttng-ust-cyg-profile` | |
1481 | *** `liblttng-ust-cyg-profile-fast` | |
1482 | *** `liblttng-ust-dl` | |
1483 | ** User space tracepoint provider source files generator command-line | |
1484 | tool (man:lttng-gen-tp(1)). | |
1485 | ** <<lttng-ust-agents,LTTng-UST Java agent>> to instrument and trace | |
1486 | Java applications using `java.util.logging` or | |
1487 | Apache log4j 1.2 logging. | |
1488 | ** <<lttng-ust-agents,LTTng-UST Python agent>> to instrument | |
1489 | Python applications using the standard `logging` package. | |
1490 | * **LTTng-modules**: <<lttng-modules,Linux kernel modules>> to trace | |
1491 | the kernel. | |
1492 | ** LTTng kernel tracer module. | |
1493 | ** Tracing ring buffer kernel modules. | |
1494 | ** Probe kernel modules. | |
1495 | ** LTTng logger kernel module. | |
1496 | ||
1497 | ||
1498 | [[lttng-cli]] | |
1499 | === Tracing control command-line interface | |
1500 | ||
1501 | [role="img-100"] | |
1502 | .The tracing control command-line interface. | |
1503 | image::plumbing-lttng-cli.png[] | |
1504 | ||
1505 | The _man:lttng(1) command-line tool_ is the standard user interface to | |
1506 | control LTTng <<tracing-session,tracing sessions>>. The cmd:lttng tool | |
1507 | is part of LTTng-tools. | |
1508 | ||
1509 | The cmd:lttng tool is linked with | |
1510 | <<liblttng-ctl-lttng,`liblttng-ctl`>> to communicate with | |
1511 | one or more <<lttng-sessiond,session daemons>> behind the scenes. | |
1512 | ||
1513 | The cmd:lttng tool has a Git-like interface: | |
1514 | ||
1515 | [role="term"] | |
1516 | ---- | |
ded02698 | 1517 | $ lttng <GENERAL OPTIONS> <COMMAND> <COMMAND OPTIONS> |
7adf7ee2 PP |
1518 | ---- |
1519 | ||
1520 | The <<controlling-tracing,Tracing control>> section explores the | |
1521 | available features of LTTng using the cmd:lttng tool. | |
1522 | ||
1523 | ||
1524 | [[liblttng-ctl-lttng]] | |
1525 | === Tracing control library | |
1526 | ||
1527 | [role="img-100"] | |
1528 | .The tracing control library. | |
1529 | image::plumbing-liblttng-ctl.png[] | |
1530 | ||
1531 | The _LTTng control library_, `liblttng-ctl`, is used to communicate | |
1532 | with a <<lttng-sessiond,session daemon>> using a C API that hides the | |
1533 | underlying protocol's details. `liblttng-ctl` is part of LTTng-tools. | |
1534 | ||
1535 | The <<lttng-cli,cmd:lttng command-line tool>> | |
1536 | is linked with `liblttng-ctl`. | |
1537 | ||
1538 | You can use `liblttng-ctl` in C or $$C++$$ source code by including its | |
1539 | "master" header: | |
1540 | ||
1541 | [source,c] | |
1542 | ---- | |
1543 | #include <lttng/lttng.h> | |
1544 | ---- | |
1545 | ||
1546 | Some objects are referenced by name (C string), such as tracing | |
1547 | sessions, but most of them require to create a handle first using | |
1548 | `lttng_create_handle()`. | |
1549 | ||
1550 | The best available developer documentation for `liblttng-ctl` is, as of | |
1551 | LTTng{nbsp}{revision}, its installed header files. Every function and | |
1552 | structure is thoroughly documented. | |
1553 | ||
1554 | ||
1555 | [[lttng-ust]] | |
1556 | === User space tracing library | |
1557 | ||
1558 | [role="img-100"] | |
1559 | .The user space tracing library. | |
1560 | image::plumbing-liblttng-ust.png[] | |
1561 | ||
1562 | The _user space tracing library_, `liblttng-ust` (see man:lttng-ust(3)), | |
1563 | is the LTTng user space tracer. It receives commands from a | |
1564 | <<lttng-sessiond,session daemon>>, for example to | |
1565 | enable and disable specific instrumentation points, and writes event | |
1566 | records to ring buffers shared with a | |
1567 | <<lttng-consumerd,consumer daemon>>. | |
1568 | `liblttng-ust` is part of LTTng-UST. | |
1569 | ||
1570 | Public C header files are installed beside `liblttng-ust` to | |
1571 | instrument any <<c-application,C or $$C++$$ application>>. | |
1572 | ||
1573 | <<lttng-ust-agents,LTTng-UST agents>>, which are regular Java and Python | |
1574 | packages, use their own library providing tracepoints which is | |
1575 | linked with `liblttng-ust`. | |
1576 | ||
1577 | An application or library does not have to initialize `liblttng-ust` | |
1578 | manually: its constructor does the necessary tasks to properly register | |
1579 | to a session daemon. The initialization phase also enables the | |
1580 | instrumentation points matching the <<event,event rules>> that you | |
1581 | already created. | |
1582 | ||
1583 | ||
1584 | [[lttng-ust-agents]] | |
1585 | === User space tracing agents | |
1586 | ||
1587 | [role="img-100"] | |
1588 | .The user space tracing agents. | |
1589 | image::plumbing-lttng-ust-agents.png[] | |
1590 | ||
1591 | The _LTTng-UST Java and Python agents_ are regular Java and Python | |
1592 | packages which add LTTng tracing capabilities to the | |
1593 | native logging frameworks. The LTTng-UST agents are part of LTTng-UST. | |
1594 | ||
1595 | In the case of Java, the | |
1596 | https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[`java.util.logging` | |
1597 | core logging facilities] and | |
1598 | https://logging.apache.org/log4j/1.2/[Apache log4j 1.2] are supported. | |
1599 | Note that Apache Log4{nbsp}2 is not supported. | |
1600 | ||
1601 | In the case of Python, the standard | |
1602 | https://docs.python.org/3/library/logging.html[`logging`] package | |
1603 | is supported. Both Python 2 and Python 3 modules can import the | |
1604 | LTTng-UST Python agent package. | |
1605 | ||
1606 | The applications using the LTTng-UST agents are in the | |
1607 | `java.util.logging` (JUL), | |
1608 | log4j, and Python <<domain,tracing domains>>. | |
1609 | ||
1610 | Both agents use the same mechanism to trace the log statements. When an | |
1611 | agent is initialized, it creates a log handler that attaches to the root | |
1612 | logger. The agent also registers to a <<lttng-sessiond,session daemon>>. | |
1613 | When the application executes a log statement, it is passed to the | |
1614 | agent's log handler by the root logger. The agent's log handler calls a | |
1615 | native function in a tracepoint provider package shared library linked | |
1616 | with <<lttng-ust,`liblttng-ust`>>, passing the formatted log message and | |
1617 | other fields, like its logger name and its log level. This native | |
1618 | function contains a user space instrumentation point, hence tracing the | |
1619 | log statement. | |
1620 | ||
1621 | The log level condition of an | |
1622 | <<event,event rule>> is considered when tracing | |
1623 | a Java or a Python application, and it's compatible with the standard | |
1624 | JUL, log4j, and Python log levels. | |
1625 | ||
1626 | ||
1627 | [[lttng-modules]] | |
1628 | === LTTng kernel modules | |
1629 | ||
1630 | [role="img-100"] | |
1631 | .The LTTng kernel modules. | |
1632 | image::plumbing-lttng-modules.png[] | |
1633 | ||
1634 | The _LTTng kernel modules_ are a set of Linux kernel modules | |
1635 | which implement the kernel tracer of the LTTng project. The LTTng | |
1636 | kernel modules are part of LTTng-modules. | |
1637 | ||
1638 | The LTTng kernel modules include: | |
1639 | ||
1640 | * A set of _probe_ modules. | |
1641 | + | |
1642 | Each module attaches to a specific subsystem | |
1643 | of the Linux kernel using its tracepoint instrument points. There are | |
1644 | also modules to attach to the entry and return points of the Linux | |
1645 | system call functions. | |
1646 | ||
1647 | * _Ring buffer_ modules. | |
1648 | + | |
1649 | A ring buffer implementation is provided as kernel modules. The LTTng | |
1650 | kernel tracer writes to the ring buffer; a | |
1651 | <<lttng-consumerd,consumer daemon>> reads from the ring buffer. | |
1652 | ||
1653 | * The _LTTng kernel tracer_ module. | |
1654 | * The _LTTng logger_ module. | |
1655 | + | |
1656 | The LTTng logger module implements the special path:{/proc/lttng-logger} | |
1657 | file so that any executable can generate LTTng events by opening and | |
1658 | writing to this file. | |
1659 | + | |
1660 | See <<proc-lttng-logger-abi,LTTng logger>>. | |
1661 | ||
1662 | Generally, you do not have to load the LTTng kernel modules manually | |
1663 | (using man:modprobe(8), for example): a root <<lttng-sessiond,session | |
1664 | daemon>> loads the necessary modules when starting. If you have extra | |
1665 | probe modules, you can specify to load them to the session daemon on | |
1666 | the command line. | |
1667 | ||
1668 | The LTTng kernel modules are installed in | |
1669 | +/usr/lib/modules/__release__/extra+ by default, where +__release__+ is | |
1670 | the kernel release (see `uname --kernel-release`). | |
1671 | ||
1672 | ||
1673 | [[lttng-sessiond]] | |
1674 | === Session daemon | |
1675 | ||
1676 | [role="img-100"] | |
1677 | .The session daemon. | |
1678 | image::plumbing-sessiond.png[] | |
1679 | ||
1680 | The _session daemon_, man:lttng-sessiond(8), is a daemon responsible for | |
1681 | managing tracing sessions and for controlling the various components of | |
1682 | LTTng. The session daemon is part of LTTng-tools. | |
1683 | ||
1684 | The session daemon sends control requests to and receives control | |
1685 | responses from: | |
1686 | ||
1687 | * The <<lttng-ust,user space tracing library>>. | |
1688 | + | |
1689 | Any instance of the user space tracing library first registers to | |
1690 | a session daemon. Then, the session daemon can send requests to | |
1691 | this instance, such as: | |
1692 | + | |
1693 | -- | |
1694 | ** Get the list of tracepoints. | |
1695 | ** Share an <<event,event rule>> so that the user space tracing library | |
1696 | can enable or disable tracepoints. Amongst the possible conditions | |
1697 | of an event rule is a filter expression which `liblttng-ust` evalutes | |
1698 | when an event occurs. | |
1699 | ** Share <<channel,channel>> attributes and ring buffer locations. | |
1700 | -- | |
1701 | + | |
1702 | The session daemon and the user space tracing library use a Unix | |
1703 | domain socket for their communication. | |
1704 | ||
1705 | * The <<lttng-ust-agents,user space tracing agents>>. | |
1706 | + | |
1707 | Any instance of a user space tracing agent first registers to | |
1708 | a session daemon. Then, the session daemon can send requests to | |
1709 | this instance, such as: | |
1710 | + | |
1711 | -- | |
1712 | ** Get the list of loggers. | |
1713 | ** Enable or disable a specific logger. | |
1714 | -- | |
1715 | + | |
1716 | The session daemon and the user space tracing agent use a TCP connection | |
1717 | for their communication. | |
1718 | ||
1719 | * The <<lttng-modules,LTTng kernel tracer>>. | |
1720 | * The <<lttng-consumerd,consumer daemon>>. | |
1721 | + | |
1722 | The session daemon sends requests to the consumer daemon to instruct | |
1723 | it where to send the trace data streams, amongst other information. | |
1724 | ||
1725 | * The <<lttng-relayd,relay daemon>>. | |
1726 | ||
1727 | The session daemon receives commands from the | |
1728 | <<liblttng-ctl-lttng,tracing control library>>. | |
1729 | ||
1730 | The root session daemon loads the appropriate | |
1731 | <<lttng-modules,LTTng kernel modules>> on startup. It also spawns | |
1732 | a <<lttng-consumerd,consumer daemon>> as soon as you create | |
1733 | an <<event,event rule>>. | |
1734 | ||
1735 | The session daemon does not send and receive trace data: this is the | |
1736 | role of the <<lttng-consumerd,consumer daemon>> and | |
1737 | <<lttng-relayd,relay daemon>>. It does, however, generate the | |
1738 | http://diamon.org/ctf/[CTF] metadata stream. | |
1739 | ||
1740 | Each Unix user can have its own session daemon instance. The | |
1741 | tracing sessions managed by different session daemons are completely | |
1742 | independent. | |
1743 | ||
1744 | The root user's session daemon is the only one which is | |
1745 | allowed to control the LTTng kernel tracer, and its spawned consumer | |
1746 | daemon is the only one which is allowed to consume trace data from the | |
1747 | LTTng kernel tracer. Note, however, that any Unix user which is a member | |
1748 | of the <<tracing-group,tracing group>> is allowed | |
1749 | to create <<channel,channels>> in the | |
1750 | Linux kernel <<domain,tracing domain>>, and thus to trace the Linux | |
1751 | kernel. | |
1752 | ||
1753 | The <<lttng-cli,cmd:lttng command-line tool>> automatically starts a | |
1754 | session daemon when using its `create` command if none is currently | |
1755 | running. You can also start the session daemon manually. | |
1756 | ||
1757 | ||
1758 | [[lttng-consumerd]] | |
1759 | === Consumer daemon | |
1760 | ||
1761 | [role="img-100"] | |
1762 | .The consumer daemon. | |
1763 | image::plumbing-consumerd.png[] | |
1764 | ||
a9f3997c | 1765 | The _consumer daemon_, cmd:lttng-consumerd, is a daemon which shares |
7adf7ee2 PP |
1766 | ring buffers with user applications or with the LTTng kernel modules to |
1767 | collect trace data and send it to some location (on disk or to a | |
1768 | <<lttng-relayd,relay daemon>> over the network). The consumer daemon | |
1769 | is part of LTTng-tools. | |
1770 | ||
1771 | You do not start a consumer daemon manually: a consumer daemon is always | |
1772 | spawned by a <<lttng-sessiond,session daemon>> as soon as you create an | |
1773 | <<event,event rule>>, that is, before you start tracing. When you kill | |
1774 | its owner session daemon, the consumer daemon also exits because it is | |
1775 | the session daemon's child process. Command-line options of | |
1776 | man:lttng-sessiond(8) target the consumer daemon process. | |
1777 | ||
1778 | There are up to two running consumer daemons per Unix user, whereas only | |
1779 | one session daemon can run per user. This is because each process can be | |
1780 | either 32-bit or 64-bit: if the target system runs a mixture of 32-bit | |
1781 | and 64-bit processes, it is more efficient to have separate | |
1782 | corresponding 32-bit and 64-bit consumer daemons. The root user is an | |
1783 | exception: it can have up to _three_ running consumer daemons: 32-bit | |
1784 | and 64-bit instances for its user applications, and one more | |
1785 | reserved for collecting kernel trace data. | |
1786 | ||
1787 | ||
1788 | [[lttng-relayd]] | |
1789 | === Relay daemon | |
1790 | ||
1791 | [role="img-100"] | |
1792 | .The relay daemon. | |
1793 | image::plumbing-relayd.png[] | |
1794 | ||
1795 | The _relay daemon_, man:lttng-relayd(8), is a daemon acting as a bridge | |
1796 | between remote session and consumer daemons, local trace files, and a | |
1797 | remote live trace viewer. The relay daemon is part of LTTng-tools. | |
1798 | ||
1799 | The main purpose of the relay daemon is to implement a receiver of | |
1800 | <<sending-trace-data-over-the-network,trace data over the network>>. | |
1801 | This is useful when the target system does not have much file system | |
1802 | space to record trace files locally. | |
1803 | ||
1804 | The relay daemon is also a server to which a | |
1805 | <<lttng-live,live trace viewer>> can | |
1806 | connect. The live trace viewer sends requests to the relay daemon to | |
1807 | receive trace data as the target system emits events. The | |
1808 | communication protocol is named _LTTng live_; it is used over TCP | |
1809 | connections. | |
1810 | ||
1811 | Note that you can start the relay daemon on the target system directly. | |
1812 | This is the setup of choice when the use case is to view events as | |
1813 | the target system emits them without the need of a remote system. | |
1814 | ||
1815 | ||
1816 | [[instrumenting]] | |
1817 | == [[using-lttng]]Instrumentation | |
1818 | ||
1819 | There are many examples of tracing and monitoring in our everyday life: | |
1820 | ||
1821 | * You have access to real-time and historical weather reports and | |
1822 | forecasts thanks to weather stations installed around the country. | |
1823 | * You know your heart is safe thanks to an electrocardiogram. | |
1824 | * You make sure not to drive your car too fast and to have enough fuel | |
1825 | to reach your destination thanks to gauges visible on your dashboard. | |
1826 | ||
1827 | All the previous examples have something in common: they rely on | |
1828 | **instruments**. Without the electrodes attached to the surface of your | |
1829 | body's skin, cardiac monitoring is futile. | |
1830 | ||
1831 | LTTng, as a tracer, is no different from those real life examples. If | |
1832 | you're about to trace a software system or, in other words, record its | |
1833 | history of execution, you better have **instrumentation points** in the | |
1834 | subject you're tracing, that is, the actual software. | |
1835 | ||
1836 | Various ways were developed to instrument a piece of software for LTTng | |
1837 | tracing. The most straightforward one is to manually place | |
1838 | instrumentation points, called _tracepoints_, in the software's source | |
1839 | code. It is also possible to add instrumentation points dynamically in | |
1840 | the Linux kernel <<domain,tracing domain>>. | |
1841 | ||
1842 | If you're only interested in tracing the Linux kernel, your | |
1843 | instrumentation needs are probably already covered by LTTng's built-in | |
1844 | <<lttng-modules,Linux kernel tracepoints>>. You may also wish to trace a | |
1845 | user application which is already instrumented for LTTng tracing. | |
1846 | In such cases, you can skip this whole section and read the topics of | |
1847 | the <<controlling-tracing,Tracing control>> section. | |
1848 | ||
1849 | Many methods are available to instrument a piece of software for LTTng | |
1850 | tracing. They are: | |
1851 | ||
1852 | * <<c-application,User space instrumentation for C and $$C++$$ | |
1853 | applications>>. | |
1854 | * <<prebuilt-ust-helpers,Prebuilt user space tracing helpers>>. | |
1855 | * <<java-application,User space Java agent>>. | |
1856 | * <<python-application,User space Python agent>>. | |
1857 | * <<proc-lttng-logger-abi,LTTng logger>>. | |
1858 | * <<instrumenting-linux-kernel,LTTng kernel tracepoints>>. | |
1859 | ||
1860 | ||
1861 | [[c-application]] | |
1862 | === [[cxx-application]]User space instrumentation for C and $$C++$$ applications | |
1863 | ||
1864 | The procedure to instrument a C or $$C++$$ user application with | |
1865 | the <<lttng-ust,LTTng user space tracing library>>, `liblttng-ust`, is: | |
1866 | ||
1867 | . <<tracepoint-provider,Create the source files of a tracepoint provider | |
1868 | package>>. | |
1869 | . <<probing-the-application-source-code,Add tracepoints to | |
1870 | the application's source code>>. | |
1871 | . <<building-tracepoint-providers-and-user-application,Build and link | |
1872 | a tracepoint provider package and the user application>>. | |
1873 | ||
1874 | If you need quick, man:printf(3)-like instrumentation, you can skip | |
1875 | those steps and use <<tracef,`tracef()`>> or <<tracelog,`tracelog()`>> | |
1876 | instead. | |
1877 | ||
1878 | IMPORTANT: You need to <<installing-lttng,install>> LTTng-UST to | |
1879 | instrument a user application with `liblttng-ust`. | |
1880 | ||
1881 | ||
1882 | [[tracepoint-provider]] | |
1883 | ==== Create the source files of a tracepoint provider package | |
1884 | ||
1885 | A _tracepoint provider_ is a set of compiled functions which provide | |
1886 | **tracepoints** to an application, the type of instrumentation point | |
1887 | supported by LTTng-UST. Those functions can emit events with | |
1888 | user-defined fields and serialize those events as event records to one | |
1889 | or more LTTng-UST <<channel,channel>> sub-buffers. The `tracepoint()` | |
1890 | macro, which you <<probing-the-application-source-code,insert in a user | |
1891 | application's source code>>, calls those functions. | |
1892 | ||
1893 | A _tracepoint provider package_ is an object file (`.o`) or a shared | |
1894 | library (`.so`) which contains one or more tracepoint providers. | |
1895 | Its source files are: | |
1896 | ||
1897 | * One or more <<tpp-header,tracepoint provider header>> (`.h`). | |
1898 | * A <<tpp-source,tracepoint provider package source>> (`.c`). | |
1899 | ||
1900 | A tracepoint provider package is dynamically linked with `liblttng-ust`, | |
1901 | the LTTng user space tracer, at run time. | |
1902 | ||
1903 | [role="img-100"] | |
1904 | .User application linked with `liblttng-ust` and containing a tracepoint provider. | |
1905 | image::ust-app.png[] | |
1906 | ||
1907 | NOTE: If you need quick, man:printf(3)-like instrumentation, you can | |
1908 | skip creating and using a tracepoint provider and use | |
1909 | <<tracef,`tracef()`>> or <<tracelog,`tracelog()`>> instead. | |
1910 | ||
1911 | ||
1912 | [[tpp-header]] | |
1913 | ===== Create a tracepoint provider header file template | |
1914 | ||
1915 | A _tracepoint provider header file_ contains the tracepoint | |
1916 | definitions of a tracepoint provider. | |
1917 | ||
1918 | To create a tracepoint provider header file: | |
1919 | ||
1920 | . Start from this template: | |
1921 | + | |
1922 | -- | |
1923 | [source,c] | |
1924 | .Tracepoint provider header file template (`.h` file extension). | |
1925 | ---- | |
1926 | #undef TRACEPOINT_PROVIDER | |
1927 | #define TRACEPOINT_PROVIDER provider_name | |
1928 | ||
1929 | #undef TRACEPOINT_INCLUDE | |
1930 | #define TRACEPOINT_INCLUDE "./tp.h" | |
1931 | ||
1932 | #if !defined(_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ) | |
1933 | #define _TP_H | |
1934 | ||
1935 | #include <lttng/tracepoint.h> | |
1936 | ||
1937 | /* | |
1938 | * Use TRACEPOINT_EVENT(), TRACEPOINT_EVENT_CLASS(), | |
1939 | * TRACEPOINT_EVENT_INSTANCE(), and TRACEPOINT_LOGLEVEL() here. | |
1940 | */ | |
1941 | ||
1942 | #endif /* _TP_H */ | |
1943 | ||
1944 | #include <lttng/tracepoint-event.h> | |
1945 | ---- | |
1946 | -- | |
1947 | ||
1948 | . Replace: | |
1949 | + | |
1950 | * `provider_name` with the name of your tracepoint provider. | |
1951 | * `"tp.h"` with the name of your tracepoint provider header file. | |
1952 | ||
1953 | . Below the `#include <lttng/tracepoint.h>` line, put your | |
1954 | <<defining-tracepoints,tracepoint definitions>>. | |
1955 | ||
1956 | Your tracepoint provider name must be unique amongst all the possible | |
1957 | tracepoint provider names used on the same target system. We | |
1958 | suggest to include the name of your project or company in the name, | |
1959 | for example, `org_lttng_my_project_tpp`. | |
1960 | ||
1961 | TIP: [[lttng-gen-tp]]You can use the man:lttng-gen-tp(1) tool to create | |
1962 | this boilerplate for you. When using cmd:lttng-gen-tp, all you need to | |
1963 | write are the <<defining-tracepoints,tracepoint definitions>>. | |
1964 | ||
1965 | ||
1966 | [[defining-tracepoints]] | |
1967 | ===== Create a tracepoint definition | |
1968 | ||
1969 | A _tracepoint definition_ defines, for a given tracepoint: | |
1970 | ||
1971 | * Its **input arguments**. They are the macro parameters that the | |
1972 | `tracepoint()` macro accepts for this particular tracepoint | |
1973 | in the user application's source code. | |
1974 | * Its **output event fields**. They are the sources of event fields | |
1975 | that form the payload of any event that the execution of the | |
1976 | `tracepoint()` macro emits for this particular tracepoint. | |
1977 | ||
1978 | You can create a tracepoint definition by using the | |
1979 | `TRACEPOINT_EVENT()` macro below the `#include <lttng/tracepoint.h>` | |
1980 | line in the | |
1981 | <<tpp-header,tracepoint provider header file template>>. | |
1982 | ||
1983 | The syntax of the `TRACEPOINT_EVENT()` macro is: | |
1984 | ||
1985 | [source,c] | |
1986 | .`TRACEPOINT_EVENT()` macro syntax. | |
1987 | ---- | |
1988 | TRACEPOINT_EVENT( | |
1989 | /* Tracepoint provider name */ | |
1990 | provider_name, | |
1991 | ||
1992 | /* Tracepoint name */ | |
1993 | tracepoint_name, | |
1994 | ||
1995 | /* Input arguments */ | |
1996 | TP_ARGS( | |
1997 | arguments | |
1998 | ), | |
1999 | ||
2000 | /* Output event fields */ | |
2001 | TP_FIELDS( | |
2002 | fields | |
2003 | ) | |
2004 | ) | |
2005 | ---- | |
2006 | ||
2007 | Replace: | |
2008 | ||
2009 | * `provider_name` with your tracepoint provider name. | |
2010 | * `tracepoint_name` with your tracepoint name. | |
2011 | * `arguments` with the <<tpp-def-input-args,input arguments>>. | |
2012 | * `fields` with the <<tpp-def-output-fields,output event field>> | |
2013 | definitions. | |
2014 | ||
2015 | This tracepoint emits events named `provider_name:tracepoint_name`. | |
2016 | ||
2017 | [IMPORTANT] | |
2018 | .Event name's length limitation | |
2019 | ==== | |
2020 | The concatenation of the tracepoint provider name and the | |
2021 | tracepoint name must not exceed **254 characters**. If it does, the | |
2022 | instrumented application compiles and runs, but LTTng throws multiple | |
2023 | warnings and you could experience serious issues. | |
2024 | ==== | |
2025 | ||
2026 | [[tpp-def-input-args]]The syntax of the `TP_ARGS()` macro is: | |
2027 | ||
2028 | [source,c] | |
2029 | .`TP_ARGS()` macro syntax. | |
2030 | ---- | |
2031 | TP_ARGS( | |
2032 | type, arg_name | |
2033 | ) | |
2034 | ---- | |
2035 | ||
2036 | Replace: | |
2037 | ||
2038 | * `type` with the C type of the argument. | |
2039 | * `arg_name` with the argument name. | |
2040 | ||
2041 | You can repeat `type` and `arg_name` up to 10 times to have | |
2042 | more than one argument. | |
2043 | ||
2044 | .`TP_ARGS()` usage with three arguments. | |
2045 | ==== | |
2046 | [source,c] | |
2047 | ---- | |
2048 | TP_ARGS( | |
2049 | int, count, | |
2050 | float, ratio, | |
2051 | const char*, query | |
2052 | ) | |
2053 | ---- | |
2054 | ==== | |
2055 | ||
2056 | The `TP_ARGS()` and `TP_ARGS(void)` forms are valid to create a | |
2057 | tracepoint definition with no input arguments. | |
2058 | ||
2059 | [[tpp-def-output-fields]]The `TP_FIELDS()` macro contains a list of | |
2060 | `ctf_*()` macros. Each `ctf_*()` macro defines one event field. See | |
2061 | man:lttng-ust(3) for a complete description of the available `ctf_*()` | |
2062 | macros. A `ctf_*()` macro specifies the type, size, and byte order of | |
2063 | one event field. | |
2064 | ||
2065 | Each `ctf_*()` macro takes an _argument expression_ parameter. This is a | |
2066 | C expression that the tracer evalutes at the `tracepoint()` macro site | |
2067 | in the application's source code. This expression provides a field's | |
2068 | source of data. The argument expression can include input argument names | |
2069 | listed in the `TP_ARGS()` macro. | |
2070 | ||
2071 | Each `ctf_*()` macro also takes a _field name_ parameter. Field names | |
2072 | must be unique within a given tracepoint definition. | |
2073 | ||
2074 | Here's a complete tracepoint definition example: | |
2075 | ||
2076 | .Tracepoint definition. | |
2077 | ==== | |
2078 | The following tracepoint definition defines a tracepoint which takes | |
2079 | three input arguments and has four output event fields. | |
2080 | ||
2081 | [source,c] | |
2082 | ---- | |
2083 | #include "my-custom-structure.h" | |
2084 | ||
2085 | TRACEPOINT_EVENT( | |
2086 | my_provider, | |
2087 | my_tracepoint, | |
2088 | TP_ARGS( | |
2089 | const struct my_custom_structure*, my_custom_structure, | |
2090 | float, ratio, | |
2091 | const char*, query | |
2092 | ), | |
2093 | TP_FIELDS( | |
2094 | ctf_string(query_field, query) | |
2095 | ctf_float(double, ratio_field, ratio) | |
2096 | ctf_integer(int, recv_size, my_custom_structure->recv_size) | |
2097 | ctf_integer(int, send_size, my_custom_structure->send_size) | |
2098 | ) | |
2099 | ) | |
2100 | ---- | |
2101 | ||
2102 | You can refer to this tracepoint definition with the `tracepoint()` | |
2103 | macro in your application's source code like this: | |
2104 | ||
2105 | [source,c] | |
2106 | ---- | |
2107 | tracepoint(my_provider, my_tracepoint, | |
2108 | my_structure, some_ratio, the_query); | |
2109 | ---- | |
2110 | ==== | |
2111 | ||
2112 | NOTE: The LTTng tracer only evaluates tracepoint arguments at run time | |
2113 | if they satisfy an enabled <<event,event rule>>. | |
2114 | ||
2115 | ||
2116 | [[using-tracepoint-classes]] | |
2117 | ===== Use a tracepoint class | |
2118 | ||
2119 | A _tracepoint class_ is a class of tracepoints which share the same | |
2120 | output event field definitions. A _tracepoint instance_ is one | |
2121 | instance of such a defined tracepoint class, with its own tracepoint | |
2122 | name. | |
2123 | ||
2124 | The <<defining-tracepoints,`TRACEPOINT_EVENT()` macro>> is actually a | |
2125 | shorthand which defines both a tracepoint class and a tracepoint | |
2126 | instance at the same time. | |
2127 | ||
2128 | When you build a tracepoint provider package, the C or $$C++$$ compiler | |
2129 | creates one serialization function for each **tracepoint class**. A | |
2130 | serialization function is responsible for serializing the event fields | |
2131 | of a tracepoint to a sub-buffer when tracing. | |
2132 | ||
2133 | For various performance reasons, when your situation requires multiple | |
2134 | tracepoint definitions with different names, but with the same event | |
2135 | fields, we recommend that you manually create a tracepoint class | |
2136 | and instantiate as many tracepoint instances as needed. One positive | |
2137 | effect of such a design, amongst other advantages, is that all | |
2138 | tracepoint instances of the same tracepoint class reuse the same | |
2139 | serialization function, thus reducing | |
2140 | https://en.wikipedia.org/wiki/Cache_pollution[cache pollution]. | |
2141 | ||
2142 | .Use a tracepoint class and tracepoint instances. | |
2143 | ==== | |
2144 | Consider the following three tracepoint definitions: | |
2145 | ||
2146 | [source,c] | |
2147 | ---- | |
2148 | TRACEPOINT_EVENT( | |
2149 | my_app, | |
2150 | get_account, | |
2151 | TP_ARGS( | |
2152 | int, userid, | |
2153 | size_t, len | |
2154 | ), | |
2155 | TP_FIELDS( | |
2156 | ctf_integer(int, userid, userid) | |
2157 | ctf_integer(size_t, len, len) | |
2158 | ) | |
2159 | ) | |
2160 | ||
2161 | TRACEPOINT_EVENT( | |
2162 | my_app, | |
2163 | get_settings, | |
2164 | TP_ARGS( | |
2165 | int, userid, | |
2166 | size_t, len | |
2167 | ), | |
2168 | TP_FIELDS( | |
2169 | ctf_integer(int, userid, userid) | |
2170 | ctf_integer(size_t, len, len) | |
2171 | ) | |
2172 | ) | |
2173 | ||
2174 | TRACEPOINT_EVENT( | |
2175 | my_app, | |
2176 | get_transaction, | |
2177 | TP_ARGS( | |
2178 | int, userid, | |
2179 | size_t, len | |
2180 | ), | |
2181 | TP_FIELDS( | |
2182 | ctf_integer(int, userid, userid) | |
2183 | ctf_integer(size_t, len, len) | |
2184 | ) | |
2185 | ) | |
2186 | ---- | |
2187 | ||
2188 | In this case, we create three tracepoint classes, with one implicit | |
2189 | tracepoint instance for each of them: `get_account`, `get_settings`, and | |
2190 | `get_transaction`. However, they all share the same event field names | |
2191 | and types. Hence three identical, yet independent serialization | |
2192 | functions are created when you build the tracepoint provider package. | |
2193 | ||
2194 | A better design choice is to define a single tracepoint class and three | |
2195 | tracepoint instances: | |
2196 | ||
2197 | [source,c] | |
2198 | ---- | |
2199 | /* The tracepoint class */ | |
2200 | TRACEPOINT_EVENT_CLASS( | |
2201 | /* Tracepoint provider name */ | |
2202 | my_app, | |
2203 | ||
2204 | /* Tracepoint class name */ | |
2205 | my_class, | |
2206 | ||
2207 | /* Input arguments */ | |
2208 | TP_ARGS( | |
2209 | int, userid, | |
2210 | size_t, len | |
2211 | ), | |
2212 | ||
2213 | /* Output event fields */ | |
2214 | TP_FIELDS( | |
2215 | ctf_integer(int, userid, userid) | |
2216 | ctf_integer(size_t, len, len) | |
2217 | ) | |
2218 | ) | |
2219 | ||
2220 | /* The tracepoint instances */ | |
2221 | TRACEPOINT_EVENT_INSTANCE( | |
2222 | /* Tracepoint provider name */ | |
2223 | my_app, | |
2224 | ||
2225 | /* Tracepoint class name */ | |
2226 | my_class, | |
2227 | ||
2228 | /* Tracepoint name */ | |
2229 | get_account, | |
2230 | ||
2231 | /* Input arguments */ | |
2232 | TP_ARGS( | |
2233 | int, userid, | |
2234 | size_t, len | |
2235 | ) | |
2236 | ) | |
2237 | TRACEPOINT_EVENT_INSTANCE( | |
2238 | my_app, | |
2239 | my_class, | |
2240 | get_settings, | |
2241 | TP_ARGS( | |
2242 | int, userid, | |
2243 | size_t, len | |
2244 | ) | |
2245 | ) | |
2246 | TRACEPOINT_EVENT_INSTANCE( | |
2247 | my_app, | |
2248 | my_class, | |
2249 | get_transaction, | |
2250 | TP_ARGS( | |
2251 | int, userid, | |
2252 | size_t, len | |
2253 | ) | |
2254 | ) | |
2255 | ---- | |
2256 | ==== | |
2257 | ||
2258 | ||
2259 | [[assigning-log-levels]] | |
2260 | ===== Assign a log level to a tracepoint definition | |
2261 | ||
2262 | You can assign an optional _log level_ to a | |
2263 | <<defining-tracepoints,tracepoint definition>>. | |
2264 | ||
2265 | Assigning different levels of severity to tracepoint definitions can | |
2266 | be useful: when you <<enabling-disabling-events,create an event rule>>, | |
2267 | you can target tracepoints having a log level as severe as a specific | |
2268 | value. | |
2269 | ||
2270 | The concept of LTTng-UST log levels is similar to the levels found | |
2271 | in typical logging frameworks: | |
2272 | ||
2273 | * In a logging framework, the log level is given by the function | |
2274 | or method name you use at the log statement site: `debug()`, | |
2275 | `info()`, `warn()`, `error()`, and so on. | |
2276 | * In LTTng-UST, you statically assign the log level to a tracepoint | |
2277 | definition; any `tracepoint()` macro invocation which refers to | |
2278 | this definition has this log level. | |
2279 | ||
2280 | You can assign a log level to a tracepoint definition with the | |
2281 | `TRACEPOINT_LOGLEVEL()` macro. You must use this macro _after_ the | |
2282 | <<defining-tracepoints,`TRACEPOINT_EVENT()`>> or | |
2283 | <<using-tracepoint-classes,`TRACEPOINT_INSTANCE()`>> macro for a given | |
2284 | tracepoint. | |
2285 | ||
2286 | The syntax of the `TRACEPOINT_LOGLEVEL()` macro is: | |
2287 | ||
2288 | [source,c] | |
2289 | .`TRACEPOINT_LOGLEVEL()` macro syntax. | |
2290 | ---- | |
2291 | TRACEPOINT_LOGLEVEL(provider_name, tracepoint_name, log_level) | |
2292 | ---- | |
2293 | ||
2294 | Replace: | |
2295 | ||
2296 | * `provider_name` with the tracepoint provider name. | |
2297 | * `tracepoint_name` with the tracepoint name. | |
2298 | * `log_level` with the log level to assign to the tracepoint | |
2299 | definition named `tracepoint_name` in the `provider_name` | |
2300 | tracepoint provider. | |
2301 | + | |
2302 | See man:lttng-ust(3) for a list of available log level names. | |
2303 | ||
2304 | .Assign the `TRACE_DEBUG_UNIT` log level to a tracepoint definition. | |
2305 | ==== | |
2306 | [source,c] | |
2307 | ---- | |
2308 | /* Tracepoint definition */ | |
2309 | TRACEPOINT_EVENT( | |
2310 | my_app, | |
2311 | get_transaction, | |
2312 | TP_ARGS( | |
2313 | int, userid, | |
2314 | size_t, len | |
2315 | ), | |
2316 | TP_FIELDS( | |
2317 | ctf_integer(int, userid, userid) | |
2318 | ctf_integer(size_t, len, len) | |
2319 | ) | |
2320 | ) | |
2321 | ||
2322 | /* Log level assignment */ | |
2323 | TRACEPOINT_LOGLEVEL(my_app, get_transaction, TRACE_DEBUG_UNIT) | |
2324 | ---- | |
2325 | ==== | |
2326 | ||
2327 | ||
2328 | [[tpp-source]] | |
2329 | ===== Create a tracepoint provider package source file | |
2330 | ||
2331 | A _tracepoint provider package source file_ is a C source file which | |
2332 | includes a <<tpp-header,tracepoint provider header file>> to expand its | |
2333 | macros into event serialization and other functions. | |
2334 | ||
2335 | You can always use the following tracepoint provider package source | |
2336 | file template: | |
2337 | ||
2338 | [source,c] | |
2339 | .Tracepoint provider package source file template. | |
2340 | ---- | |
2341 | #define TRACEPOINT_CREATE_PROBES | |
2342 | ||
2343 | #include "tp.h" | |
2344 | ---- | |
2345 | ||
2346 | Replace `tp.h` with the name of your <<tpp-header,tracepoint provider | |
2347 | header file>> name. You may also include more than one tracepoint | |
2348 | provider header file here to create a tracepoint provider package | |
2349 | holding more than one tracepoint providers. | |
2350 | ||
2351 | ||
2352 | [[probing-the-application-source-code]] | |
2353 | ==== Add tracepoints to an application's source code | |
2354 | ||
2355 | Once you <<tpp-header,create a tracepoint provider header file>>, you | |
2356 | can use the `tracepoint()` macro in your application's | |
2357 | source code to insert the tracepoints that this header | |
30240715 | 2358 | <<defining-tracepoints,defines>>. |
7adf7ee2 PP |
2359 | |
2360 | The `tracepoint()` macro takes at least two parameters: the tracepoint | |
2361 | provider name and the tracepoint name. The corresponding tracepoint | |
2362 | definition defines the other parameters. | |
2363 | ||
2364 | .`tracepoint()` usage. | |
2365 | ==== | |
2366 | The following <<defining-tracepoints,tracepoint definition>> defines a | |
2367 | tracepoint which takes two input arguments and has two output event | |
2368 | fields. | |
2369 | ||
2370 | [source,c] | |
2371 | .Tracepoint provider header file. | |
2372 | ---- | |
2373 | #include "my-custom-structure.h" | |
2374 | ||
2375 | TRACEPOINT_EVENT( | |
2376 | my_provider, | |
2377 | my_tracepoint, | |
2378 | TP_ARGS( | |
2379 | int, argc, | |
2380 | const char*, cmd_name | |
2381 | ), | |
2382 | TP_FIELDS( | |
2383 | ctf_string(cmd_name, cmd_name) | |
2384 | ctf_integer(int, number_of_args, argc) | |
2385 | ) | |
2386 | ) | |
2387 | ---- | |
2388 | ||
2389 | You can refer to this tracepoint definition with the `tracepoint()` | |
2390 | macro in your application's source code like this: | |
2391 | ||
2392 | [source,c] | |
2393 | .Application's source file. | |
2394 | ---- | |
2395 | #include "tp.h" | |
2396 | ||
2397 | int main(int argc, char* argv[]) | |
2398 | { | |
2399 | tracepoint(my_provider, my_tracepoint, argc, argv[0]); | |
2400 | ||
2401 | return 0; | |
2402 | } | |
2403 | ---- | |
2404 | ||
2405 | Note how the application's source code includes | |
2406 | the tracepoint provider header file containing the tracepoint | |
2407 | definitions to use, path:{tp.h}. | |
2408 | ==== | |
2409 | ||
2410 | .`tracepoint()` usage with a complex tracepoint definition. | |
2411 | ==== | |
2412 | Consider this complex tracepoint definition, where multiple event | |
2413 | fields refer to the same input arguments in their argument expression | |
2414 | parameter: | |
2415 | ||
2416 | [source,c] | |
2417 | .Tracepoint provider header file. | |
2418 | ---- | |
2419 | /* For `struct stat` */ | |
2420 | #include <sys/types.h> | |
2421 | #include <sys/stat.h> | |
2422 | #include <unistd.h> | |
2423 | ||
2424 | TRACEPOINT_EVENT( | |
2425 | my_provider, | |
2426 | my_tracepoint, | |
2427 | TP_ARGS( | |
2428 | int, my_int_arg, | |
2429 | char*, my_str_arg, | |
2430 | struct stat*, st | |
2431 | ), | |
2432 | TP_FIELDS( | |
2433 | ctf_integer(int, my_constant_field, 23 + 17) | |
2434 | ctf_integer(int, my_int_arg_field, my_int_arg) | |
2435 | ctf_integer(int, my_int_arg_field2, my_int_arg * my_int_arg) | |
2436 | ctf_integer(int, sum4_field, my_str_arg[0] + my_str_arg[1] + | |
2437 | my_str_arg[2] + my_str_arg[3]) | |
2438 | ctf_string(my_str_arg_field, my_str_arg) | |
2439 | ctf_integer_hex(off_t, size_field, st->st_size) | |
2440 | ctf_float(double, size_dbl_field, (double) st->st_size) | |
2441 | ctf_sequence_text(char, half_my_str_arg_field, my_str_arg, | |
2442 | size_t, strlen(my_str_arg) / 2) | |
2443 | ) | |
2444 | ) | |
2445 | ---- | |
2446 | ||
2447 | You can refer to this tracepoint definition with the `tracepoint()` | |
2448 | macro in your application's source code like this: | |
2449 | ||
2450 | [source,c] | |
2451 | .Application's source file. | |
2452 | ---- | |
2453 | #define TRACEPOINT_DEFINE | |
2454 | #include "tp.h" | |
2455 | ||
2456 | int main(void) | |
2457 | { | |
2458 | struct stat s; | |
2459 | ||
2460 | stat("/etc/fstab", &s); | |
2461 | tracepoint(my_provider, my_tracepoint, 23, "Hello, World!", &s); | |
2462 | ||
2463 | return 0; | |
2464 | } | |
2465 | ---- | |
2466 | ||
2467 | If you look at the event record that LTTng writes when tracing this | |
2468 | program, assuming the file size of path:{/etc/fstab} is 301{nbsp}bytes, | |
2469 | it should look like this: | |
2470 | ||
2471 | .Event record fields | |
2472 | |==== | |
2473 | |Field's name |Field's value | |
2474 | |`my_constant_field` |40 | |
2475 | |`my_int_arg_field` |23 | |
2476 | |`my_int_arg_field2` |529 | |
2477 | |`sum4_field` |389 | |
2478 | |`my_str_arg_field` |`Hello, World!` | |
2479 | |`size_field` |0x12d | |
2480 | |`size_dbl_field` |301.0 | |
2481 | |`half_my_str_arg_field` |`Hello,` | |
2482 | |==== | |
2483 | ==== | |
2484 | ||
2485 | Sometimes, the arguments you pass to `tracepoint()` are expensive to | |
2486 | compute--they use the call stack, for example. To avoid this | |
2487 | computation when the tracepoint is disabled, you can use the | |
2488 | `tracepoint_enabled()` and `do_tracepoint()` macros. | |
2489 | ||
2490 | The syntax of the `tracepoint_enabled()` and `do_tracepoint()` macros | |
2491 | is: | |
2492 | ||
2493 | [source,c] | |
2494 | .`tracepoint_enabled()` and `do_tracepoint()` macros syntax. | |
2495 | ---- | |
2496 | tracepoint_enabled(provider_name, tracepoint_name) | |
2497 | do_tracepoint(provider_name, tracepoint_name, ...) | |
2498 | ---- | |
2499 | ||
2500 | Replace: | |
2501 | ||
2502 | * `provider_name` with the tracepoint provider name. | |
2503 | * `tracepoint_name` with the tracepoint name. | |
2504 | ||
2505 | `tracepoint_enabled()` returns a non-zero value if the tracepoint named | |
2506 | `tracepoint_name` from the provider named `provider_name` is enabled | |
2507 | **at run time**. | |
2508 | ||
2509 | `do_tracepoint()` is like `tracepoint()`, except that it doesn't check | |
2510 | if the tracepoint is enabled. Using `tracepoint()` with | |
2511 | `tracepoint_enabled()` is dangerous since `tracepoint()` also contains | |
2512 | the `tracepoint_enabled()` check, thus a race condition is | |
2513 | possible in this situation: | |
2514 | ||
2515 | [source,c] | |
2516 | .Possible race condition when using `tracepoint_enabled()` with `tracepoint()`. | |
2517 | ---- | |
2518 | if (tracepoint_enabled(my_provider, my_tracepoint)) { | |
2519 | stuff = prepare_stuff(); | |
2520 | } | |
2521 | ||
2522 | tracepoint(my_provider, my_tracepoint, stuff); | |
2523 | ---- | |
2524 | ||
2525 | If the tracepoint is enabled after the condition, then `stuff` is not | |
2526 | prepared: the emitted event will either contain wrong data, or the whole | |
2527 | application could crash (segmentation fault, for example). | |
2528 | ||
2529 | NOTE: Neither `tracepoint_enabled()` nor `do_tracepoint()` have an | |
2530 | `STAP_PROBEV()` call. If you need it, you must emit | |
2531 | this call yourself. | |
2532 | ||
2533 | ||
2534 | [[building-tracepoint-providers-and-user-application]] | |
2535 | ==== Build and link a tracepoint provider package and an application | |
2536 | ||
2537 | Once you have one or more <<tpp-header,tracepoint provider header | |
2538 | files>> and a <<tpp-source,tracepoint provider package source file>>, | |
2539 | you can create the tracepoint provider package by compiling its source | |
2540 | file. From here, multiple build and run scenarios are possible. The | |
2541 | following table shows common application and library configurations | |
2542 | along with the required command lines to achieve them. | |
2543 | ||
2544 | In the following diagrams, we use the following file names: | |
2545 | ||
2546 | `app`:: | |
2547 | Executable application. | |
2548 | ||
2549 | `app.o`:: | |
2550 | Application's object file. | |
2551 | ||
2552 | `tpp.o`:: | |
2553 | Tracepoint provider package object file. | |
2554 | ||
2555 | `tpp.a`:: | |
2556 | Tracepoint provider package archive file. | |
2557 | ||
2558 | `libtpp.so`:: | |
2559 | Tracepoint provider package shared object file. | |
2560 | ||
2561 | `emon.o`:: | |
2562 | User library object file. | |
2563 | ||
2564 | `libemon.so`:: | |
2565 | User library shared object file. | |
2566 | ||
30240715 PP |
2567 | We use the following symbols in the diagrams of table below: |
2568 | ||
2569 | [role="img-100"] | |
2570 | .Symbols used in the build scenario diagrams. | |
2571 | image::ust-sit-symbols.png[] | |
7adf7ee2 PP |
2572 | |
2573 | We assume that path:{.} is part of the env:LD_LIBRARY_PATH environment | |
2574 | variable in the following instructions. | |
2575 | ||
2576 | [role="growable ust-scenarios",cols="asciidoc,asciidoc"] | |
2577 | .Common tracepoint provider package scenarios. | |
2578 | |==== | |
2579 | |Scenario |Instructions | |
2580 | ||
2581 | | | |
2582 | The instrumented application is statically linked with | |
2583 | the tracepoint provider package object. | |
2584 | ||
2585 | image::ust-sit+app-linked-with-tp-o+app-instrumented.png[] | |
2586 | ||
2587 | | | |
2588 | include::../common/ust-sit-step-tp-o.txt[] | |
2589 | ||
2590 | To build the instrumented application: | |
2591 | ||
2592 | . In path:{app.c}, before including path:{tpp.h}, add the following line: | |
2593 | + | |
2594 | -- | |
2595 | [source,c] | |
2596 | ---- | |
2597 | #define TRACEPOINT_DEFINE | |
2598 | ---- | |
2599 | -- | |
2600 | ||
2601 | . Compile the application source file: | |
2602 | + | |
2603 | -- | |
2604 | [role="term"] | |
2605 | ---- | |
ded02698 | 2606 | $ gcc -c app.c |
7adf7ee2 PP |
2607 | ---- |
2608 | -- | |
2609 | ||
2610 | . Build the application: | |
2611 | + | |
2612 | -- | |
2613 | [role="term"] | |
2614 | ---- | |
ded02698 | 2615 | $ gcc -o app app.o tpp.o -llttng-ust -ldl |
7adf7ee2 PP |
2616 | ---- |
2617 | -- | |
2618 | ||
2619 | To run the instrumented application: | |
2620 | ||
2621 | * Start the application: | |
2622 | + | |
2623 | -- | |
2624 | [role="term"] | |
2625 | ---- | |
ded02698 | 2626 | $ ./app |
7adf7ee2 PP |
2627 | ---- |
2628 | -- | |
2629 | ||
2630 | | | |
2631 | The instrumented application is statically linked with the | |
2632 | tracepoint provider package archive file. | |
2633 | ||
2634 | image::ust-sit+app-linked-with-tp-a+app-instrumented.png[] | |
2635 | ||
2636 | | | |
2637 | To create the tracepoint provider package archive file: | |
2638 | ||
2639 | . Compile the <<tpp-source,tracepoint provider package source file>>: | |
2640 | + | |
2641 | -- | |
2642 | [role="term"] | |
2643 | ---- | |
ded02698 | 2644 | $ gcc -I. -c tpp.c |
7adf7ee2 PP |
2645 | ---- |
2646 | -- | |
2647 | ||
2648 | . Create the tracepoint provider package archive file: | |
2649 | + | |
2650 | -- | |
2651 | [role="term"] | |
2652 | ---- | |
ded02698 | 2653 | $ ar rcs tpp.a tpp.o |
7adf7ee2 PP |
2654 | ---- |
2655 | -- | |
2656 | ||
2657 | To build the instrumented application: | |
2658 | ||
2659 | . In path:{app.c}, before including path:{tpp.h}, add the following line: | |
2660 | + | |
2661 | -- | |
2662 | [source,c] | |
2663 | ---- | |
2664 | #define TRACEPOINT_DEFINE | |
2665 | ---- | |
2666 | -- | |
2667 | ||
2668 | . Compile the application source file: | |
2669 | + | |
2670 | -- | |
2671 | [role="term"] | |
2672 | ---- | |
ded02698 | 2673 | $ gcc -c app.c |
7adf7ee2 PP |
2674 | ---- |
2675 | -- | |
2676 | ||
2677 | . Build the application: | |
2678 | + | |
2679 | -- | |
2680 | [role="term"] | |
2681 | ---- | |
ded02698 | 2682 | $ gcc -o app app.o tpp.a -llttng-ust -ldl |
7adf7ee2 PP |
2683 | ---- |
2684 | -- | |
2685 | ||
2686 | To run the instrumented application: | |
2687 | ||
2688 | * Start the application: | |
2689 | + | |
2690 | -- | |
2691 | [role="term"] | |
2692 | ---- | |
ded02698 | 2693 | $ ./app |
7adf7ee2 PP |
2694 | ---- |
2695 | -- | |
2696 | ||
2697 | | | |
2698 | The instrumented application is linked with the tracepoint provider | |
2699 | package shared object. | |
2700 | ||
2701 | image::ust-sit+app-linked-with-tp-so+app-instrumented.png[] | |
2702 | ||
2703 | | | |
2704 | include::../common/ust-sit-step-tp-so.txt[] | |
2705 | ||
2706 | To build the instrumented application: | |
2707 | ||
2708 | . In path:{app.c}, before including path:{tpp.h}, add the following line: | |
2709 | + | |
2710 | -- | |
2711 | [source,c] | |
2712 | ---- | |
2713 | #define TRACEPOINT_DEFINE | |
2714 | ---- | |
2715 | -- | |
2716 | ||
2717 | . Compile the application source file: | |
2718 | + | |
2719 | -- | |
2720 | [role="term"] | |
2721 | ---- | |
ded02698 | 2722 | $ gcc -c app.c |
7adf7ee2 PP |
2723 | ---- |
2724 | -- | |
2725 | ||
2726 | . Build the application: | |
2727 | + | |
2728 | -- | |
2729 | [role="term"] | |
2730 | ---- | |
ded02698 | 2731 | $ gcc -o app app.o -ldl -L. -ltpp |
7adf7ee2 PP |
2732 | ---- |
2733 | -- | |
2734 | ||
2735 | To run the instrumented application: | |
2736 | ||
2737 | * Start the application: | |
2738 | + | |
2739 | -- | |
2740 | [role="term"] | |
2741 | ---- | |
ded02698 | 2742 | $ ./app |
7adf7ee2 PP |
2743 | ---- |
2744 | -- | |
2745 | ||
2746 | | | |
2747 | The tracepoint provider package shared object is preloaded before the | |
2748 | instrumented application starts. | |
2749 | ||
2750 | image::ust-sit+tp-so-preloaded+app-instrumented.png[] | |
2751 | ||
2752 | | | |
2753 | include::../common/ust-sit-step-tp-so.txt[] | |
2754 | ||
2755 | To build the instrumented application: | |
2756 | ||
2757 | . In path:{app.c}, before including path:{tpp.h}, add the | |
2758 | following lines: | |
2759 | + | |
2760 | -- | |
2761 | [source,c] | |
2762 | ---- | |
2763 | #define TRACEPOINT_DEFINE | |
2764 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
2765 | ---- | |
2766 | -- | |
2767 | ||
2768 | . Compile the application source file: | |
2769 | + | |
2770 | -- | |
2771 | [role="term"] | |
2772 | ---- | |
ded02698 | 2773 | $ gcc -c app.c |
7adf7ee2 PP |
2774 | ---- |
2775 | -- | |
2776 | ||
2777 | . Build the application: | |
2778 | + | |
2779 | -- | |
2780 | [role="term"] | |
2781 | ---- | |
ded02698 | 2782 | $ gcc -o app app.o -ldl |
7adf7ee2 PP |
2783 | ---- |
2784 | -- | |
2785 | ||
2786 | To run the instrumented application with tracing support: | |
2787 | ||
2788 | * Preload the tracepoint provider package shared object and | |
2789 | start the application: | |
2790 | + | |
2791 | -- | |
2792 | [role="term"] | |
2793 | ---- | |
ded02698 | 2794 | $ LD_PRELOAD=./libtpp.so ./app |
7adf7ee2 PP |
2795 | ---- |
2796 | -- | |
2797 | ||
2798 | To run the instrumented application without tracing support: | |
2799 | ||
2800 | * Start the application: | |
2801 | + | |
2802 | -- | |
2803 | [role="term"] | |
2804 | ---- | |
ded02698 | 2805 | $ ./app |
7adf7ee2 PP |
2806 | ---- |
2807 | -- | |
2808 | ||
2809 | | | |
2810 | The instrumented application dynamically loads the tracepoint provider | |
2811 | package shared object. | |
2812 | ||
2813 | See the <<dlclose-warning,warning about `dlclose()`>>. | |
2814 | ||
2815 | image::ust-sit+app-dlopens-tp-so+app-instrumented.png[] | |
2816 | ||
2817 | | | |
2818 | include::../common/ust-sit-step-tp-so.txt[] | |
2819 | ||
2820 | To build the instrumented application: | |
2821 | ||
2822 | . In path:{app.c}, before including path:{tpp.h}, add the | |
2823 | following lines: | |
2824 | + | |
2825 | -- | |
2826 | [source,c] | |
2827 | ---- | |
2828 | #define TRACEPOINT_DEFINE | |
2829 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
2830 | ---- | |
2831 | -- | |
2832 | ||
2833 | . Compile the application source file: | |
2834 | + | |
2835 | -- | |
2836 | [role="term"] | |
2837 | ---- | |
ded02698 | 2838 | $ gcc -c app.c |
7adf7ee2 PP |
2839 | ---- |
2840 | -- | |
2841 | ||
2842 | . Build the application: | |
2843 | + | |
2844 | -- | |
2845 | [role="term"] | |
2846 | ---- | |
ded02698 | 2847 | $ gcc -o app app.o -ldl |
7adf7ee2 PP |
2848 | ---- |
2849 | -- | |
2850 | ||
2851 | To run the instrumented application: | |
2852 | ||
2853 | * Start the application: | |
2854 | + | |
2855 | -- | |
2856 | [role="term"] | |
2857 | ---- | |
ded02698 | 2858 | $ ./app |
7adf7ee2 PP |
2859 | ---- |
2860 | -- | |
2861 | ||
2862 | | | |
2863 | The application is linked with the instrumented user library. | |
2864 | ||
2865 | The instrumented user library is statically linked with the tracepoint | |
2866 | provider package object file. | |
2867 | ||
2868 | image::ust-sit+app-linked-with-lib+lib-linked-with-tp-o+lib-instrumented.png[] | |
2869 | ||
2870 | | | |
2871 | include::../common/ust-sit-step-tp-o-fpic.txt[] | |
2872 | ||
2873 | To build the instrumented user library: | |
2874 | ||
2875 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
2876 | following line: | |
2877 | + | |
2878 | -- | |
2879 | [source,c] | |
2880 | ---- | |
2881 | #define TRACEPOINT_DEFINE | |
2882 | ---- | |
2883 | -- | |
2884 | ||
2885 | . Compile the user library source file: | |
2886 | + | |
2887 | -- | |
2888 | [role="term"] | |
2889 | ---- | |
ded02698 | 2890 | $ gcc -I. -fpic -c emon.c |
7adf7ee2 PP |
2891 | ---- |
2892 | -- | |
2893 | ||
2894 | . Build the user library shared object: | |
2895 | + | |
2896 | -- | |
2897 | [role="term"] | |
2898 | ---- | |
ded02698 | 2899 | $ gcc -shared -o libemon.so emon.o tpp.o -llttng-ust -ldl |
7adf7ee2 PP |
2900 | ---- |
2901 | -- | |
2902 | ||
2903 | To build the application: | |
2904 | ||
2905 | . Compile the application source file: | |
2906 | + | |
2907 | -- | |
2908 | [role="term"] | |
2909 | ---- | |
ded02698 | 2910 | $ gcc -c app.c |
7adf7ee2 PP |
2911 | ---- |
2912 | -- | |
2913 | ||
2914 | . Build the application: | |
2915 | + | |
2916 | -- | |
2917 | [role="term"] | |
2918 | ---- | |
ded02698 | 2919 | $ gcc -o app app.o -L. -lemon |
7adf7ee2 PP |
2920 | ---- |
2921 | -- | |
2922 | ||
2923 | To run the application: | |
2924 | ||
2925 | * Start the application: | |
2926 | + | |
2927 | -- | |
2928 | [role="term"] | |
2929 | ---- | |
ded02698 | 2930 | $ ./app |
7adf7ee2 PP |
2931 | ---- |
2932 | -- | |
2933 | ||
2934 | | | |
2935 | The application is linked with the instrumented user library. | |
2936 | ||
2937 | The instrumented user library is linked with the tracepoint provider | |
2938 | package shared object. | |
2939 | ||
2940 | image::ust-sit+app-linked-with-lib+lib-linked-with-tp-so+lib-instrumented.png[] | |
2941 | ||
2942 | | | |
2943 | include::../common/ust-sit-step-tp-so.txt[] | |
2944 | ||
2945 | To build the instrumented user library: | |
2946 | ||
2947 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
2948 | following line: | |
2949 | + | |
2950 | -- | |
2951 | [source,c] | |
2952 | ---- | |
2953 | #define TRACEPOINT_DEFINE | |
2954 | ---- | |
2955 | -- | |
2956 | ||
2957 | . Compile the user library source file: | |
2958 | + | |
2959 | -- | |
2960 | [role="term"] | |
2961 | ---- | |
ded02698 | 2962 | $ gcc -I. -fpic -c emon.c |
7adf7ee2 PP |
2963 | ---- |
2964 | -- | |
2965 | ||
2966 | . Build the user library shared object: | |
2967 | + | |
2968 | -- | |
2969 | [role="term"] | |
2970 | ---- | |
ded02698 | 2971 | $ gcc -shared -o libemon.so emon.o -ldl -L. -ltpp |
7adf7ee2 PP |
2972 | ---- |
2973 | -- | |
2974 | ||
2975 | To build the application: | |
2976 | ||
2977 | . Compile the application source file: | |
2978 | + | |
2979 | -- | |
2980 | [role="term"] | |
2981 | ---- | |
ded02698 | 2982 | $ gcc -c app.c |
7adf7ee2 PP |
2983 | ---- |
2984 | -- | |
2985 | ||
2986 | . Build the application: | |
2987 | + | |
2988 | -- | |
2989 | [role="term"] | |
2990 | ---- | |
ded02698 | 2991 | $ gcc -o app app.o -L. -lemon |
7adf7ee2 PP |
2992 | ---- |
2993 | -- | |
2994 | ||
2995 | To run the application: | |
2996 | ||
2997 | * Start the application: | |
2998 | + | |
2999 | -- | |
3000 | [role="term"] | |
3001 | ---- | |
ded02698 | 3002 | $ ./app |
7adf7ee2 PP |
3003 | ---- |
3004 | -- | |
3005 | ||
3006 | | | |
3007 | The tracepoint provider package shared object is preloaded before the | |
3008 | application starts. | |
3009 | ||
3010 | The application is linked with the instrumented user library. | |
3011 | ||
3012 | image::ust-sit+tp-so-preloaded+app-linked-with-lib+lib-instrumented.png[] | |
3013 | ||
3014 | | | |
3015 | include::../common/ust-sit-step-tp-so.txt[] | |
3016 | ||
3017 | To build the instrumented user library: | |
3018 | ||
3019 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
1e0fb3c5 | 3020 | following lines: |
7adf7ee2 PP |
3021 | + |
3022 | -- | |
3023 | [source,c] | |
3024 | ---- | |
3025 | #define TRACEPOINT_DEFINE | |
3026 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
3027 | ---- | |
3028 | -- | |
3029 | ||
3030 | . Compile the user library source file: | |
3031 | + | |
3032 | -- | |
3033 | [role="term"] | |
3034 | ---- | |
ded02698 | 3035 | $ gcc -I. -fpic -c emon.c |
7adf7ee2 PP |
3036 | ---- |
3037 | -- | |
3038 | ||
3039 | . Build the user library shared object: | |
3040 | + | |
3041 | -- | |
3042 | [role="term"] | |
3043 | ---- | |
ded02698 | 3044 | $ gcc -shared -o libemon.so emon.o -ldl |
7adf7ee2 PP |
3045 | ---- |
3046 | -- | |
3047 | ||
3048 | To build the application: | |
3049 | ||
3050 | . Compile the application source file: | |
3051 | + | |
3052 | -- | |
3053 | [role="term"] | |
3054 | ---- | |
ded02698 | 3055 | $ gcc -c app.c |
7adf7ee2 PP |
3056 | ---- |
3057 | -- | |
3058 | ||
3059 | . Build the application: | |
3060 | + | |
3061 | -- | |
3062 | [role="term"] | |
3063 | ---- | |
ded02698 | 3064 | $ gcc -o app app.o -L. -lemon |
7adf7ee2 PP |
3065 | ---- |
3066 | -- | |
3067 | ||
3068 | To run the application with tracing support: | |
3069 | ||
3070 | * Preload the tracepoint provider package shared object and | |
3071 | start the application: | |
3072 | + | |
3073 | -- | |
3074 | [role="term"] | |
3075 | ---- | |
ded02698 | 3076 | $ LD_PRELOAD=./libtpp.so ./app |
7adf7ee2 PP |
3077 | ---- |
3078 | -- | |
3079 | ||
3080 | To run the application without tracing support: | |
3081 | ||
3082 | * Start the application: | |
3083 | + | |
3084 | -- | |
3085 | [role="term"] | |
3086 | ---- | |
ded02698 | 3087 | $ ./app |
7adf7ee2 PP |
3088 | ---- |
3089 | -- | |
3090 | ||
3091 | | | |
3092 | The application is linked with the instrumented user library. | |
3093 | ||
3094 | The instrumented user library dynamically loads the tracepoint provider | |
3095 | package shared object. | |
3096 | ||
3097 | See the <<dlclose-warning,warning about `dlclose()`>>. | |
3098 | ||
3099 | image::ust-sit+app-linked-with-lib+lib-dlopens-tp-so+lib-instrumented.png[] | |
3100 | ||
3101 | | | |
3102 | include::../common/ust-sit-step-tp-so.txt[] | |
3103 | ||
3104 | To build the instrumented user library: | |
3105 | ||
3106 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
1e0fb3c5 | 3107 | following lines: |
7adf7ee2 PP |
3108 | + |
3109 | -- | |
3110 | [source,c] | |
3111 | ---- | |
3112 | #define TRACEPOINT_DEFINE | |
3113 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
3114 | ---- | |
3115 | -- | |
3116 | ||
3117 | . Compile the user library source file: | |
3118 | + | |
3119 | -- | |
3120 | [role="term"] | |
3121 | ---- | |
ded02698 | 3122 | $ gcc -I. -fpic -c emon.c |
7adf7ee2 PP |
3123 | ---- |
3124 | -- | |
3125 | ||
3126 | . Build the user library shared object: | |
3127 | + | |
3128 | -- | |
3129 | [role="term"] | |
3130 | ---- | |
ded02698 | 3131 | $ gcc -shared -o libemon.so emon.o -ldl |
7adf7ee2 PP |
3132 | ---- |
3133 | -- | |
3134 | ||
3135 | To build the application: | |
3136 | ||
3137 | . Compile the application source file: | |
3138 | + | |
3139 | -- | |
3140 | [role="term"] | |
3141 | ---- | |
ded02698 | 3142 | $ gcc -c app.c |
7adf7ee2 PP |
3143 | ---- |
3144 | -- | |
3145 | ||
3146 | . Build the application: | |
3147 | + | |
3148 | -- | |
3149 | [role="term"] | |
3150 | ---- | |
ded02698 | 3151 | $ gcc -o app app.o -L. -lemon |
7adf7ee2 PP |
3152 | ---- |
3153 | -- | |
3154 | ||
3155 | To run the application: | |
3156 | ||
3157 | * Start the application: | |
3158 | + | |
3159 | -- | |
3160 | [role="term"] | |
3161 | ---- | |
ded02698 | 3162 | $ ./app |
7adf7ee2 PP |
3163 | ---- |
3164 | -- | |
3165 | ||
3166 | | | |
3167 | The application dynamically loads the instrumented user library. | |
3168 | ||
3169 | The instrumented user library is linked with the tracepoint provider | |
3170 | package shared object. | |
3171 | ||
3172 | See the <<dlclose-warning,warning about `dlclose()`>>. | |
3173 | ||
3174 | image::ust-sit+app-dlopens-lib+lib-linked-with-tp-so+lib-instrumented.png[] | |
3175 | ||
3176 | | | |
3177 | include::../common/ust-sit-step-tp-so.txt[] | |
3178 | ||
3179 | To build the instrumented user library: | |
3180 | ||
3181 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
3182 | following line: | |
3183 | + | |
3184 | -- | |
3185 | [source,c] | |
3186 | ---- | |
3187 | #define TRACEPOINT_DEFINE | |
3188 | ---- | |
3189 | -- | |
3190 | ||
3191 | . Compile the user library source file: | |
3192 | + | |
3193 | -- | |
3194 | [role="term"] | |
3195 | ---- | |
ded02698 | 3196 | $ gcc -I. -fpic -c emon.c |
7adf7ee2 PP |
3197 | ---- |
3198 | -- | |
3199 | ||
3200 | . Build the user library shared object: | |
3201 | + | |
3202 | -- | |
3203 | [role="term"] | |
3204 | ---- | |
ded02698 | 3205 | $ gcc -shared -o libemon.so emon.o -ldl -L. -ltpp |
7adf7ee2 PP |
3206 | ---- |
3207 | -- | |
3208 | ||
3209 | To build the application: | |
3210 | ||
3211 | . Compile the application source file: | |
3212 | + | |
3213 | -- | |
3214 | [role="term"] | |
3215 | ---- | |
ded02698 | 3216 | $ gcc -c app.c |
7adf7ee2 PP |
3217 | ---- |
3218 | -- | |
3219 | ||
3220 | . Build the application: | |
3221 | + | |
3222 | -- | |
3223 | [role="term"] | |
3224 | ---- | |
ded02698 | 3225 | $ gcc -o app app.o -ldl -L. -lemon |
7adf7ee2 PP |
3226 | ---- |
3227 | -- | |
3228 | ||
3229 | To run the application: | |
3230 | ||
3231 | * Start the application: | |
3232 | + | |
3233 | -- | |
3234 | [role="term"] | |
3235 | ---- | |
ded02698 | 3236 | $ ./app |
7adf7ee2 PP |
3237 | ---- |
3238 | -- | |
3239 | ||
3240 | | | |
3241 | The application dynamically loads the instrumented user library. | |
3242 | ||
3243 | The instrumented user library dynamically loads the tracepoint provider | |
3244 | package shared object. | |
3245 | ||
3246 | See the <<dlclose-warning,warning about `dlclose()`>>. | |
3247 | ||
3248 | image::ust-sit+app-dlopens-lib+lib-dlopens-tp-so+lib-instrumented.png[] | |
3249 | ||
3250 | | | |
3251 | include::../common/ust-sit-step-tp-so.txt[] | |
3252 | ||
3253 | To build the instrumented user library: | |
3254 | ||
3255 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
1e0fb3c5 | 3256 | following lines: |
7adf7ee2 PP |
3257 | + |
3258 | -- | |
3259 | [source,c] | |
3260 | ---- | |
3261 | #define TRACEPOINT_DEFINE | |
3262 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
3263 | ---- | |
3264 | -- | |
3265 | ||
3266 | . Compile the user library source file: | |
3267 | + | |
3268 | -- | |
3269 | [role="term"] | |
3270 | ---- | |
ded02698 | 3271 | $ gcc -I. -fpic -c emon.c |
7adf7ee2 PP |
3272 | ---- |
3273 | -- | |
3274 | ||
3275 | . Build the user library shared object: | |
3276 | + | |
3277 | -- | |
3278 | [role="term"] | |
3279 | ---- | |
ded02698 | 3280 | $ gcc -shared -o libemon.so emon.o -ldl |
7adf7ee2 PP |
3281 | ---- |
3282 | -- | |
3283 | ||
3284 | To build the application: | |
3285 | ||
3286 | . Compile the application source file: | |
3287 | + | |
3288 | -- | |
3289 | [role="term"] | |
3290 | ---- | |
ded02698 | 3291 | $ gcc -c app.c |
7adf7ee2 PP |
3292 | ---- |
3293 | -- | |
3294 | ||
3295 | . Build the application: | |
3296 | + | |
3297 | -- | |
3298 | [role="term"] | |
3299 | ---- | |
ded02698 | 3300 | $ gcc -o app app.o -ldl -L. -lemon |
7adf7ee2 PP |
3301 | ---- |
3302 | -- | |
3303 | ||
3304 | To run the application: | |
3305 | ||
3306 | * Start the application: | |
3307 | + | |
3308 | -- | |
3309 | [role="term"] | |
3310 | ---- | |
ded02698 | 3311 | $ ./app |
7adf7ee2 PP |
3312 | ---- |
3313 | -- | |
3314 | ||
3315 | | | |
3316 | The tracepoint provider package shared object is preloaded before the | |
3317 | application starts. | |
3318 | ||
3319 | The application dynamically loads the instrumented user library. | |
3320 | ||
3321 | image::ust-sit+tp-so-preloaded+app-dlopens-lib+lib-instrumented.png[] | |
3322 | ||
3323 | | | |
3324 | include::../common/ust-sit-step-tp-so.txt[] | |
3325 | ||
3326 | To build the instrumented user library: | |
3327 | ||
3328 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
1e0fb3c5 | 3329 | following lines: |
7adf7ee2 PP |
3330 | + |
3331 | -- | |
3332 | [source,c] | |
3333 | ---- | |
3334 | #define TRACEPOINT_DEFINE | |
3335 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
3336 | ---- | |
3337 | -- | |
3338 | ||
3339 | . Compile the user library source file: | |
3340 | + | |
3341 | -- | |
3342 | [role="term"] | |
3343 | ---- | |
ded02698 | 3344 | $ gcc -I. -fpic -c emon.c |
7adf7ee2 PP |
3345 | ---- |
3346 | -- | |
3347 | ||
3348 | . Build the user library shared object: | |
3349 | + | |
3350 | -- | |
3351 | [role="term"] | |
3352 | ---- | |
ded02698 | 3353 | $ gcc -shared -o libemon.so emon.o -ldl |
7adf7ee2 PP |
3354 | ---- |
3355 | -- | |
3356 | ||
3357 | To build the application: | |
3358 | ||
3359 | . Compile the application source file: | |
3360 | + | |
3361 | -- | |
3362 | [role="term"] | |
3363 | ---- | |
ded02698 | 3364 | $ gcc -c app.c |
7adf7ee2 PP |
3365 | ---- |
3366 | -- | |
3367 | ||
3368 | . Build the application: | |
3369 | + | |
3370 | -- | |
3371 | [role="term"] | |
3372 | ---- | |
ded02698 | 3373 | $ gcc -o app app.o -L. -lemon |
7adf7ee2 PP |
3374 | ---- |
3375 | -- | |
3376 | ||
3377 | To run the application with tracing support: | |
3378 | ||
3379 | * Preload the tracepoint provider package shared object and | |
3380 | start the application: | |
3381 | + | |
3382 | -- | |
3383 | [role="term"] | |
3384 | ---- | |
ded02698 | 3385 | $ LD_PRELOAD=./libtpp.so ./app |
7adf7ee2 PP |
3386 | ---- |
3387 | -- | |
3388 | ||
3389 | To run the application without tracing support: | |
3390 | ||
3391 | * Start the application: | |
3392 | + | |
3393 | -- | |
3394 | [role="term"] | |
3395 | ---- | |
ded02698 | 3396 | $ ./app |
7adf7ee2 PP |
3397 | ---- |
3398 | -- | |
3399 | ||
3400 | | | |
3401 | The application is statically linked with the tracepoint provider | |
3402 | package object file. | |
3403 | ||
3404 | The application is linked with the instrumented user library. | |
3405 | ||
3406 | image::ust-sit+app-linked-with-tp-o+app-linked-with-lib+lib-instrumented.png[] | |
3407 | ||
3408 | | | |
3409 | include::../common/ust-sit-step-tp-o.txt[] | |
3410 | ||
3411 | To build the instrumented user library: | |
3412 | ||
3413 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
3414 | following line: | |
3415 | + | |
3416 | -- | |
3417 | [source,c] | |
3418 | ---- | |
3419 | #define TRACEPOINT_DEFINE | |
3420 | ---- | |
3421 | -- | |
3422 | ||
3423 | . Compile the user library source file: | |
3424 | + | |
3425 | -- | |
3426 | [role="term"] | |
3427 | ---- | |
ded02698 | 3428 | $ gcc -I. -fpic -c emon.c |
7adf7ee2 PP |
3429 | ---- |
3430 | -- | |
3431 | ||
3432 | . Build the user library shared object: | |
3433 | + | |
3434 | -- | |
3435 | [role="term"] | |
3436 | ---- | |
ded02698 | 3437 | $ gcc -shared -o libemon.so emon.o |
7adf7ee2 PP |
3438 | ---- |
3439 | -- | |
3440 | ||
3441 | To build the application: | |
3442 | ||
3443 | . Compile the application source file: | |
3444 | + | |
3445 | -- | |
3446 | [role="term"] | |
3447 | ---- | |
ded02698 | 3448 | $ gcc -c app.c |
7adf7ee2 PP |
3449 | ---- |
3450 | -- | |
3451 | ||
3452 | . Build the application: | |
3453 | + | |
3454 | -- | |
3455 | [role="term"] | |
3456 | ---- | |
ded02698 | 3457 | $ gcc -o app app.o tpp.o -llttng-ust -ldl -L. -lemon |
7adf7ee2 PP |
3458 | ---- |
3459 | -- | |
3460 | ||
3461 | To run the instrumented application: | |
3462 | ||
3463 | * Start the application: | |
3464 | + | |
3465 | -- | |
3466 | [role="term"] | |
3467 | ---- | |
ded02698 | 3468 | $ ./app |
7adf7ee2 PP |
3469 | ---- |
3470 | -- | |
3471 | ||
3472 | | | |
3473 | The application is statically linked with the tracepoint provider | |
3474 | package object file. | |
3475 | ||
3476 | The application dynamically loads the instrumented user library. | |
3477 | ||
3478 | image::ust-sit+app-linked-with-tp-o+app-dlopens-lib+lib-instrumented.png[] | |
3479 | ||
3480 | | | |
3481 | include::../common/ust-sit-step-tp-o.txt[] | |
3482 | ||
3483 | To build the application: | |
3484 | ||
3485 | . In path:{app.c}, before including path:{tpp.h}, add the following line: | |
3486 | + | |
3487 | -- | |
3488 | [source,c] | |
3489 | ---- | |
3490 | #define TRACEPOINT_DEFINE | |
3491 | ---- | |
3492 | -- | |
3493 | ||
3494 | . Compile the application source file: | |
3495 | + | |
3496 | -- | |
3497 | [role="term"] | |
3498 | ---- | |
ded02698 | 3499 | $ gcc -c app.c |
7adf7ee2 PP |
3500 | ---- |
3501 | -- | |
3502 | ||
3503 | . Build the application: | |
3504 | + | |
3505 | -- | |
3506 | [role="term"] | |
3507 | ---- | |
ded02698 | 3508 | $ gcc -Wl,--export-dynamic -o app app.o tpp.o \ |
7adf7ee2 PP |
3509 | -llttng-ust -ldl |
3510 | ---- | |
3511 | -- | |
3512 | + | |
3513 | The `--export-dynamic` option passed to the linker is necessary for the | |
3514 | dynamically loaded library to ``see'' the tracepoint symbols defined in | |
3515 | the application. | |
3516 | ||
3517 | To build the instrumented user library: | |
3518 | ||
3519 | . Compile the user library source file: | |
3520 | + | |
3521 | -- | |
3522 | [role="term"] | |
3523 | ---- | |
ded02698 | 3524 | $ gcc -I. -fpic -c emon.c |
7adf7ee2 PP |
3525 | ---- |
3526 | -- | |
3527 | ||
3528 | . Build the user library shared object: | |
3529 | + | |
3530 | -- | |
3531 | [role="term"] | |
3532 | ---- | |
ded02698 | 3533 | $ gcc -shared -o libemon.so emon.o |
7adf7ee2 PP |
3534 | ---- |
3535 | -- | |
3536 | ||
3537 | To run the application: | |
3538 | ||
3539 | * Start the application: | |
3540 | + | |
3541 | -- | |
3542 | [role="term"] | |
3543 | ---- | |
ded02698 | 3544 | $ ./app |
7adf7ee2 PP |
3545 | ---- |
3546 | -- | |
3547 | |==== | |
3548 | ||
3549 | [[dlclose-warning]] | |
3550 | [IMPORTANT] | |
3551 | .Do not use man:dlclose(3) on a tracepoint provider package | |
3552 | ==== | |
3553 | Never use man:dlclose(3) on any shared object which: | |
3554 | ||
3555 | * Is linked with, statically or dynamically, a tracepoint provider | |
3556 | package. | |
3557 | * Calls man:dlopen(3) itself to dynamically open a tracepoint provider | |
3558 | package shared object. | |
3559 | ||
3560 | This is currently considered **unsafe** due to a lack of reference | |
3561 | counting from LTTng-UST to the shared object. | |
3562 | ||
3563 | A known workaround (available since glibc 2.2) is to use the | |
3564 | `RTLD_NODELETE` flag when calling man:dlopen(3) initially. This has the | |
3565 | effect of not unloading the loaded shared object, even if man:dlclose(3) | |
3566 | is called. | |
3567 | ||
3568 | You can also preload the tracepoint provider package shared object with | |
3569 | the env:LD_PRELOAD environment variable to overcome this limitation. | |
3570 | ==== | |
3571 | ||
3572 | ||
3573 | [[using-lttng-ust-with-daemons]] | |
3574 | ===== Use noch:{LTTng-UST} with daemons | |
3575 | ||
3576 | If your instrumented application calls man:fork(2), man:clone(2), | |
3577 | or BSD's man:rfork(2), without a following man:exec(3)-family | |
3578 | system call, you must preload the path:{liblttng-ust-fork.so} shared | |
3579 | object when starting the application. | |
3580 | ||
3581 | [role="term"] | |
3582 | ---- | |
ded02698 | 3583 | $ LD_PRELOAD=liblttng-ust-fork.so ./my-app |
7adf7ee2 PP |
3584 | ---- |
3585 | ||
3586 | If your tracepoint provider package is | |
3587 | a shared library which you also preload, you must put both | |
3588 | shared objects in env:LD_PRELOAD: | |
3589 | ||
3590 | [role="term"] | |
3591 | ---- | |
ded02698 | 3592 | $ LD_PRELOAD=liblttng-ust-fork.so:/path/to/tp.so ./my-app |
7adf7ee2 PP |
3593 | ---- |
3594 | ||
3595 | ||
3596 | [[lttng-ust-pkg-config]] | |
3597 | ===== Use noch:{pkg-config} | |
3598 | ||
3599 | On some distributions, LTTng-UST ships with a | |
3600 | https://www.freedesktop.org/wiki/Software/pkg-config/[pkg-config] | |
3601 | metadata file. If this is your case, then you can use cmd:pkg-config to | |
3602 | build an application on the command line: | |
3603 | ||
3604 | [role="term"] | |
3605 | ---- | |
ded02698 | 3606 | $ gcc -o my-app my-app.o tp.o $(pkg-config --cflags --libs lttng-ust) |
7adf7ee2 PP |
3607 | ---- |
3608 | ||
3609 | ||
3610 | [[instrumenting-32-bit-app-on-64-bit-system]] | |
3611 | ===== [[advanced-instrumenting-techniques]]Build a 32-bit instrumented application for a 64-bit target system | |
3612 | ||
3613 | In order to trace a 32-bit application running on a 64-bit system, | |
3614 | LTTng must use a dedicated 32-bit | |
3615 | <<lttng-consumerd,consumer daemon>>. | |
3616 | ||
3617 | The following steps show how to build and install a 32-bit consumer | |
3618 | daemon, which is _not_ part of the default 64-bit LTTng build, how to | |
3619 | build and install the 32-bit LTTng-UST libraries, and how to build and | |
3620 | link an instrumented 32-bit application in that context. | |
3621 | ||
3622 | To build a 32-bit instrumented application for a 64-bit target system, | |
3623 | assuming you have a fresh target system with no installed Userspace RCU | |
3624 | or LTTng packages: | |
3625 | ||
3626 | . Download, build, and install a 32-bit version of Userspace RCU: | |
3627 | + | |
3628 | -- | |
3629 | [role="term"] | |
3630 | ---- | |
ded02698 | 3631 | $ cd $(mktemp -d) && |
7adf7ee2 PP |
3632 | wget http://lttng.org/files/urcu/userspace-rcu-latest-0.9.tar.bz2 && |
3633 | tar -xf userspace-rcu-latest-0.9.tar.bz2 && | |
3634 | cd userspace-rcu-0.9.* && | |
3635 | ./configure --libdir=/usr/local/lib32 CFLAGS=-m32 && | |
3636 | make && | |
3637 | sudo make install && | |
3638 | sudo ldconfig | |
3639 | ---- | |
3640 | -- | |
3641 | ||
3642 | . Using your distribution's package manager, or from source, install | |
3643 | the following 32-bit versions of the following dependencies of | |
3644 | LTTng-tools and LTTng-UST: | |
3645 | + | |
3646 | -- | |
3647 | * https://sourceforge.net/projects/libuuid/[libuuid] | |
3648 | * http://directory.fsf.org/wiki/Popt[popt] | |
3649 | * http://www.xmlsoft.org/[libxml2] | |
3650 | -- | |
3651 | ||
3652 | . Download, build, and install a 32-bit version of the latest | |
3653 | LTTng-UST{nbsp}{revision}: | |
3654 | + | |
3655 | -- | |
3656 | [role="term"] | |
3657 | ---- | |
ded02698 | 3658 | $ cd $(mktemp -d) && |
7adf7ee2 PP |
3659 | wget http://lttng.org/files/lttng-ust/lttng-ust-latest-2.8.tar.bz2 && |
3660 | tar -xf lttng-ust-latest-2.8.tar.bz2 && | |
3661 | cd lttng-ust-2.8.* && | |
3662 | ./configure --libdir=/usr/local/lib32 \ | |
3663 | CFLAGS=-m32 CXXFLAGS=-m32 \ | |
3664 | LDFLAGS='-L/usr/local/lib32 -L/usr/lib32' && | |
3665 | make && | |
3666 | sudo make install && | |
3667 | sudo ldconfig | |
3668 | ---- | |
3669 | -- | |
3670 | + | |
3671 | [NOTE] | |
3672 | ==== | |
3673 | Depending on your distribution, | |
3674 | 32-bit libraries could be installed at a different location than | |
3675 | `/usr/lib32`. For example, Debian is known to install | |
3676 | some 32-bit libraries in `/usr/lib/i386-linux-gnu`. | |
3677 | ||
3678 | In this case, make sure to set `LDFLAGS` to all the | |
3679 | relevant 32-bit library paths, for example: | |
3680 | ||
3681 | [role="term"] | |
3682 | ---- | |
ded02698 | 3683 | $ LDFLAGS='-L/usr/lib/i386-linux-gnu -L/usr/lib32' |
7adf7ee2 PP |
3684 | ---- |
3685 | ==== | |
3686 | ||
3687 | . Download the latest LTTng-tools{nbsp}{revision}, build, and install | |
3688 | the 32-bit consumer daemon: | |
3689 | + | |
3690 | -- | |
3691 | [role="term"] | |
3692 | ---- | |
ded02698 | 3693 | $ cd $(mktemp -d) && |
7adf7ee2 PP |
3694 | wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.8.tar.bz2 && |
3695 | tar -xf lttng-tools-latest-2.8.tar.bz2 && | |
3696 | cd lttng-tools-2.8.* && | |
3697 | ./configure --libdir=/usr/local/lib32 CFLAGS=-m32 CXXFLAGS=-m32 \ | |
060d8534 JG |
3698 | LDFLAGS='-L/usr/local/lib32 -L/usr/lib32' \ |
3699 | --disable-bin-lttng --disable-bin-lttng-crash \ | |
3700 | --disable-bin-lttng-relayd --disable-bin-lttng-sessiond && | |
7adf7ee2 PP |
3701 | make && |
3702 | cd src/bin/lttng-consumerd && | |
3703 | sudo make install && | |
3704 | sudo ldconfig | |
3705 | ---- | |
3706 | -- | |
3707 | ||
3708 | . From your distribution or from source, | |
3709 | <<installing-lttng,install>> the 64-bit versions of | |
3710 | LTTng-UST and Userspace RCU. | |
3711 | . Download, build, and install the 64-bit version of the | |
3712 | latest LTTng-tools{nbsp}{revision}: | |
3713 | + | |
3714 | -- | |
3715 | [role="term"] | |
3716 | ---- | |
ded02698 | 3717 | $ cd $(mktemp -d) && |
7adf7ee2 PP |
3718 | wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.8.tar.bz2 && |
3719 | tar -xf lttng-tools-latest-2.8.tar.bz2 && | |
3720 | cd lttng-tools-2.8.* && | |
3721 | ./configure --with-consumerd32-libdir=/usr/local/lib32 \ | |
3722 | --with-consumerd32-bin=/usr/local/lib32/lttng/libexec/lttng-consumerd && | |
3723 | make && | |
3724 | sudo make install && | |
3725 | sudo ldconfig | |
3726 | ---- | |
3727 | -- | |
3728 | ||
3729 | . Pass the following options to man:gcc(1), man:g++(1), or man:clang(1) | |
3730 | when linking your 32-bit application: | |
3731 | + | |
3732 | ---- | |
3733 | -m32 -L/usr/lib32 -L/usr/local/lib32 \ | |
3734 | -Wl,-rpath,/usr/lib32,-rpath,/usr/local/lib32 | |
3735 | ---- | |
3736 | + | |
3737 | For example, let's rebuild the quick start example in | |
3738 | <<tracing-your-own-user-application,Trace a user application>> as an | |
3739 | instrumented 32-bit application: | |
3740 | + | |
3741 | -- | |
3742 | [role="term"] | |
3743 | ---- | |
ded02698 PP |
3744 | $ gcc -m32 -c -I. hello-tp.c |
3745 | $ gcc -m32 -c hello.c | |
3746 | $ gcc -m32 -o hello hello.o hello-tp.o \ | |
7adf7ee2 PP |
3747 | -L/usr/lib32 -L/usr/local/lib32 \ |
3748 | -Wl,-rpath,/usr/lib32,-rpath,/usr/local/lib32 \ | |
3749 | -llttng-ust -ldl | |
3750 | ---- | |
3751 | -- | |
3752 | ||
3753 | No special action is required to execute the 32-bit application and | |
3754 | to trace it: use the command-line man:lttng(1) tool as usual. | |
3755 | ||
3756 | ||
3757 | [role="since-2.5"] | |
3758 | [[tracef]] | |
3759 | ==== Use `tracef()` | |
3760 | ||
3761 | man:tracef(3) is a small LTTng-UST API designed for quick, | |
3762 | man:printf(3)-like instrumentation without the burden of | |
3763 | <<tracepoint-provider,creating>> and | |
3764 | <<building-tracepoint-providers-and-user-application,building>> | |
3765 | a tracepoint provider package. | |
3766 | ||
3767 | To use `tracef()` in your application: | |
3768 | ||
3769 | . In the C or C++ source files where you need to use `tracef()`, | |
3770 | include `<lttng/tracef.h>`: | |
3771 | + | |
3772 | -- | |
3773 | [source,c] | |
3774 | ---- | |
3775 | #include <lttng/tracef.h> | |
3776 | ---- | |
3777 | -- | |
3778 | ||
3779 | . In the application's source code, use `tracef()` like you would use | |
3780 | man:printf(3): | |
3781 | + | |
3782 | -- | |
3783 | [source,c] | |
3784 | ---- | |
3785 | /* ... */ | |
3786 | ||
3787 | tracef("my message: %d (%s)", my_integer, my_string); | |
3788 | ||
3789 | /* ... */ | |
3790 | ---- | |
3791 | -- | |
3792 | ||
3793 | . Link your application with `liblttng-ust`: | |
3794 | + | |
3795 | -- | |
3796 | [role="term"] | |
3797 | ---- | |
ded02698 | 3798 | $ gcc -o app app.c -llttng-ust |
7adf7ee2 PP |
3799 | ---- |
3800 | -- | |
3801 | ||
3802 | To trace the events that `tracef()` calls emit: | |
3803 | ||
3804 | * <<enabling-disabling-events,Create an event rule>> which matches the | |
3805 | `lttng_ust_tracef:*` event name: | |
3806 | + | |
3807 | -- | |
3808 | [role="term"] | |
3809 | ---- | |
ded02698 | 3810 | $ lttng enable-event --userspace 'lttng_ust_tracef:*' |
7adf7ee2 PP |
3811 | ---- |
3812 | -- | |
3813 | ||
3814 | [IMPORTANT] | |
3815 | .Limitations of `tracef()` | |
3816 | ==== | |
3817 | The `tracef()` utility function was developed to make user space tracing | |
3818 | super simple, albeit with notable disadvantages compared to | |
3819 | <<defining-tracepoints,user-defined tracepoints>>: | |
3820 | ||
3821 | * All the emitted events have the same tracepoint provider and | |
3822 | tracepoint names, respectively `lttng_ust_tracef` and `event`. | |
3823 | * There is no static type checking. | |
3824 | * The only event record field you actually get, named `msg`, is a string | |
3825 | potentially containing the values you passed to `tracef()` | |
3826 | using your own format string. This also means that you cannot filter | |
3827 | events with a custom expression at run time because there are no | |
3828 | isolated fields. | |
3829 | * Since `tracef()` uses the C standard library's man:vasprintf(3) | |
3830 | function behind the scenes to format the strings at run time, its | |
3831 | expected performance is lower than with user-defined tracepoints, | |
3832 | which do not require a conversion to a string. | |
3833 | ||
3834 | Taking this into consideration, `tracef()` is useful for some quick | |
3835 | prototyping and debugging, but you should not consider it for any | |
3836 | permanent and serious applicative instrumentation. | |
3837 | ==== | |
3838 | ||
3839 | ||
3840 | [role="since-2.7"] | |
3841 | [[tracelog]] | |
3842 | ==== Use `tracelog()` | |
3843 | ||
3844 | The man:tracelog(3) API is very similar to <<tracef,`tracef()`>>, with | |
3845 | the difference that it accepts an additional log level parameter. | |
3846 | ||
3847 | The goal of `tracelog()` is to ease the migration from logging to | |
3848 | tracing. | |
3849 | ||
3850 | To use `tracelog()` in your application: | |
3851 | ||
3852 | . In the C or C++ source files where you need to use `tracelog()`, | |
3853 | include `<lttng/tracelog.h>`: | |
3854 | + | |
3855 | -- | |
3856 | [source,c] | |
3857 | ---- | |
3858 | #include <lttng/tracelog.h> | |
3859 | ---- | |
3860 | -- | |
3861 | ||
3862 | . In the application's source code, use `tracelog()` like you would use | |
3863 | man:printf(3), except for the first parameter which is the log | |
3864 | level: | |
3865 | + | |
3866 | -- | |
3867 | [source,c] | |
3868 | ---- | |
3869 | /* ... */ | |
3870 | ||
3871 | tracelog(TRACE_WARNING, "my message: %d (%s)", | |
3872 | my_integer, my_string); | |
3873 | ||
3874 | /* ... */ | |
3875 | ---- | |
3876 | -- | |
3877 | + | |
3878 | See man:lttng-ust(3) for a list of available log level names. | |
3879 | ||
3880 | . Link your application with `liblttng-ust`: | |
3881 | + | |
3882 | -- | |
3883 | [role="term"] | |
3884 | ---- | |
ded02698 | 3885 | $ gcc -o app app.c -llttng-ust |
7adf7ee2 PP |
3886 | ---- |
3887 | -- | |
3888 | ||
3889 | To trace the events that `tracelog()` calls emit with a log level | |
3890 | _as severe as_ a specific log level: | |
3891 | ||
3892 | * <<enabling-disabling-events,Create an event rule>> which matches the | |
3893 | `lttng_ust_tracelog:*` event name and a minimum level | |
3894 | of severity: | |
3895 | + | |
3896 | -- | |
3897 | [role="term"] | |
3898 | ---- | |
ded02698 | 3899 | $ lttng enable-event --userspace 'lttng_ust_tracelog:*' |
7adf7ee2 PP |
3900 | --loglevel=TRACE_WARNING |
3901 | ---- | |
3902 | -- | |
3903 | ||
3904 | To trace the events that `tracelog()` calls emit with a | |
3905 | _specific log level_: | |
3906 | ||
3907 | * Create an event rule which matches the `lttng_ust_tracelog:*` | |
3908 | event name and a specific log level: | |
3909 | + | |
3910 | -- | |
3911 | [role="term"] | |
3912 | ---- | |
ded02698 | 3913 | $ lttng enable-event --userspace 'lttng_ust_tracelog:*' |
7adf7ee2 PP |
3914 | --loglevel-only=TRACE_INFO |
3915 | ---- | |
3916 | -- | |
3917 | ||
3918 | ||
3919 | [[prebuilt-ust-helpers]] | |
3920 | === Prebuilt user space tracing helpers | |
3921 | ||
146d7451 | 3922 | The LTTng-UST package provides a few helpers in the form of preloadable |
7adf7ee2 PP |
3923 | shared objects which automatically instrument system functions and |
3924 | calls. | |
3925 | ||
3926 | The helper shared objects are normally found in dir:{/usr/lib}. If you | |
3927 | built LTTng-UST <<building-from-source,from source>>, they are probably | |
3928 | located in dir:{/usr/local/lib}. | |
3929 | ||
3930 | The installed user space tracing helpers in LTTng-UST{nbsp}{revision} | |
3931 | are: | |
3932 | ||
3933 | path:{liblttng-ust-libc-wrapper.so}:: | |
3934 | path:{liblttng-ust-pthread-wrapper.so}:: | |
3935 | <<liblttng-ust-libc-pthread-wrapper,C{nbsp}standard library | |
3936 | memory and POSIX threads function tracing>>. | |
3937 | ||
3938 | path:{liblttng-ust-cyg-profile.so}:: | |
3939 | path:{liblttng-ust-cyg-profile-fast.so}:: | |
3940 | <<liblttng-ust-cyg-profile,Function entry and exit tracing>>. | |
3941 | ||
3942 | path:{liblttng-ust-dl.so}:: | |
3943 | <<liblttng-ust-dl,Dynamic linker tracing>>. | |
3944 | ||
3945 | To use a user space tracing helper with any user application: | |
3946 | ||
3947 | * Preload the helper shared object when you start the application: | |
3948 | + | |
3949 | -- | |
3950 | [role="term"] | |
3951 | ---- | |
ded02698 | 3952 | $ LD_PRELOAD=liblttng-ust-libc-wrapper.so my-app |
7adf7ee2 PP |
3953 | ---- |
3954 | -- | |
3955 | + | |
3956 | You can preload more than one helper: | |
3957 | + | |
3958 | -- | |
3959 | [role="term"] | |
3960 | ---- | |
ded02698 | 3961 | $ LD_PRELOAD=liblttng-ust-libc-wrapper.so:liblttng-ust-dl.so my-app |
7adf7ee2 PP |
3962 | ---- |
3963 | -- | |
3964 | ||
3965 | ||
3966 | [role="since-2.3"] | |
3967 | [[liblttng-ust-libc-pthread-wrapper]] | |
3968 | ==== Instrument C standard library memory and POSIX threads functions | |
3969 | ||
3970 | The path:{liblttng-ust-libc-wrapper.so} and | |
3971 | path:{liblttng-ust-pthread-wrapper.so} helpers | |
3972 | add instrumentation to some C standard library and POSIX | |
3973 | threads functions. | |
3974 | ||
3975 | [role="growable"] | |
3976 | .Functions instrumented by preloading path:{liblttng-ust-libc-wrapper.so}. | |
3977 | |==== | |
3978 | |TP provider name |TP name |Instrumented function | |
3979 | ||
3980 | .6+|`lttng_ust_libc` |`malloc` |man:malloc(3) | |
3981 | |`calloc` |man:calloc(3) | |
3982 | |`realloc` |man:realloc(3) | |
3983 | |`free` |man:free(3) | |
3984 | |`memalign` |man:memalign(3) | |
3985 | |`posix_memalign` |man:posix_memalign(3) | |
3986 | |==== | |
3987 | ||
3988 | [role="growable"] | |
3989 | .Functions instrumented by preloading path:{liblttng-ust-pthread-wrapper.so}. | |
3990 | |==== | |
3991 | |TP provider name |TP name |Instrumented function | |
3992 | ||
3993 | .4+|`lttng_ust_pthread` |`pthread_mutex_lock_req` |man:pthread_mutex_lock(3p) (request time) | |
3994 | |`pthread_mutex_lock_acq` |man:pthread_mutex_lock(3p) (acquire time) | |
3995 | |`pthread_mutex_trylock` |man:pthread_mutex_trylock(3p) | |
3996 | |`pthread_mutex_unlock` |man:pthread_mutex_unlock(3p) | |
3997 | |==== | |
3998 | ||
3999 | When you preload the shared object, it replaces the functions listed | |
4000 | in the previous tables by wrappers which contain tracepoints and call | |
4001 | the replaced functions. | |
4002 | ||
4003 | ||
4004 | [[liblttng-ust-cyg-profile]] | |
4005 | ==== Instrument function entry and exit | |
4006 | ||
4007 | The path:{liblttng-ust-cyg-profile*.so} helpers can add instrumentation | |
4008 | to the entry and exit points of functions. | |
4009 | ||
4010 | man:gcc(1) and man:clang(1) have an option named | |
20036e91 | 4011 | https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html[`-finstrument-functions`] |
7adf7ee2 PP |
4012 | which generates instrumentation calls for entry and exit to functions. |
4013 | The LTTng-UST function tracing helpers, | |
4014 | path:{liblttng-ust-cyg-profile.so} and | |
4015 | path:{liblttng-ust-cyg-profile-fast.so}, take advantage of this feature | |
4016 | to add tracepoints to the two generated functions (which contain | |
4017 | `cyg_profile` in their names, hence the helper's name). | |
4018 | ||
4019 | To use the LTTng-UST function tracing helper, the source files to | |
4020 | instrument must be built using the `-finstrument-functions` compiler | |
4021 | flag. | |
4022 | ||
4023 | There are two versions of the LTTng-UST function tracing helper: | |
4024 | ||
4025 | * **path:{liblttng-ust-cyg-profile-fast.so}** is a lightweight variant | |
4026 | that you should only use when it can be _guaranteed_ that the | |
4027 | complete event stream is recorded without any lost event record. | |
4028 | Any kind of duplicate information is left out. | |
4029 | + | |
4030 | Assuming no event record is lost, having only the function addresses on | |
4031 | entry is enough to create a call graph, since an event record always | |
4032 | contains the ID of the CPU that generated it. | |
4033 | + | |
55e90f33 PP |
4034 | You can use a tool like man:addr2line(1) to convert function addresses |
4035 | back to source file names and line numbers. | |
7adf7ee2 PP |
4036 | |
4037 | * **path:{liblttng-ust-cyg-profile.so}** is a more robust variant | |
4038 | which also works in use cases where event records might get discarded or | |
4039 | not recorded from application startup. | |
4040 | In these cases, the trace analyzer needs more information to be | |
4041 | able to reconstruct the program flow. | |
4042 | ||
4043 | See man:lttng-ust-cyg-profile(3) to learn more about the instrumentation | |
4044 | points of this helper. | |
4045 | ||
4046 | All the tracepoints that this helper provides have the | |
4047 | log level `TRACE_DEBUG_FUNCTION` (see man:lttng-ust(3)). | |
4048 | ||
4049 | TIP: It's sometimes a good idea to limit the number of source files that | |
4050 | you compile with the `-finstrument-functions` option to prevent LTTng | |
4051 | from writing an excessive amount of trace data at run time. When using | |
4052 | man:gcc(1), you can use the | |
4053 | `-finstrument-functions-exclude-function-list` option to avoid | |
4054 | instrument entries and exits of specific function names. | |
4055 | ||
4056 | ||
4057 | [role="since-2.4"] | |
4058 | [[liblttng-ust-dl]] | |
4059 | ==== Instrument the dynamic linker | |
4060 | ||
4061 | The path:{liblttng-ust-dl.so} helper adds instrumentation to the | |
4062 | man:dlopen(3) and man:dlclose(3) function calls. | |
4063 | ||
4064 | See man:lttng-ust-dl(3) to learn more about the instrumentation points | |
4065 | of this helper. | |
4066 | ||
4067 | ||
4068 | [role="since-2.4"] | |
4069 | [[java-application]] | |
4070 | === User space Java agent | |
4071 | ||
4072 | You can instrument any Java application which uses one of the following | |
4073 | logging frameworks: | |
4074 | ||
4075 | * The https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[**`java.util.logging`**] | |
4076 | (JUL) core logging facilities. | |
4077 | * http://logging.apache.org/log4j/1.2/[**Apache log4j 1.2**], since | |
4078 | LTTng 2.6. Note that Apache Log4j{nbsp}2 is not supported. | |
4079 | ||
4080 | [role="img-100"] | |
4081 | .LTTng-UST Java agent imported by a Java application. | |
4082 | image::java-app.png[] | |
4083 | ||
d0f6a241 | 4084 | Note that the methods described below are new in LTTng{nbsp}2.8. |
7adf7ee2 PP |
4085 | Previous LTTng versions use another technique. |
4086 | ||
4087 | NOTE: We use http://openjdk.java.net/[OpenJDK]{nbsp}8 for development | |
4088 | and https://ci.lttng.org/[continuous integration], thus this version is | |
4089 | directly supported. However, the LTTng-UST Java agent is also tested | |
4090 | with OpenJDK{nbsp}7. | |
4091 | ||
4092 | ||
4093 | [role="since-2.8"] | |
4094 | [[jul]] | |
4095 | ==== Use the LTTng-UST Java agent for `java.util.logging` | |
4096 | ||
4097 | To use the LTTng-UST Java agent in a Java application which uses | |
4098 | `java.util.logging` (JUL): | |
4099 | ||
4100 | . In the Java application's source code, import the LTTng-UST | |
4101 | log handler package for `java.util.logging`: | |
4102 | + | |
4103 | -- | |
4104 | [source,java] | |
4105 | ---- | |
4106 | import org.lttng.ust.agent.jul.LttngLogHandler; | |
4107 | ---- | |
4108 | -- | |
4109 | ||
4110 | . Create an LTTng-UST JUL log handler: | |
4111 | + | |
4112 | -- | |
4113 | [source,java] | |
4114 | ---- | |
4115 | Handler lttngUstLogHandler = new LttngLogHandler(); | |
4116 | ---- | |
4117 | -- | |
4118 | ||
4119 | . Add this handler to the JUL loggers which should emit LTTng events: | |
4120 | + | |
4121 | -- | |
4122 | [source,java] | |
4123 | ---- | |
4124 | Logger myLogger = Logger.getLogger("some-logger"); | |
4125 | ||
4126 | myLogger.addHandler(lttngUstLogHandler); | |
4127 | ---- | |
4128 | -- | |
4129 | ||
4130 | . Use `java.util.logging` log statements and configuration as usual. | |
4131 | The loggers with an attached LTTng-UST log handler can emit | |
4132 | LTTng events. | |
4133 | ||
4134 | . Before exiting the application, remove the LTTng-UST log handler from | |
4135 | the loggers attached to it and call its `close()` method: | |
4136 | + | |
4137 | -- | |
4138 | [source,java] | |
4139 | ---- | |
4140 | myLogger.removeHandler(lttngUstLogHandler); | |
4141 | lttngUstLogHandler.close(); | |
4142 | ---- | |
4143 | -- | |
4144 | + | |
4145 | This is not strictly necessary, but it is recommended for a clean | |
4146 | disposal of the handler's resources. | |
4147 | ||
4148 | . Include the LTTng-UST Java agent's common and JUL-specific JAR files, | |
4149 | path:{lttng-ust-agent-common.jar} and path:{lttng-ust-agent-jul.jar}, | |
4150 | in the | |
4151 | https://docs.oracle.com/javase/tutorial/essential/environment/paths.html[class | |
4152 | path] when you build the Java application. | |
4153 | + | |
4154 | The JAR files are typically located in dir:{/usr/share/java}. | |
4155 | + | |
4156 | IMPORTANT: The LTTng-UST Java agent must be | |
4157 | <<installing-lttng,installed>> for the logging framework your | |
4158 | application uses. | |
4159 | ||
4160 | .Use the LTTng-UST Java agent for `java.util.logging`. | |
4161 | ==== | |
4162 | [source,java] | |
4163 | .path:{Test.java} | |
4164 | ---- | |
4165 | import java.io.IOException; | |
4166 | import java.util.logging.Handler; | |
4167 | import java.util.logging.Logger; | |
4168 | import org.lttng.ust.agent.jul.LttngLogHandler; | |
4169 | ||
4170 | public class Test | |
4171 | { | |
4172 | private static final int answer = 42; | |
4173 | ||
4174 | public static void main(String[] argv) throws Exception | |
4175 | { | |
4176 | // Create a logger | |
4177 | Logger logger = Logger.getLogger("jello"); | |
4178 | ||
4179 | // Create an LTTng-UST log handler | |
4180 | Handler lttngUstLogHandler = new LttngLogHandler(); | |
4181 | ||
4182 | // Add the LTTng-UST log handler to our logger | |
4183 | logger.addHandler(lttngUstLogHandler); | |
4184 | ||
4185 | // Log at will! | |
4186 | logger.info("some info"); | |
4187 | logger.warning("some warning"); | |
4188 | Thread.sleep(500); | |
4189 | logger.finer("finer information; the answer is " + answer); | |
4190 | Thread.sleep(123); | |
4191 | logger.severe("error!"); | |
4192 | ||
4193 | // Not mandatory, but cleaner | |
4194 | logger.removeHandler(lttngUstLogHandler); | |
4195 | lttngUstLogHandler.close(); | |
4196 | } | |
4197 | } | |
4198 | ---- | |
4199 | ||
4200 | Build this example: | |
4201 | ||
4202 | [role="term"] | |
4203 | ---- | |
ded02698 | 4204 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar Test.java |
7adf7ee2 PP |
4205 | ---- |
4206 | ||
4207 | <<creating-destroying-tracing-sessions,Create a tracing session>>, | |
4208 | <<enabling-disabling-events,create an event rule>> matching the | |
4209 | `jello` JUL logger, and <<basic-tracing-session-control,start tracing>>: | |
4210 | ||
4211 | [role="term"] | |
4212 | ---- | |
ded02698 PP |
4213 | $ lttng create |
4214 | $ lttng enable-event --jul jello | |
4215 | $ lttng start | |
7adf7ee2 PP |
4216 | ---- |
4217 | ||
4218 | Run the compiled class: | |
4219 | ||
4220 | [role="term"] | |
4221 | ---- | |
ded02698 | 4222 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar:. Test |
7adf7ee2 PP |
4223 | ---- |
4224 | ||
4225 | <<basic-tracing-session-control,Stop tracing>> and inspect the | |
4226 | recorded events: | |
4227 | ||
4228 | [role="term"] | |
4229 | ---- | |
ded02698 PP |
4230 | $ lttng stop |
4231 | $ lttng view | |
7adf7ee2 PP |
4232 | ---- |
4233 | ==== | |
4234 | ||
44eda56c PP |
4235 | In the resulting trace, an <<event,event record>> generated by a Java |
4236 | application using `java.util.logging` is named `lttng_jul:event` and | |
4237 | has the following fields: | |
4238 | ||
4239 | `msg`:: | |
4240 | Log record's message. | |
4241 | ||
4242 | `logger_name`:: | |
4243 | Logger name. | |
4244 | ||
4245 | `class_name`:: | |
4246 | Name of the class in which the log statement was executed. | |
4247 | ||
4248 | `method_name`:: | |
4249 | Name of the method in which the log statement was executed. | |
4250 | ||
4251 | `long_millis`:: | |
4252 | Logging time (timestamp in milliseconds). | |
4253 | ||
4254 | `int_loglevel`:: | |
4255 | Log level integer value. | |
4256 | ||
4257 | `int_threadid`:: | |
4258 | ID of the thread in which the log statement was executed. | |
4259 | ||
7adf7ee2 PP |
4260 | You can use the opt:lttng-enable-event(1):--loglevel or |
4261 | opt:lttng-enable-event(1):--loglevel-only option of the | |
4262 | man:lttng-enable-event(1) command to target a range of JUL log levels | |
4263 | or a specific JUL log level. | |
4264 | ||
4265 | ||
4266 | [role="since-2.8"] | |
4267 | [[log4j]] | |
4268 | ==== Use the LTTng-UST Java agent for Apache log4j | |
4269 | ||
4270 | To use the LTTng-UST Java agent in a Java application which uses | |
4271 | Apache log4j 1.2: | |
4272 | ||
4273 | . In the Java application's source code, import the LTTng-UST | |
4274 | log appender package for Apache log4j: | |
4275 | + | |
4276 | -- | |
4277 | [source,java] | |
4278 | ---- | |
4279 | import org.lttng.ust.agent.log4j.LttngLogAppender; | |
4280 | ---- | |
4281 | -- | |
4282 | ||
4283 | . Create an LTTng-UST log4j log appender: | |
4284 | + | |
4285 | -- | |
4286 | [source,java] | |
4287 | ---- | |
4288 | Appender lttngUstLogAppender = new LttngLogAppender(); | |
4289 | ---- | |
4290 | -- | |
4291 | ||
4292 | . Add this appender to the log4j loggers which should emit LTTng events: | |
4293 | + | |
4294 | -- | |
4295 | [source,java] | |
4296 | ---- | |
4297 | Logger myLogger = Logger.getLogger("some-logger"); | |
4298 | ||
4299 | myLogger.addAppender(lttngUstLogAppender); | |
4300 | ---- | |
4301 | -- | |
4302 | ||
4303 | . Use Apache log4j log statements and configuration as usual. The | |
4304 | loggers with an attached LTTng-UST log appender can emit LTTng events. | |
4305 | ||
4306 | . Before exiting the application, remove the LTTng-UST log appender from | |
4307 | the loggers attached to it and call its `close()` method: | |
4308 | + | |
4309 | -- | |
4310 | [source,java] | |
4311 | ---- | |
4312 | myLogger.removeAppender(lttngUstLogAppender); | |
4313 | lttngUstLogAppender.close(); | |
4314 | ---- | |
4315 | -- | |
4316 | + | |
4317 | This is not strictly necessary, but it is recommended for a clean | |
4318 | disposal of the appender's resources. | |
4319 | ||
4320 | . Include the LTTng-UST Java agent's common and log4j-specific JAR | |
4321 | files, path:{lttng-ust-agent-common.jar} and | |
4322 | path:{lttng-ust-agent-log4j.jar}, in the | |
4323 | https://docs.oracle.com/javase/tutorial/essential/environment/paths.html[class | |
4324 | path] when you build the Java application. | |
4325 | + | |
4326 | The JAR files are typically located in dir:{/usr/share/java}. | |
4327 | + | |
4328 | IMPORTANT: The LTTng-UST Java agent must be | |
4329 | <<installing-lttng,installed>> for the logging framework your | |
4330 | application uses. | |
4331 | ||
4332 | .Use the LTTng-UST Java agent for Apache log4j. | |
4333 | ==== | |
4334 | [source,java] | |
4335 | .path:{Test.java} | |
4336 | ---- | |
4337 | import org.apache.log4j.Appender; | |
4338 | import org.apache.log4j.Logger; | |
4339 | import org.lttng.ust.agent.log4j.LttngLogAppender; | |
4340 | ||
4341 | public class Test | |
4342 | { | |
4343 | private static final int answer = 42; | |
4344 | ||
4345 | public static void main(String[] argv) throws Exception | |
4346 | { | |
4347 | // Create a logger | |
4348 | Logger logger = Logger.getLogger("jello"); | |
4349 | ||
4350 | // Create an LTTng-UST log appender | |
4351 | Appender lttngUstLogAppender = new LttngLogAppender(); | |
4352 | ||
4353 | // Add the LTTng-UST log appender to our logger | |
4354 | logger.addAppender(lttngUstLogAppender); | |
4355 | ||
4356 | // Log at will! | |
4357 | logger.info("some info"); | |
4358 | logger.warn("some warning"); | |
4359 | Thread.sleep(500); | |
4360 | logger.debug("debug information; the answer is " + answer); | |
4361 | Thread.sleep(123); | |
4362 | logger.fatal("error!"); | |
4363 | ||
4364 | // Not mandatory, but cleaner | |
4365 | logger.removeAppender(lttngUstLogAppender); | |
4366 | lttngUstLogAppender.close(); | |
4367 | } | |
4368 | } | |
4369 | ||
4370 | ---- | |
4371 | ||
4372 | Build this example (`$LOG4JPATH` is the path to the Apache log4j JAR | |
4373 | file): | |
4374 | ||
4375 | [role="term"] | |
4376 | ---- | |
ded02698 | 4377 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-log4j.jar:$LOG4JPATH Test.java |
7adf7ee2 PP |
4378 | ---- |
4379 | ||
4380 | <<creating-destroying-tracing-sessions,Create a tracing session>>, | |
4381 | <<enabling-disabling-events,create an event rule>> matching the | |
4382 | `jello` log4j logger, and <<basic-tracing-session-control,start tracing>>: | |
4383 | ||
4384 | [role="term"] | |
4385 | ---- | |
ded02698 PP |
4386 | $ lttng create |
4387 | $ lttng enable-event --log4j jello | |
4388 | $ lttng start | |
7adf7ee2 PP |
4389 | ---- |
4390 | ||
4391 | Run the compiled class: | |
4392 | ||
4393 | [role="term"] | |
4394 | ---- | |
ded02698 | 4395 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-log4j.jar:$LOG4JPATH:. Test |
7adf7ee2 PP |
4396 | ---- |
4397 | ||
4398 | <<basic-tracing-session-control,Stop tracing>> and inspect the | |
4399 | recorded events: | |
4400 | ||
4401 | [role="term"] | |
4402 | ---- | |
ded02698 PP |
4403 | $ lttng stop |
4404 | $ lttng view | |
7adf7ee2 PP |
4405 | ---- |
4406 | ==== | |
4407 | ||
44eda56c PP |
4408 | In the resulting trace, an <<event,event record>> generated by a Java |
4409 | application using log4j is named `lttng_log4j:event` and | |
4410 | has the following fields: | |
4411 | ||
4412 | `msg`:: | |
4413 | Log record's message. | |
4414 | ||
4415 | `logger_name`:: | |
4416 | Logger name. | |
4417 | ||
4418 | `class_name`:: | |
4419 | Name of the class in which the log statement was executed. | |
4420 | ||
4421 | `method_name`:: | |
4422 | Name of the method in which the log statement was executed. | |
4423 | ||
4424 | `filename`:: | |
4425 | Name of the file in which the executed log statement is located. | |
4426 | ||
4427 | `line_number`:: | |
4428 | Line number at which the log statement was executed. | |
4429 | ||
4430 | `timestamp`:: | |
4431 | Logging timestamp. | |
4432 | ||
4433 | `int_loglevel`:: | |
4434 | Log level integer value. | |
4435 | ||
4436 | `thread_name`:: | |
4437 | Name of the Java thread in which the log statement was executed. | |
4438 | ||
7adf7ee2 PP |
4439 | You can use the opt:lttng-enable-event(1):--loglevel or |
4440 | opt:lttng-enable-event(1):--loglevel-only option of the | |
4441 | man:lttng-enable-event(1) command to target a range of Apache log4j log levels | |
4442 | or a specific log4j log level. | |
4443 | ||
4444 | ||
4445 | [role="since-2.8"] | |
4446 | [[java-application-context]] | |
4447 | ==== Provide application-specific context fields in a Java application | |
4448 | ||
4449 | A Java application-specific context field is a piece of state provided | |
4450 | by the application which <<adding-context,you can add>>, using the | |
4451 | man:lttng-add-context(1) command, to each <<event,event record>> | |
4452 | produced by the log statements of this application. | |
4453 | ||
4454 | For example, a given object might have a current request ID variable. | |
4455 | You can create a context information retriever for this object and | |
4456 | assign a name to this current request ID. You can then, using the | |
4457 | man:lttng-add-context(1) command, add this context field by name to | |
4458 | the JUL or log4j <<channel,channel>>. | |
4459 | ||
4460 | To provide application-specific context fields in a Java application: | |
4461 | ||
4462 | . In the Java application's source code, import the LTTng-UST | |
4463 | Java agent context classes and interfaces: | |
4464 | + | |
4465 | -- | |
4466 | [source,java] | |
4467 | ---- | |
4468 | import org.lttng.ust.agent.context.ContextInfoManager; | |
4469 | import org.lttng.ust.agent.context.IContextInfoRetriever; | |
4470 | ---- | |
4471 | -- | |
4472 | ||
4473 | . Create a context information retriever class, that is, a class which | |
4474 | implements the `IContextInfoRetriever` interface: | |
4475 | + | |
4476 | -- | |
4477 | [source,java] | |
4478 | ---- | |
4479 | class MyContextInfoRetriever implements IContextInfoRetriever | |
4480 | { | |
4481 | @Override | |
4482 | public Object retrieveContextInfo(String key) | |
4483 | { | |
4484 | if (key.equals("intCtx")) { | |
4485 | return (short) 17; | |
4486 | } else if (key.equals("strContext")) { | |
4487 | return "context value!"; | |
4488 | } else { | |
4489 | return null; | |
4490 | } | |
4491 | } | |
4492 | } | |
4493 | ---- | |
4494 | -- | |
4495 | + | |
4496 | This `retrieveContextInfo()` method is the only member of the | |
4497 | `IContextInfoRetriever` interface. Its role is to return the current | |
4498 | value of a state by name to create a context field. The names of the | |
4499 | context fields and which state variables they return depends on your | |
4500 | specific scenario. | |
4501 | + | |
4502 | All primitive types and objects are supported as context fields. | |
4503 | When `retrieveContextInfo()` returns an object, the context field | |
4504 | serializer calls its `toString()` method to add a string field to | |
4505 | event records. The method can also return `null`, which means that | |
4506 | no context field is available for the required name. | |
4507 | ||
4508 | . Register an instance of your context information retriever class to | |
4509 | the context information manager singleton: | |
4510 | + | |
4511 | -- | |
4512 | [source,java] | |
4513 | ---- | |
4514 | IContextInfoRetriever cir = new MyContextInfoRetriever(); | |
4515 | ContextInfoManager cim = ContextInfoManager.getInstance(); | |
4516 | cim.registerContextInfoRetriever("retrieverName", cir); | |
4517 | ---- | |
4518 | -- | |
4519 | ||
4520 | . Before exiting the application, remove your context information | |
4521 | retriever from the context information manager singleton: | |
4522 | + | |
4523 | -- | |
4524 | [source,java] | |
4525 | ---- | |
4526 | ContextInfoManager cim = ContextInfoManager.getInstance(); | |
4527 | cim.unregisterContextInfoRetriever("retrieverName"); | |
4528 | ---- | |
4529 | -- | |
4530 | + | |
4531 | This is not strictly necessary, but it is recommended for a clean | |
4532 | disposal of some manager's resources. | |
4533 | ||
4534 | . Build your Java application with LTTng-UST Java agent support as | |
4535 | usual, following the procedure for either the <<jul,JUL>> or | |
4536 | <<log4j,Apache log4j>> framework. | |
4537 | ||
4538 | ||
4539 | .Provide application-specific context fields in a Java application. | |
4540 | ==== | |
4541 | [source,java] | |
4542 | .path:{Test.java} | |
4543 | ---- | |
4544 | import java.util.logging.Handler; | |
4545 | import java.util.logging.Logger; | |
4546 | import org.lttng.ust.agent.jul.LttngLogHandler; | |
4547 | import org.lttng.ust.agent.context.ContextInfoManager; | |
4548 | import org.lttng.ust.agent.context.IContextInfoRetriever; | |
4549 | ||
4550 | public class Test | |
4551 | { | |
4552 | // Our context information retriever class | |
4553 | private static class MyContextInfoRetriever | |
4554 | implements IContextInfoRetriever | |
4555 | { | |
4556 | @Override | |
4557 | public Object retrieveContextInfo(String key) { | |
4558 | if (key.equals("intCtx")) { | |
4559 | return (short) 17; | |
4560 | } else if (key.equals("strContext")) { | |
4561 | return "context value!"; | |
4562 | } else { | |
4563 | return null; | |
4564 | } | |
4565 | } | |
4566 | } | |
4567 | ||
4568 | private static final int answer = 42; | |
4569 | ||
4570 | public static void main(String args[]) throws Exception | |
4571 | { | |
4572 | // Get the context information manager instance | |
4573 | ContextInfoManager cim = ContextInfoManager.getInstance(); | |
4574 | ||
4575 | // Create and register our context information retriever | |
4576 | IContextInfoRetriever cir = new MyContextInfoRetriever(); | |
4577 | cim.registerContextInfoRetriever("myRetriever", cir); | |
4578 | ||
4579 | // Create a logger | |
4580 | Logger logger = Logger.getLogger("jello"); | |
4581 | ||
4582 | // Create an LTTng-UST log handler | |
4583 | Handler lttngUstLogHandler = new LttngLogHandler(); | |
4584 | ||
4585 | // Add the LTTng-UST log handler to our logger | |
4586 | logger.addHandler(lttngUstLogHandler); | |
4587 | ||
4588 | // Log at will! | |
4589 | logger.info("some info"); | |
4590 | logger.warning("some warning"); | |
4591 | Thread.sleep(500); | |
4592 | logger.finer("finer information; the answer is " + answer); | |
4593 | Thread.sleep(123); | |
4594 | logger.severe("error!"); | |
4595 | ||
4596 | // Not mandatory, but cleaner | |
4597 | logger.removeHandler(lttngUstLogHandler); | |
4598 | lttngUstLogHandler.close(); | |
4599 | cim.unregisterContextInfoRetriever("myRetriever"); | |
4600 | } | |
4601 | } | |
4602 | ---- | |
4603 | ||
4604 | Build this example: | |
4605 | ||
4606 | [role="term"] | |
4607 | ---- | |
ded02698 | 4608 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar Test.java |
7adf7ee2 PP |
4609 | ---- |
4610 | ||
4611 | <<creating-destroying-tracing-sessions,Create a tracing session>> | |
4612 | and <<enabling-disabling-events,create an event rule>> matching the | |
4613 | `jello` JUL logger: | |
4614 | ||
4615 | [role="term"] | |
4616 | ---- | |
ded02698 PP |
4617 | $ lttng create |
4618 | $ lttng enable-event --jul jello | |
7adf7ee2 PP |
4619 | ---- |
4620 | ||
4621 | <<adding-context,Add the application-specific context fields>> to the | |
4622 | JUL channel: | |
4623 | ||
4624 | [role="term"] | |
4625 | ---- | |
ded02698 PP |
4626 | $ lttng add-context --jul --type='$app.myRetriever:intCtx' |
4627 | $ lttng add-context --jul --type='$app.myRetriever:strContext' | |
7adf7ee2 PP |
4628 | ---- |
4629 | ||
4630 | <<basic-tracing-session-control,Start tracing>>: | |
4631 | ||
4632 | [role="term"] | |
4633 | ---- | |
ded02698 | 4634 | $ lttng start |
7adf7ee2 PP |
4635 | ---- |
4636 | ||
4637 | Run the compiled class: | |
4638 | ||
4639 | [role="term"] | |
4640 | ---- | |
ded02698 | 4641 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar:. Test |
7adf7ee2 PP |
4642 | ---- |
4643 | ||
4644 | <<basic-tracing-session-control,Stop tracing>> and inspect the | |
4645 | recorded events: | |
4646 | ||
4647 | [role="term"] | |
4648 | ---- | |
ded02698 PP |
4649 | $ lttng stop |
4650 | $ lttng view | |
7adf7ee2 PP |
4651 | ---- |
4652 | ==== | |
4653 | ||
4654 | ||
4655 | [role="since-2.7"] | |
4656 | [[python-application]] | |
4657 | === User space Python agent | |
4658 | ||
4659 | You can instrument a Python 2 or Python 3 application which uses the | |
4660 | standard https://docs.python.org/3/library/logging.html[`logging`] | |
4661 | package. | |
4662 | ||
4663 | Each log statement emits an LTTng event once the | |
4664 | application module imports the | |
4665 | <<lttng-ust-agents,LTTng-UST Python agent>> package. | |
4666 | ||
4667 | [role="img-100"] | |
4668 | .A Python application importing the LTTng-UST Python agent. | |
4669 | image::python-app.png[] | |
4670 | ||
4671 | To use the LTTng-UST Python agent: | |
4672 | ||
4673 | . In the Python application's source code, import the LTTng-UST Python | |
4674 | agent: | |
4675 | + | |
4676 | -- | |
4677 | [source,python] | |
4678 | ---- | |
4679 | import lttngust | |
4680 | ---- | |
4681 | -- | |
4682 | + | |
4683 | The LTTng-UST Python agent automatically adds its logging handler to the | |
4684 | root logger at import time. | |
4685 | + | |
4686 | Any log statement that the application executes before this import does | |
4687 | not emit an LTTng event. | |
4688 | + | |
4689 | IMPORTANT: The LTTng-UST Python agent must be | |
4690 | <<installing-lttng,installed>>. | |
4691 | ||
4692 | . Use log statements and logging configuration as usual. | |
4693 | Since the LTTng-UST Python agent adds a handler to the _root_ | |
4694 | logger, you can trace any log statement from any logger. | |
4695 | ||
4696 | .Use the LTTng-UST Python agent. | |
4697 | ==== | |
4698 | [source,python] | |
4699 | .path:{test.py} | |
4700 | ---- | |
4701 | import lttngust | |
4702 | import logging | |
4703 | import time | |
4704 | ||
4705 | ||
4706 | def example(): | |
4707 | logging.basicConfig() | |
4708 | logger = logging.getLogger('my-logger') | |
4709 | ||
4710 | while True: | |
4711 | logger.debug('debug message') | |
4712 | logger.info('info message') | |
4713 | logger.warn('warn message') | |
4714 | logger.error('error message') | |
4715 | logger.critical('critical message') | |
4716 | time.sleep(1) | |
4717 | ||
4718 | ||
4719 | if __name__ == '__main__': | |
4720 | example() | |
4721 | ---- | |
4722 | ||
4723 | NOTE: `logging.basicConfig()`, which adds to the root logger a basic | |
4724 | logging handler which prints to the standard error stream, is not | |
4725 | strictly required for LTTng-UST tracing to work, but in versions of | |
4726 | Python preceding 3.2, you could see a warning message which indicates | |
4727 | that no handler exists for the logger `my-logger`. | |
4728 | ||
4729 | <<creating-destroying-tracing-sessions,Create a tracing session>>, | |
4730 | <<enabling-disabling-events,create an event rule>> matching the | |
4731 | `my-logger` Python logger, and <<basic-tracing-session-control,start | |
4732 | tracing>>: | |
4733 | ||
4734 | [role="term"] | |
4735 | ---- | |
ded02698 PP |
4736 | $ lttng create |
4737 | $ lttng enable-event --python my-logger | |
4738 | $ lttng start | |
7adf7ee2 PP |
4739 | ---- |
4740 | ||
4741 | Run the Python script: | |
4742 | ||
4743 | [role="term"] | |
4744 | ---- | |
ded02698 | 4745 | $ python test.py |
7adf7ee2 PP |
4746 | ---- |
4747 | ||
4748 | <<basic-tracing-session-control,Stop tracing>> and inspect the recorded | |
4749 | events: | |
4750 | ||
4751 | [role="term"] | |
4752 | ---- | |
ded02698 PP |
4753 | $ lttng stop |
4754 | $ lttng view | |
7adf7ee2 PP |
4755 | ---- |
4756 | ==== | |
4757 | ||
44eda56c PP |
4758 | In the resulting trace, an <<event,event record>> generated by a Python |
4759 | application is named `lttng_python:event` and has the following fields: | |
4760 | ||
4761 | `asctime`:: | |
4762 | Logging time (string). | |
4763 | ||
4764 | `msg`:: | |
4765 | Log record's message. | |
4766 | ||
4767 | `logger_name`:: | |
4768 | Logger name. | |
4769 | ||
4770 | `funcName`:: | |
4771 | Name of the function in which the log statement was executed. | |
4772 | ||
4773 | `lineno`:: | |
4774 | Line number at which the log statement was executed. | |
4775 | ||
4776 | `int_loglevel`:: | |
4777 | Log level integer value. | |
4778 | ||
4779 | `thread`:: | |
4780 | ID of the Python thread in which the log statement was executed. | |
4781 | ||
4782 | `threadName`:: | |
4783 | Name of the Python thread in which the log statement was executed. | |
4784 | ||
7adf7ee2 PP |
4785 | You can use the opt:lttng-enable-event(1):--loglevel or |
4786 | opt:lttng-enable-event(1):--loglevel-only option of the | |
4787 | man:lttng-enable-event(1) command to target a range of Python log levels | |
4788 | or a specific Python log level. | |
4789 | ||
4790 | When an application imports the LTTng-UST Python agent, the agent tries | |
4791 | to register to a <<lttng-sessiond,session daemon>>. Note that you must | |
4792 | <<start-sessiond,start the session daemon>> _before_ you run the Python | |
4793 | application. If a session daemon is found, the agent tries to register | |
4794 | to it during 5{nbsp}seconds, after which the application continues | |
4795 | without LTTng tracing support. You can override this timeout value with | |
4796 | the env:LTTNG_UST_PYTHON_REGISTER_TIMEOUT environment variable | |
4797 | (milliseconds). | |
4798 | ||
4799 | If the session daemon stops while a Python application with an imported | |
4800 | LTTng-UST Python agent runs, the agent retries to connect and to | |
4801 | register to a session daemon every 3{nbsp}seconds. You can override this | |
4802 | delay with the env:LTTNG_UST_PYTHON_REGISTER_RETRY_DELAY environment | |
4803 | variable. | |
4804 | ||
4805 | ||
4806 | [role="since-2.5"] | |
4807 | [[proc-lttng-logger-abi]] | |
4808 | === LTTng logger | |
4809 | ||
4810 | The `lttng-tracer` Linux kernel module, part of | |
4811 | <<lttng-modules,LTTng-modules>>, creates the special LTTng logger file | |
4812 | path:{/proc/lttng-logger} when it's loaded. Any application can write | |
4813 | text data to this file to emit an LTTng event. | |
4814 | ||
4815 | [role="img-100"] | |
4816 | .An application writes to the LTTng logger file to emit an LTTng event. | |
4817 | image::lttng-logger.png[] | |
4818 | ||
4819 | The LTTng logger is the quickest method--not the most efficient, | |
4820 | however--to add instrumentation to an application. It is designed | |
4821 | mostly to instrument shell scripts: | |
4822 | ||
4823 | [role="term"] | |
4824 | ---- | |
ded02698 | 4825 | $ echo "Some message, some $variable" > /proc/lttng-logger |
7adf7ee2 PP |
4826 | ---- |
4827 | ||
4828 | Any event that the LTTng logger emits is named `lttng_logger` and | |
4829 | belongs to the Linux kernel <<domain,tracing domain>>. However, unlike | |
4830 | other instrumentation points in the kernel tracing domain, **any Unix | |
4831 | user** can <<enabling-disabling-events,create an event rule>> which | |
2e333859 PP |
4832 | matches its event name, not only the root user or users in the |
4833 | <<tracing-group,tracing group>>. | |
7adf7ee2 PP |
4834 | |
4835 | To use the LTTng logger: | |
4836 | ||
4837 | * From any application, write text data to the path:{/proc/lttng-logger} | |
4838 | file. | |
4839 | ||
4840 | The `msg` field of `lttng_logger` event records contains the | |
4841 | recorded message. | |
4842 | ||
4843 | NOTE: The maximum message length of an LTTng logger event is | |
4844 | 1024{nbsp}bytes. Writing more than this makes the LTTng logger emit more | |
4845 | than one event to contain the remaining data. | |
4846 | ||
4847 | You should not use the LTTng logger to trace a user application which | |
4848 | can be instrumented in a more efficient way, namely: | |
4849 | ||
4850 | * <<c-application,C and $$C++$$ applications>>. | |
4851 | * <<java-application,Java applications>>. | |
4852 | * <<python-application,Python applications>>. | |
4853 | ||
4854 | .Use the LTTng logger. | |
4855 | ==== | |
4856 | [source,bash] | |
4857 | .path:{test.bash} | |
4858 | ---- | |
4859 | echo 'Hello, World!' > /proc/lttng-logger | |
4860 | sleep 2 | |
4861 | df --human-readable --print-type / > /proc/lttng-logger | |
4862 | ---- | |
4863 | ||
4864 | <<creating-destroying-tracing-sessions,Create a tracing session>>, | |
4865 | <<enabling-disabling-events,create an event rule>> matching the | |
4866 | `lttng_logger` Linux kernel tracepoint, and | |
4867 | <<basic-tracing-session-control,start tracing>>: | |
4868 | ||
4869 | [role="term"] | |
4870 | ---- | |
ded02698 PP |
4871 | $ lttng create |
4872 | $ lttng enable-event --kernel lttng_logger | |
4873 | $ lttng start | |
7adf7ee2 PP |
4874 | ---- |
4875 | ||
4876 | Run the Bash script: | |
4877 | ||
4878 | [role="term"] | |
4879 | ---- | |
ded02698 | 4880 | $ bash test.bash |
7adf7ee2 PP |
4881 | ---- |
4882 | ||
4883 | <<basic-tracing-session-control,Stop tracing>> and inspect the recorded | |
4884 | events: | |
4885 | ||
4886 | [role="term"] | |
4887 | ---- | |
ded02698 PP |
4888 | $ lttng stop |
4889 | $ lttng view | |
7adf7ee2 PP |
4890 | ---- |
4891 | ==== | |
4892 | ||
4893 | ||
4894 | [[instrumenting-linux-kernel]] | |
4895 | === LTTng kernel tracepoints | |
4896 | ||
4897 | NOTE: This section shows how to _add_ instrumentation points to the | |
4898 | Linux kernel. The kernel's subsystems are already thoroughly | |
4899 | instrumented at strategic places for LTTng when you | |
4900 | <<installing-lttng,install>> the <<lttng-modules,LTTng-modules>> | |
4901 | package. | |
4902 | ||
4903 | //// | |
4904 | There are two methods to instrument the Linux kernel: | |
4905 | ||
4906 | . <<linux-add-lttng-layer,Add an LTTng layer>> over an existing ftrace | |
4907 | tracepoint which uses the `TRACE_EVENT()` API. | |
4908 | + | |
4909 | Choose this if you want to instrumentation a Linux kernel tree with an | |
4910 | instrumentation point compatible with ftrace, perf, and SystemTap. | |
4911 | ||
4912 | . Use an <<linux-lttng-tracepoint-event,LTTng-only approach>> to | |
4913 | instrument an out-of-tree kernel module. | |
4914 | + | |
4915 | Choose this if you don't need ftrace, perf, or SystemTap support. | |
4916 | //// | |
4917 | ||
4918 | ||
4919 | [[linux-add-lttng-layer]] | |
4920 | ==== [[instrumenting-linux-kernel-itself]][[mainline-trace-event]][[lttng-adaptation-layer]]Add an LTTng layer to an existing ftrace tracepoint | |
4921 | ||
4922 | This section shows how to add an LTTng layer to existing ftrace | |
4923 | instrumentation using the `TRACE_EVENT()` API. | |
4924 | ||
4925 | This section does not document the `TRACE_EVENT()` macro. You can | |
4926 | read the following articles to learn more about this API: | |
4927 | ||
4928 | * http://lwn.net/Articles/379903/[Using the TRACE_EVENT() macro (Part 1)] | |
4929 | * http://lwn.net/Articles/381064/[Using the TRACE_EVENT() macro (Part 2)] | |
4930 | * http://lwn.net/Articles/383362/[Using the TRACE_EVENT() macro (Part 3)] | |
4931 | ||
4932 | The following procedure assumes that your ftrace tracepoints are | |
4933 | correctly defined in their own header and that they are created in | |
4934 | one source file using the `CREATE_TRACE_POINTS` definition. | |
4935 | ||
4936 | To add an LTTng layer over an existing ftrace tracepoint: | |
4937 | ||
4938 | . Make sure the following kernel configuration options are | |
4939 | enabled: | |
4940 | + | |
4941 | -- | |
4942 | * `CONFIG_MODULES` | |
4943 | * `CONFIG_KALLSYMS` | |
4944 | * `CONFIG_HIGH_RES_TIMERS` | |
4945 | * `CONFIG_TRACEPOINTS` | |
4946 | -- | |
4947 | ||
4948 | . Build the Linux source tree with your custom ftrace tracepoints. | |
4949 | . Boot the resulting Linux image on your target system. | |
4950 | + | |
4951 | Confirm that the tracepoints exist by looking for their names in the | |
4952 | dir:{/sys/kernel/debug/tracing/events/subsys} directory, where `subsys` | |
4953 | is your subsystem's name. | |
4954 | ||
4955 | . Get a copy of the latest LTTng-modules{nbsp}{revision}: | |
4956 | + | |
4957 | -- | |
4958 | [role="term"] | |
4959 | ---- | |
ded02698 | 4960 | $ cd $(mktemp -d) && |
7adf7ee2 PP |
4961 | wget http://lttng.org/files/lttng-modules/lttng-modules-latest-2.8.tar.bz2 && |
4962 | tar -xf lttng-modules-latest-2.8.tar.bz2 && | |
4963 | cd lttng-modules-2.8.* | |
4964 | ---- | |
4965 | -- | |
4966 | ||
4967 | . In dir:{instrumentation/events/lttng-module}, relative to the root | |
4968 | of the LTTng-modules source tree, create a header file named | |
4969 | +__subsys__.h+ for your custom subsystem +__subsys__+ and write your | |
4970 | LTTng-modules tracepoint definitions using the LTTng-modules | |
4971 | macros in it. | |
4972 | + | |
4973 | Start with this template: | |
4974 | + | |
4975 | -- | |
4976 | [source,c] | |
4977 | .path:{instrumentation/events/lttng-module/my_subsys.h} | |
4978 | ---- | |
4979 | #undef TRACE_SYSTEM | |
4980 | #define TRACE_SYSTEM my_subsys | |
4981 | ||
4982 | #if !defined(_LTTNG_MY_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) | |
4983 | #define _LTTNG_MY_SUBSYS_H | |
4984 | ||
4985 | #include "../../../probes/lttng-tracepoint-event.h" | |
4986 | #include <linux/tracepoint.h> | |
4987 | ||
4988 | LTTNG_TRACEPOINT_EVENT( | |
4989 | /* | |
4990 | * Format is identical to TRACE_EVENT()'s version for the three | |
4991 | * following macro parameters: | |
4992 | */ | |
4993 | my_subsys_my_event, | |
4994 | TP_PROTO(int my_int, const char *my_string), | |
4995 | TP_ARGS(my_int, my_string), | |
4996 | ||
4997 | /* LTTng-modules specific macros */ | |
4998 | TP_FIELDS( | |
4999 | ctf_integer(int, my_int_field, my_int) | |
5000 | ctf_string(my_bar_field, my_bar) | |
5001 | ) | |
5002 | ) | |
5003 | ||
5004 | #endif /* !defined(_LTTNG_MY_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) */ | |
5005 | ||
5006 | #include "../../../probes/define_trace.h" | |
5007 | ---- | |
5008 | -- | |
5009 | + | |
5010 | The entries in the `TP_FIELDS()` section are the list of fields for the | |
5011 | LTTng tracepoint. This is similar to the `TP_STRUCT__entry()` part of | |
5012 | ftrace's `TRACE_EVENT()` macro. | |
5013 | + | |
5014 | See <<lttng-modules-tp-fields,Tracepoint fields macros>> for a | |
5015 | complete description of the available `ctf_*()` macros. | |
5016 | ||
5017 | . Create the LTTng-modules probe's kernel module C source file, | |
5018 | +probes/lttng-probe-__subsys__.c+, where +__subsys__+ is your | |
5019 | subsystem name: | |
5020 | + | |
5021 | -- | |
5022 | [source,c] | |
5023 | .path:{probes/lttng-probe-my-subsys.c} | |
5024 | ---- | |
5025 | #include <linux/module.h> | |
5026 | #include "../lttng-tracer.h" | |
5027 | ||
5028 | /* | |
5029 | * Build-time verification of mismatch between mainline | |
5030 | * TRACE_EVENT() arguments and the LTTng-modules adaptation | |
5031 | * layer LTTNG_TRACEPOINT_EVENT() arguments. | |
5032 | */ | |
5033 | #include <trace/events/my_subsys.h> | |
5034 | ||
5035 | /* Create LTTng tracepoint probes */ | |
5036 | #define LTTNG_PACKAGE_BUILD | |
5037 | #define CREATE_TRACE_POINTS | |
5038 | #define TRACE_INCLUDE_PATH ../instrumentation/events/lttng-module | |
5039 | ||
5040 | #include "../instrumentation/events/lttng-module/my_subsys.h" | |
5041 | ||
5042 | MODULE_LICENSE("GPL and additional rights"); | |
5043 | MODULE_AUTHOR("Your name <your-email>"); | |
5044 | MODULE_DESCRIPTION("LTTng my_subsys probes"); | |
5045 | MODULE_VERSION(__stringify(LTTNG_MODULES_MAJOR_VERSION) "." | |
5046 | __stringify(LTTNG_MODULES_MINOR_VERSION) "." | |
5047 | __stringify(LTTNG_MODULES_PATCHLEVEL_VERSION) | |
5048 | LTTNG_MODULES_EXTRAVERSION); | |
5049 | ---- | |
5050 | -- | |
5051 | ||
f4d8d998 | 5052 | . Edit path:{probes/KBuild} and add your new kernel module object |
7adf7ee2 PP |
5053 | next to the existing ones: |
5054 | + | |
5055 | -- | |
5056 | [source,make] | |
f4d8d998 | 5057 | .path:{probes/KBuild} |
7adf7ee2 PP |
5058 | ---- |
5059 | # ... | |
5060 | ||
5061 | obj-m += lttng-probe-module.o | |
5062 | obj-m += lttng-probe-power.o | |
5063 | ||
5064 | obj-m += lttng-probe-my-subsys.o | |
5065 | ||
5066 | # ... | |
5067 | ---- | |
5068 | -- | |
5069 | ||
5070 | . Build and install the LTTng kernel modules: | |
5071 | + | |
5072 | -- | |
5073 | [role="term"] | |
5074 | ---- | |
ded02698 PP |
5075 | $ make KERNELDIR=/path/to/linux |
5076 | # make modules_install && depmod -a | |
7adf7ee2 PP |
5077 | ---- |
5078 | -- | |
5079 | + | |
5080 | Replace `/path/to/linux` with the path to the Linux source tree where | |
5081 | you defined and used tracepoints with ftrace's `TRACE_EVENT()` macro. | |
5082 | ||
5083 | Note that you can also use the | |
5084 | <<lttng-tracepoint-event-code,`LTTNG_TRACEPOINT_EVENT_CODE()` macro>> | |
5085 | instead of `LTTNG_TRACEPOINT_EVENT()` to use custom local variables and | |
5086 | C code that need to be executed before the event fields are recorded. | |
5087 | ||
5088 | The best way to learn how to use the previous LTTng-modules macros is to | |
5089 | inspect the existing LTTng-modules tracepoint definitions in the | |
5090 | dir:{instrumentation/events/lttng-module} header files. Compare them | |
5091 | with the Linux kernel mainline versions in the | |
5092 | dir:{include/trace/events} directory of the Linux source tree. | |
5093 | ||
5094 | ||
5095 | [role="since-2.7"] | |
5096 | [[lttng-tracepoint-event-code]] | |
5097 | ===== Use custom C code to access the data for tracepoint fields | |
5098 | ||
5099 | Although we recommended to always use the | |
5100 | <<lttng-adaptation-layer,`LTTNG_TRACEPOINT_EVENT()`>> macro to describe | |
5101 | the arguments and fields of an LTTng-modules tracepoint when possible, | |
5102 | sometimes you need a more complex process to access the data that the | |
5103 | tracer records as event record fields. In other words, you need local | |
5104 | variables and multiple C{nbsp}statements instead of simple | |
5105 | argument-based expressions that you pass to the | |
5106 | <<lttng-modules-tp-fields,`ctf_*()` macros of `TP_FIELDS()`>>. | |
5107 | ||
5108 | You can use the `LTTNG_TRACEPOINT_EVENT_CODE()` macro instead of | |
5109 | `LTTNG_TRACEPOINT_EVENT()` to declare custom local variables and define | |
5110 | a block of C{nbsp}code to be executed before LTTng records the fields. | |
5111 | The structure of this macro is: | |
5112 | ||
5113 | [source,c] | |
5114 | .`LTTNG_TRACEPOINT_EVENT_CODE()` macro syntax. | |
5115 | ---- | |
5116 | LTTNG_TRACEPOINT_EVENT_CODE( | |
5117 | /* | |
5118 | * Format identical to the LTTNG_TRACEPOINT_EVENT() | |
5119 | * version for the following three macro parameters: | |
5120 | */ | |
5121 | my_subsys_my_event, | |
5122 | TP_PROTO(int my_int, const char *my_string), | |
5123 | TP_ARGS(my_int, my_string), | |
5124 | ||
5125 | /* Declarations of custom local variables */ | |
5126 | TP_locvar( | |
5127 | int a = 0; | |
5128 | unsigned long b = 0; | |
5129 | const char *name = "(undefined)"; | |
5130 | struct my_struct *my_struct; | |
5131 | ), | |
5132 | ||
5133 | /* | |
5134 | * Custom code which uses both tracepoint arguments | |
5135 | * (in TP_ARGS()) and local variables (in TP_locvar()). | |
5136 | * | |
5137 | * Local variables are actually members of a structure pointed | |
5138 | * to by the special variable tp_locvar. | |
5139 | */ | |
5140 | TP_code( | |
5141 | if (my_int) { | |
5142 | tp_locvar->a = my_int + 17; | |
5143 | tp_locvar->my_struct = get_my_struct_at(tp_locvar->a); | |
5144 | tp_locvar->b = my_struct_compute_b(tp_locvar->my_struct); | |
5145 | tp_locvar->name = my_struct_get_name(tp_locvar->my_struct); | |
5146 | put_my_struct(tp_locvar->my_struct); | |
5147 | ||
5148 | if (tp_locvar->b) { | |
5149 | tp_locvar->a = 1; | |
5150 | } | |
5151 | } | |
5152 | ), | |
5153 | ||
5154 | /* | |
5155 | * Format identical to the LTTNG_TRACEPOINT_EVENT() | |
5156 | * version for this, except that tp_locvar members can be | |
5157 | * used in the argument expression parameters of | |
5158 | * the ctf_*() macros. | |
5159 | */ | |
5160 | TP_FIELDS( | |
5161 | ctf_integer(unsigned long, my_struct_b, tp_locvar->b) | |
5162 | ctf_integer(int, my_struct_a, tp_locvar->a) | |
5163 | ctf_string(my_string_field, my_string) | |
5164 | ctf_string(my_struct_name, tp_locvar->name) | |
5165 | ) | |
5166 | ) | |
5167 | ---- | |
5168 | ||
5169 | IMPORTANT: The C code defined in `TP_code()` must not have any side | |
5170 | effects when executed. In particular, the code must not allocate | |
5171 | memory or get resources without deallocating this memory or putting | |
5172 | those resources afterwards. | |
5173 | ||
5174 | ||
5175 | [[instrumenting-linux-kernel-tracing]] | |
5176 | ==== Load and unload a custom probe kernel module | |
5177 | ||
5178 | You must load a <<lttng-adaptation-layer,created LTTng-modules probe | |
5179 | kernel module>> in the kernel before it can emit LTTng events. | |
5180 | ||
5181 | To load the default probe kernel modules and a custom probe kernel | |
5182 | module: | |
5183 | ||
5184 | * Use the opt:lttng-sessiond(8):--extra-kmod-probes option to give extra | |
5185 | probe modules to load when starting a root <<lttng-sessiond,session | |
5186 | daemon>>: | |
5187 | + | |
5188 | -- | |
5189 | .Load the `my_subsys`, `usb`, and the default probe modules. | |
5190 | ==== | |
5191 | [role="term"] | |
5192 | ---- | |
ded02698 | 5193 | # lttng-sessiond --extra-kmod-probes=my_subsys,usb |
7adf7ee2 PP |
5194 | ---- |
5195 | ==== | |
5196 | -- | |
5197 | + | |
5198 | You only need to pass the subsystem name, not the whole kernel module | |
5199 | name. | |
5200 | ||
5201 | To load _only_ a given custom probe kernel module: | |
5202 | ||
5203 | * Use the opt:lttng-sessiond(8):--kmod-probes option to give the probe | |
5204 | modules to load when starting a root session daemon: | |
5205 | + | |
5206 | -- | |
5207 | .Load only the `my_subsys` and `usb` probe modules. | |
5208 | ==== | |
5209 | [role="term"] | |
5210 | ---- | |
ded02698 | 5211 | # lttng-sessiond --kmod-probes=my_subsys,usb |
7adf7ee2 PP |
5212 | ---- |
5213 | ==== | |
5214 | -- | |
5215 | ||
5216 | To confirm that a probe module is loaded: | |
5217 | ||
5218 | * Use man:lsmod(8): | |
5219 | + | |
5220 | -- | |
5221 | [role="term"] | |
5222 | ---- | |
ded02698 | 5223 | $ lsmod | grep lttng_probe_usb |
7adf7ee2 PP |
5224 | ---- |
5225 | -- | |
5226 | ||
5227 | To unload the loaded probe modules: | |
5228 | ||
5229 | * Kill the session daemon with `SIGTERM`: | |
5230 | + | |
5231 | -- | |
5232 | [role="term"] | |
5233 | ---- | |
ded02698 | 5234 | # pkill lttng-sessiond |
7adf7ee2 PP |
5235 | ---- |
5236 | -- | |
5237 | + | |
5238 | You can also use man:modprobe(8)'s `--remove` option if the session | |
5239 | daemon terminates abnormally. | |
5240 | ||
5241 | ||
5242 | [[controlling-tracing]] | |
5243 | == Tracing control | |
5244 | ||
5245 | Once an application or a Linux kernel is | |
5246 | <<instrumenting,instrumented>> for LTTng tracing, | |
5247 | you can _trace_ it. | |
5248 | ||
5249 | This section is divided in topics on how to use the various | |
5250 | <<plumbing,components of LTTng>>, in particular the <<lttng-cli,cmd:lttng | |
5251 | command-line tool>>, to _control_ the LTTng daemons and tracers. | |
5252 | ||
5253 | NOTE: In the following subsections, we refer to an man:lttng(1) command | |
5254 | using its man page name. For example, instead of _Run the `create` | |
5255 | command to..._, we use _Run the man:lttng-create(1) command to..._. | |
5256 | ||
5257 | ||
5258 | [[start-sessiond]] | |
5259 | === Start a session daemon | |
5260 | ||
5261 | In some situations, you need to run a <<lttng-sessiond,session daemon>> | |
5262 | (man:lttng-sessiond(8)) _before_ you can use the man:lttng(1) | |
5263 | command-line tool. | |
5264 | ||
5265 | You will see the following error when you run a command while no session | |
5266 | daemon is running: | |
5267 | ||
5268 | ---- | |
5269 | Error: No session daemon is available | |
5270 | ---- | |
5271 | ||
5272 | The only command that automatically runs a session daemon is | |
5273 | man:lttng-create(1), which you use to | |
5274 | <<creating-destroying-tracing-sessions,create a tracing session>>. While | |
5275 | this is most of the time the first operation that you do, sometimes it's | |
5276 | not. Some examples are: | |
5277 | ||
5278 | * <<list-instrumentation-points,List the available instrumentation points>>. | |
5279 | * <<saving-loading-tracing-session,Load a tracing session configuration>>. | |
5280 | ||
5281 | [[tracing-group]] Each Unix user must have its own running session | |
5282 | daemon to trace user applications. The session daemon that the root user | |
5283 | starts is the only one allowed to control the LTTng kernel tracer. Users | |
5284 | that are part of the _tracing group_ can control the root session | |
5285 | daemon. The default tracing group name is `tracing`; you can set it to | |
5286 | something else with the opt:lttng-sessiond(8):--group option when you | |
5287 | start the root session daemon. | |
5288 | ||
5289 | To start a user session daemon: | |
5290 | ||
5291 | * Run man:lttng-sessiond(8): | |
5292 | + | |
5293 | -- | |
5294 | [role="term"] | |
5295 | ---- | |
ded02698 | 5296 | $ lttng-sessiond --daemonize |
7adf7ee2 PP |
5297 | ---- |
5298 | -- | |
5299 | ||
5300 | To start the root session daemon: | |
5301 | ||
5302 | * Run man:lttng-sessiond(8) as the root user: | |
5303 | + | |
5304 | -- | |
5305 | [role="term"] | |
5306 | ---- | |
ded02698 | 5307 | # lttng-sessiond --daemonize |
7adf7ee2 PP |
5308 | ---- |
5309 | -- | |
5310 | ||
5311 | In both cases, remove the opt:lttng-sessiond(8):--daemonize option to | |
5312 | start the session daemon in foreground. | |
5313 | ||
5314 | To stop a session daemon, use man:kill(1) on its process ID (standard | |
5315 | `TERM` signal). | |
5316 | ||
5317 | Note that some Linux distributions could manage the LTTng session daemon | |
5318 | as a service. In this case, you should use the service manager to | |
5319 | start, restart, and stop session daemons. | |
5320 | ||
5321 | ||
5322 | [[creating-destroying-tracing-sessions]] | |
5323 | === Create and destroy a tracing session | |
5324 | ||
5325 | Almost all the LTTng control operations happen in the scope of | |
5326 | a <<tracing-session,tracing session>>, which is the dialogue between the | |
5327 | <<lttng-sessiond,session daemon>> and you. | |
5328 | ||
5329 | To create a tracing session with a generated name: | |
5330 | ||
5331 | * Use the man:lttng-create(1) command: | |
5332 | + | |
5333 | -- | |
5334 | [role="term"] | |
5335 | ---- | |
ded02698 | 5336 | $ lttng create |
7adf7ee2 PP |
5337 | ---- |
5338 | -- | |
5339 | ||
5340 | The created tracing session's name is `auto` followed by the | |
5341 | creation date. | |
5342 | ||
5343 | To create a tracing session with a specific name: | |
5344 | ||
5345 | * Use the optional argument of the man:lttng-create(1) command: | |
5346 | + | |
5347 | -- | |
5348 | [role="term"] | |
5349 | ---- | |
ded02698 | 5350 | $ lttng create my-session |
7adf7ee2 PP |
5351 | ---- |
5352 | -- | |
5353 | + | |
5354 | Replace `my-session` with the specific tracing session name. | |
5355 | ||
5356 | LTTng appends the creation date to the created tracing session's name. | |
5357 | ||
5358 | LTTng writes the traces of a tracing session in | |
5359 | +$LTTNG_HOME/lttng-trace/__name__+ by default, where +__name__+ is the | |
5360 | name of the tracing session. Note that the env:LTTNG_HOME environment | |
5361 | variable defaults to `$HOME` if not set. | |
5362 | ||
5363 | To output LTTng traces to a non-default location: | |
5364 | ||
5365 | * Use the opt:lttng-create(1):--output option of the man:lttng-create(1) command: | |
5366 | + | |
5367 | -- | |
5368 | [role="term"] | |
5369 | ---- | |
ded02698 | 5370 | $ lttng create my-session --output=/tmp/some-directory |
7adf7ee2 PP |
5371 | ---- |
5372 | -- | |
5373 | ||
5374 | You may create as many tracing sessions as you wish. | |
5375 | ||
5376 | To list all the existing tracing sessions for your Unix user: | |
5377 | ||
5378 | * Use the man:lttng-list(1) command: | |
5379 | + | |
5380 | -- | |
5381 | [role="term"] | |
5382 | ---- | |
ded02698 | 5383 | $ lttng list |
7adf7ee2 PP |
5384 | ---- |
5385 | -- | |
5386 | ||
5387 | When you create a tracing session, it is set as the _current tracing | |
5388 | session_. The following man:lttng(1) commands operate on the current | |
5389 | tracing session when you don't specify one: | |
5390 | ||
5391 | [role="list-3-cols"] | |
5392 | * `add-context` | |
5393 | * `destroy` | |
5394 | * `disable-channel` | |
5395 | * `disable-event` | |
5396 | * `enable-channel` | |
5397 | * `enable-event` | |
5398 | * `load` | |
5399 | * `save` | |
5400 | * `snapshot` | |
5401 | * `start` | |
5402 | * `stop` | |
5403 | * `track` | |
5404 | * `untrack` | |
5405 | * `view` | |
5406 | ||
5407 | To change the current tracing session: | |
5408 | ||
5409 | * Use the man:lttng-set-session(1) command: | |
5410 | + | |
5411 | -- | |
5412 | [role="term"] | |
5413 | ---- | |
ded02698 | 5414 | $ lttng set-session new-session |
7adf7ee2 PP |
5415 | ---- |
5416 | -- | |
5417 | + | |
5418 | Replace `new-session` by the name of the new current tracing session. | |
5419 | ||
5420 | When you are done tracing in a given tracing session, you can destroy | |
5421 | it. This operation frees the resources taken by the tracing session | |
5422 | to destroy; it does not destroy the trace data that LTTng wrote for | |
5423 | this tracing session. | |
5424 | ||
5425 | To destroy the current tracing session: | |
5426 | ||
5427 | * Use the man:lttng-destroy(1) command: | |
5428 | + | |
5429 | -- | |
5430 | [role="term"] | |
5431 | ---- | |
ded02698 | 5432 | $ lttng destroy |
7adf7ee2 PP |
5433 | ---- |
5434 | -- | |
5435 | ||
5436 | ||
5437 | [[list-instrumentation-points]] | |
5438 | === List the available instrumentation points | |
5439 | ||
5440 | The <<lttng-sessiond,session daemon>> can query the running instrumented | |
5441 | user applications and the Linux kernel to get a list of available | |
5442 | instrumentation points. For the Linux kernel <<domain,tracing domain>>, | |
5443 | they are tracepoints and system calls. For the user space tracing | |
5444 | domain, they are tracepoints. For the other tracing domains, they are | |
5445 | logger names. | |
5446 | ||
5447 | To list the available instrumentation points: | |
5448 | ||
5449 | * Use the man:lttng-list(1) command with the requested tracing domain's | |
5450 | option amongst: | |
5451 | + | |
5452 | -- | |
5453 | * opt:lttng-list(1):--kernel: Linux kernel tracepoints (your Unix user | |
5454 | must be a root user, or it must be a member of the | |
5455 | <<tracing-group,tracing group>>). | |
5456 | * opt:lttng-list(1):--kernel with opt:lttng-list(1):--syscall: Linux | |
5457 | kernel system calls (your Unix user must be a root user, or it must be | |
5458 | a member of the tracing group). | |
5459 | * opt:lttng-list(1):--userspace: user space tracepoints. | |
5460 | * opt:lttng-list(1):--jul: `java.util.logging` loggers. | |
5461 | * opt:lttng-list(1):--log4j: Apache log4j loggers. | |
5462 | * opt:lttng-list(1):--python: Python loggers. | |
5463 | -- | |
5464 | ||
5465 | .List the available user space tracepoints. | |
5466 | ==== | |
5467 | [role="term"] | |
5468 | ---- | |
ded02698 | 5469 | $ lttng list --userspace |
7adf7ee2 PP |
5470 | ---- |
5471 | ==== | |
5472 | ||
5473 | .List the available Linux kernel system call tracepoints. | |
5474 | ==== | |
5475 | [role="term"] | |
5476 | ---- | |
ded02698 | 5477 | $ lttng list --kernel --syscall |
7adf7ee2 PP |
5478 | ---- |
5479 | ==== | |
5480 | ||
5481 | ||
5482 | [[enabling-disabling-events]] | |
5483 | === Create and enable an event rule | |
5484 | ||
5485 | Once you <<creating-destroying-tracing-sessions,create a tracing | |
5486 | session>>, you can create <<event,event rules>> with the | |
5487 | man:lttng-enable-event(1) command. | |
5488 | ||
5489 | You specify each condition with a command-line option. The available | |
5490 | condition options are shown in the following table. | |
5491 | ||
5492 | [role="growable",cols="asciidoc,asciidoc,default"] | |
5493 | .Condition command-line options for the man:lttng-enable-event(1) command. | |
5494 | |==== | |
5495 | |Option |Description |Applicable tracing domains | |
5496 | ||
5497 | | | |
5498 | One of: | |
5499 | ||
5500 | . `--syscall` | |
5501 | . +--probe=__ADDR__+ | |
5502 | . +--function=__ADDR__+ | |
5503 | ||
5504 | | | |
5505 | Instead of using the default _tracepoint_ instrumentation type, use: | |
5506 | ||
5507 | . A Linux system call. | |
5508 | . A Linux https://lwn.net/Articles/132196/[KProbe] (symbol or address). | |
5509 | . The entry and return points of a Linux function (symbol or address). | |
5510 | ||
5511 | |Linux kernel. | |
5512 | ||
5513 | |First positional argument. | |
5514 | ||
5515 | | | |
5516 | Tracepoint or system call name. In the case of a Linux KProbe or | |
5517 | function, this is a custom name given to the event rule. With the | |
5518 | JUL, log4j, and Python domains, this is a logger name. | |
5519 | ||
5520 | With a tracepoint, logger, or system call name, the last character | |
5521 | can be `*` to match anything that remains. | |
5522 | ||
5523 | |All. | |
5524 | ||
5525 | | | |
5526 | One of: | |
5527 | ||
5528 | . +--loglevel=__LEVEL__+ | |
5529 | . +--loglevel-only=__LEVEL__+ | |
5530 | ||
5531 | | | |
5532 | . Match only tracepoints or log statements with a logging level at | |
5533 | least as severe as +__LEVEL__+. | |
5534 | . Match only tracepoints or log statements with a logging level | |
5535 | equal to +__LEVEL__+. | |
5536 | ||
5537 | See man:lttng-enable-event(1) for the list of available logging level | |
5538 | names. | |
5539 | ||
5540 | |User space, JUL, log4j, and Python. | |
5541 | ||
5542 | |+--exclude=__EXCLUSIONS__+ | |
5543 | ||
5544 | | | |
5545 | When you use a `*` character at the end of the tracepoint or logger | |
5546 | name (first positional argument), exclude the specific names in the | |
5547 | comma-delimited list +__EXCLUSIONS__+. | |
5548 | ||
5549 | | | |
5550 | User space, JUL, log4j, and Python. | |
5551 | ||
5552 | |+--filter=__EXPR__+ | |
5553 | ||
5554 | | | |
5555 | Match only events which satisfy the expression +__EXPR__+. | |
5556 | ||
5557 | See man:lttng-enable-event(1) to learn more about the syntax of a | |
5558 | filter expression. | |
5559 | ||
5560 | |All. | |
5561 | ||
5562 | |==== | |
5563 | ||
5564 | You attach an event rule to a <<channel,channel>> on creation. If you do | |
5565 | not specify the channel with the opt:lttng-enable-event(1):--channel | |
5566 | option, and if the event rule to create is the first in its | |
5567 | <<domain,tracing domain>> for a given tracing session, then LTTng | |
5568 | creates a _default channel_ for you. This default channel is reused in | |
5569 | subsequent invocations of the man:lttng-enable-event(1) command for the | |
5570 | same tracing domain. | |
5571 | ||
5572 | An event rule is always enabled at creation time. | |
5573 | ||
5574 | The following examples show how you can combine the previous | |
5575 | command-line options to create simple to more complex event rules. | |
5576 | ||
5577 | .Create an event rule targetting a Linux kernel tracepoint (default channel). | |
5578 | ==== | |
5579 | [role="term"] | |
5580 | ---- | |
ded02698 | 5581 | $ lttng enable-event --kernel sched_switch |
7adf7ee2 PP |
5582 | ---- |
5583 | ==== | |
5584 | ||
5585 | .Create an event rule matching four Linux kernel system calls (default channel). | |
5586 | ==== | |
5587 | [role="term"] | |
5588 | ---- | |
ded02698 | 5589 | $ lttng enable-event --kernel --syscall open,write,read,close |
7adf7ee2 PP |
5590 | ---- |
5591 | ==== | |
5592 | ||
5593 | .Create event rules matching tracepoints with filter expressions (default channel). | |
5594 | ==== | |
5595 | [role="term"] | |
5596 | ---- | |
ded02698 | 5597 | $ lttng enable-event --kernel sched_switch --filter='prev_comm == "bash"' |
7adf7ee2 PP |
5598 | ---- |
5599 | ||
5600 | [role="term"] | |
5601 | ---- | |
ded02698 | 5602 | $ lttng enable-event --kernel --all \ |
7adf7ee2 PP |
5603 | --filter='$ctx.tid == 1988 || $ctx.tid == 1534' |
5604 | ---- | |
5605 | ||
5606 | [role="term"] | |
5607 | ---- | |
ded02698 | 5608 | $ lttng enable-event --jul my_logger \ |
7adf7ee2 PP |
5609 | --filter='$app.retriever:cur_msg_id > 3' |
5610 | ---- | |
5611 | ||
5612 | IMPORTANT: Make sure to always quote the filter string when you | |
5613 | use man:lttng(1) from a shell. | |
5614 | ==== | |
5615 | ||
5616 | .Create an event rule matching any user space tracepoint of a given tracepoint provider with a log level range (default channel). | |
5617 | ==== | |
5618 | [role="term"] | |
5619 | ---- | |
ded02698 | 5620 | $ lttng enable-event --userspace my_app:'*' --loglevel=TRACE_INFO |
7adf7ee2 PP |
5621 | ---- |
5622 | ||
5623 | IMPORTANT: Make sure to always quote the wildcard character when you | |
5624 | use man:lttng(1) from a shell. | |
5625 | ==== | |
5626 | ||
5627 | .Create an event rule matching multiple Python loggers with a wildcard and with exclusions (default channel). | |
5628 | ==== | |
5629 | [role="term"] | |
5630 | ---- | |
ded02698 | 5631 | $ lttng enable-event --python my-app.'*' \ |
7adf7ee2 PP |
5632 | --exclude='my-app.module,my-app.hello' |
5633 | ---- | |
5634 | ==== | |
5635 | ||
5636 | .Create an event rule matching any Apache log4j logger with a specific log level (default channel). | |
5637 | ==== | |
5638 | [role="term"] | |
5639 | ---- | |
ded02698 | 5640 | $ lttng enable-event --log4j --all --loglevel-only=LOG4J_WARN |
7adf7ee2 PP |
5641 | ---- |
5642 | ==== | |
5643 | ||
5644 | .Create an event rule attached to a specific channel matching a specific user space tracepoint provider and tracepoint. | |
5645 | ==== | |
5646 | [role="term"] | |
5647 | ---- | |
ded02698 | 5648 | $ lttng enable-event --userspace my_app:my_tracepoint --channel=my-channel |
7adf7ee2 PP |
5649 | ---- |
5650 | ==== | |
5651 | ||
5652 | The event rules of a given channel form a whitelist: as soon as an | |
5653 | emitted event passes one of them, LTTng can record the event. For | |
5654 | example, an event named `my_app:my_tracepoint` emitted from a user space | |
5655 | tracepoint with a `TRACE_ERROR` log level passes both of the following | |
5656 | rules: | |
5657 | ||
5658 | [role="term"] | |
5659 | ---- | |
ded02698 PP |
5660 | $ lttng enable-event --userspace my_app:my_tracepoint |
5661 | $ lttng enable-event --userspace my_app:my_tracepoint \ | |
7adf7ee2 PP |
5662 | --loglevel=TRACE_INFO |
5663 | ---- | |
5664 | ||
5665 | The second event rule is redundant: the first one includes | |
5666 | the second one. | |
5667 | ||
5668 | ||
5669 | [[disable-event-rule]] | |
5670 | === Disable an event rule | |
5671 | ||
5672 | To disable an event rule that you <<enabling-disabling-events,created>> | |
5673 | previously, use the man:lttng-disable-event(1) command. This command | |
5674 | disables _all_ the event rules (of a given tracing domain and channel) | |
5675 | which match an instrumentation point. The other conditions are not | |
5676 | supported as of LTTng{nbsp}{revision}. | |
5677 | ||
5678 | The LTTng tracer does not record an emitted event which passes | |
5679 | a _disabled_ event rule. | |
5680 | ||
5681 | .Disable an event rule matching a Python logger (default channel). | |
5682 | ==== | |
5683 | [role="term"] | |
5684 | ---- | |
ded02698 | 5685 | $ lttng disable-event --python my-logger |
7adf7ee2 PP |
5686 | ---- |
5687 | ==== | |
5688 | ||
5689 | .Disable an event rule matching all `java.util.logging` loggers (default channel). | |
5690 | ==== | |
5691 | [role="term"] | |
5692 | ---- | |
ded02698 | 5693 | $ lttng disable-event --jul '*' |
7adf7ee2 PP |
5694 | ---- |
5695 | ==== | |
5696 | ||
5697 | .Disable _all_ the event rules of the default channel. | |
5698 | ==== | |
5699 | The opt:lttng-disable-event(1):--all-events option is not, like the | |
5700 | opt:lttng-enable-event(1):--all option of man:lttng-enable-event(1), the | |
5701 | equivalent of the event name `*` (wildcard): it disables _all_ the event | |
5702 | rules of a given channel. | |
5703 | ||
5704 | [role="term"] | |
5705 | ---- | |
ded02698 | 5706 | $ lttng disable-event --jul --all-events |
7adf7ee2 PP |
5707 | ---- |
5708 | ==== | |
5709 | ||
5710 | NOTE: You cannot delete an event rule once you create it. | |
5711 | ||
5712 | ||
5713 | [[status]] | |
5714 | === Get the status of a tracing session | |
5715 | ||
5716 | To get the status of the current tracing session, that is, its | |
5717 | parameters, its channels, event rules, and their attributes: | |
5718 | ||
5719 | * Use the man:lttng-status(1) command: | |
5720 | + | |
5721 | -- | |
5722 | [role="term"] | |
5723 | ---- | |
ded02698 | 5724 | $ lttng status |
7adf7ee2 PP |
5725 | ---- |
5726 | -- | |
5727 | + | |
5728 | ||
5729 | To get the status of any tracing session: | |
5730 | ||
5731 | * Use the man:lttng-list(1) command with the tracing session's name: | |
5732 | + | |
5733 | -- | |
5734 | [role="term"] | |
5735 | ---- | |
ded02698 | 5736 | $ lttng list my-session |
7adf7ee2 PP |
5737 | ---- |
5738 | -- | |
5739 | + | |
5740 | Replace `my-session` with the desired tracing session's name. | |
5741 | ||
5742 | ||
5743 | [[basic-tracing-session-control]] | |
5744 | === Start and stop a tracing session | |
5745 | ||
5746 | Once you <<creating-destroying-tracing-sessions,create a tracing | |
5747 | session>> and | |
5748 | <<enabling-disabling-events,create one or more event rules>>, | |
5749 | you can start and stop the tracers for this tracing session. | |
5750 | ||
5751 | To start tracing in the current tracing session: | |
5752 | ||
5753 | * Use the man:lttng-start(1) command: | |
5754 | + | |
5755 | -- | |
5756 | [role="term"] | |
5757 | ---- | |
ded02698 | 5758 | $ lttng start |
7adf7ee2 PP |
5759 | ---- |
5760 | -- | |
5761 | ||
5762 | LTTng is very flexible: you can launch user applications before | |
5763 | or after the you start the tracers. The tracers only record the events | |
5764 | if they pass enabled event rules and if they occur while the tracers are | |
5765 | started. | |
5766 | ||
5767 | To stop tracing in the current tracing session: | |
5768 | ||
5769 | * Use the man:lttng-stop(1) command: | |
5770 | + | |
5771 | -- | |
5772 | [role="term"] | |
5773 | ---- | |
ded02698 | 5774 | $ lttng stop |
7adf7ee2 PP |
5775 | ---- |
5776 | -- | |
5777 | + | |
5778 | If there were <<channel-overwrite-mode-vs-discard-mode,lost event | |
5779 | records>> or lost sub-buffers since the last time you ran | |
5780 | man:lttng-start(1), warnings are printed when you run the | |
5781 | man:lttng-stop(1) command. | |
5782 | ||
5783 | ||
5784 | [[enabling-disabling-channels]] | |
5785 | === Create a channel | |
5786 | ||
5787 | Once you create a tracing session, you can create a <<channel,channel>> | |
5788 | with the man:lttng-enable-channel(1) command. | |
5789 | ||
5790 | Note that LTTng automatically creates a default channel when, for a | |
5791 | given <<domain,tracing domain>>, no channels exist and you | |
5792 | <<enabling-disabling-events,create>> the first event rule. This default | |
5793 | channel is named `channel0` and its attributes are set to reasonable | |
5794 | values. Therefore, you only need to create a channel when you need | |
5795 | non-default attributes. | |
5796 | ||
5797 | You specify each non-default channel attribute with a command-line | |
5798 | option when you use the man:lttng-enable-channel(1) command. The | |
5799 | available command-line options are: | |
5800 | ||
5801 | [role="growable",cols="asciidoc,asciidoc"] | |
5802 | .Command-line options for the man:lttng-enable-channel(1) command. | |
5803 | |==== | |
5804 | |Option |Description | |
5805 | ||
5806 | |`--overwrite` | |
5807 | ||
5808 | | | |
5809 | Use the _overwrite_ | |
5810 | <<channel-overwrite-mode-vs-discard-mode,event loss mode>> instead of | |
5811 | the default _discard_ mode. | |
5812 | ||
5813 | |`--buffers-pid` (user space tracing domain only) | |
5814 | ||
5815 | | | |
5816 | Use the per-process <<channel-buffering-schemes,buffering scheme>> | |
5817 | instead of the default per-user buffering scheme. | |
5818 | ||
5819 | |+--subbuf-size=__SIZE__+ | |
5820 | ||
5821 | | | |
5822 | Allocate sub-buffers of +__SIZE__+ bytes (power of two), for each CPU, | |
5823 | either for each Unix user (default), or for each instrumented process. | |
5824 | ||
5825 | See <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>>. | |
5826 | ||
5827 | |+--num-subbuf=__COUNT__+ | |
5828 | ||
5829 | | | |
5830 | Allocate +__COUNT__+ sub-buffers (power of two), for each CPU, either | |
5831 | for each Unix user (default), or for each instrumented process. | |
5832 | ||
5833 | See <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>>. | |
5834 | ||
5835 | |+--tracefile-size=__SIZE__+ | |
5836 | ||
5837 | | | |
5838 | Set the maximum size of each trace file that this channel writes within | |
5839 | a stream to +__SIZE__+ bytes instead of no maximum. | |
5840 | ||
5841 | See <<tracefile-rotation,Trace file count and size>>. | |
5842 | ||
5843 | |+--tracefile-count=__COUNT__+ | |
5844 | ||
5845 | | | |
5846 | Limit the number of trace files that this channel creates to | |
5847 | +__COUNT__+ channels instead of no limit. | |
5848 | ||
5849 | See <<tracefile-rotation,Trace file count and size>>. | |
5850 | ||
5851 | |+--switch-timer=__PERIODUS__+ | |
5852 | ||
5853 | | | |
5854 | Set the <<channel-switch-timer,switch timer period>> | |
5855 | to +__PERIODUS__+{nbsp}µs. | |
5856 | ||
5857 | |+--read-timer=__PERIODUS__+ | |
5858 | ||
5859 | | | |
5860 | Set the <<channel-read-timer,read timer period>> | |
5861 | to +__PERIODUS__+{nbsp}µs. | |
5862 | ||
5863 | |+--output=__TYPE__+ (Linux kernel tracing domain only) | |
5864 | ||
5865 | | | |
5866 | Set the channel's output type to +__TYPE__+, either `mmap` or `splice`. | |
5867 | ||
5868 | |==== | |
5869 | ||
5870 | You can only create a channel in the Linux kernel and user space | |
5871 | <<domain,tracing domains>>: other tracing domains have their own channel | |
5872 | created on the fly when <<enabling-disabling-events,creating event | |
5873 | rules>>. | |
5874 | ||
5875 | [IMPORTANT] | |
5876 | ==== | |
5877 | Because of a current LTTng limitation, you must create all channels | |
5878 | _before_ you <<basic-tracing-session-control,start tracing>> in a given | |
5879 | tracing session, that is, before the first time you run | |
5880 | man:lttng-start(1). | |
5881 | ||
5882 | Since LTTng automatically creates a default channel when you use the | |
5883 | man:lttng-enable-event(1) command with a specific tracing domain, you | |
5884 | cannot, for example, create a Linux kernel event rule, start tracing, | |
5885 | and then create a user space event rule, because no user space channel | |
5886 | exists yet and it's too late to create one. | |
5887 | ||
5888 | For this reason, make sure to configure your channels properly | |
5889 | before starting the tracers for the first time! | |
5890 | ==== | |
5891 | ||
5892 | The following examples show how you can combine the previous | |
5893 | command-line options to create simple to more complex channels. | |
5894 | ||
5895 | .Create a Linux kernel channel with default attributes. | |
5896 | ==== | |
5897 | [role="term"] | |
5898 | ---- | |
ded02698 | 5899 | $ lttng enable-channel --kernel my-channel |
7adf7ee2 PP |
5900 | ---- |
5901 | ==== | |
5902 | ||
5903 | .Create a user space channel with 4 sub-buffers or 1{nbsp}MiB each, per CPU, per instrumented process. | |
5904 | ==== | |
5905 | [role="term"] | |
5906 | ---- | |
ded02698 | 5907 | $ lttng enable-channel --userspace --num-subbuf=4 --subbuf-size=1M \ |
7adf7ee2 PP |
5908 | --buffers-pid my-channel |
5909 | ---- | |
5910 | ==== | |
5911 | ||
5912 | .Create a Linux kernel channel which rotates 8 trace files of 4{nbsp}MiB each for each stream | |
5913 | ==== | |
5914 | [role="term"] | |
5915 | ---- | |
ded02698 | 5916 | $ lttng enable-channel --kernel --tracefile-count=8 \ |
7adf7ee2 PP |
5917 | --tracefile-size=4194304 my-channel |
5918 | ---- | |
5919 | ==== | |
5920 | ||
5921 | .Create a user space channel in overwrite (or _flight recorder_) mode. | |
5922 | ==== | |
5923 | [role="term"] | |
5924 | ---- | |
ded02698 | 5925 | $ lttng enable-channel --userspace --overwrite my-channel |
7adf7ee2 PP |
5926 | ---- |
5927 | ==== | |
5928 | ||
5929 | You can <<enabling-disabling-events,create>> the same event rule in | |
5930 | two different channels: | |
5931 | ||
5932 | [role="term"] | |
5933 | ---- | |
ded02698 PP |
5934 | $ lttng enable-event --userspace --channel=my-channel app:tp |
5935 | $ lttng enable-event --userspace --channel=other-channel app:tp | |
7adf7ee2 PP |
5936 | ---- |
5937 | ||
5938 | If both channels are enabled, when a tracepoint named `app:tp` is | |
5939 | reached, LTTng records two events, one for each channel. | |
5940 | ||
5941 | ||
5942 | [[disable-channel]] | |
5943 | === Disable a channel | |
5944 | ||
5945 | To disable a specific channel that you <<enabling-disabling-channels,created>> | |
5946 | previously, use the man:lttng-disable-channel(1) command. | |
5947 | ||
5948 | .Disable a specific Linux kernel channel. | |
5949 | ==== | |
5950 | [role="term"] | |
5951 | ---- | |
ded02698 | 5952 | $ lttng disable-channel --kernel my-channel |
7adf7ee2 PP |
5953 | ---- |
5954 | ==== | |
5955 | ||
5956 | The state of a channel precedes the individual states of event rules | |
5957 | attached to it: event rules which belong to a disabled channel, even if | |
5958 | they are enabled, are also considered disabled. | |
5959 | ||
5960 | ||
5961 | [[adding-context]] | |
5962 | === Add context fields to a channel | |
5963 | ||
5964 | Event record fields in trace files provide important information about | |
5965 | events that occured previously, but sometimes some external context may | |
5966 | help you solve a problem faster. Examples of context fields are: | |
5967 | ||
5968 | * The **process ID**, **thread ID**, **process name**, and | |
5969 | **process priority** of the thread in which the event occurs. | |
5970 | * The **hostname** of the system on which the event occurs. | |
5971 | * The current values of many possible **performance counters** using | |
5972 | perf, for example: | |
5973 | ** CPU cycles, stalled cycles, idle cycles, and the other cycle types. | |
5974 | ** Cache misses. | |
5975 | ** Branch instructions, misses, and loads. | |
5976 | ** CPU faults. | |
5977 | * Any context defined at the application level (supported for the | |
5978 | JUL and log4j <<domain,tracing domains>>). | |
5979 | ||
5980 | To get the full list of available context fields, see | |
5981 | `lttng add-context --list`. Some context fields are reserved for a | |
5982 | specific <<domain,tracing domain>> (Linux kernel or user space). | |
5983 | ||
5984 | You add context fields to <<channel,channels>>. All the events | |
5985 | that a channel with added context fields records contain those fields. | |
5986 | ||
5987 | To add context fields to one or all the channels of a given tracing | |
5988 | session: | |
5989 | ||
5990 | * Use the man:lttng-add-context(1) command. | |
5991 | ||
5992 | .Add context fields to all the channels of the current tracing session. | |
5993 | ==== | |
5994 | The following command line adds the virtual process identifier and | |
5995 | the per-thread CPU cycles count fields to all the user space channels | |
5996 | of the current tracing session. | |
5997 | ||
5998 | [role="term"] | |
5999 | ---- | |
ded02698 | 6000 | $ lttng add-context --userspace --type=vpid --type=perf:thread:cpu-cycles |
7adf7ee2 PP |
6001 | ---- |
6002 | ==== | |
6003 | ||
6004 | .Add a context field to a specific channel. | |
6005 | ==== | |
6006 | The following command line adds the thread identifier context field | |
6007 | to the Linux kernel channel named `my-channel` in the current | |
6008 | tracing session. | |
6009 | ||
6010 | [role="term"] | |
6011 | ---- | |
ded02698 | 6012 | $ lttng add-context --kernel --channel=my-channel --type=tid |
7adf7ee2 PP |
6013 | ---- |
6014 | ==== | |
6015 | ||
6016 | .Add an application-specific context field to a specific channel. | |
6017 | ==== | |
6018 | The following command line adds the `cur_msg_id` context field of the | |
6019 | `retriever` context retriever for all the instrumented | |
6020 | <<java-application,Java applications>> recording <<event,event records>> | |
6021 | in the channel named `my-channel`: | |
6022 | ||
6023 | [role="term"] | |
6024 | ---- | |
ded02698 | 6025 | $ lttng add-context --kernel --channel=my-channel \ |
7adf7ee2 PP |
6026 | --type='$app:retriever:cur_msg_id' |
6027 | ---- | |
6028 | ||
6029 | IMPORTANT: Make sure to always quote the `$` character when you | |
6030 | use man:lttng-add-context(1) from a shell. | |
6031 | ==== | |
6032 | ||
6033 | NOTE: You cannot remove context fields from a channel once you add it. | |
6034 | ||
6035 | ||
6036 | [role="since-2.7"] | |
6037 | [[pid-tracking]] | |
6038 | === Track process IDs | |
6039 | ||
6040 | It's often useful to allow only specific process IDs (PIDs) to emit | |
6041 | events. For example, you may wish to record all the system calls made by | |
6042 | a given process (à la http://linux.die.net/man/1/strace[strace]). | |
6043 | ||
6044 | The man:lttng-track(1) and man:lttng-untrack(1) commands serve this | |
6045 | purpose. Both commands operate on a whitelist of process IDs. You _add_ | |
6046 | entries to this whitelist with the man:lttng-track(1) command and remove | |
6047 | entries with the man:lttng-untrack(1) command. Any process which has one | |
6048 | of the PIDs in the whitelist is allowed to emit LTTng events which pass | |
6049 | an enabled <<event,event rule>>. | |
6050 | ||
6051 | NOTE: The PID tracker tracks the _numeric process IDs_. Should a | |
6052 | process with a given tracked ID exit and another process be given this | |
6053 | ID, then the latter would also be allowed to emit events. | |
6054 | ||
6055 | .Track and untrack process IDs. | |
6056 | ==== | |
6057 | For the sake of the following example, assume the target system has 16 | |
6058 | possible PIDs. | |
6059 | ||
6060 | When you | |
6061 | <<creating-destroying-tracing-sessions,create a tracing session>>, | |
6062 | the whitelist contains all the possible PIDs: | |
6063 | ||
6064 | [role="img-100"] | |
6065 | .All PIDs are tracked. | |
6066 | image::track-all.png[] | |
6067 | ||
6068 | When the whitelist is full and you use the man:lttng-track(1) command to | |
6069 | specify some PIDs to track, LTTng first clears the whitelist, then it | |
6070 | tracks the specific PIDs. After: | |
6071 | ||
6072 | [role="term"] | |
6073 | ---- | |
ded02698 | 6074 | $ lttng track --pid=3,4,7,10,13 |
7adf7ee2 PP |
6075 | ---- |
6076 | ||
6077 | the whitelist is: | |
6078 | ||
6079 | [role="img-100"] | |
6080 | .PIDs 3, 4, 7, 10, and 13 are tracked. | |
6081 | image::track-3-4-7-10-13.png[] | |
6082 | ||
6083 | You can add more PIDs to the whitelist afterwards: | |
6084 | ||
6085 | [role="term"] | |
6086 | ---- | |
ded02698 | 6087 | $ lttng track --pid=1,15,16 |
7adf7ee2 PP |
6088 | ---- |
6089 | ||
6090 | The result is: | |
6091 | ||
6092 | [role="img-100"] | |
6093 | .PIDs 1, 15, and 16 are added to the whitelist. | |
6094 | image::track-1-3-4-7-10-13-15-16.png[] | |
6095 | ||
6096 | The man:lttng-untrack(1) command removes entries from the PID tracker's | |
6097 | whitelist. Given the previous example, the following command: | |
6098 | ||
6099 | [role="term"] | |
6100 | ---- | |
ded02698 | 6101 | $ lttng untrack --pid=3,7,10,13 |
7adf7ee2 PP |
6102 | ---- |
6103 | ||
6104 | leads to this whitelist: | |
6105 | ||
6106 | [role="img-100"] | |
6107 | .PIDs 3, 7, 10, and 13 are removed from the whitelist. | |
6108 | image::track-1-4-15-16.png[] | |
6109 | ||
a9f3997c PP |
6110 | LTTng can track all possible PIDs again using the |
6111 | opt:lttng-track(1):--all option: | |
7adf7ee2 PP |
6112 | |
6113 | [role="term"] | |
6114 | ---- | |
ded02698 | 6115 | $ lttng track --pid --all |
7adf7ee2 PP |
6116 | ---- |
6117 | ||
6118 | The result is, again: | |
6119 | ||
6120 | [role="img-100"] | |
6121 | .All PIDs are tracked. | |
6122 | image::track-all.png[] | |
6123 | ==== | |
6124 | ||
6125 | .Track only specific PIDs | |
6126 | ==== | |
6127 | A very typical use case with PID tracking is to start with an empty | |
6128 | whitelist, then <<basic-tracing-session-control,start the tracers>>, and | |
6129 | then add PIDs manually while tracers are active. You can accomplish this | |
6130 | by using the opt:lttng-untrack(1):--all option of the | |
6131 | man:lttng-untrack(1) command to clear the whitelist after you | |
6132 | <<creating-destroying-tracing-sessions,create a tracing session>>: | |
6133 | ||
6134 | [role="term"] | |
6135 | ---- | |
ded02698 | 6136 | $ lttng untrack --pid --all |
7adf7ee2 PP |
6137 | ---- |
6138 | ||
6139 | gives: | |
6140 | ||
6141 | [role="img-100"] | |
6142 | .No PIDs are tracked. | |
6143 | image::untrack-all.png[] | |
6144 | ||
6145 | If you trace with this whitelist configuration, the tracer records no | |
6146 | events for this <<domain,tracing domain>> because no processes are | |
6147 | tracked. You can use the man:lttng-track(1) command as usual to track | |
6148 | specific PIDs, for example: | |
6149 | ||
6150 | [role="term"] | |
6151 | ---- | |
ded02698 | 6152 | $ lttng track --pid=6,11 |
7adf7ee2 PP |
6153 | ---- |
6154 | ||
6155 | Result: | |
6156 | ||
6157 | [role="img-100"] | |
6158 | .PIDs 6 and 11 are tracked. | |
6159 | image::track-6-11.png[] | |
6160 | ==== | |
6161 | ||
6162 | ||
6163 | [role="since-2.5"] | |
6164 | [[saving-loading-tracing-session]] | |
6165 | === Save and load tracing session configurations | |
6166 | ||
6167 | Configuring a <<tracing-session,tracing session>> can be long. Some of | |
6168 | the tasks involved are: | |
6169 | ||
6170 | * <<enabling-disabling-channels,Create channels>> with | |
6171 | specific attributes. | |
6172 | * <<adding-context,Add context fields>> to specific channels. | |
6173 | * <<enabling-disabling-events,Create event rules>> with specific log | |
6174 | level and filter conditions. | |
6175 | ||
6176 | If you use LTTng to solve real world problems, chances are you have to | |
6177 | record events using the same tracing session setup over and over, | |
6178 | modifying a few variables each time in your instrumented program | |
6179 | or environment. To avoid constant tracing session reconfiguration, | |
6180 | the man:lttng(1) command-line tool can save and load tracing session | |
6181 | configurations to/from XML files. | |
6182 | ||
6183 | To save a given tracing session configuration: | |
6184 | ||
6185 | * Use the man:lttng-save(1) command: | |
6186 | + | |
6187 | -- | |
6188 | [role="term"] | |
6189 | ---- | |
ded02698 | 6190 | $ lttng save my-session |
7adf7ee2 PP |
6191 | ---- |
6192 | -- | |
6193 | + | |
6194 | Replace `my-session` with the name of the tracing session to save. | |
6195 | ||
6196 | LTTng saves tracing session configurations to | |
6197 | dir:{$LTTNG_HOME/.lttng/sessions} by default. Note that the | |
6198 | env:LTTNG_HOME environment variable defaults to `$HOME` if not set. Use | |
6199 | the opt:lttng-save(1):--output-path option to change this destination | |
6200 | directory. | |
6201 | ||
6202 | LTTng saves all configuration parameters, for example: | |
6203 | ||
6204 | * The tracing session name. | |
6205 | * The trace data output path. | |
6206 | * The channels with their state and all their attributes. | |
6207 | * The context fields you added to channels. | |
6208 | * The event rules with their state, log level and filter conditions. | |
6209 | ||
6210 | To load a tracing session: | |
6211 | ||
6212 | * Use the man:lttng-load(1) command: | |
6213 | + | |
6214 | -- | |
6215 | [role="term"] | |
6216 | ---- | |
ded02698 | 6217 | $ lttng load my-session |
7adf7ee2 PP |
6218 | ---- |
6219 | -- | |
6220 | + | |
6221 | Replace `my-session` with the name of the tracing session to load. | |
6222 | ||
6223 | When LTTng loads a configuration, it restores your saved tracing session | |
6224 | as if you just configured it manually. | |
6225 | ||
6226 | See man:lttng(1) for the complete list of command-line options. You | |
6227 | can also save and load all many sessions at a time, and decide in which | |
6228 | directory to output the XML files. | |
6229 | ||
6230 | ||
6231 | [[sending-trace-data-over-the-network]] | |
6232 | === Send trace data over the network | |
6233 | ||
6234 | LTTng can send the recorded trace data to a remote system over the | |
6235 | network instead of writing it to the local file system. | |
6236 | ||
6237 | To send the trace data over the network: | |
6238 | ||
6239 | . On the _remote_ system (which can also be the target system), | |
6240 | start an LTTng <<lttng-relayd,relay daemon>> (man:lttng-relayd(8)): | |
6241 | + | |
6242 | -- | |
6243 | [role="term"] | |
6244 | ---- | |
ded02698 | 6245 | $ lttng-relayd |
7adf7ee2 PP |
6246 | ---- |
6247 | -- | |
6248 | ||
6249 | . On the _target_ system, create a tracing session configured to | |
6250 | send trace data over the network: | |
6251 | + | |
6252 | -- | |
6253 | [role="term"] | |
6254 | ---- | |
ded02698 | 6255 | $ lttng create my-session --set-url=net://remote-system |
7adf7ee2 PP |
6256 | ---- |
6257 | -- | |
6258 | + | |
6259 | Replace `remote-system` by the host name or IP address of the | |
6260 | remote system. See man:lttng-create(1) for the exact URL format. | |
6261 | ||
6262 | . On the target system, use the man:lttng(1) command-line tool as usual. | |
6263 | When tracing is active, the target's consumer daemon sends sub-buffers | |
d1b6c345 | 6264 | to the relay daemon running on the remote system instead of flushing |
7adf7ee2 PP |
6265 | them to the local file system. The relay daemon writes the received |
6266 | packets to the local file system. | |
6267 | ||
6268 | The relay daemon writes trace files to | |
6269 | +$LTTNG_HOME/lttng-traces/__hostname__/__session__+ by default, where | |
6270 | +__hostname__+ is the host name of the target system and +__session__+ | |
6271 | is the tracing session name. Note that the env:LTTNG_HOME environment | |
6272 | variable defaults to `$HOME` if not set. Use the | |
6273 | opt:lttng-relayd(8):--output option of man:lttng-relayd(8) to write | |
6274 | trace files to another base directory. | |
6275 | ||
6276 | ||
6277 | [role="since-2.4"] | |
6278 | [[lttng-live]] | |
6279 | === View events as LTTng emits them (noch:{LTTng} live) | |
6280 | ||
6281 | LTTng live is a network protocol implemented by the <<lttng-relayd,relay | |
6282 | daemon>> (man:lttng-relayd(8)) to allow compatible trace viewers to | |
6283 | display events as LTTng emits them on the target system while tracing is | |
6284 | active. | |
6285 | ||
6286 | The relay daemon creates a _tee_: it forwards the trace data to both | |
6287 | the local file system and to connected live viewers: | |
6288 | ||
6289 | [role="img-90"] | |
6290 | .The relay daemon creates a _tee_, forwarding the trace data to both trace files and a connected live viewer. | |
6291 | image::live.png[] | |
6292 | ||
6293 | To use LTTng live: | |
6294 | ||
6295 | . On the _target system_, create a <<tracing-session,tracing session>> | |
6296 | in _live mode_: | |
6297 | + | |
6298 | -- | |
6299 | [role="term"] | |
6300 | ---- | |
ded02698 | 6301 | $ lttng create my-session --live |
7adf7ee2 PP |
6302 | ---- |
6303 | -- | |
6304 | + | |
6305 | This spawns a local relay daemon. | |
6306 | ||
6307 | . Start the live viewer and configure it to connect to the relay | |
6308 | daemon. For example, with http://diamon.org/babeltrace[Babeltrace]: | |
6309 | + | |
6310 | -- | |
6311 | [role="term"] | |
6312 | ---- | |
ded02698 PP |
6313 | $ babeltrace --input-format=lttng-live |
6314 | net://localhost/host/hostname/my-session | |
7adf7ee2 PP |
6315 | ---- |
6316 | -- | |
6317 | + | |
6318 | Replace: | |
6319 | + | |
6320 | -- | |
6321 | * `hostname` with the host name of the target system. | |
6322 | * `my-session` with the name of the tracing session to view. | |
6323 | -- | |
6324 | ||
6325 | . Configure the tracing session as usual with the man:lttng(1) | |
6326 | command-line tool, and <<basic-tracing-session-control,start tracing>>. | |
6327 | ||
6328 | You can list the available live tracing sessions with Babeltrace: | |
6329 | ||
6330 | [role="term"] | |
6331 | ---- | |
ded02698 | 6332 | $ babeltrace --input-format=lttng-live net://localhost |
7adf7ee2 PP |
6333 | ---- |
6334 | ||
6335 | You can start the relay daemon on another system. In this case, you need | |
6336 | to specify the relay daemon's URL when you create the tracing session | |
6337 | with the opt:lttng-create(1):--set-url option. You also need to replace | |
6338 | `localhost` in the procedure above with the host name of the system on | |
6339 | which the relay daemon is running. | |
6340 | ||
6341 | See man:lttng-create(1) and man:lttng-relayd(8) for the complete list of | |
6342 | command-line options. | |
6343 | ||
6344 | ||
6345 | [role="since-2.3"] | |
6346 | [[taking-a-snapshot]] | |
6347 | === Take a snapshot of the current sub-buffers of a tracing session | |
6348 | ||
6349 | The normal behavior of LTTng is to append full sub-buffers to growing | |
6350 | trace data files. This is ideal to keep a full history of the events | |
6351 | that occurred on the target system, but it can | |
6352 | represent too much data in some situations. For example, you may wish | |
6353 | to trace your application continuously until some critical situation | |
6354 | happens, in which case you only need the latest few recorded | |
6355 | events to perform the desired analysis, not multi-gigabyte trace files. | |
6356 | ||
6357 | With the man:lttng-snapshot(1) command, you can take a snapshot of the | |
6358 | current sub-buffers of a given <<tracing-session,tracing session>>. | |
6359 | LTTng can write the snapshot to the local file system or send it over | |
6360 | the network. | |
6361 | ||
6362 | To take a snapshot: | |
6363 | ||
6364 | . Create a tracing session in _snapshot mode_: | |
6365 | + | |
6366 | -- | |
6367 | [role="term"] | |
6368 | ---- | |
ded02698 | 6369 | $ lttng create my-session --snapshot |
7adf7ee2 PP |
6370 | ---- |
6371 | -- | |
6372 | + | |
6373 | The <<channel-overwrite-mode-vs-discard-mode,event loss mode>> of | |
6374 | <<channel,channels>> created in this mode is automatically set to | |
6375 | _overwrite_ (flight recorder mode). | |
6376 | ||
6377 | . Configure the tracing session as usual with the man:lttng(1) | |
6378 | command-line tool, and <<basic-tracing-session-control,start tracing>>. | |
6379 | ||
6380 | . **Optional**: When you need to take a snapshot, | |
6381 | <<basic-tracing-session-control,stop tracing>>. | |
6382 | + | |
6383 | You can take a snapshot when the tracers are active, but if you stop | |
6384 | them first, you are sure that the data in the sub-buffers does not | |
6385 | change before you actually take the snapshot. | |
6386 | ||
6387 | . Take a snapshot: | |
6388 | + | |
6389 | -- | |
6390 | [role="term"] | |
6391 | ---- | |
ded02698 | 6392 | $ lttng snapshot record --name=my-first-snapshot |
7adf7ee2 PP |
6393 | ---- |
6394 | -- | |
6395 | + | |
6396 | LTTng writes the current sub-buffers of all the current tracing | |
6397 | session's channels to trace files on the local file system. Those trace | |
6398 | files have `my-first-snapshot` in their name. | |
6399 | ||
6400 | There is no difference between the format of a normal trace file and the | |
6401 | format of a snapshot: viewers of LTTng traces also support LTTng | |
6402 | snapshots. | |
6403 | ||
6404 | By default, LTTng writes snapshot files to the path shown by | |
6405 | `lttng snapshot list-output`. You can change this path or decide to send | |
6406 | snapshots over the network using either: | |
6407 | ||
6408 | . An output path or URL that you specify when you create the | |
6409 | tracing session. | |
6410 | . An snapshot output path or URL that you add using | |
6411 | `lttng snapshot add-output` | |
6412 | . An output path or URL that you provide directly to the | |
6413 | `lttng snapshot record` command. | |
6414 | ||
6415 | Method 3 overrides method 2, which overrides method 1. When you | |
6416 | specify a URL, a relay daemon must listen on a remote system (see | |
6417 | <<sending-trace-data-over-the-network,Send trace data over the network>>). | |
6418 | ||
6419 | ||
6420 | [role="since-2.6"] | |
6421 | [[mi]] | |
6422 | === Use the machine interface | |
6423 | ||
6424 | With any command of the man:lttng(1) command-line tool, you can set the | |
6425 | opt:lttng(1):--mi option to `xml` (before the command name) to get an | |
6426 | XML machine interface output, for example: | |
6427 | ||
6428 | [role="term"] | |
6429 | ---- | |
ded02698 | 6430 | $ lttng --mi=xml enable-event --kernel --syscall open |
7adf7ee2 PP |
6431 | ---- |
6432 | ||
6433 | A schema definition (XSD) is | |
6434 | https://github.com/lttng/lttng-tools/blob/stable-2.8/src/common/mi-lttng-3.0.xsd[available] | |
6435 | to ease the integration with external tools as much as possible. | |
6436 | ||
6437 | ||
6438 | [role="since-2.8"] | |
6439 | [[metadata-regenerate]] | |
6440 | === Regenerate the metadata of an LTTng trace | |
6441 | ||
6442 | An LTTng trace, which is a http://diamon.org/ctf[CTF] trace, has both | |
6443 | data stream files and a metadata file. This metadata file contains, | |
6444 | amongst other things, information about the offset of the clock sources | |
6445 | used to timestamp <<event,event records>> when tracing. | |
6446 | ||
6447 | If, once a <<tracing-session,tracing session>> is | |
6448 | <<basic-tracing-session-control,started>>, a major | |
6449 | https://en.wikipedia.org/wiki/Network_Time_Protocol[NTP] correction | |
6450 | happens, the trace's clock offset also needs to be updated. You | |
6451 | can use the man:lttng-metadata(1) command to do so. | |
6452 | ||
6453 | The main use case of this command is to allow a system to boot with | |
6454 | an incorrect wall time and trace it with LTTng before its wall time | |
6455 | is corrected. Once the system is known to be in a state where its | |
6456 | wall time is correct, it can run `lttng metadata regenerate`. | |
6457 | ||
6458 | To regenerate the metadata of an LTTng trace: | |
6459 | ||
6460 | * Use the `regenerate` action of the man:lttng-metadata(1) command: | |
6461 | + | |
6462 | -- | |
6463 | [role="term"] | |
6464 | ---- | |
ded02698 | 6465 | $ lttng metadata regenerate |
7adf7ee2 PP |
6466 | ---- |
6467 | -- | |
6468 | ||
6469 | [IMPORTANT] | |
6470 | ==== | |
6471 | `lttng metadata regenerate` has the following limitations: | |
6472 | ||
6473 | * Tracing session <<creating-destroying-tracing-sessions,created>> | |
6474 | in non-live mode. | |
6475 | * User space <<channel,channels>>, if any, using | |
6476 | <<channel-buffering-schemes,per-user buffering>>. | |
6477 | ==== | |
6478 | ||
6479 | ||
6480 | [role="since-2.7"] | |
6481 | [[persistent-memory-file-systems]] | |
6482 | === Record trace data on persistent memory file systems | |
6483 | ||
6484 | https://en.wikipedia.org/wiki/Non-volatile_random-access_memory[Non-volatile random-access memory] | |
6485 | (NVRAM) is random-access memory that retains its information when power | |
6486 | is turned off (non-volatile). Systems with such memory can store data | |
6487 | structures in RAM and retrieve them after a reboot, without flushing | |
6488 | to typical _storage_. | |
6489 | ||
6490 | Linux supports NVRAM file systems thanks to either | |
6491 | http://pramfs.sourceforge.net/[PRAMFS] or | |
6492 | https://www.kernel.org/doc/Documentation/filesystems/dax.txt[DAX]{nbsp}+{nbsp}http://lkml.iu.edu/hypermail/linux/kernel/1504.1/03463.html[pmem] | |
6493 | (requires Linux 4.1+). | |
6494 | ||
6495 | This section does not describe how to operate such file systems; | |
6496 | we assume that you have a working persistent memory file system. | |
6497 | ||
6498 | When you create a <<tracing-session,tracing session>>, you can specify | |
6499 | the path of the shared memory holding the sub-buffers. If you specify a | |
6500 | location on an NVRAM file system, then you can retrieve the latest | |
6501 | recorded trace data when the system reboots after a crash. | |
6502 | ||
6503 | To record trace data on a persistent memory file system and retrieve the | |
6504 | trace data after a system crash: | |
6505 | ||
6506 | . Create a tracing session with a sub-buffer shared memory path located | |
6507 | on an NVRAM file system: | |
6508 | + | |
6509 | -- | |
6510 | [role="term"] | |
6511 | ---- | |
ded02698 | 6512 | $ lttng create my-session --shm-path=/path/to/shm |
7adf7ee2 PP |
6513 | ---- |
6514 | -- | |
6515 | ||
6516 | . Configure the tracing session as usual with the man:lttng(1) | |
6517 | command-line tool, and <<basic-tracing-session-control,start tracing>>. | |
6518 | ||
6519 | . After a system crash, use the man:lttng-crash(1) command-line tool to | |
6520 | view the trace data recorded on the NVRAM file system: | |
6521 | + | |
6522 | -- | |
6523 | [role="term"] | |
6524 | ---- | |
ded02698 | 6525 | $ lttng-crash /path/to/shm |
7adf7ee2 PP |
6526 | ---- |
6527 | -- | |
6528 | ||
6529 | The binary layout of the ring buffer files is not exactly the same as | |
6530 | the trace files layout. This is why you need to use man:lttng-crash(1) | |
6531 | instead of your preferred trace viewer directly. | |
6532 | ||
6533 | To convert the ring buffer files to LTTng trace files: | |
6534 | ||
6535 | * Use the opt:lttng-crash(1):--extract option of man:lttng-crash(1): | |
6536 | + | |
6537 | -- | |
6538 | [role="term"] | |
6539 | ---- | |
ded02698 | 6540 | $ lttng-crash --extract=/path/to/trace /path/to/shm |
7adf7ee2 PP |
6541 | ---- |
6542 | -- | |
6543 | ||
6544 | ||
6545 | [[reference]] | |
6546 | == Reference | |
6547 | ||
6548 | [[lttng-modules-ref]] | |
6549 | === noch:{LTTng-modules} | |
6550 | ||
6551 | [role="since-2.7"] | |
6552 | [[lttng-modules-tp-fields]] | |
6553 | ==== Tracepoint fields macros (for `TP_FIELDS()`) | |
6554 | ||
6555 | [[tp-fast-assign]][[tp-struct-entry]]The available macros to define | |
6556 | tracepoint fields, which must be listed within `TP_FIELDS()` in | |
6557 | `LTTNG_TRACEPOINT_EVENT()`, are: | |
6558 | ||
6559 | [role="func-desc growable",cols="asciidoc,asciidoc"] | |
6560 | .Available macros to define LTTng-modules tracepoint fields | |
6561 | |==== | |
6562 | |Macro |Description and parameters | |
6563 | ||
6564 | | | |
6565 | +ctf_integer(__t__, __n__, __e__)+ | |
6566 | ||
6567 | +ctf_integer_nowrite(__t__, __n__, __e__)+ | |
6568 | ||
6569 | +ctf_user_integer(__t__, __n__, __e__)+ | |
6570 | ||
6571 | +ctf_user_integer_nowrite(__t__, __n__, __e__)+ | |
6572 | | | |
6573 | Standard integer, displayed in base 10. | |
6574 | ||
6575 | +__t__+:: | |
6576 | Integer C type (`int`, `long`, `size_t`, ...). | |
6577 | ||
6578 | +__n__+:: | |
6579 | Field name. | |
6580 | ||
6581 | +__e__+:: | |
6582 | Argument expression. | |
6583 | ||
6584 | | | |
6585 | +ctf_integer_hex(__t__, __n__, __e__)+ | |
6586 | ||
6587 | +ctf_user_integer_hex(__t__, __n__, __e__)+ | |
6588 | | | |
6589 | Standard integer, displayed in base 16. | |
6590 | ||
6591 | +__t__+:: | |
6592 | Integer C type. | |
6593 | ||
6594 | +__n__+:: | |
6595 | Field name. | |
6596 | ||
6597 | +__e__+:: | |
6598 | Argument expression. | |
6599 | ||
6600 | |+ctf_integer_oct(__t__, __n__, __e__)+ | |
6601 | | | |
6602 | Standard integer, displayed in base 8. | |
6603 | ||
6604 | +__t__+:: | |
6605 | Integer C type. | |
6606 | ||
6607 | +__n__+:: | |
6608 | Field name. | |
6609 | ||
6610 | +__e__+:: | |
6611 | Argument expression. | |
6612 | ||
6613 | | | |
6614 | +ctf_integer_network(__t__, __n__, __e__)+ | |
6615 | ||
6616 | +ctf_user_integer_network(__t__, __n__, __e__)+ | |
6617 | | | |
6618 | Integer in network byte order (big-endian), displayed in base 10. | |
6619 | ||
6620 | +__t__+:: | |
6621 | Integer C type. | |
6622 | ||
6623 | +__n__+:: | |
6624 | Field name. | |
6625 | ||
6626 | +__e__+:: | |
6627 | Argument expression. | |
6628 | ||
6629 | | | |
6630 | +ctf_integer_network_hex(__t__, __n__, __e__)+ | |
6631 | ||
6632 | +ctf_user_integer_network_hex(__t__, __n__, __e__)+ | |
6633 | | | |
6634 | Integer in network byte order, displayed in base 16. | |
6635 | ||
6636 | +__t__+:: | |
6637 | Integer C type. | |
6638 | ||
6639 | +__n__+:: | |
6640 | Field name. | |
6641 | ||
6642 | +__e__+:: | |
6643 | Argument expression. | |
6644 | ||
6645 | | | |
6646 | +ctf_string(__n__, __e__)+ | |
6647 | ||
6648 | +ctf_string_nowrite(__n__, __e__)+ | |
6649 | ||
6650 | +ctf_user_string(__n__, __e__)+ | |
6651 | ||
6652 | +ctf_user_string_nowrite(__n__, __e__)+ | |
6653 | | | |
6654 | Null-terminated string; undefined behavior if +__e__+ is `NULL`. | |
6655 | ||
6656 | +__n__+:: | |
6657 | Field name. | |
6658 | ||
6659 | +__e__+:: | |
6660 | Argument expression. | |
6661 | ||
6662 | | | |
6663 | +ctf_array(__t__, __n__, __e__, __s__)+ | |
6664 | ||
6665 | +ctf_array_nowrite(__t__, __n__, __e__, __s__)+ | |
6666 | ||
6667 | +ctf_user_array(__t__, __n__, __e__, __s__)+ | |
6668 | ||
6669 | +ctf_user_array_nowrite(__t__, __n__, __e__, __s__)+ | |
6670 | | | |
6671 | Statically-sized array of integers. | |
6672 | ||
6673 | +__t__+:: | |
6674 | Array element C type. | |
6675 | ||
6676 | +__n__+:: | |
6677 | Field name. | |
6678 | ||
6679 | +__e__+:: | |
6680 | Argument expression. | |
6681 | ||
6682 | +__s__+:: | |
6683 | Number of elements. | |
6684 | ||
6685 | | | |
6686 | +ctf_array_bitfield(__t__, __n__, __e__, __s__)+ | |
6687 | ||
6688 | +ctf_array_bitfield_nowrite(__t__, __n__, __e__, __s__)+ | |
6689 | ||
6690 | +ctf_user_array_bitfield(__t__, __n__, __e__, __s__)+ | |
6691 | ||
6692 | +ctf_user_array_bitfield_nowrite(__t__, __n__, __e__, __s__)+ | |
6693 | | | |
6694 | Statically-sized array of bits. | |
6695 | ||
6696 | The type of +__e__+ must be an integer type. +__s__+ is the number | |
6697 | of elements of such type in +__e__+, not the number of bits. | |
6698 | ||
6699 | +__t__+:: | |
6700 | Array element C type. | |
6701 | ||
6702 | +__n__+:: | |
6703 | Field name. | |
6704 | ||
6705 | +__e__+:: | |
6706 | Argument expression. | |
6707 | ||
6708 | +__s__+:: | |
6709 | Number of elements. | |
6710 | ||
6711 | | | |
6712 | +ctf_array_text(__t__, __n__, __e__, __s__)+ | |
6713 | ||
6714 | +ctf_array_text_nowrite(__t__, __n__, __e__, __s__)+ | |
6715 | ||
6716 | +ctf_user_array_text(__t__, __n__, __e__, __s__)+ | |
6717 | ||
6718 | +ctf_user_array_text_nowrite(__t__, __n__, __e__, __s__)+ | |
6719 | | | |
6720 | Statically-sized array, printed as text. | |
6721 | ||
6722 | The string does not need to be null-terminated. | |
6723 | ||
6724 | +__t__+:: | |
6725 | Array element C type (always `char`). | |
6726 | ||
6727 | +__n__+:: | |
6728 | Field name. | |
6729 | ||
6730 | +__e__+:: | |
6731 | Argument expression. | |
6732 | ||
6733 | +__s__+:: | |
6734 | Number of elements. | |
6735 | ||
6736 | | | |
6737 | +ctf_sequence(__t__, __n__, __e__, __T__, __E__)+ | |
6738 | ||
6739 | +ctf_sequence_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
6740 | ||
6741 | +ctf_user_sequence(__t__, __n__, __e__, __T__, __E__)+ | |
6742 | ||
6743 | +ctf_user_sequence_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
6744 | | | |
6745 | Dynamically-sized array of integers. | |
6746 | ||
6747 | The type of +__E__+ must be unsigned. | |
6748 | ||
6749 | +__t__+:: | |
6750 | Array element C type. | |
6751 | ||
6752 | +__n__+:: | |
6753 | Field name. | |
6754 | ||
6755 | +__e__+:: | |
6756 | Argument expression. | |
6757 | ||
6758 | +__T__+:: | |
6759 | Length expression C type. | |
6760 | ||
6761 | +__E__+:: | |
6762 | Length expression. | |
6763 | ||
6764 | | | |
6765 | +ctf_sequence_hex(__t__, __n__, __e__, __T__, __E__)+ | |
6766 | ||
6767 | +ctf_user_sequence_hex(__t__, __n__, __e__, __T__, __E__)+ | |
6768 | | | |
6769 | Dynamically-sized array of integers, displayed in base 16. | |
6770 | ||
6771 | The type of +__E__+ must be unsigned. | |
6772 | ||
6773 | +__t__+:: | |
6774 | Array element C type. | |
6775 | ||
6776 | +__n__+:: | |
6777 | Field name. | |
6778 | ||
6779 | +__e__+:: | |
6780 | Argument expression. | |
6781 | ||
6782 | +__T__+:: | |
6783 | Length expression C type. | |
6784 | ||
6785 | +__E__+:: | |
6786 | Length expression. | |
6787 | ||
6788 | |+ctf_sequence_network(__t__, __n__, __e__, __T__, __E__)+ | |
6789 | | | |
6790 | Dynamically-sized array of integers in network byte order (big-endian), | |
6791 | displayed in base 10. | |
6792 | ||
6793 | The type of +__E__+ must be unsigned. | |
6794 | ||
6795 | +__t__+:: | |
6796 | Array element C type. | |
6797 | ||
6798 | +__n__+:: | |
6799 | Field name. | |
6800 | ||
6801 | +__e__+:: | |
6802 | Argument expression. | |
6803 | ||
6804 | +__T__+:: | |
6805 | Length expression C type. | |
6806 | ||
6807 | +__E__+:: | |
6808 | Length expression. | |
6809 | ||
6810 | | | |
6811 | +ctf_sequence_bitfield(__t__, __n__, __e__, __T__, __E__)+ | |
6812 | ||
6813 | +ctf_sequence_bitfield_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
6814 | ||
6815 | +ctf_user_sequence_bitfield(__t__, __n__, __e__, __T__, __E__)+ | |
6816 | ||
6817 | +ctf_user_sequence_bitfield_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
6818 | | | |
6819 | Dynamically-sized array of bits. | |
6820 | ||
6821 | The type of +__e__+ must be an integer type. +__s__+ is the number | |
6822 | of elements of such type in +__e__+, not the number of bits. | |
6823 | ||
6824 | The type of +__E__+ must be unsigned. | |
6825 | ||
6826 | +__t__+:: | |
6827 | Array element C type. | |
6828 | ||
6829 | +__n__+:: | |
6830 | Field name. | |
6831 | ||
6832 | +__e__+:: | |
6833 | Argument expression. | |
6834 | ||
6835 | +__T__+:: | |
6836 | Length expression C type. | |
6837 | ||
6838 | +__E__+:: | |
6839 | Length expression. | |
6840 | ||
6841 | | | |
6842 | +ctf_sequence_text(__t__, __n__, __e__, __T__, __E__)+ | |
6843 | ||
6844 | +ctf_sequence_text_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
6845 | ||
6846 | +ctf_user_sequence_text(__t__, __n__, __e__, __T__, __E__)+ | |
6847 | ||
6848 | +ctf_user_sequence_text_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
6849 | | | |
6850 | Dynamically-sized array, displayed as text. | |
6851 | ||
6852 | The string does not need to be null-terminated. | |
6853 | ||
6854 | The type of +__E__+ must be unsigned. | |
6855 | ||
6856 | The behaviour is undefined if +__e__+ is `NULL`. | |
6857 | ||
6858 | +__t__+:: | |
6859 | Sequence element C type (always `char`). | |
6860 | ||
6861 | +__n__+:: | |
6862 | Field name. | |
6863 | ||
6864 | +__e__+:: | |
6865 | Argument expression. | |
6866 | ||
6867 | +__T__+:: | |
6868 | Length expression C type. | |
6869 | ||
6870 | +__E__+:: | |
6871 | Length expression. | |
6872 | |==== | |
6873 | ||
6874 | Use the `_user` versions when the argument expression, `e`, is | |
6875 | a user space address. In the cases of `ctf_user_integer*()` and | |
6876 | `ctf_user_float*()`, `&e` must be a user space address, thus `e` must | |
6877 | be addressable. | |
6878 | ||
6879 | The `_nowrite` versions omit themselves from the session trace, but are | |
6880 | otherwise identical. This means the `_nowrite` fields won't be written | |
6881 | in the recorded trace. Their primary purpose is to make some | |
6882 | of the event context available to the | |
6883 | <<enabling-disabling-events,event filters>> without having to | |
6884 | commit the data to sub-buffers. | |
6885 | ||
6886 | ||
6887 | [[glossary]] | |
6888 | == Glossary | |
6889 | ||
6890 | Terms related to LTTng and to tracing in general: | |
6891 | ||
6892 | Babeltrace:: | |
6893 | The http://diamon.org/babeltrace[Babeltrace] project, which includes | |
6894 | the cmd:babeltrace command, some libraries, and Python bindings. | |
6895 | ||
6896 | <<channel-buffering-schemes,buffering scheme>>:: | |
6897 | A layout of sub-buffers applied to a given channel. | |
6898 | ||
6899 | <<channel,channel>>:: | |
6900 | An entity which is responsible for a set of ring buffers. | |
6901 | + | |
6902 | <<event,Event rules>> are always attached to a specific channel. | |
6903 | ||
6904 | clock:: | |
6905 | A reference of time for a tracer. | |
6906 | ||
6907 | <<lttng-consumerd,consumer daemon>>:: | |
6908 | A process which is responsible for consuming the full sub-buffers | |
6909 | and write them to a file system or send them over the network. | |
6910 | ||
6911 | <<channel-overwrite-mode-vs-discard-mode,discard mode>>:: The event loss | |
6912 | mode in which the tracer _discards_ new event records when there's no | |
6913 | sub-buffer space left to store them. | |
6914 | ||
6915 | event:: | |
6916 | The consequence of the execution of an instrumentation | |
6917 | point, like a tracepoint that you manually place in some source code, | |
6918 | or a Linux kernel KProbe. | |
6919 | + | |
6920 | An event is said to _occur_ at a specific time. Different actions can | |
310431f4 | 6921 | be taken upon the occurrence of an event, like record the event's payload |
7adf7ee2 PP |
6922 | to a sub-buffer. |
6923 | ||
6924 | <<channel-overwrite-mode-vs-discard-mode,event loss mode>>:: | |
6925 | The mechanism by which event records of a given channel are lost | |
6926 | (not recorded) when there is no sub-buffer space left to store them. | |
6927 | ||
6928 | [[def-event-name]]event name:: | |
6929 | The name of an event, which is also the name of the event record. | |
6930 | This is also called the _instrumentation point name_. | |
6931 | ||
6932 | event record:: | |
6933 | A record, in a trace, of the payload of an event which occured. | |
6934 | ||
6935 | <<event,event rule>>:: | |
6936 | Set of conditions which must be satisfied for one or more occuring | |
6937 | events to be recorded. | |
6938 | ||
6939 | `java.util.logging`:: | |
6940 | Java platform's | |
6941 | https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[core logging facilities]. | |
6942 | ||
6943 | <<instrumenting,instrumentation>>:: | |
6944 | The use of LTTng probes to make a piece of software traceable. | |
6945 | ||
6946 | instrumentation point:: | |
6947 | A point in the execution path of a piece of software that, when | |
6948 | reached by this execution, can emit an event. | |
6949 | ||
6950 | instrumentation point name:: | |
6951 | See _<<def-event-name,event name>>_. | |
6952 | ||
6953 | log4j:: | |
6954 | A http://logging.apache.org/log4j/1.2/[logging library] for Java | |
6955 | developed by the Apache Software Foundation. | |
6956 | ||
6957 | log level:: | |
6958 | Level of severity of a log statement or user space | |
6959 | instrumentation point. | |
6960 | ||
6961 | LTTng:: | |
6962 | The _Linux Trace Toolkit: next generation_ project. | |
6963 | ||
6964 | <<lttng-cli,cmd:lttng>>:: | |
6965 | A command-line tool provided by the LTTng-tools project which you | |
6966 | can use to send and receive control messages to and from a | |
6967 | session daemon. | |
6968 | ||
6969 | LTTng analyses:: | |
6970 | The https://github.com/lttng/lttng-analyses[LTTng analyses] project, | |
6971 | which is a set of analyzing programs that are used to obtain a | |
6972 | higher level view of an LTTng trace. | |
6973 | ||
6974 | cmd:lttng-consumerd:: | |
6975 | The name of the consumer daemon program. | |
6976 | ||
6977 | cmd:lttng-crash:: | |
6978 | A utility provided by the LTTng-tools project which can convert | |
6979 | ring buffer files (usually | |
6980 | <<persistent-memory-file-systems,saved on a persistent memory file system>>) | |
6981 | to trace files. | |
6982 | ||
6983 | LTTng Documentation:: | |
6984 | This document. | |
6985 | ||
6986 | <<lttng-live,LTTng live>>:: | |
6987 | A communication protocol between the relay daemon and live viewers | |
6988 | which makes it possible to see events "live", as they are received by | |
6989 | the relay daemon. | |
6990 | ||
6991 | <<lttng-modules,LTTng-modules>>:: | |
6992 | The https://github.com/lttng/lttng-modules[LTTng-modules] project, | |
6993 | which contains the Linux kernel modules to make the Linux kernel | |
6994 | instrumentation points available for LTTng tracing. | |
6995 | ||
6996 | cmd:lttng-relayd:: | |
6997 | The name of the relay daemon program. | |
6998 | ||
6999 | cmd:lttng-sessiond:: | |
7000 | The name of the session daemon program. | |
7001 | ||
7002 | LTTng-tools:: | |
7003 | The https://github.com/lttng/lttng-tools[LTTng-tools] project, which | |
7004 | contains the various programs and libraries used to | |
7005 | <<controlling-tracing,control tracing>>. | |
7006 | ||
7007 | <<lttng-ust,LTTng-UST>>:: | |
7008 | The https://github.com/lttng/lttng-ust[LTTng-UST] project, which | |
7009 | contains libraries to instrument user applications. | |
7010 | ||
7011 | <<lttng-ust-agents,LTTng-UST Java agent>>:: | |
7012 | A Java package provided by the LTTng-UST project to allow the | |
7013 | LTTng instrumentation of `java.util.logging` and Apache log4j 1.2 | |
7014 | logging statements. | |
7015 | ||
7016 | <<lttng-ust-agents,LTTng-UST Python agent>>:: | |
7017 | A Python package provided by the LTTng-UST project to allow the | |
7018 | LTTng instrumentation of Python logging statements. | |
7019 | ||
7020 | <<channel-overwrite-mode-vs-discard-mode,overwrite mode>>:: | |
7021 | The event loss mode in which new event records overwrite older | |
7022 | event records when there's no sub-buffer space left to store them. | |
7023 | ||
7024 | <<channel-buffering-schemes,per-process buffering>>:: | |
7025 | A buffering scheme in which each instrumented process has its own | |
7026 | sub-buffers for a given user space channel. | |
7027 | ||
7028 | <<channel-buffering-schemes,per-user buffering>>:: | |
7029 | A buffering scheme in which all the processes of a Unix user share the | |
7030 | same sub-buffer for a given user space channel. | |
7031 | ||
7032 | <<lttng-relayd,relay daemon>>:: | |
7033 | A process which is responsible for receiving the trace data sent by | |
7034 | a distant consumer daemon. | |
7035 | ||
7036 | ring buffer:: | |
7037 | A set of sub-buffers. | |
7038 | ||
7039 | <<lttng-sessiond,session daemon>>:: | |
7040 | A process which receives control commands from you and orchestrates | |
7041 | the tracers and various LTTng daemons. | |
7042 | ||
7043 | <<taking-a-snapshot,snapshot>>:: | |
7044 | A copy of the current data of all the sub-buffers of a given tracing | |
7045 | session, saved as trace files. | |
7046 | ||
7047 | sub-buffer:: | |
7048 | One part of an LTTng ring buffer which contains event records. | |
7049 | ||
7050 | timestamp:: | |
7051 | The time information attached to an event when it is emitted. | |
7052 | ||
7053 | trace (_noun_):: | |
7054 | A set of files which are the concatenations of one or more | |
7055 | flushed sub-buffers. | |
7056 | ||
7057 | trace (_verb_):: | |
7058 | The action of recording the events emitted by an application | |
7059 | or by a system, or to initiate such recording by controlling | |
7060 | a tracer. | |
7061 | ||
7062 | Trace Compass:: | |
7063 | The http://tracecompass.org[Trace Compass] project and application. | |
7064 | ||
7065 | tracepoint:: | |
7066 | An instrumentation point using the tracepoint mechanism of the Linux | |
7067 | kernel or of LTTng-UST. | |
7068 | ||
7069 | tracepoint definition:: | |
7070 | The definition of a single tracepoint. | |
7071 | ||
7072 | tracepoint name:: | |
7073 | The name of a tracepoint. | |
7074 | ||
7075 | tracepoint provider:: | |
7076 | A set of functions providing tracepoints to an instrumented user | |
7077 | application. | |
7078 | + | |
7079 | Not to be confused with a _tracepoint provider package_: many tracepoint | |
7080 | providers can exist within a tracepoint provider package. | |
7081 | ||
7082 | tracepoint provider package:: | |
7083 | One or more tracepoint providers compiled as an object file or as | |
7084 | a shared library. | |
7085 | ||
7086 | tracer:: | |
7087 | A software which records emitted events. | |
7088 | ||
7089 | <<domain,tracing domain>>:: | |
7090 | A namespace for event sources. | |
7091 | ||
2e333859 | 7092 | <<tracing-group,tracing group>>:: |
7adf7ee2 PP |
7093 | The Unix group in which a Unix user can be to be allowed to trace the |
7094 | Linux kernel. | |
7095 | ||
7096 | <<tracing-session,tracing session>>:: | |
7097 | A stateful dialogue between you and a <<lttng-sessiond,session | |
7098 | daemon>>. | |
7099 | ||
7100 | user application:: | |
7101 | An application running in user space, as opposed to a Linux kernel | |
7102 | module, for example. |