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1 | The LTTng Documentation |
2 | ======================= | |
3 | Philippe Proulx <pproulx@efficios.com> | |
7568806b | 4 | v2.10, 1 August 2017 |
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5 | |
6 | ||
7 | include::../common/copyright.txt[] | |
8 | ||
9 | ||
10 | include::../common/welcome.txt[] | |
11 | ||
12 | ||
13 | include::../common/audience.txt[] | |
14 | ||
15 | ||
16 | [[chapters]] | |
17 | === What's in this documentation? | |
18 | ||
19 | The LTTng Documentation is divided into the following sections: | |
20 | ||
21 | * **<<nuts-and-bolts,Nuts and bolts>>** explains the | |
22 | rudiments of software tracing and the rationale behind the | |
23 | LTTng project. | |
24 | + | |
25 | You can skip this section if you’re familiar with software tracing and | |
26 | with the LTTng project. | |
27 | ||
28 | * **<<installing-lttng,Installation>>** describes the steps to | |
29 | install the LTTng packages on common Linux distributions and from | |
30 | their sources. | |
31 | + | |
32 | You can skip this section if you already properly installed LTTng on | |
33 | your target system. | |
34 | ||
35 | * **<<getting-started,Quick start>>** is a concise guide to | |
36 | getting started quickly with LTTng kernel and user space tracing. | |
37 | + | |
38 | We recommend this section if you're new to LTTng or to software tracing | |
39 | in general. | |
40 | + | |
41 | You can skip this section if you're not new to LTTng. | |
42 | ||
43 | * **<<core-concepts,Core concepts>>** explains the concepts at | |
44 | the heart of LTTng. | |
45 | + | |
46 | It's a good idea to become familiar with the core concepts | |
47 | before attempting to use the toolkit. | |
48 | ||
49 | * **<<plumbing,Components of LTTng>>** describes the various components | |
50 | of the LTTng machinery, like the daemons, the libraries, and the | |
51 | command-line interface. | |
52 | * **<<instrumenting,Instrumentation>>** shows different ways to | |
53 | instrument user applications and the Linux kernel. | |
54 | + | |
55 | Instrumenting source code is essential to provide a meaningful | |
56 | source of events. | |
57 | + | |
58 | You can skip this section if you do not have a programming background. | |
59 | ||
60 | * **<<controlling-tracing,Tracing control>>** is divided into topics | |
61 | which demonstrate how to use the vast array of features that | |
62 | LTTng{nbsp}{revision} offers. | |
63 | * **<<reference,Reference>>** contains reference tables. | |
64 | * **<<glossary,Glossary>>** is a specialized dictionary of terms related | |
65 | to LTTng or to the field of software tracing. | |
66 | ||
67 | ||
68 | include::../common/convention.txt[] | |
69 | ||
70 | ||
71 | include::../common/acknowledgements.txt[] | |
72 | ||
73 | ||
74 | [[whats-new]] | |
75 | == What's new in LTTng {revision}? | |
76 | ||
77 | LTTng{nbsp}{revision} bears the name _KeKriek_. From | |
78 | http://brasseriedunham.com/[Brasserie Dunham], the _**KeKriek**_ is a | |
79 | sour mashed golden wheat ale fermented with local sour cherries from | |
80 | Tougas orchards. Fresh sweet cherry notes with some tartness, lively | |
81 | carbonation with a dry finish. | |
82 | ||
83 | New features and changes in LTTng{nbsp}{revision}: | |
84 | ||
85 | * **Tracing control**: | |
86 | ** You can put more than one wildcard special character (`*`), and not | |
87 | only at the end, when you <<enabling-disabling-events,create an event | |
88 | rule>>, in both the instrumentation point name and the literal | |
89 | strings of | |
a2211984 | 90 | link:/man/1/lttng-enable-event/v{revision}/#doc-filter-syntax[filter expressions]: |
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91 | + |
92 | -- | |
93 | [role="term"] | |
94 | ---- | |
95 | # lttng enable-event --kernel 'x86_*_local_timer_*' \ | |
96 | --filter='name == "*a*b*c*d*e" && count >= 23' | |
97 | ---- | |
98 | -- | |
99 | + | |
100 | -- | |
101 | [role="term"] | |
102 | ---- | |
103 | $ lttng enable-event --userspace '*_my_org:*msg*' | |
104 | ---- | |
105 | -- | |
106 | ||
107 | ** New trigger and notification API for | |
108 | <<liblttng-ctl-lttng,`liblttng-ctl`>>. This new subsystem allows you | |
109 | to register triggers which emit a notification when a given | |
110 | condition is satisfied. As of LTTng{nbsp}{revision}, only | |
111 | <<channel,channel>> buffer usage conditions are available. | |
112 | Documentation is available in the | |
113 | https://github.com/lttng/lttng-tools/tree/stable-{revision}/include/lttng[`liblttng-ctl` | |
90c4e38a PP |
114 | header files] and in |
115 | <<notif-trigger-api,Get notified when a channel's buffer usage is too | |
116 | high or too low>>. | |
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117 | |
118 | ** You can now embed the whole textual LTTng-tools man pages into the | |
119 | executables at build time with the `--enable-embedded-help` | |
120 | configuration option. Thanks to this option, you don't need the | |
121 | http://www.methods.co.nz/asciidoc/[AsciiDoc] and | |
122 | https://directory.fsf.org/wiki/Xmlto[xmlto] tools at build time, and | |
123 | a manual pager at run time, to get access to this documentation. | |
124 | ||
125 | * **User space tracing**: | |
126 | ** New blocking mode: an LTTng-UST tracepoint can now block until | |
127 | <<channel,sub-buffer>> space is available instead of discarding event | |
128 | records in <<channel-overwrite-mode-vs-discard-mode,discard mode>>. | |
129 | With this feature, you can be sure that no event records are | |
130 | discarded during your application's execution at the expense of | |
131 | performance. | |
132 | + | |
133 | For example, the following command lines create a user space tracing | |
134 | channel with an infinite blocking timeout and run an application | |
135 | instrumented with LTTng-UST which is explicitly allowed to block: | |
136 | + | |
137 | -- | |
138 | [role="term"] | |
139 | ---- | |
140 | $ lttng create | |
000f69a6 | 141 | $ lttng enable-channel --userspace --blocking-timeout=inf blocking-channel |
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142 | $ lttng enable-event --userspace --channel=blocking-channel --all |
143 | $ lttng start | |
144 | $ LTTNG_UST_ALLOW_BLOCKING=1 my-app | |
145 | ---- | |
146 | -- | |
147 | + | |
148 | See the complete <<blocking-timeout-example,blocking timeout example>>. | |
149 | ||
150 | * **Linux kernel tracing**: | |
151 | ** Linux 4.10, 4.11, and 4.12 support. | |
152 | ** The thread state dump events recorded by LTTng-modules now contain | |
153 | the task's CPU identifier. This improves the precision of the | |
154 | scheduler model for analyses. | |
155 | ** Extended man:socketpair(2) system call tracing data. | |
156 | ||
157 | ||
158 | [[nuts-and-bolts]] | |
159 | == Nuts and bolts | |
160 | ||
161 | What is LTTng? As its name suggests, the _Linux Trace Toolkit: next | |
162 | generation_ is a modern toolkit for tracing Linux systems and | |
163 | applications. So your first question might be: | |
164 | **what is tracing?** | |
165 | ||
166 | ||
167 | [[what-is-tracing]] | |
168 | === What is tracing? | |
169 | ||
170 | As the history of software engineering progressed and led to what | |
171 | we now take for granted--complex, numerous and | |
172 | interdependent software applications running in parallel on | |
173 | sophisticated operating systems like Linux--the authors of such | |
174 | components, software developers, began feeling a natural | |
175 | urge to have tools that would ensure the robustness and good performance | |
176 | of their masterpieces. | |
177 | ||
178 | One major achievement in this field is, inarguably, the | |
179 | https://www.gnu.org/software/gdb/[GNU debugger (GDB)], | |
180 | an essential tool for developers to find and fix bugs. But even the best | |
181 | debugger won't help make your software run faster, and nowadays, faster | |
182 | software means either more work done by the same hardware, or cheaper | |
183 | hardware for the same work. | |
184 | ||
185 | A _profiler_ is often the tool of choice to identify performance | |
186 | bottlenecks. Profiling is suitable to identify _where_ performance is | |
187 | lost in a given software. The profiler outputs a profile, a statistical | |
188 | summary of observed events, which you may use to discover which | |
189 | functions took the most time to execute. However, a profiler won't | |
190 | report _why_ some identified functions are the bottleneck. Bottlenecks | |
191 | might only occur when specific conditions are met, conditions that are | |
192 | sometimes impossible to capture by a statistical profiler, or impossible | |
193 | to reproduce with an application altered by the overhead of an | |
194 | event-based profiler. For a thorough investigation of software | |
195 | performance issues, a history of execution is essential, with the | |
196 | recorded values of variables and context fields you choose, and | |
197 | with as little influence as possible on the instrumented software. This | |
198 | is where tracing comes in handy. | |
199 | ||
200 | _Tracing_ is a technique used to understand what goes on in a running | |
201 | software system. The software used for tracing is called a _tracer_, | |
202 | which is conceptually similar to a tape recorder. When recording, | |
203 | specific instrumentation points placed in the software source code | |
204 | generate events that are saved on a giant tape: a _trace_ file. You | |
205 | can trace user applications and the operating system at the same time, | |
206 | opening the possibility of resolving a wide range of problems that would | |
207 | otherwise be extremely challenging. | |
208 | ||
209 | Tracing is often compared to _logging_. However, tracers and loggers are | |
210 | two different tools, serving two different purposes. Tracers are | |
211 | designed to record much lower-level events that occur much more | |
212 | frequently than log messages, often in the range of thousands per | |
213 | second, with very little execution overhead. Logging is more appropriate | |
214 | for a very high-level analysis of less frequent events: user accesses, | |
215 | exceptional conditions (errors and warnings, for example), database | |
216 | transactions, instant messaging communications, and such. Simply put, | |
217 | logging is one of the many use cases that can be satisfied with tracing. | |
218 | ||
219 | The list of recorded events inside a trace file can be read manually | |
220 | like a log file for the maximum level of detail, but it is generally | |
221 | much more interesting to perform application-specific analyses to | |
222 | produce reduced statistics and graphs that are useful to resolve a | |
223 | given problem. Trace viewers and analyzers are specialized tools | |
224 | designed to do this. | |
225 | ||
226 | In the end, this is what LTTng is: a powerful, open source set of | |
227 | tools to trace the Linux kernel and user applications at the same time. | |
228 | LTTng is composed of several components actively maintained and | |
229 | developed by its link:/community/#where[community]. | |
230 | ||
231 | ||
232 | [[lttng-alternatives]] | |
233 | === Alternatives to noch:{LTTng} | |
234 | ||
235 | Excluding proprietary solutions, a few competing software tracers | |
236 | exist for Linux: | |
237 | ||
238 | * https://github.com/dtrace4linux/linux[dtrace4linux] is a port of | |
239 | Sun Microsystems's DTrace to Linux. The cmd:dtrace tool interprets | |
240 | user scripts and is responsible for loading code into the | |
241 | Linux kernel for further execution and collecting the outputted data. | |
242 | * https://en.wikipedia.org/wiki/Berkeley_Packet_Filter[eBPF] is a | |
243 | subsystem in the Linux kernel in which a virtual machine can execute | |
244 | programs passed from the user space to the kernel. You can attach | |
245 | such programs to tracepoints and KProbes thanks to a system call, and | |
246 | they can output data to the user space when executed thanks to | |
247 | different mechanisms (pipe, VM register values, and eBPF maps, to name | |
248 | a few). | |
249 | * https://www.kernel.org/doc/Documentation/trace/ftrace.txt[ftrace] | |
250 | is the de facto function tracer of the Linux kernel. Its user | |
251 | interface is a set of special files in sysfs. | |
252 | * https://perf.wiki.kernel.org/[perf] is | |
253 | a performance analyzing tool for Linux which supports hardware | |
254 | performance counters, tracepoints, as well as other counters and | |
255 | types of probes. perf's controlling utility is the cmd:perf command | |
256 | line/curses tool. | |
257 | * http://linux.die.net/man/1/strace[strace] | |
258 | is a command-line utility which records system calls made by a | |
259 | user process, as well as signal deliveries and changes of process | |
260 | state. strace makes use of https://en.wikipedia.org/wiki/Ptrace[ptrace] | |
261 | to fulfill its function. | |
262 | * http://www.sysdig.org/[sysdig], like SystemTap, uses scripts to | |
263 | analyze Linux kernel events. You write scripts, or _chisels_ in | |
264 | sysdig's jargon, in Lua and sysdig executes them while the system is | |
265 | being traced or afterwards. sysdig's interface is the cmd:sysdig | |
266 | command-line tool as well as the curses-based cmd:csysdig tool. | |
267 | * https://sourceware.org/systemtap/[SystemTap] is a Linux kernel and | |
268 | user space tracer which uses custom user scripts to produce plain text | |
269 | traces. SystemTap converts the scripts to the C language, and then | |
270 | compiles them as Linux kernel modules which are loaded to produce | |
271 | trace data. SystemTap's primary user interface is the cmd:stap | |
272 | command-line tool. | |
273 | ||
274 | The main distinctive features of LTTng is that it produces correlated | |
275 | kernel and user space traces, as well as doing so with the lowest | |
276 | overhead amongst other solutions. It produces trace files in the | |
277 | http://diamon.org/ctf[CTF] format, a file format optimized | |
278 | for the production and analyses of multi-gigabyte data. | |
279 | ||
280 | LTTng is the result of more than 10 years of active open source | |
281 | development by a community of passionate developers. | |
282 | LTTng{nbsp}{revision} is currently available on major desktop and server | |
283 | Linux distributions. | |
284 | ||
285 | The main interface for tracing control is a single command-line tool | |
286 | named cmd:lttng. The latter can create several tracing sessions, enable | |
287 | and disable events on the fly, filter events efficiently with custom | |
288 | user expressions, start and stop tracing, and much more. LTTng can | |
289 | record the traces on the file system or send them over the network, and | |
290 | keep them totally or partially. You can view the traces once tracing | |
291 | becomes inactive or in real-time. | |
292 | ||
293 | <<installing-lttng,Install LTTng now>> and | |
294 | <<getting-started,start tracing>>! | |
295 | ||
296 | ||
297 | [[installing-lttng]] | |
298 | == Installation | |
299 | ||
300 | **LTTng** is a set of software <<plumbing,components>> which interact to | |
301 | <<instrumenting,instrument>> the Linux kernel and user applications, and | |
302 | to <<controlling-tracing,control tracing>> (start and stop | |
303 | tracing, enable and disable event rules, and the rest). Those | |
304 | components are bundled into the following packages: | |
305 | ||
306 | * **LTTng-tools**: Libraries and command-line interface to | |
307 | control tracing. | |
308 | * **LTTng-modules**: Linux kernel modules to instrument and | |
309 | trace the kernel. | |
310 | * **LTTng-UST**: Libraries and Java/Python packages to instrument and | |
311 | trace user applications. | |
312 | ||
313 | Most distributions mark the LTTng-modules and LTTng-UST packages as | |
314 | optional when installing LTTng-tools (which is always required). In the | |
315 | following sections, we always provide the steps to install all three, | |
316 | but note that: | |
317 | ||
318 | * You only need to install LTTng-modules if you intend to trace the | |
319 | Linux kernel. | |
320 | * You only need to install LTTng-UST if you intend to trace user | |
321 | applications. | |
322 | ||
323 | [role="growable"] | |
324 | .Availability of LTTng{nbsp}{revision} for major Linux distributions as of 25 July 2017. | |
325 | |==== | |
326 | |Distribution |Available in releases |Alternatives | |
327 | ||
328 | |https://www.ubuntu.com/[Ubuntu] | |
329 | |Ubuntu{nbsp}14.04 _Trusty Tahr_ and Ubuntu{nbsp}16.04 _Xenial Xerus_: | |
330 | <<ubuntu-ppa,use the LTTng Stable{nbsp}{revision} PPA>>. | |
331 | |link:/docs/v2.9#doc-ubuntu[LTTng{nbsp}2.9 for Ubuntu{nbsp}17.04 _Zesty Zapus_]. | |
332 | ||
333 | <<building-from-source,Build LTTng{nbsp}{revision} from source>> for | |
334 | other Ubuntu releases. | |
335 | ||
336 | |https://getfedora.org/[Fedora] | |
337 | |_Not available_ | |
338 | |link:/docs/v2.9#doc-fedora[LTTng{nbsp}2.9 for Fedora 26]. | |
339 | ||
340 | <<building-from-source,Build LTTng{nbsp}{revision} from source>>. | |
341 | ||
342 | |https://www.debian.org/[Debian] | |
343 | |_Not available_ | |
344 | |link:/docs/v2.9#doc-debian[LTTng{nbsp}2.9 for Debian "stretch" | |
345 | (stable), Debian "buster" (testing), and Debian "sid" (unstable)]. | |
346 | ||
347 | <<building-from-source,Build LTTng{nbsp}{revision} from source>>. | |
348 | ||
349 | |https://www.archlinux.org/[Arch Linux] | |
350 | |_Not available_ | |
351 | |link:/docs/v2.9#doc-arch-linux[LTTng{nbsp}2.9 in the latest AUR packages]. | |
352 | ||
353 | |https://alpinelinux.org/[Alpine Linux] | |
354 | |_Not available_ | |
355 | |link:/docs/v2.9#doc-alpine-linux[LTTng{nbsp}2.9 for Alpine Linux "edge"]. | |
356 | ||
357 | <<building-from-source,Build LTTng{nbsp}{revision} from source>>. | |
358 | ||
359 | |https://www.redhat.com/[RHEL] and https://www.suse.com/[SLES] | |
360 | |See http://packages.efficios.com/[EfficiOS Enterprise Packages]. | |
361 | | | |
362 | ||
363 | |https://buildroot.org/[Buildroot] | |
364 | |_Not available_ | |
365 | |link:/docs/v2.9#doc-buildroot[LTTng{nbsp}2.9 for Buildroot{nbsp}2017.02 and | |
366 | Buildroot{nbsp}2017.05]. | |
367 | ||
368 | <<building-from-source,Build LTTng{nbsp}{revision} from source>>. | |
369 | ||
370 | |http://www.openembedded.org/wiki/Main_Page[OpenEmbedded] and | |
371 | https://www.yoctoproject.org/[Yocto] | |
372 | |_Not available_ | |
373 | |link:/docs/v2.9#doc-oe-yocto[LTTng{nbsp}2.9 for Yocto Project{nbsp}2.3 _Pyro_] | |
374 | (`openembedded-core` layer). | |
375 | ||
376 | <<building-from-source,Build LTTng{nbsp}{revision} from source>>. | |
377 | |==== | |
378 | ||
379 | ||
380 | [[ubuntu]] | |
381 | === [[ubuntu-official-repositories]]Ubuntu | |
382 | ||
383 | [[ubuntu-ppa]] | |
384 | ==== noch:{LTTng} Stable {revision} PPA | |
385 | ||
386 | The https://launchpad.net/~lttng/+archive/ubuntu/stable-{revision}[LTTng | |
387 | Stable{nbsp}{revision} PPA] offers the latest stable | |
388 | LTTng{nbsp}{revision} packages for: | |
389 | ||
390 | * Ubuntu{nbsp}14.04 _Trusty Tahr_ | |
391 | * Ubuntu{nbsp}16.04 _Xenial Xerus_ | |
392 | ||
393 | To install LTTng{nbsp}{revision} from the LTTng Stable{nbsp}{revision} PPA: | |
394 | ||
395 | . Add the LTTng Stable{nbsp}{revision} PPA repository and update the | |
396 | list of packages: | |
397 | + | |
398 | -- | |
399 | [role="term"] | |
400 | ---- | |
401 | # apt-add-repository ppa:lttng/stable-2.10 | |
402 | # apt-get update | |
403 | ---- | |
404 | -- | |
405 | ||
406 | . Install the main LTTng{nbsp}{revision} packages: | |
407 | + | |
408 | -- | |
409 | [role="term"] | |
410 | ---- | |
411 | # apt-get install lttng-tools | |
412 | # apt-get install lttng-modules-dkms | |
413 | # apt-get install liblttng-ust-dev | |
414 | ---- | |
415 | -- | |
416 | ||
417 | . **If you need to instrument and trace | |
418 | <<java-application,Java applications>>**, install the LTTng-UST | |
419 | Java agent: | |
420 | + | |
421 | -- | |
422 | [role="term"] | |
423 | ---- | |
424 | # apt-get install liblttng-ust-agent-java | |
425 | ---- | |
426 | -- | |
427 | ||
428 | . **If you need to instrument and trace | |
429 | <<python-application,Python{nbsp}3 applications>>**, install the | |
430 | LTTng-UST Python agent: | |
431 | + | |
432 | -- | |
433 | [role="term"] | |
434 | ---- | |
435 | # apt-get install python3-lttngust | |
436 | ---- | |
437 | -- | |
438 | ||
439 | ||
440 | [[enterprise-distributions]] | |
441 | === RHEL, SUSE, and other enterprise distributions | |
442 | ||
443 | To install LTTng on enterprise Linux distributions, such as Red Hat | |
444 | Enterprise Linux (RHEL) and SUSE Linux Enterprise Server (SUSE), please | |
445 | see http://packages.efficios.com/[EfficiOS Enterprise Packages]. | |
446 | ||
447 | ||
448 | [[building-from-source]] | |
449 | === Build from source | |
450 | ||
451 | To build and install LTTng{nbsp}{revision} from source: | |
452 | ||
453 | . Using your distribution's package manager, or from source, install | |
454 | the following dependencies of LTTng-tools and LTTng-UST: | |
455 | + | |
456 | -- | |
457 | * https://sourceforge.net/projects/libuuid/[libuuid] | |
458 | * http://directory.fsf.org/wiki/Popt[popt] | |
459 | * http://liburcu.org/[Userspace RCU] | |
460 | * http://www.xmlsoft.org/[libxml2] | |
461 | -- | |
462 | ||
463 | . Download, build, and install the latest LTTng-modules{nbsp}{revision}: | |
464 | + | |
465 | -- | |
466 | [role="term"] | |
467 | ---- | |
468 | $ cd $(mktemp -d) && | |
469 | wget http://lttng.org/files/lttng-modules/lttng-modules-latest-2.10.tar.bz2 && | |
470 | tar -xf lttng-modules-latest-2.10.tar.bz2 && | |
471 | cd lttng-modules-2.10.* && | |
472 | make && | |
473 | sudo make modules_install && | |
474 | sudo depmod -a | |
475 | ---- | |
476 | -- | |
477 | ||
478 | . Download, build, and install the latest LTTng-UST{nbsp}{revision}: | |
479 | + | |
480 | -- | |
481 | [role="term"] | |
482 | ---- | |
483 | $ cd $(mktemp -d) && | |
484 | wget http://lttng.org/files/lttng-ust/lttng-ust-latest-2.10.tar.bz2 && | |
485 | tar -xf lttng-ust-latest-2.10.tar.bz2 && | |
486 | cd lttng-ust-2.10.* && | |
487 | ./configure && | |
488 | make && | |
489 | sudo make install && | |
490 | sudo ldconfig | |
491 | ---- | |
492 | -- | |
493 | + | |
494 | -- | |
495 | [IMPORTANT] | |
496 | .Java and Python application tracing | |
497 | ==== | |
498 | If you need to instrument and trace <<java-application,Java | |
499 | applications>>, pass the `--enable-java-agent-jul`, | |
500 | `--enable-java-agent-log4j`, or `--enable-java-agent-all` options to the | |
501 | `configure` script, depending on which Java logging framework you use. | |
502 | ||
503 | If you need to instrument and trace <<python-application,Python | |
504 | applications>>, pass the `--enable-python-agent` option to the | |
505 | `configure` script. You can set the `PYTHON` environment variable to the | |
506 | path to the Python interpreter for which to install the LTTng-UST Python | |
507 | agent package. | |
508 | ==== | |
509 | -- | |
510 | + | |
511 | -- | |
512 | [NOTE] | |
513 | ==== | |
514 | By default, LTTng-UST libraries are installed to | |
515 | dir:{/usr/local/lib}, which is the de facto directory in which to | |
516 | keep self-compiled and third-party libraries. | |
517 | ||
518 | When <<building-tracepoint-providers-and-user-application,linking an | |
519 | instrumented user application with `liblttng-ust`>>: | |
520 | ||
521 | * Append `/usr/local/lib` to the env:LD_LIBRARY_PATH environment | |
522 | variable. | |
523 | * Pass the `-L/usr/local/lib` and `-Wl,-rpath,/usr/local/lib` options to | |
524 | man:gcc(1), man:g++(1), or man:clang(1). | |
525 | ==== | |
526 | -- | |
527 | ||
528 | . Download, build, and install the latest LTTng-tools{nbsp}{revision}: | |
529 | + | |
530 | -- | |
531 | [role="term"] | |
532 | ---- | |
533 | $ cd $(mktemp -d) && | |
534 | wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.10.tar.bz2 && | |
535 | tar -xf lttng-tools-latest-2.10.tar.bz2 && | |
536 | cd lttng-tools-2.10.* && | |
537 | ./configure && | |
538 | make && | |
539 | sudo make install && | |
540 | sudo ldconfig | |
541 | ---- | |
542 | -- | |
543 | ||
544 | TIP: The https://github.com/eepp/vlttng[vlttng tool] can do all the | |
545 | previous steps automatically for a given version of LTTng and confine | |
546 | the installed files in a specific directory. This can be useful to test | |
547 | LTTng without installing it on your system. | |
548 | ||
549 | ||
550 | [[getting-started]] | |
551 | == Quick start | |
552 | ||
553 | This is a short guide to get started quickly with LTTng kernel and user | |
554 | space tracing. | |
555 | ||
556 | Before you follow this guide, make sure to <<installing-lttng,install>> | |
557 | LTTng. | |
558 | ||
559 | This tutorial walks you through the steps to: | |
560 | ||
561 | . <<tracing-the-linux-kernel,Trace the Linux kernel>>. | |
562 | . <<tracing-your-own-user-application,Trace a user application>> written | |
563 | in C. | |
564 | . <<viewing-and-analyzing-your-traces,View and analyze the | |
565 | recorded events>>. | |
566 | ||
567 | ||
568 | [[tracing-the-linux-kernel]] | |
569 | === Trace the Linux kernel | |
570 | ||
571 | The following command lines start with the `#` prompt because you need | |
572 | root privileges to trace the Linux kernel. You can also trace the kernel | |
573 | as a regular user if your Unix user is a member of the | |
574 | <<tracing-group,tracing group>>. | |
575 | ||
576 | . Create a <<tracing-session,tracing session>> which writes its traces | |
577 | to dir:{/tmp/my-kernel-trace}: | |
578 | + | |
579 | -- | |
580 | [role="term"] | |
581 | ---- | |
582 | # lttng create my-kernel-session --output=/tmp/my-kernel-trace | |
583 | ---- | |
584 | -- | |
585 | ||
586 | . List the available kernel tracepoints and system calls: | |
587 | + | |
588 | -- | |
589 | [role="term"] | |
590 | ---- | |
591 | # lttng list --kernel | |
592 | # lttng list --kernel --syscall | |
593 | ---- | |
594 | -- | |
595 | ||
596 | . Create <<event,event rules>> which match the desired instrumentation | |
597 | point names, for example the `sched_switch` and `sched_process_fork` | |
598 | tracepoints, and the man:open(2) and man:close(2) system calls: | |
599 | + | |
600 | -- | |
601 | [role="term"] | |
602 | ---- | |
603 | # lttng enable-event --kernel sched_switch,sched_process_fork | |
604 | # lttng enable-event --kernel --syscall open,close | |
605 | ---- | |
606 | -- | |
607 | + | |
608 | You can also create an event rule which matches _all_ the Linux kernel | |
609 | tracepoints (this will generate a lot of data when tracing): | |
610 | + | |
611 | -- | |
612 | [role="term"] | |
613 | ---- | |
614 | # lttng enable-event --kernel --all | |
615 | ---- | |
616 | -- | |
617 | ||
618 | . <<basic-tracing-session-control,Start tracing>>: | |
619 | + | |
620 | -- | |
621 | [role="term"] | |
622 | ---- | |
623 | # lttng start | |
624 | ---- | |
625 | -- | |
626 | ||
627 | . Do some operation on your system for a few seconds. For example, | |
628 | load a website, or list the files of a directory. | |
629 | . <<basic-tracing-session-control,Stop tracing>> and destroy the | |
630 | tracing session: | |
631 | + | |
632 | -- | |
633 | [role="term"] | |
634 | ---- | |
635 | # lttng stop | |
636 | # lttng destroy | |
637 | ---- | |
638 | -- | |
639 | + | |
640 | The man:lttng-destroy(1) command does not destroy the trace data; it | |
641 | only destroys the state of the tracing session. | |
642 | ||
643 | . For the sake of this example, make the recorded trace accessible to | |
644 | the non-root users: | |
645 | + | |
646 | -- | |
647 | [role="term"] | |
648 | ---- | |
649 | # chown -R $(whoami) /tmp/my-kernel-trace | |
650 | ---- | |
651 | -- | |
652 | ||
653 | See <<viewing-and-analyzing-your-traces,View and analyze the | |
654 | recorded events>> to view the recorded events. | |
655 | ||
656 | ||
657 | [[tracing-your-own-user-application]] | |
658 | === Trace a user application | |
659 | ||
660 | This section steps you through a simple example to trace a | |
661 | _Hello world_ program written in C. | |
662 | ||
663 | To create the traceable user application: | |
664 | ||
665 | . Create the tracepoint provider header file, which defines the | |
666 | tracepoints and the events they can generate: | |
667 | + | |
668 | -- | |
669 | [source,c] | |
670 | .path:{hello-tp.h} | |
671 | ---- | |
672 | #undef TRACEPOINT_PROVIDER | |
673 | #define TRACEPOINT_PROVIDER hello_world | |
674 | ||
675 | #undef TRACEPOINT_INCLUDE | |
676 | #define TRACEPOINT_INCLUDE "./hello-tp.h" | |
677 | ||
678 | #if !defined(_HELLO_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ) | |
679 | #define _HELLO_TP_H | |
680 | ||
681 | #include <lttng/tracepoint.h> | |
682 | ||
683 | TRACEPOINT_EVENT( | |
684 | hello_world, | |
685 | my_first_tracepoint, | |
686 | TP_ARGS( | |
687 | int, my_integer_arg, | |
688 | char*, my_string_arg | |
689 | ), | |
690 | TP_FIELDS( | |
691 | ctf_string(my_string_field, my_string_arg) | |
692 | ctf_integer(int, my_integer_field, my_integer_arg) | |
693 | ) | |
694 | ) | |
695 | ||
696 | #endif /* _HELLO_TP_H */ | |
697 | ||
698 | #include <lttng/tracepoint-event.h> | |
699 | ---- | |
700 | -- | |
701 | ||
702 | . Create the tracepoint provider package source file: | |
703 | + | |
704 | -- | |
705 | [source,c] | |
706 | .path:{hello-tp.c} | |
707 | ---- | |
708 | #define TRACEPOINT_CREATE_PROBES | |
709 | #define TRACEPOINT_DEFINE | |
710 | ||
711 | #include "hello-tp.h" | |
712 | ---- | |
713 | -- | |
714 | ||
715 | . Build the tracepoint provider package: | |
716 | + | |
717 | -- | |
718 | [role="term"] | |
719 | ---- | |
720 | $ gcc -c -I. hello-tp.c | |
721 | ---- | |
722 | -- | |
723 | ||
724 | . Create the _Hello World_ application source file: | |
725 | + | |
726 | -- | |
727 | [source,c] | |
728 | .path:{hello.c} | |
729 | ---- | |
730 | #include <stdio.h> | |
731 | #include "hello-tp.h" | |
732 | ||
733 | int main(int argc, char *argv[]) | |
734 | { | |
735 | int x; | |
736 | ||
737 | puts("Hello, World!\nPress Enter to continue..."); | |
738 | ||
739 | /* | |
740 | * The following getchar() call is only placed here for the purpose | |
741 | * of this demonstration, to pause the application in order for | |
742 | * you to have time to list its tracepoints. It is not | |
743 | * needed otherwise. | |
744 | */ | |
745 | getchar(); | |
746 | ||
747 | /* | |
748 | * A tracepoint() call. | |
749 | * | |
750 | * Arguments, as defined in hello-tp.h: | |
751 | * | |
752 | * 1. Tracepoint provider name (required) | |
753 | * 2. Tracepoint name (required) | |
754 | * 3. my_integer_arg (first user-defined argument) | |
755 | * 4. my_string_arg (second user-defined argument) | |
756 | * | |
757 | * Notice the tracepoint provider and tracepoint names are | |
758 | * NOT strings: they are in fact parts of variables that the | |
759 | * macros in hello-tp.h create. | |
760 | */ | |
761 | tracepoint(hello_world, my_first_tracepoint, 23, "hi there!"); | |
762 | ||
763 | for (x = 0; x < argc; ++x) { | |
764 | tracepoint(hello_world, my_first_tracepoint, x, argv[x]); | |
765 | } | |
766 | ||
767 | puts("Quitting now!"); | |
768 | tracepoint(hello_world, my_first_tracepoint, x * x, "x^2"); | |
769 | ||
770 | return 0; | |
771 | } | |
772 | ---- | |
773 | -- | |
774 | ||
775 | . Build the application: | |
776 | + | |
777 | -- | |
778 | [role="term"] | |
779 | ---- | |
780 | $ gcc -c hello.c | |
781 | ---- | |
782 | -- | |
783 | ||
784 | . Link the application with the tracepoint provider package, | |
785 | `liblttng-ust`, and `libdl`: | |
786 | + | |
787 | -- | |
788 | [role="term"] | |
789 | ---- | |
790 | $ gcc -o hello hello.o hello-tp.o -llttng-ust -ldl | |
791 | ---- | |
792 | -- | |
793 | ||
794 | Here's the whole build process: | |
795 | ||
796 | [role="img-100"] | |
797 | .User space tracing tutorial's build steps. | |
798 | image::ust-flow.png[] | |
799 | ||
800 | To trace the user application: | |
801 | ||
802 | . Run the application with a few arguments: | |
803 | + | |
804 | -- | |
805 | [role="term"] | |
806 | ---- | |
807 | $ ./hello world and beyond | |
808 | ---- | |
809 | -- | |
810 | + | |
811 | You see: | |
812 | + | |
813 | -- | |
814 | ---- | |
815 | Hello, World! | |
816 | Press Enter to continue... | |
817 | ---- | |
818 | -- | |
819 | ||
820 | . Start an LTTng <<lttng-sessiond,session daemon>>: | |
821 | + | |
822 | -- | |
823 | [role="term"] | |
824 | ---- | |
825 | $ lttng-sessiond --daemonize | |
826 | ---- | |
827 | -- | |
828 | + | |
829 | Note that a session daemon might already be running, for example as | |
830 | a service that the distribution's service manager started. | |
831 | ||
832 | . List the available user space tracepoints: | |
833 | + | |
834 | -- | |
835 | [role="term"] | |
836 | ---- | |
837 | $ lttng list --userspace | |
838 | ---- | |
839 | -- | |
840 | + | |
841 | You see the `hello_world:my_first_tracepoint` tracepoint listed | |
842 | under the `./hello` process. | |
843 | ||
844 | . Create a <<tracing-session,tracing session>>: | |
845 | + | |
846 | -- | |
847 | [role="term"] | |
848 | ---- | |
849 | $ lttng create my-user-space-session | |
850 | ---- | |
851 | -- | |
852 | ||
853 | . Create an <<event,event rule>> which matches the | |
854 | `hello_world:my_first_tracepoint` event name: | |
855 | + | |
856 | -- | |
857 | [role="term"] | |
858 | ---- | |
859 | $ lttng enable-event --userspace hello_world:my_first_tracepoint | |
860 | ---- | |
861 | -- | |
862 | ||
863 | . <<basic-tracing-session-control,Start tracing>>: | |
864 | + | |
865 | -- | |
866 | [role="term"] | |
867 | ---- | |
868 | $ lttng start | |
869 | ---- | |
870 | -- | |
871 | ||
872 | . Go back to the running `hello` application and press Enter. The | |
873 | program executes all `tracepoint()` instrumentation points and exits. | |
874 | . <<basic-tracing-session-control,Stop tracing>> and destroy the | |
875 | tracing session: | |
876 | + | |
877 | -- | |
878 | [role="term"] | |
879 | ---- | |
880 | $ lttng stop | |
881 | $ lttng destroy | |
882 | ---- | |
883 | -- | |
884 | + | |
885 | The man:lttng-destroy(1) command does not destroy the trace data; it | |
886 | only destroys the state of the tracing session. | |
887 | ||
888 | By default, LTTng saves the traces in | |
889 | +$LTTNG_HOME/lttng-traces/__name__-__date__-__time__+, | |
890 | where +__name__+ is the tracing session name. The | |
891 | env:LTTNG_HOME environment variable defaults to `$HOME` if not set. | |
892 | ||
893 | See <<viewing-and-analyzing-your-traces,View and analyze the | |
894 | recorded events>> to view the recorded events. | |
895 | ||
896 | ||
897 | [[viewing-and-analyzing-your-traces]] | |
898 | === View and analyze the recorded events | |
899 | ||
900 | Once you have completed the <<tracing-the-linux-kernel,Trace the Linux | |
901 | kernel>> and <<tracing-your-own-user-application,Trace a user | |
902 | application>> tutorials, you can inspect the recorded events. | |
903 | ||
904 | Many tools are available to read LTTng traces: | |
905 | ||
906 | * **cmd:babeltrace** is a command-line utility which converts trace | |
907 | formats; it supports the format that LTTng produces, CTF, as well as a | |
908 | basic text output which can be ++grep++ed. The cmd:babeltrace command | |
909 | is part of the http://diamon.org/babeltrace[Babeltrace] project. | |
910 | * Babeltrace also includes | |
911 | **https://www.python.org/[Python] bindings** so | |
912 | that you can easily open and read an LTTng trace with your own script, | |
913 | benefiting from the power of Python. | |
914 | * http://tracecompass.org/[**Trace Compass**] | |
915 | is a graphical user interface for viewing and analyzing any type of | |
916 | logs or traces, including LTTng's. | |
917 | * https://github.com/lttng/lttng-analyses[**LTTng analyses**] is a | |
918 | project which includes many high-level analyses of LTTng kernel | |
919 | traces, like scheduling statistics, interrupt frequency distribution, | |
920 | top CPU usage, and more. | |
921 | ||
922 | NOTE: This section assumes that the traces recorded during the previous | |
923 | tutorials were saved to their default location, in the | |
924 | dir:{$LTTNG_HOME/lttng-traces} directory. The env:LTTNG_HOME | |
925 | environment variable defaults to `$HOME` if not set. | |
926 | ||
927 | ||
928 | [[viewing-and-analyzing-your-traces-bt]] | |
929 | ==== Use the cmd:babeltrace command-line tool | |
930 | ||
931 | The simplest way to list all the recorded events of a trace is to pass | |
932 | its path to cmd:babeltrace with no options: | |
933 | ||
934 | [role="term"] | |
935 | ---- | |
936 | $ babeltrace ~/lttng-traces/my-user-space-session* | |
937 | ---- | |
938 | ||
939 | cmd:babeltrace finds all traces recursively within the given path and | |
940 | prints all their events, merging them in chronological order. | |
941 | ||
942 | You can pipe the output of cmd:babeltrace into a tool like man:grep(1) for | |
943 | further filtering: | |
944 | ||
945 | [role="term"] | |
946 | ---- | |
947 | $ babeltrace /tmp/my-kernel-trace | grep _switch | |
948 | ---- | |
949 | ||
950 | You can pipe the output of cmd:babeltrace into a tool like man:wc(1) to | |
951 | count the recorded events: | |
952 | ||
953 | [role="term"] | |
954 | ---- | |
955 | $ babeltrace /tmp/my-kernel-trace | grep _open | wc --lines | |
956 | ---- | |
957 | ||
958 | ||
959 | [[viewing-and-analyzing-your-traces-bt-python]] | |
960 | ==== Use the Babeltrace Python bindings | |
961 | ||
962 | The <<viewing-and-analyzing-your-traces-bt,text output of cmd:babeltrace>> | |
963 | is useful to isolate events by simple matching using man:grep(1) and | |
964 | similar utilities. However, more elaborate filters, such as keeping only | |
965 | event records with a field value falling within a specific range, are | |
966 | not trivial to write using a shell. Moreover, reductions and even the | |
967 | most basic computations involving multiple event records are virtually | |
968 | impossible to implement. | |
969 | ||
970 | Fortunately, Babeltrace ships with Python 3 bindings which makes it easy | |
971 | to read the event records of an LTTng trace sequentially and compute the | |
972 | desired information. | |
973 | ||
974 | The following script accepts an LTTng Linux kernel trace path as its | |
975 | first argument and prints the short names of the top 5 running processes | |
976 | on CPU 0 during the whole trace: | |
977 | ||
978 | [source,python] | |
979 | .path:{top5proc.py} | |
980 | ---- | |
981 | from collections import Counter | |
982 | import babeltrace | |
983 | import sys | |
984 | ||
985 | ||
986 | def top5proc(): | |
987 | if len(sys.argv) != 2: | |
988 | msg = 'Usage: python3 {} TRACEPATH'.format(sys.argv[0]) | |
989 | print(msg, file=sys.stderr) | |
990 | return False | |
991 | ||
992 | # A trace collection contains one or more traces | |
993 | col = babeltrace.TraceCollection() | |
994 | ||
995 | # Add the trace provided by the user (LTTng traces always have | |
996 | # the 'ctf' format) | |
997 | if col.add_trace(sys.argv[1], 'ctf') is None: | |
998 | raise RuntimeError('Cannot add trace') | |
999 | ||
1000 | # This counter dict contains execution times: | |
1001 | # | |
1002 | # task command name -> total execution time (ns) | |
1003 | exec_times = Counter() | |
1004 | ||
1005 | # This contains the last `sched_switch` timestamp | |
1006 | last_ts = None | |
1007 | ||
1008 | # Iterate on events | |
1009 | for event in col.events: | |
1010 | # Keep only `sched_switch` events | |
1011 | if event.name != 'sched_switch': | |
1012 | continue | |
1013 | ||
1014 | # Keep only events which happened on CPU 0 | |
1015 | if event['cpu_id'] != 0: | |
1016 | continue | |
1017 | ||
1018 | # Event timestamp | |
1019 | cur_ts = event.timestamp | |
1020 | ||
1021 | if last_ts is None: | |
1022 | # We start here | |
1023 | last_ts = cur_ts | |
1024 | ||
1025 | # Previous task command (short) name | |
1026 | prev_comm = event['prev_comm'] | |
1027 | ||
1028 | # Initialize entry in our dict if not yet done | |
1029 | if prev_comm not in exec_times: | |
1030 | exec_times[prev_comm] = 0 | |
1031 | ||
1032 | # Compute previous command execution time | |
1033 | diff = cur_ts - last_ts | |
1034 | ||
1035 | # Update execution time of this command | |
1036 | exec_times[prev_comm] += diff | |
1037 | ||
1038 | # Update last timestamp | |
1039 | last_ts = cur_ts | |
1040 | ||
1041 | # Display top 5 | |
1042 | for name, ns in exec_times.most_common(5): | |
1043 | s = ns / 1000000000 | |
1044 | print('{:20}{} s'.format(name, s)) | |
1045 | ||
1046 | return True | |
1047 | ||
1048 | ||
1049 | if __name__ == '__main__': | |
1050 | sys.exit(0 if top5proc() else 1) | |
1051 | ---- | |
1052 | ||
1053 | Run this script: | |
1054 | ||
1055 | [role="term"] | |
1056 | ---- | |
1057 | $ python3 top5proc.py /tmp/my-kernel-trace/kernel | |
1058 | ---- | |
1059 | ||
1060 | Output example: | |
1061 | ||
1062 | ---- | |
1063 | swapper/0 48.607245889 s | |
1064 | chromium 7.192738188 s | |
1065 | pavucontrol 0.709894415 s | |
1066 | Compositor 0.660867933 s | |
1067 | Xorg.bin 0.616753786 s | |
1068 | ---- | |
1069 | ||
1070 | Note that `swapper/0` is the "idle" process of CPU 0 on Linux; since we | |
1071 | weren't using the CPU that much when tracing, its first position in the | |
1072 | list makes sense. | |
1073 | ||
1074 | ||
1075 | [[core-concepts]] | |
1076 | == [[understanding-lttng]]Core concepts | |
1077 | ||
1078 | From a user's perspective, the LTTng system is built on a few concepts, | |
1079 | or objects, on which the <<lttng-cli,cmd:lttng command-line tool>> | |
1080 | operates by sending commands to the <<lttng-sessiond,session daemon>>. | |
1081 | Understanding how those objects relate to eachother is key in mastering | |
1082 | the toolkit. | |
1083 | ||
1084 | The core concepts are: | |
1085 | ||
1086 | * <<tracing-session,Tracing session>> | |
1087 | * <<domain,Tracing domain>> | |
1088 | * <<channel,Channel and ring buffer>> | |
1089 | * <<"event","Instrumentation point, event rule, event, and event record">> | |
1090 | ||
1091 | ||
1092 | [[tracing-session]] | |
1093 | === Tracing session | |
1094 | ||
1095 | A _tracing session_ is a stateful dialogue between you and | |
1096 | a <<lttng-sessiond,session daemon>>. You can | |
1097 | <<creating-destroying-tracing-sessions,create a new tracing | |
1098 | session>> with the `lttng create` command. | |
1099 | ||
1100 | Anything that you do when you control LTTng tracers happens within a | |
1101 | tracing session. In particular, a tracing session: | |
1102 | ||
1103 | * Has its own name. | |
1104 | * Has its own set of trace files. | |
1105 | * Has its own state of activity (started or stopped). | |
1106 | * Has its own <<tracing-session-mode,mode>> (local, network streaming, | |
1107 | snapshot, or live). | |
1108 | * Has its own <<channel,channels>> which have their own | |
1109 | <<event,event rules>>. | |
1110 | ||
1111 | [role="img-100"] | |
1112 | .A _tracing session_ contains <<channel,channels>> that are members of <<domain,tracing domains>> and contain <<event,event rules>>. | |
1113 | image::concepts.png[] | |
1114 | ||
1115 | Those attributes and objects are completely isolated between different | |
1116 | tracing sessions. | |
1117 | ||
1118 | A tracing session is analogous to a cash machine session: | |
1119 | the operations you do on the banking system through the cash machine do | |
1120 | not alter the data of other users of the same system. In the case of | |
1121 | the cash machine, a session lasts as long as your bank card is inside. | |
1122 | In the case of LTTng, a tracing session lasts from the `lttng create` | |
1123 | command to the `lttng destroy` command. | |
1124 | ||
1125 | [role="img-100"] | |
1126 | .Each Unix user has its own set of tracing sessions. | |
1127 | image::many-sessions.png[] | |
1128 | ||
1129 | ||
1130 | [[tracing-session-mode]] | |
1131 | ==== Tracing session mode | |
1132 | ||
1133 | LTTng can send the generated trace data to different locations. The | |
1134 | _tracing session mode_ dictates where to send it. The following modes | |
1135 | are available in LTTng{nbsp}{revision}: | |
1136 | ||
1137 | Local mode:: | |
1138 | LTTng writes the traces to the file system of the machine being traced | |
1139 | (target system). | |
1140 | ||
1141 | Network streaming mode:: | |
1142 | LTTng sends the traces over the network to a | |
1143 | <<lttng-relayd,relay daemon>> running on a remote system. | |
1144 | ||
1145 | Snapshot mode:: | |
1146 | LTTng does not write the traces by default. Instead, you can request | |
1147 | LTTng to <<taking-a-snapshot,take a snapshot>>, that is, a copy of the | |
1148 | current tracing buffers, and to write it to the target's file system | |
1149 | or to send it over the network to a <<lttng-relayd,relay daemon>> | |
1150 | running on a remote system. | |
1151 | ||
1152 | Live mode:: | |
1153 | This mode is similar to the network streaming mode, but a live | |
1154 | trace viewer can connect to the distant relay daemon to | |
1155 | <<lttng-live,view event records as LTTng generates them>> by | |
1156 | the tracers. | |
1157 | ||
1158 | ||
1159 | [[domain]] | |
1160 | === Tracing domain | |
1161 | ||
1162 | A _tracing domain_ is a namespace for event sources. A tracing domain | |
1163 | has its own properties and features. | |
1164 | ||
1165 | There are currently five available tracing domains: | |
1166 | ||
1167 | * Linux kernel | |
1168 | * User space | |
1169 | * `java.util.logging` (JUL) | |
1170 | * log4j | |
1171 | * Python | |
1172 | ||
1173 | You must specify a tracing domain when using some commands to avoid | |
1174 | ambiguity. For example, since all the domains support named tracepoints | |
1175 | as event sources (instrumentation points that you manually insert in the | |
1176 | source code), you need to specify a tracing domain when | |
1177 | <<enabling-disabling-events,creating an event rule>> because all the | |
1178 | tracing domains could have tracepoints with the same names. | |
1179 | ||
1180 | Some features are reserved to specific tracing domains. Dynamic function | |
1181 | entry and return instrumentation points, for example, are currently only | |
1182 | supported in the Linux kernel tracing domain, but support for other | |
1183 | tracing domains could be added in the future. | |
1184 | ||
1185 | You can create <<channel,channels>> in the Linux kernel and user space | |
1186 | tracing domains. The other tracing domains have a single default | |
1187 | channel. | |
1188 | ||
1189 | ||
1190 | [[channel]] | |
1191 | === Channel and ring buffer | |
1192 | ||
1193 | A _channel_ is an object which is responsible for a set of ring buffers. | |
1194 | Each ring buffer is divided into multiple sub-buffers. When an LTTng | |
1195 | tracer emits an event, it can record it to one or more | |
1196 | sub-buffers. The attributes of a channel determine what to do when | |
1197 | there's no space left for a new event record because all sub-buffers | |
1198 | are full, where to send a full sub-buffer, and other behaviours. | |
1199 | ||
1200 | A channel is always associated to a <<domain,tracing domain>>. The | |
1201 | `java.util.logging` (JUL), log4j, and Python tracing domains each have | |
1202 | a default channel which you cannot configure. | |
1203 | ||
1204 | A channel also owns <<event,event rules>>. When an LTTng tracer emits | |
1205 | an event, it records it to the sub-buffers of all | |
1206 | the enabled channels with a satisfied event rule, as long as those | |
1207 | channels are part of active <<tracing-session,tracing sessions>>. | |
1208 | ||
1209 | ||
1210 | [[channel-buffering-schemes]] | |
1211 | ==== Per-user vs. per-process buffering schemes | |
1212 | ||
1213 | A channel has at least one ring buffer _per CPU_. LTTng always | |
1214 | records an event to the ring buffer associated to the CPU on which it | |
1215 | occurred. | |
1216 | ||
1217 | Two _buffering schemes_ are available when you | |
1218 | <<enabling-disabling-channels,create a channel>> in the | |
1219 | user space <<domain,tracing domain>>: | |
1220 | ||
1221 | Per-user buffering:: | |
1222 | Allocate one set of ring buffers--one per CPU--shared by all the | |
1223 | instrumented processes of each Unix user. | |
1224 | + | |
1225 | -- | |
1226 | [role="img-100"] | |
1227 | .Per-user buffering scheme. | |
1228 | image::per-user-buffering.png[] | |
1229 | -- | |
1230 | ||
1231 | Per-process buffering:: | |
1232 | Allocate one set of ring buffers--one per CPU--for each | |
1233 | instrumented process. | |
1234 | + | |
1235 | -- | |
1236 | [role="img-100"] | |
1237 | .Per-process buffering scheme. | |
1238 | image::per-process-buffering.png[] | |
1239 | -- | |
1240 | + | |
1241 | The per-process buffering scheme tends to consume more memory than the | |
1242 | per-user option because systems generally have more instrumented | |
1243 | processes than Unix users running instrumented processes. However, the | |
1244 | per-process buffering scheme ensures that one process having a high | |
1245 | event throughput won't fill all the shared sub-buffers of the same | |
1246 | user, only its own. | |
1247 | ||
1248 | The Linux kernel tracing domain has only one available buffering scheme | |
1249 | which is to allocate a single set of ring buffers for the whole system. | |
1250 | This scheme is similar to the per-user option, but with a single, global | |
1251 | user "running" the kernel. | |
1252 | ||
1253 | ||
1254 | [[channel-overwrite-mode-vs-discard-mode]] | |
1255 | ==== Overwrite vs. discard event loss modes | |
1256 | ||
1257 | When an event occurs, LTTng records it to a specific sub-buffer (yellow | |
1258 | arc in the following animation) of a specific channel's ring buffer. | |
1259 | When there's no space left in a sub-buffer, the tracer marks it as | |
1260 | consumable (red) and another, empty sub-buffer starts receiving the | |
1261 | following event records. A <<lttng-consumerd,consumer daemon>> | |
1262 | eventually consumes the marked sub-buffer (returns to white). | |
1263 | ||
1264 | [NOTE] | |
1265 | [role="docsvg-channel-subbuf-anim"] | |
1266 | ==== | |
1267 | {note-no-anim} | |
1268 | ==== | |
1269 | ||
1270 | In an ideal world, sub-buffers are consumed faster than they are filled, | |
1271 | as is the case in the previous animation. In the real world, | |
1272 | however, all sub-buffers can be full at some point, leaving no space to | |
1273 | record the following events. | |
1274 | ||
1275 | By default, LTTng-modules and LTTng-UST are _non-blocking_ tracers: when | |
1276 | no empty sub-buffer is available, it is acceptable to lose event records | |
1277 | when the alternative would be to cause substantial delays in the | |
1278 | instrumented application's execution. LTTng privileges performance over | |
1279 | integrity; it aims at perturbing the traced system as little as possible | |
1280 | in order to make tracing of subtle race conditions and rare interrupt | |
1281 | cascades possible. | |
1282 | ||
1283 | Starting from LTTng{nbsp}2.10, the LTTng user space tracer, LTTng-UST, | |
1284 | supports a _blocking mode_. See the <<blocking-timeout-example,blocking | |
1285 | timeout example>> to learn how to use the blocking mode. | |
1286 | ||
1287 | When it comes to losing event records because no empty sub-buffer is | |
1288 | available, or because the <<opt-blocking-timeout,blocking timeout>> is | |
1289 | reached, the channel's _event loss mode_ determines what to do. The | |
1290 | available event loss modes are: | |
1291 | ||
1292 | Discard mode:: | |
eeb71496 PP |
1293 | Drop the newest event records until a the tracer releases a |
1294 | sub-buffer. | |
1295 | + | |
1296 | This is the only available mode when you specify a | |
1297 | <<opt-blocking-timeout,blocking timeout>>. | |
85c29972 PP |
1298 | |
1299 | Overwrite mode:: | |
1300 | Clear the sub-buffer containing the oldest event records and start | |
1301 | writing the newest event records there. | |
1302 | + | |
1303 | This mode is sometimes called _flight recorder mode_ because it's | |
1304 | similar to a | |
1305 | https://en.wikipedia.org/wiki/Flight_recorder[flight recorder]: | |
1306 | always keep a fixed amount of the latest data. | |
1307 | ||
1308 | Which mechanism you should choose depends on your context: prioritize | |
1309 | the newest or the oldest event records in the ring buffer? | |
1310 | ||
4089946d | 1311 | Beware that, in overwrite mode, the tracer abandons a _whole sub-buffer_ |
85c29972 PP |
1312 | as soon as a there's no space left for a new event record, whereas in |
1313 | discard mode, the tracer only discards the event record that doesn't | |
1314 | fit. | |
1315 | ||
4089946d PP |
1316 | In discard mode, LTTng increments a count of lost event records when an |
1317 | event record is lost and saves this count to the trace. In overwrite | |
1318 | mode, since LTTng 2.8, LTTng increments a count of lost sub-buffers when | |
1319 | a sub-buffer is lost and saves this count to the trace. In this mode, | |
1320 | the exact number of lost event records in those lost sub-buffers is not | |
1321 | saved to the trace. Trace analyses can use the trace's saved discarded | |
1322 | event record and sub-buffer counts to decide whether or not to perform | |
1323 | the analyses even if trace data is known to be missing. | |
85c29972 PP |
1324 | |
1325 | There are a few ways to decrease your probability of losing event | |
1326 | records. | |
1327 | <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>> shows | |
1328 | how you can fine-une the sub-buffer count and size of a channel to | |
1329 | virtually stop losing event records, though at the cost of greater | |
1330 | memory usage. | |
1331 | ||
1332 | ||
1333 | [[channel-subbuf-size-vs-subbuf-count]] | |
1334 | ==== Sub-buffer count and size | |
1335 | ||
1336 | When you <<enabling-disabling-channels,create a channel>>, you can | |
1337 | set its number of sub-buffers and their size. | |
1338 | ||
1339 | Note that there is noticeable CPU overhead introduced when | |
1340 | switching sub-buffers (marking a full one as consumable and switching | |
1341 | to an empty one for the following events to be recorded). Knowing this, | |
1342 | the following list presents a few practical situations along with how | |
1343 | to configure the sub-buffer count and size for them: | |
1344 | ||
1345 | * **High event throughput**: In general, prefer bigger sub-buffers to | |
1346 | lower the risk of losing event records. | |
1347 | + | |
1348 | Having bigger sub-buffers also ensures a lower | |
1349 | <<channel-switch-timer,sub-buffer switching frequency>>. | |
1350 | + | |
1351 | The number of sub-buffers is only meaningful if you create the channel | |
1352 | in overwrite mode: in this case, if a sub-buffer overwrite happens, the | |
1353 | other sub-buffers are left unaltered. | |
1354 | ||
1355 | * **Low event throughput**: In general, prefer smaller sub-buffers | |
1356 | since the risk of losing event records is low. | |
1357 | + | |
1358 | Because events occur less frequently, the sub-buffer switching frequency | |
1359 | should remain low and thus the tracer's overhead should not be a | |
1360 | problem. | |
1361 | ||
1362 | * **Low memory system**: If your target system has a low memory | |
1363 | limit, prefer fewer first, then smaller sub-buffers. | |
1364 | + | |
1365 | Even if the system is limited in memory, you want to keep the | |
1366 | sub-buffers as big as possible to avoid a high sub-buffer switching | |
1367 | frequency. | |
1368 | ||
1369 | Note that LTTng uses http://diamon.org/ctf/[CTF] as its trace format, | |
1370 | which means event data is very compact. For example, the average | |
1371 | LTTng kernel event record weights about 32{nbsp}bytes. Thus, a | |
1372 | sub-buffer size of 1{nbsp}MiB is considered big. | |
1373 | ||
1374 | The previous situations highlight the major trade-off between a few big | |
1375 | sub-buffers and more, smaller sub-buffers: sub-buffer switching | |
1376 | frequency vs. how much data is lost in overwrite mode. Assuming a | |
1377 | constant event throughput and using the overwrite mode, the two | |
1378 | following configurations have the same ring buffer total size: | |
1379 | ||
1380 | [NOTE] | |
1381 | [role="docsvg-channel-subbuf-size-vs-count-anim"] | |
1382 | ==== | |
1383 | {note-no-anim} | |
1384 | ==== | |
1385 | ||
1386 | * **2 sub-buffers of 4{nbsp}MiB each**: Expect a very low sub-buffer | |
1387 | switching frequency, but if a sub-buffer overwrite happens, half of | |
1388 | the event records so far (4{nbsp}MiB) are definitely lost. | |
1389 | * **8 sub-buffers of 1{nbsp}MiB each**: Expect 4{nbsp}times the tracer's | |
1390 | overhead as the previous configuration, but if a sub-buffer | |
1391 | overwrite happens, only the eighth of event records so far are | |
1392 | definitely lost. | |
1393 | ||
1394 | In discard mode, the sub-buffers count parameter is pointless: use two | |
1395 | sub-buffers and set their size according to the requirements of your | |
1396 | situation. | |
1397 | ||
1398 | ||
1399 | [[channel-switch-timer]] | |
1400 | ==== Switch timer period | |
1401 | ||
1402 | The _switch timer period_ is an important configurable attribute of | |
1403 | a channel to ensure periodic sub-buffer flushing. | |
1404 | ||
1405 | When the _switch timer_ expires, a sub-buffer switch happens. You can | |
1406 | set the switch timer period attribute when you | |
1407 | <<enabling-disabling-channels,create a channel>> to ensure that event | |
1408 | data is consumed and committed to trace files or to a distant relay | |
1409 | daemon periodically in case of a low event throughput. | |
1410 | ||
1411 | [NOTE] | |
1412 | [role="docsvg-channel-switch-timer"] | |
1413 | ==== | |
1414 | {note-no-anim} | |
1415 | ==== | |
1416 | ||
1417 | This attribute is also convenient when you use big sub-buffers to cope | |
1418 | with a sporadic high event throughput, even if the throughput is | |
1419 | normally low. | |
1420 | ||
1421 | ||
1422 | [[channel-read-timer]] | |
1423 | ==== Read timer period | |
1424 | ||
1425 | By default, the LTTng tracers use a notification mechanism to signal a | |
1426 | full sub-buffer so that a consumer daemon can consume it. When such | |
1427 | notifications must be avoided, for example in real-time applications, | |
1428 | you can use the channel's _read timer_ instead. When the read timer | |
1429 | fires, the <<lttng-consumerd,consumer daemon>> checks for full, | |
1430 | consumable sub-buffers. | |
1431 | ||
1432 | ||
1433 | [[tracefile-rotation]] | |
1434 | ==== Trace file count and size | |
1435 | ||
1436 | By default, trace files can grow as large as needed. You can set the | |
1437 | maximum size of each trace file that a channel writes when you | |
1438 | <<enabling-disabling-channels,create a channel>>. When the size of | |
1439 | a trace file reaches the channel's fixed maximum size, LTTng creates | |
1440 | another file to contain the next event records. LTTng appends a file | |
1441 | count to each trace file name in this case. | |
1442 | ||
1443 | If you set the trace file size attribute when you create a channel, the | |
1444 | maximum number of trace files that LTTng creates is _unlimited_ by | |
1445 | default. To limit them, you can also set a maximum number of trace | |
1446 | files. When the number of trace files reaches the channel's fixed | |
1447 | maximum count, the oldest trace file is overwritten. This mechanism is | |
1448 | called _trace file rotation_. | |
1449 | ||
1450 | ||
1451 | [[event]] | |
1452 | === Instrumentation point, event rule, event, and event record | |
1453 | ||
1454 | An _event rule_ is a set of conditions which must be **all** satisfied | |
1455 | for LTTng to record an occuring event. | |
1456 | ||
1457 | You set the conditions when you <<enabling-disabling-events,create | |
1458 | an event rule>>. | |
1459 | ||
1460 | You always attach an event rule to <<channel,channel>> when you create | |
1461 | it. | |
1462 | ||
1463 | When an event passes the conditions of an event rule, LTTng records it | |
1464 | in one of the attached channel's sub-buffers. | |
1465 | ||
1466 | The available conditions, as of LTTng{nbsp}{revision}, are: | |
1467 | ||
1468 | * The event rule _is enabled_. | |
1469 | * The instrumentation point's type _is{nbsp}T_. | |
1470 | * The instrumentation point's name (sometimes called _event name_) | |
1471 | _matches{nbsp}N_, but _is not{nbsp}E_. | |
1472 | * The instrumentation point's log level _is as severe as{nbsp}L_, or | |
1473 | _is exactly{nbsp}L_. | |
1474 | * The fields of the event's payload _satisfy_ a filter | |
1475 | expression{nbsp}__F__. | |
1476 | ||
1477 | As you can see, all the conditions but the dynamic filter are related to | |
1478 | the event rule's status or to the instrumentation point, not to the | |
1479 | occurring events. This is why, without a filter, checking if an event | |
1480 | passes an event rule is not a dynamic task: when you create or modify an | |
1481 | event rule, all the tracers of its tracing domain enable or disable the | |
1482 | instrumentation points themselves once. This is possible because the | |
1483 | attributes of an instrumentation point (type, name, and log level) are | |
1484 | defined statically. In other words, without a dynamic filter, the tracer | |
1485 | _does not evaluate_ the arguments of an instrumentation point unless it | |
1486 | matches an enabled event rule. | |
1487 | ||
1488 | Note that, for LTTng to record an event, the <<channel,channel>> to | |
1489 | which a matching event rule is attached must also be enabled, and the | |
1490 | tracing session owning this channel must be active. | |
1491 | ||
1492 | [role="img-100"] | |
1493 | .Logical path from an instrumentation point to an event record. | |
1494 | image::event-rule.png[] | |
1495 | ||
1496 | .Event, event record, or event rule? | |
1497 | **** | |
1498 | With so many similar terms, it's easy to get confused. | |
1499 | ||
1500 | An **event** is the consequence of the execution of an _instrumentation | |
1501 | point_, like a tracepoint that you manually place in some source code, | |
1502 | or a Linux kernel KProbe. An event is said to _occur_ at a specific | |
1503 | time. Different actions can be taken upon the occurrence of an event, | |
1504 | like record the event's payload to a buffer. | |
1505 | ||
1506 | An **event record** is the representation of an event in a sub-buffer. A | |
1507 | tracer is responsible for capturing the payload of an event, current | |
1508 | context variables, the event's ID, and the event's timestamp. LTTng | |
1509 | can append this sub-buffer to a trace file. | |
1510 | ||
1511 | An **event rule** is a set of conditions which must all be satisfied for | |
1512 | LTTng to record an occuring event. Events still occur without | |
1513 | satisfying event rules, but LTTng does not record them. | |
1514 | **** | |
1515 | ||
1516 | ||
1517 | [[plumbing]] | |
1518 | == Components of noch:{LTTng} | |
1519 | ||
1520 | The second _T_ in _LTTng_ stands for _toolkit_: it would be wrong | |
1521 | to call LTTng a simple _tool_ since it is composed of multiple | |
1522 | interacting components. This section describes those components, | |
1523 | explains their respective roles, and shows how they connect together to | |
1524 | form the LTTng ecosystem. | |
1525 | ||
1526 | The following diagram shows how the most important components of LTTng | |
1527 | interact with user applications, the Linux kernel, and you: | |
1528 | ||
1529 | [role="img-100"] | |
1530 | .Control and trace data paths between LTTng components. | |
1531 | image::plumbing.png[] | |
1532 | ||
1533 | The LTTng project incorporates: | |
1534 | ||
1535 | * **LTTng-tools**: Libraries and command-line interface to | |
1536 | control tracing sessions. | |
1537 | ** <<lttng-sessiond,Session daemon>> (man:lttng-sessiond(8)). | |
1538 | ** <<lttng-consumerd,Consumer daemon>> (man:lttng-consumerd(8)). | |
1539 | ** <<lttng-relayd,Relay daemon>> (man:lttng-relayd(8)). | |
1540 | ** <<liblttng-ctl-lttng,Tracing control library>> (`liblttng-ctl`). | |
1541 | ** <<lttng-cli,Tracing control command-line tool>> (man:lttng(1)). | |
1542 | * **LTTng-UST**: Libraries and Java/Python packages to trace user | |
1543 | applications. | |
1544 | ** <<lttng-ust,User space tracing library>> (`liblttng-ust`) and its | |
1545 | headers to instrument and trace any native user application. | |
1546 | ** <<prebuilt-ust-helpers,Preloadable user space tracing helpers>>: | |
1547 | *** `liblttng-ust-libc-wrapper` | |
1548 | *** `liblttng-ust-pthread-wrapper` | |
1549 | *** `liblttng-ust-cyg-profile` | |
1550 | *** `liblttng-ust-cyg-profile-fast` | |
1551 | *** `liblttng-ust-dl` | |
1552 | ** User space tracepoint provider source files generator command-line | |
1553 | tool (man:lttng-gen-tp(1)). | |
1554 | ** <<lttng-ust-agents,LTTng-UST Java agent>> to instrument and trace | |
1555 | Java applications using `java.util.logging` or | |
1556 | Apache log4j 1.2 logging. | |
1557 | ** <<lttng-ust-agents,LTTng-UST Python agent>> to instrument | |
1558 | Python applications using the standard `logging` package. | |
1559 | * **LTTng-modules**: <<lttng-modules,Linux kernel modules>> to trace | |
1560 | the kernel. | |
1561 | ** LTTng kernel tracer module. | |
1562 | ** Tracing ring buffer kernel modules. | |
1563 | ** Probe kernel modules. | |
1564 | ** LTTng logger kernel module. | |
1565 | ||
1566 | ||
1567 | [[lttng-cli]] | |
1568 | === Tracing control command-line interface | |
1569 | ||
1570 | [role="img-100"] | |
1571 | .The tracing control command-line interface. | |
1572 | image::plumbing-lttng-cli.png[] | |
1573 | ||
1574 | The _man:lttng(1) command-line tool_ is the standard user interface to | |
1575 | control LTTng <<tracing-session,tracing sessions>>. The cmd:lttng tool | |
1576 | is part of LTTng-tools. | |
1577 | ||
1578 | The cmd:lttng tool is linked with | |
1579 | <<liblttng-ctl-lttng,`liblttng-ctl`>> to communicate with | |
1580 | one or more <<lttng-sessiond,session daemons>> behind the scenes. | |
1581 | ||
1582 | The cmd:lttng tool has a Git-like interface: | |
1583 | ||
1584 | [role="term"] | |
1585 | ---- | |
1586 | $ lttng <GENERAL OPTIONS> <COMMAND> <COMMAND OPTIONS> | |
1587 | ---- | |
1588 | ||
1589 | The <<controlling-tracing,Tracing control>> section explores the | |
1590 | available features of LTTng using the cmd:lttng tool. | |
1591 | ||
1592 | ||
1593 | [[liblttng-ctl-lttng]] | |
1594 | === Tracing control library | |
1595 | ||
1596 | [role="img-100"] | |
1597 | .The tracing control library. | |
1598 | image::plumbing-liblttng-ctl.png[] | |
1599 | ||
1600 | The _LTTng control library_, `liblttng-ctl`, is used to communicate | |
1601 | with a <<lttng-sessiond,session daemon>> using a C API that hides the | |
1602 | underlying protocol's details. `liblttng-ctl` is part of LTTng-tools. | |
1603 | ||
1604 | The <<lttng-cli,cmd:lttng command-line tool>> | |
1605 | is linked with `liblttng-ctl`. | |
1606 | ||
1607 | You can use `liblttng-ctl` in C or $$C++$$ source code by including its | |
1608 | "master" header: | |
1609 | ||
1610 | [source,c] | |
1611 | ---- | |
1612 | #include <lttng/lttng.h> | |
1613 | ---- | |
1614 | ||
1615 | Some objects are referenced by name (C string), such as tracing | |
1616 | sessions, but most of them require to create a handle first using | |
1617 | `lttng_create_handle()`. | |
1618 | ||
1619 | The best available developer documentation for `liblttng-ctl` is, as of | |
1620 | LTTng{nbsp}{revision}, its installed header files. Every function and | |
1621 | structure is thoroughly documented. | |
1622 | ||
1623 | ||
1624 | [[lttng-ust]] | |
1625 | === User space tracing library | |
1626 | ||
1627 | [role="img-100"] | |
1628 | .The user space tracing library. | |
1629 | image::plumbing-liblttng-ust.png[] | |
1630 | ||
1631 | The _user space tracing library_, `liblttng-ust` (see man:lttng-ust(3)), | |
1632 | is the LTTng user space tracer. It receives commands from a | |
1633 | <<lttng-sessiond,session daemon>>, for example to | |
1634 | enable and disable specific instrumentation points, and writes event | |
1635 | records to ring buffers shared with a | |
1636 | <<lttng-consumerd,consumer daemon>>. | |
1637 | `liblttng-ust` is part of LTTng-UST. | |
1638 | ||
1639 | Public C header files are installed beside `liblttng-ust` to | |
1640 | instrument any <<c-application,C or $$C++$$ application>>. | |
1641 | ||
1642 | <<lttng-ust-agents,LTTng-UST agents>>, which are regular Java and Python | |
1643 | packages, use their own library providing tracepoints which is | |
1644 | linked with `liblttng-ust`. | |
1645 | ||
1646 | An application or library does not have to initialize `liblttng-ust` | |
1647 | manually: its constructor does the necessary tasks to properly register | |
1648 | to a session daemon. The initialization phase also enables the | |
1649 | instrumentation points matching the <<event,event rules>> that you | |
1650 | already created. | |
1651 | ||
1652 | ||
1653 | [[lttng-ust-agents]] | |
1654 | === User space tracing agents | |
1655 | ||
1656 | [role="img-100"] | |
1657 | .The user space tracing agents. | |
1658 | image::plumbing-lttng-ust-agents.png[] | |
1659 | ||
1660 | The _LTTng-UST Java and Python agents_ are regular Java and Python | |
1661 | packages which add LTTng tracing capabilities to the | |
1662 | native logging frameworks. The LTTng-UST agents are part of LTTng-UST. | |
1663 | ||
1664 | In the case of Java, the | |
1665 | https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[`java.util.logging` | |
1666 | core logging facilities] and | |
1667 | https://logging.apache.org/log4j/1.2/[Apache log4j 1.2] are supported. | |
1668 | Note that Apache Log4{nbsp}2 is not supported. | |
1669 | ||
1670 | In the case of Python, the standard | |
1671 | https://docs.python.org/3/library/logging.html[`logging`] package | |
1672 | is supported. Both Python 2 and Python 3 modules can import the | |
1673 | LTTng-UST Python agent package. | |
1674 | ||
1675 | The applications using the LTTng-UST agents are in the | |
1676 | `java.util.logging` (JUL), | |
1677 | log4j, and Python <<domain,tracing domains>>. | |
1678 | ||
1679 | Both agents use the same mechanism to trace the log statements. When an | |
1680 | agent is initialized, it creates a log handler that attaches to the root | |
1681 | logger. The agent also registers to a <<lttng-sessiond,session daemon>>. | |
1682 | When the application executes a log statement, it is passed to the | |
1683 | agent's log handler by the root logger. The agent's log handler calls a | |
1684 | native function in a tracepoint provider package shared library linked | |
1685 | with <<lttng-ust,`liblttng-ust`>>, passing the formatted log message and | |
1686 | other fields, like its logger name and its log level. This native | |
1687 | function contains a user space instrumentation point, hence tracing the | |
1688 | log statement. | |
1689 | ||
1690 | The log level condition of an | |
1691 | <<event,event rule>> is considered when tracing | |
1692 | a Java or a Python application, and it's compatible with the standard | |
1693 | JUL, log4j, and Python log levels. | |
1694 | ||
1695 | ||
1696 | [[lttng-modules]] | |
1697 | === LTTng kernel modules | |
1698 | ||
1699 | [role="img-100"] | |
1700 | .The LTTng kernel modules. | |
1701 | image::plumbing-lttng-modules.png[] | |
1702 | ||
1703 | The _LTTng kernel modules_ are a set of Linux kernel modules | |
1704 | which implement the kernel tracer of the LTTng project. The LTTng | |
1705 | kernel modules are part of LTTng-modules. | |
1706 | ||
1707 | The LTTng kernel modules include: | |
1708 | ||
1709 | * A set of _probe_ modules. | |
1710 | + | |
1711 | Each module attaches to a specific subsystem | |
1712 | of the Linux kernel using its tracepoint instrument points. There are | |
1713 | also modules to attach to the entry and return points of the Linux | |
1714 | system call functions. | |
1715 | ||
1716 | * _Ring buffer_ modules. | |
1717 | + | |
1718 | A ring buffer implementation is provided as kernel modules. The LTTng | |
1719 | kernel tracer writes to the ring buffer; a | |
1720 | <<lttng-consumerd,consumer daemon>> reads from the ring buffer. | |
1721 | ||
1722 | * The _LTTng kernel tracer_ module. | |
1723 | * The _LTTng logger_ module. | |
1724 | + | |
1725 | The LTTng logger module implements the special path:{/proc/lttng-logger} | |
1726 | file so that any executable can generate LTTng events by opening and | |
1727 | writing to this file. | |
1728 | + | |
1729 | See <<proc-lttng-logger-abi,LTTng logger>>. | |
1730 | ||
1731 | Generally, you do not have to load the LTTng kernel modules manually | |
1732 | (using man:modprobe(8), for example): a root <<lttng-sessiond,session | |
1733 | daemon>> loads the necessary modules when starting. If you have extra | |
1734 | probe modules, you can specify to load them to the session daemon on | |
1735 | the command line. | |
1736 | ||
1737 | The LTTng kernel modules are installed in | |
1738 | +/usr/lib/modules/__release__/extra+ by default, where +__release__+ is | |
1739 | the kernel release (see `uname --kernel-release`). | |
1740 | ||
1741 | ||
1742 | [[lttng-sessiond]] | |
1743 | === Session daemon | |
1744 | ||
1745 | [role="img-100"] | |
1746 | .The session daemon. | |
1747 | image::plumbing-sessiond.png[] | |
1748 | ||
1749 | The _session daemon_, man:lttng-sessiond(8), is a daemon responsible for | |
1750 | managing tracing sessions and for controlling the various components of | |
1751 | LTTng. The session daemon is part of LTTng-tools. | |
1752 | ||
1753 | The session daemon sends control requests to and receives control | |
1754 | responses from: | |
1755 | ||
1756 | * The <<lttng-ust,user space tracing library>>. | |
1757 | + | |
1758 | Any instance of the user space tracing library first registers to | |
1759 | a session daemon. Then, the session daemon can send requests to | |
1760 | this instance, such as: | |
1761 | + | |
1762 | -- | |
1763 | ** Get the list of tracepoints. | |
1764 | ** Share an <<event,event rule>> so that the user space tracing library | |
1765 | can enable or disable tracepoints. Amongst the possible conditions | |
1766 | of an event rule is a filter expression which `liblttng-ust` evalutes | |
1767 | when an event occurs. | |
1768 | ** Share <<channel,channel>> attributes and ring buffer locations. | |
1769 | -- | |
1770 | + | |
1771 | The session daemon and the user space tracing library use a Unix | |
1772 | domain socket for their communication. | |
1773 | ||
1774 | * The <<lttng-ust-agents,user space tracing agents>>. | |
1775 | + | |
1776 | Any instance of a user space tracing agent first registers to | |
1777 | a session daemon. Then, the session daemon can send requests to | |
1778 | this instance, such as: | |
1779 | + | |
1780 | -- | |
1781 | ** Get the list of loggers. | |
1782 | ** Enable or disable a specific logger. | |
1783 | -- | |
1784 | + | |
1785 | The session daemon and the user space tracing agent use a TCP connection | |
1786 | for their communication. | |
1787 | ||
1788 | * The <<lttng-modules,LTTng kernel tracer>>. | |
1789 | * The <<lttng-consumerd,consumer daemon>>. | |
1790 | + | |
1791 | The session daemon sends requests to the consumer daemon to instruct | |
1792 | it where to send the trace data streams, amongst other information. | |
1793 | ||
1794 | * The <<lttng-relayd,relay daemon>>. | |
1795 | ||
1796 | The session daemon receives commands from the | |
1797 | <<liblttng-ctl-lttng,tracing control library>>. | |
1798 | ||
1799 | The root session daemon loads the appropriate | |
1800 | <<lttng-modules,LTTng kernel modules>> on startup. It also spawns | |
1801 | a <<lttng-consumerd,consumer daemon>> as soon as you create | |
1802 | an <<event,event rule>>. | |
1803 | ||
1804 | The session daemon does not send and receive trace data: this is the | |
1805 | role of the <<lttng-consumerd,consumer daemon>> and | |
1806 | <<lttng-relayd,relay daemon>>. It does, however, generate the | |
1807 | http://diamon.org/ctf/[CTF] metadata stream. | |
1808 | ||
1809 | Each Unix user can have its own session daemon instance. The | |
1810 | tracing sessions managed by different session daemons are completely | |
1811 | independent. | |
1812 | ||
1813 | The root user's session daemon is the only one which is | |
1814 | allowed to control the LTTng kernel tracer, and its spawned consumer | |
1815 | daemon is the only one which is allowed to consume trace data from the | |
1816 | LTTng kernel tracer. Note, however, that any Unix user which is a member | |
1817 | of the <<tracing-group,tracing group>> is allowed | |
1818 | to create <<channel,channels>> in the | |
1819 | Linux kernel <<domain,tracing domain>>, and thus to trace the Linux | |
1820 | kernel. | |
1821 | ||
1822 | The <<lttng-cli,cmd:lttng command-line tool>> automatically starts a | |
1823 | session daemon when using its `create` command if none is currently | |
1824 | running. You can also start the session daemon manually. | |
1825 | ||
1826 | ||
1827 | [[lttng-consumerd]] | |
1828 | === Consumer daemon | |
1829 | ||
1830 | [role="img-100"] | |
1831 | .The consumer daemon. | |
1832 | image::plumbing-consumerd.png[] | |
1833 | ||
1834 | The _consumer daemon_, man:lttng-consumerd(8), is a daemon which shares | |
1835 | ring buffers with user applications or with the LTTng kernel modules to | |
1836 | collect trace data and send it to some location (on disk or to a | |
1837 | <<lttng-relayd,relay daemon>> over the network). The consumer daemon | |
1838 | is part of LTTng-tools. | |
1839 | ||
1840 | You do not start a consumer daemon manually: a consumer daemon is always | |
1841 | spawned by a <<lttng-sessiond,session daemon>> as soon as you create an | |
1842 | <<event,event rule>>, that is, before you start tracing. When you kill | |
1843 | its owner session daemon, the consumer daemon also exits because it is | |
1844 | the session daemon's child process. Command-line options of | |
1845 | man:lttng-sessiond(8) target the consumer daemon process. | |
1846 | ||
1847 | There are up to two running consumer daemons per Unix user, whereas only | |
1848 | one session daemon can run per user. This is because each process can be | |
1849 | either 32-bit or 64-bit: if the target system runs a mixture of 32-bit | |
1850 | and 64-bit processes, it is more efficient to have separate | |
1851 | corresponding 32-bit and 64-bit consumer daemons. The root user is an | |
1852 | exception: it can have up to _three_ running consumer daemons: 32-bit | |
1853 | and 64-bit instances for its user applications, and one more | |
1854 | reserved for collecting kernel trace data. | |
1855 | ||
1856 | ||
1857 | [[lttng-relayd]] | |
1858 | === Relay daemon | |
1859 | ||
1860 | [role="img-100"] | |
1861 | .The relay daemon. | |
1862 | image::plumbing-relayd.png[] | |
1863 | ||
1864 | The _relay daemon_, man:lttng-relayd(8), is a daemon acting as a bridge | |
1865 | between remote session and consumer daemons, local trace files, and a | |
1866 | remote live trace viewer. The relay daemon is part of LTTng-tools. | |
1867 | ||
1868 | The main purpose of the relay daemon is to implement a receiver of | |
1869 | <<sending-trace-data-over-the-network,trace data over the network>>. | |
1870 | This is useful when the target system does not have much file system | |
1871 | space to record trace files locally. | |
1872 | ||
1873 | The relay daemon is also a server to which a | |
1874 | <<lttng-live,live trace viewer>> can | |
1875 | connect. The live trace viewer sends requests to the relay daemon to | |
1876 | receive trace data as the target system emits events. The | |
1877 | communication protocol is named _LTTng live_; it is used over TCP | |
1878 | connections. | |
1879 | ||
1880 | Note that you can start the relay daemon on the target system directly. | |
1881 | This is the setup of choice when the use case is to view events as | |
1882 | the target system emits them without the need of a remote system. | |
1883 | ||
1884 | ||
1885 | [[instrumenting]] | |
1886 | == [[using-lttng]]Instrumentation | |
1887 | ||
1888 | There are many examples of tracing and monitoring in our everyday life: | |
1889 | ||
1890 | * You have access to real-time and historical weather reports and | |
1891 | forecasts thanks to weather stations installed around the country. | |
1892 | * You know your heart is safe thanks to an electrocardiogram. | |
1893 | * You make sure not to drive your car too fast and to have enough fuel | |
1894 | to reach your destination thanks to gauges visible on your dashboard. | |
1895 | ||
1896 | All the previous examples have something in common: they rely on | |
1897 | **instruments**. Without the electrodes attached to the surface of your | |
1898 | body's skin, cardiac monitoring is futile. | |
1899 | ||
1900 | LTTng, as a tracer, is no different from those real life examples. If | |
1901 | you're about to trace a software system or, in other words, record its | |
1902 | history of execution, you better have **instrumentation points** in the | |
1903 | subject you're tracing, that is, the actual software. | |
1904 | ||
1905 | Various ways were developed to instrument a piece of software for LTTng | |
1906 | tracing. The most straightforward one is to manually place | |
1907 | instrumentation points, called _tracepoints_, in the software's source | |
1908 | code. It is also possible to add instrumentation points dynamically in | |
1909 | the Linux kernel <<domain,tracing domain>>. | |
1910 | ||
1911 | If you're only interested in tracing the Linux kernel, your | |
1912 | instrumentation needs are probably already covered by LTTng's built-in | |
1913 | <<lttng-modules,Linux kernel tracepoints>>. You may also wish to trace a | |
1914 | user application which is already instrumented for LTTng tracing. | |
1915 | In such cases, you can skip this whole section and read the topics of | |
1916 | the <<controlling-tracing,Tracing control>> section. | |
1917 | ||
1918 | Many methods are available to instrument a piece of software for LTTng | |
1919 | tracing. They are: | |
1920 | ||
1921 | * <<c-application,User space instrumentation for C and $$C++$$ | |
1922 | applications>>. | |
1923 | * <<prebuilt-ust-helpers,Prebuilt user space tracing helpers>>. | |
1924 | * <<java-application,User space Java agent>>. | |
1925 | * <<python-application,User space Python agent>>. | |
1926 | * <<proc-lttng-logger-abi,LTTng logger>>. | |
1927 | * <<instrumenting-linux-kernel,LTTng kernel tracepoints>>. | |
1928 | ||
1929 | ||
1930 | [[c-application]] | |
1931 | === [[cxx-application]]User space instrumentation for C and $$C++$$ applications | |
1932 | ||
1933 | The procedure to instrument a C or $$C++$$ user application with | |
1934 | the <<lttng-ust,LTTng user space tracing library>>, `liblttng-ust`, is: | |
1935 | ||
1936 | . <<tracepoint-provider,Create the source files of a tracepoint provider | |
1937 | package>>. | |
1938 | . <<probing-the-application-source-code,Add tracepoints to | |
1939 | the application's source code>>. | |
1940 | . <<building-tracepoint-providers-and-user-application,Build and link | |
1941 | a tracepoint provider package and the user application>>. | |
1942 | ||
1943 | If you need quick, man:printf(3)-like instrumentation, you can skip | |
1944 | those steps and use <<tracef,`tracef()`>> or <<tracelog,`tracelog()`>> | |
1945 | instead. | |
1946 | ||
1947 | IMPORTANT: You need to <<installing-lttng,install>> LTTng-UST to | |
1948 | instrument a user application with `liblttng-ust`. | |
1949 | ||
1950 | ||
1951 | [[tracepoint-provider]] | |
1952 | ==== Create the source files of a tracepoint provider package | |
1953 | ||
1954 | A _tracepoint provider_ is a set of compiled functions which provide | |
1955 | **tracepoints** to an application, the type of instrumentation point | |
1956 | supported by LTTng-UST. Those functions can emit events with | |
1957 | user-defined fields and serialize those events as event records to one | |
1958 | or more LTTng-UST <<channel,channel>> sub-buffers. The `tracepoint()` | |
1959 | macro, which you <<probing-the-application-source-code,insert in a user | |
1960 | application's source code>>, calls those functions. | |
1961 | ||
1962 | A _tracepoint provider package_ is an object file (`.o`) or a shared | |
1963 | library (`.so`) which contains one or more tracepoint providers. | |
1964 | Its source files are: | |
1965 | ||
1966 | * One or more <<tpp-header,tracepoint provider header>> (`.h`). | |
1967 | * A <<tpp-source,tracepoint provider package source>> (`.c`). | |
1968 | ||
1969 | A tracepoint provider package is dynamically linked with `liblttng-ust`, | |
1970 | the LTTng user space tracer, at run time. | |
1971 | ||
1972 | [role="img-100"] | |
1973 | .User application linked with `liblttng-ust` and containing a tracepoint provider. | |
1974 | image::ust-app.png[] | |
1975 | ||
1976 | NOTE: If you need quick, man:printf(3)-like instrumentation, you can | |
1977 | skip creating and using a tracepoint provider and use | |
1978 | <<tracef,`tracef()`>> or <<tracelog,`tracelog()`>> instead. | |
1979 | ||
1980 | ||
1981 | [[tpp-header]] | |
1982 | ===== Create a tracepoint provider header file template | |
1983 | ||
1984 | A _tracepoint provider header file_ contains the tracepoint | |
1985 | definitions of a tracepoint provider. | |
1986 | ||
1987 | To create a tracepoint provider header file: | |
1988 | ||
1989 | . Start from this template: | |
1990 | + | |
1991 | -- | |
1992 | [source,c] | |
1993 | .Tracepoint provider header file template (`.h` file extension). | |
1994 | ---- | |
1995 | #undef TRACEPOINT_PROVIDER | |
1996 | #define TRACEPOINT_PROVIDER provider_name | |
1997 | ||
1998 | #undef TRACEPOINT_INCLUDE | |
1999 | #define TRACEPOINT_INCLUDE "./tp.h" | |
2000 | ||
2001 | #if !defined(_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ) | |
2002 | #define _TP_H | |
2003 | ||
2004 | #include <lttng/tracepoint.h> | |
2005 | ||
2006 | /* | |
2007 | * Use TRACEPOINT_EVENT(), TRACEPOINT_EVENT_CLASS(), | |
2008 | * TRACEPOINT_EVENT_INSTANCE(), and TRACEPOINT_LOGLEVEL() here. | |
2009 | */ | |
2010 | ||
2011 | #endif /* _TP_H */ | |
2012 | ||
2013 | #include <lttng/tracepoint-event.h> | |
2014 | ---- | |
2015 | -- | |
2016 | ||
2017 | . Replace: | |
2018 | + | |
2019 | * `provider_name` with the name of your tracepoint provider. | |
2020 | * `"tp.h"` with the name of your tracepoint provider header file. | |
2021 | ||
2022 | . Below the `#include <lttng/tracepoint.h>` line, put your | |
2023 | <<defining-tracepoints,tracepoint definitions>>. | |
2024 | ||
2025 | Your tracepoint provider name must be unique amongst all the possible | |
2026 | tracepoint provider names used on the same target system. We | |
2027 | suggest to include the name of your project or company in the name, | |
2028 | for example, `org_lttng_my_project_tpp`. | |
2029 | ||
2030 | TIP: [[lttng-gen-tp]]You can use the man:lttng-gen-tp(1) tool to create | |
2031 | this boilerplate for you. When using cmd:lttng-gen-tp, all you need to | |
2032 | write are the <<defining-tracepoints,tracepoint definitions>>. | |
2033 | ||
2034 | ||
2035 | [[defining-tracepoints]] | |
2036 | ===== Create a tracepoint definition | |
2037 | ||
2038 | A _tracepoint definition_ defines, for a given tracepoint: | |
2039 | ||
2040 | * Its **input arguments**. They are the macro parameters that the | |
2041 | `tracepoint()` macro accepts for this particular tracepoint | |
2042 | in the user application's source code. | |
2043 | * Its **output event fields**. They are the sources of event fields | |
2044 | that form the payload of any event that the execution of the | |
2045 | `tracepoint()` macro emits for this particular tracepoint. | |
2046 | ||
2047 | You can create a tracepoint definition by using the | |
2048 | `TRACEPOINT_EVENT()` macro below the `#include <lttng/tracepoint.h>` | |
2049 | line in the | |
2050 | <<tpp-header,tracepoint provider header file template>>. | |
2051 | ||
2052 | The syntax of the `TRACEPOINT_EVENT()` macro is: | |
2053 | ||
2054 | [source,c] | |
2055 | .`TRACEPOINT_EVENT()` macro syntax. | |
2056 | ---- | |
2057 | TRACEPOINT_EVENT( | |
2058 | /* Tracepoint provider name */ | |
2059 | provider_name, | |
2060 | ||
2061 | /* Tracepoint name */ | |
2062 | tracepoint_name, | |
2063 | ||
2064 | /* Input arguments */ | |
2065 | TP_ARGS( | |
2066 | arguments | |
2067 | ), | |
2068 | ||
2069 | /* Output event fields */ | |
2070 | TP_FIELDS( | |
2071 | fields | |
2072 | ) | |
2073 | ) | |
2074 | ---- | |
2075 | ||
2076 | Replace: | |
2077 | ||
2078 | * `provider_name` with your tracepoint provider name. | |
2079 | * `tracepoint_name` with your tracepoint name. | |
2080 | * `arguments` with the <<tpp-def-input-args,input arguments>>. | |
2081 | * `fields` with the <<tpp-def-output-fields,output event field>> | |
2082 | definitions. | |
2083 | ||
2084 | This tracepoint emits events named `provider_name:tracepoint_name`. | |
2085 | ||
2086 | [IMPORTANT] | |
2087 | .Event name's length limitation | |
2088 | ==== | |
2089 | The concatenation of the tracepoint provider name and the | |
2090 | tracepoint name must not exceed **254 characters**. If it does, the | |
2091 | instrumented application compiles and runs, but LTTng throws multiple | |
2092 | warnings and you could experience serious issues. | |
2093 | ==== | |
2094 | ||
2095 | [[tpp-def-input-args]]The syntax of the `TP_ARGS()` macro is: | |
2096 | ||
2097 | [source,c] | |
2098 | .`TP_ARGS()` macro syntax. | |
2099 | ---- | |
2100 | TP_ARGS( | |
2101 | type, arg_name | |
2102 | ) | |
2103 | ---- | |
2104 | ||
2105 | Replace: | |
2106 | ||
2107 | * `type` with the C type of the argument. | |
2108 | * `arg_name` with the argument name. | |
2109 | ||
2110 | You can repeat `type` and `arg_name` up to 10 times to have | |
2111 | more than one argument. | |
2112 | ||
2113 | .`TP_ARGS()` usage with three arguments. | |
2114 | ==== | |
2115 | [source,c] | |
2116 | ---- | |
2117 | TP_ARGS( | |
2118 | int, count, | |
2119 | float, ratio, | |
2120 | const char*, query | |
2121 | ) | |
2122 | ---- | |
2123 | ==== | |
2124 | ||
2125 | The `TP_ARGS()` and `TP_ARGS(void)` forms are valid to create a | |
2126 | tracepoint definition with no input arguments. | |
2127 | ||
2128 | [[tpp-def-output-fields]]The `TP_FIELDS()` macro contains a list of | |
2129 | `ctf_*()` macros. Each `ctf_*()` macro defines one event field. See | |
2130 | man:lttng-ust(3) for a complete description of the available `ctf_*()` | |
2131 | macros. A `ctf_*()` macro specifies the type, size, and byte order of | |
2132 | one event field. | |
2133 | ||
2134 | Each `ctf_*()` macro takes an _argument expression_ parameter. This is a | |
2135 | C expression that the tracer evalutes at the `tracepoint()` macro site | |
2136 | in the application's source code. This expression provides a field's | |
2137 | source of data. The argument expression can include input argument names | |
2138 | listed in the `TP_ARGS()` macro. | |
2139 | ||
2140 | Each `ctf_*()` macro also takes a _field name_ parameter. Field names | |
2141 | must be unique within a given tracepoint definition. | |
2142 | ||
2143 | Here's a complete tracepoint definition example: | |
2144 | ||
2145 | .Tracepoint definition. | |
2146 | ==== | |
2147 | The following tracepoint definition defines a tracepoint which takes | |
2148 | three input arguments and has four output event fields. | |
2149 | ||
2150 | [source,c] | |
2151 | ---- | |
2152 | #include "my-custom-structure.h" | |
2153 | ||
2154 | TRACEPOINT_EVENT( | |
2155 | my_provider, | |
2156 | my_tracepoint, | |
2157 | TP_ARGS( | |
2158 | const struct my_custom_structure*, my_custom_structure, | |
2159 | float, ratio, | |
2160 | const char*, query | |
2161 | ), | |
2162 | TP_FIELDS( | |
2163 | ctf_string(query_field, query) | |
2164 | ctf_float(double, ratio_field, ratio) | |
2165 | ctf_integer(int, recv_size, my_custom_structure->recv_size) | |
2166 | ctf_integer(int, send_size, my_custom_structure->send_size) | |
2167 | ) | |
2168 | ) | |
2169 | ---- | |
2170 | ||
2171 | You can refer to this tracepoint definition with the `tracepoint()` | |
2172 | macro in your application's source code like this: | |
2173 | ||
2174 | [source,c] | |
2175 | ---- | |
2176 | tracepoint(my_provider, my_tracepoint, | |
2177 | my_structure, some_ratio, the_query); | |
2178 | ---- | |
2179 | ==== | |
2180 | ||
2181 | NOTE: The LTTng tracer only evaluates tracepoint arguments at run time | |
2182 | if they satisfy an enabled <<event,event rule>>. | |
2183 | ||
2184 | ||
2185 | [[using-tracepoint-classes]] | |
2186 | ===== Use a tracepoint class | |
2187 | ||
2188 | A _tracepoint class_ is a class of tracepoints which share the same | |
2189 | output event field definitions. A _tracepoint instance_ is one | |
2190 | instance of such a defined tracepoint class, with its own tracepoint | |
2191 | name. | |
2192 | ||
2193 | The <<defining-tracepoints,`TRACEPOINT_EVENT()` macro>> is actually a | |
2194 | shorthand which defines both a tracepoint class and a tracepoint | |
2195 | instance at the same time. | |
2196 | ||
2197 | When you build a tracepoint provider package, the C or $$C++$$ compiler | |
2198 | creates one serialization function for each **tracepoint class**. A | |
2199 | serialization function is responsible for serializing the event fields | |
2200 | of a tracepoint to a sub-buffer when tracing. | |
2201 | ||
2202 | For various performance reasons, when your situation requires multiple | |
2203 | tracepoint definitions with different names, but with the same event | |
2204 | fields, we recommend that you manually create a tracepoint class | |
2205 | and instantiate as many tracepoint instances as needed. One positive | |
2206 | effect of such a design, amongst other advantages, is that all | |
2207 | tracepoint instances of the same tracepoint class reuse the same | |
2208 | serialization function, thus reducing | |
2209 | https://en.wikipedia.org/wiki/Cache_pollution[cache pollution]. | |
2210 | ||
2211 | .Use a tracepoint class and tracepoint instances. | |
2212 | ==== | |
2213 | Consider the following three tracepoint definitions: | |
2214 | ||
2215 | [source,c] | |
2216 | ---- | |
2217 | TRACEPOINT_EVENT( | |
2218 | my_app, | |
2219 | get_account, | |
2220 | TP_ARGS( | |
2221 | int, userid, | |
2222 | size_t, len | |
2223 | ), | |
2224 | TP_FIELDS( | |
2225 | ctf_integer(int, userid, userid) | |
2226 | ctf_integer(size_t, len, len) | |
2227 | ) | |
2228 | ) | |
2229 | ||
2230 | TRACEPOINT_EVENT( | |
2231 | my_app, | |
2232 | get_settings, | |
2233 | TP_ARGS( | |
2234 | int, userid, | |
2235 | size_t, len | |
2236 | ), | |
2237 | TP_FIELDS( | |
2238 | ctf_integer(int, userid, userid) | |
2239 | ctf_integer(size_t, len, len) | |
2240 | ) | |
2241 | ) | |
2242 | ||
2243 | TRACEPOINT_EVENT( | |
2244 | my_app, | |
2245 | get_transaction, | |
2246 | TP_ARGS( | |
2247 | int, userid, | |
2248 | size_t, len | |
2249 | ), | |
2250 | TP_FIELDS( | |
2251 | ctf_integer(int, userid, userid) | |
2252 | ctf_integer(size_t, len, len) | |
2253 | ) | |
2254 | ) | |
2255 | ---- | |
2256 | ||
2257 | In this case, we create three tracepoint classes, with one implicit | |
2258 | tracepoint instance for each of them: `get_account`, `get_settings`, and | |
2259 | `get_transaction`. However, they all share the same event field names | |
2260 | and types. Hence three identical, yet independent serialization | |
2261 | functions are created when you build the tracepoint provider package. | |
2262 | ||
2263 | A better design choice is to define a single tracepoint class and three | |
2264 | tracepoint instances: | |
2265 | ||
2266 | [source,c] | |
2267 | ---- | |
2268 | /* The tracepoint class */ | |
2269 | TRACEPOINT_EVENT_CLASS( | |
2270 | /* Tracepoint provider name */ | |
2271 | my_app, | |
2272 | ||
2273 | /* Tracepoint class name */ | |
2274 | my_class, | |
2275 | ||
2276 | /* Input arguments */ | |
2277 | TP_ARGS( | |
2278 | int, userid, | |
2279 | size_t, len | |
2280 | ), | |
2281 | ||
2282 | /* Output event fields */ | |
2283 | TP_FIELDS( | |
2284 | ctf_integer(int, userid, userid) | |
2285 | ctf_integer(size_t, len, len) | |
2286 | ) | |
2287 | ) | |
2288 | ||
2289 | /* The tracepoint instances */ | |
2290 | TRACEPOINT_EVENT_INSTANCE( | |
2291 | /* Tracepoint provider name */ | |
2292 | my_app, | |
2293 | ||
2294 | /* Tracepoint class name */ | |
2295 | my_class, | |
2296 | ||
2297 | /* Tracepoint name */ | |
2298 | get_account, | |
2299 | ||
2300 | /* Input arguments */ | |
2301 | TP_ARGS( | |
2302 | int, userid, | |
2303 | size_t, len | |
2304 | ) | |
2305 | ) | |
2306 | TRACEPOINT_EVENT_INSTANCE( | |
2307 | my_app, | |
2308 | my_class, | |
2309 | get_settings, | |
2310 | TP_ARGS( | |
2311 | int, userid, | |
2312 | size_t, len | |
2313 | ) | |
2314 | ) | |
2315 | TRACEPOINT_EVENT_INSTANCE( | |
2316 | my_app, | |
2317 | my_class, | |
2318 | get_transaction, | |
2319 | TP_ARGS( | |
2320 | int, userid, | |
2321 | size_t, len | |
2322 | ) | |
2323 | ) | |
2324 | ---- | |
2325 | ==== | |
2326 | ||
2327 | ||
2328 | [[assigning-log-levels]] | |
2329 | ===== Assign a log level to a tracepoint definition | |
2330 | ||
2331 | You can assign an optional _log level_ to a | |
2332 | <<defining-tracepoints,tracepoint definition>>. | |
2333 | ||
2334 | Assigning different levels of severity to tracepoint definitions can | |
2335 | be useful: when you <<enabling-disabling-events,create an event rule>>, | |
2336 | you can target tracepoints having a log level as severe as a specific | |
2337 | value. | |
2338 | ||
2339 | The concept of LTTng-UST log levels is similar to the levels found | |
2340 | in typical logging frameworks: | |
2341 | ||
2342 | * In a logging framework, the log level is given by the function | |
2343 | or method name you use at the log statement site: `debug()`, | |
2344 | `info()`, `warn()`, `error()`, and so on. | |
2345 | * In LTTng-UST, you statically assign the log level to a tracepoint | |
2346 | definition; any `tracepoint()` macro invocation which refers to | |
2347 | this definition has this log level. | |
2348 | ||
2349 | You can assign a log level to a tracepoint definition with the | |
2350 | `TRACEPOINT_LOGLEVEL()` macro. You must use this macro _after_ the | |
2351 | <<defining-tracepoints,`TRACEPOINT_EVENT()`>> or | |
2352 | <<using-tracepoint-classes,`TRACEPOINT_INSTANCE()`>> macro for a given | |
2353 | tracepoint. | |
2354 | ||
2355 | The syntax of the `TRACEPOINT_LOGLEVEL()` macro is: | |
2356 | ||
2357 | [source,c] | |
2358 | .`TRACEPOINT_LOGLEVEL()` macro syntax. | |
2359 | ---- | |
2360 | TRACEPOINT_LOGLEVEL(provider_name, tracepoint_name, log_level) | |
2361 | ---- | |
2362 | ||
2363 | Replace: | |
2364 | ||
2365 | * `provider_name` with the tracepoint provider name. | |
2366 | * `tracepoint_name` with the tracepoint name. | |
2367 | * `log_level` with the log level to assign to the tracepoint | |
2368 | definition named `tracepoint_name` in the `provider_name` | |
2369 | tracepoint provider. | |
2370 | + | |
2371 | See man:lttng-ust(3) for a list of available log level names. | |
2372 | ||
2373 | .Assign the `TRACE_DEBUG_UNIT` log level to a tracepoint definition. | |
2374 | ==== | |
2375 | [source,c] | |
2376 | ---- | |
2377 | /* Tracepoint definition */ | |
2378 | TRACEPOINT_EVENT( | |
2379 | my_app, | |
2380 | get_transaction, | |
2381 | TP_ARGS( | |
2382 | int, userid, | |
2383 | size_t, len | |
2384 | ), | |
2385 | TP_FIELDS( | |
2386 | ctf_integer(int, userid, userid) | |
2387 | ctf_integer(size_t, len, len) | |
2388 | ) | |
2389 | ) | |
2390 | ||
2391 | /* Log level assignment */ | |
2392 | TRACEPOINT_LOGLEVEL(my_app, get_transaction, TRACE_DEBUG_UNIT) | |
2393 | ---- | |
2394 | ==== | |
2395 | ||
2396 | ||
2397 | [[tpp-source]] | |
2398 | ===== Create a tracepoint provider package source file | |
2399 | ||
2400 | A _tracepoint provider package source file_ is a C source file which | |
2401 | includes a <<tpp-header,tracepoint provider header file>> to expand its | |
2402 | macros into event serialization and other functions. | |
2403 | ||
2404 | You can always use the following tracepoint provider package source | |
2405 | file template: | |
2406 | ||
2407 | [source,c] | |
2408 | .Tracepoint provider package source file template. | |
2409 | ---- | |
2410 | #define TRACEPOINT_CREATE_PROBES | |
2411 | ||
2412 | #include "tp.h" | |
2413 | ---- | |
2414 | ||
2415 | Replace `tp.h` with the name of your <<tpp-header,tracepoint provider | |
2416 | header file>> name. You may also include more than one tracepoint | |
2417 | provider header file here to create a tracepoint provider package | |
2418 | holding more than one tracepoint providers. | |
2419 | ||
2420 | ||
2421 | [[probing-the-application-source-code]] | |
2422 | ==== Add tracepoints to an application's source code | |
2423 | ||
2424 | Once you <<tpp-header,create a tracepoint provider header file>>, you | |
2425 | can use the `tracepoint()` macro in your application's | |
2426 | source code to insert the tracepoints that this header | |
2427 | <<defining-tracepoints,defines>>. | |
2428 | ||
2429 | The `tracepoint()` macro takes at least two parameters: the tracepoint | |
2430 | provider name and the tracepoint name. The corresponding tracepoint | |
2431 | definition defines the other parameters. | |
2432 | ||
2433 | .`tracepoint()` usage. | |
2434 | ==== | |
2435 | The following <<defining-tracepoints,tracepoint definition>> defines a | |
2436 | tracepoint which takes two input arguments and has two output event | |
2437 | fields. | |
2438 | ||
2439 | [source,c] | |
2440 | .Tracepoint provider header file. | |
2441 | ---- | |
2442 | #include "my-custom-structure.h" | |
2443 | ||
2444 | TRACEPOINT_EVENT( | |
2445 | my_provider, | |
2446 | my_tracepoint, | |
2447 | TP_ARGS( | |
2448 | int, argc, | |
2449 | const char*, cmd_name | |
2450 | ), | |
2451 | TP_FIELDS( | |
2452 | ctf_string(cmd_name, cmd_name) | |
2453 | ctf_integer(int, number_of_args, argc) | |
2454 | ) | |
2455 | ) | |
2456 | ---- | |
2457 | ||
2458 | You can refer to this tracepoint definition with the `tracepoint()` | |
2459 | macro in your application's source code like this: | |
2460 | ||
2461 | [source,c] | |
2462 | .Application's source file. | |
2463 | ---- | |
2464 | #include "tp.h" | |
2465 | ||
2466 | int main(int argc, char* argv[]) | |
2467 | { | |
2468 | tracepoint(my_provider, my_tracepoint, argc, argv[0]); | |
2469 | ||
2470 | return 0; | |
2471 | } | |
2472 | ---- | |
2473 | ||
2474 | Note how the application's source code includes | |
2475 | the tracepoint provider header file containing the tracepoint | |
2476 | definitions to use, path:{tp.h}. | |
2477 | ==== | |
2478 | ||
2479 | .`tracepoint()` usage with a complex tracepoint definition. | |
2480 | ==== | |
2481 | Consider this complex tracepoint definition, where multiple event | |
2482 | fields refer to the same input arguments in their argument expression | |
2483 | parameter: | |
2484 | ||
2485 | [source,c] | |
2486 | .Tracepoint provider header file. | |
2487 | ---- | |
2488 | /* For `struct stat` */ | |
2489 | #include <sys/types.h> | |
2490 | #include <sys/stat.h> | |
2491 | #include <unistd.h> | |
2492 | ||
2493 | TRACEPOINT_EVENT( | |
2494 | my_provider, | |
2495 | my_tracepoint, | |
2496 | TP_ARGS( | |
2497 | int, my_int_arg, | |
2498 | char*, my_str_arg, | |
2499 | struct stat*, st | |
2500 | ), | |
2501 | TP_FIELDS( | |
2502 | ctf_integer(int, my_constant_field, 23 + 17) | |
2503 | ctf_integer(int, my_int_arg_field, my_int_arg) | |
2504 | ctf_integer(int, my_int_arg_field2, my_int_arg * my_int_arg) | |
2505 | ctf_integer(int, sum4_field, my_str_arg[0] + my_str_arg[1] + | |
2506 | my_str_arg[2] + my_str_arg[3]) | |
2507 | ctf_string(my_str_arg_field, my_str_arg) | |
2508 | ctf_integer_hex(off_t, size_field, st->st_size) | |
2509 | ctf_float(double, size_dbl_field, (double) st->st_size) | |
2510 | ctf_sequence_text(char, half_my_str_arg_field, my_str_arg, | |
2511 | size_t, strlen(my_str_arg) / 2) | |
2512 | ) | |
2513 | ) | |
2514 | ---- | |
2515 | ||
2516 | You can refer to this tracepoint definition with the `tracepoint()` | |
2517 | macro in your application's source code like this: | |
2518 | ||
2519 | [source,c] | |
2520 | .Application's source file. | |
2521 | ---- | |
2522 | #define TRACEPOINT_DEFINE | |
2523 | #include "tp.h" | |
2524 | ||
2525 | int main(void) | |
2526 | { | |
2527 | struct stat s; | |
2528 | ||
2529 | stat("/etc/fstab", &s); | |
2530 | tracepoint(my_provider, my_tracepoint, 23, "Hello, World!", &s); | |
2531 | ||
2532 | return 0; | |
2533 | } | |
2534 | ---- | |
2535 | ||
2536 | If you look at the event record that LTTng writes when tracing this | |
2537 | program, assuming the file size of path:{/etc/fstab} is 301{nbsp}bytes, | |
2538 | it should look like this: | |
2539 | ||
2540 | .Event record fields | |
2541 | |==== | |
2542 | |Field's name |Field's value | |
2543 | |`my_constant_field` |40 | |
2544 | |`my_int_arg_field` |23 | |
2545 | |`my_int_arg_field2` |529 | |
2546 | |`sum4_field` |389 | |
2547 | |`my_str_arg_field` |`Hello, World!` | |
2548 | |`size_field` |0x12d | |
2549 | |`size_dbl_field` |301.0 | |
2550 | |`half_my_str_arg_field` |`Hello,` | |
2551 | |==== | |
2552 | ==== | |
2553 | ||
2554 | Sometimes, the arguments you pass to `tracepoint()` are expensive to | |
2555 | compute--they use the call stack, for example. To avoid this | |
2556 | computation when the tracepoint is disabled, you can use the | |
2557 | `tracepoint_enabled()` and `do_tracepoint()` macros. | |
2558 | ||
2559 | The syntax of the `tracepoint_enabled()` and `do_tracepoint()` macros | |
2560 | is: | |
2561 | ||
2562 | [source,c] | |
2563 | .`tracepoint_enabled()` and `do_tracepoint()` macros syntax. | |
2564 | ---- | |
2565 | tracepoint_enabled(provider_name, tracepoint_name) | |
2566 | do_tracepoint(provider_name, tracepoint_name, ...) | |
2567 | ---- | |
2568 | ||
2569 | Replace: | |
2570 | ||
2571 | * `provider_name` with the tracepoint provider name. | |
2572 | * `tracepoint_name` with the tracepoint name. | |
2573 | ||
2574 | `tracepoint_enabled()` returns a non-zero value if the tracepoint named | |
2575 | `tracepoint_name` from the provider named `provider_name` is enabled | |
2576 | **at run time**. | |
2577 | ||
2578 | `do_tracepoint()` is like `tracepoint()`, except that it doesn't check | |
2579 | if the tracepoint is enabled. Using `tracepoint()` with | |
2580 | `tracepoint_enabled()` is dangerous since `tracepoint()` also contains | |
2581 | the `tracepoint_enabled()` check, thus a race condition is | |
2582 | possible in this situation: | |
2583 | ||
2584 | [source,c] | |
2585 | .Possible race condition when using `tracepoint_enabled()` with `tracepoint()`. | |
2586 | ---- | |
2587 | if (tracepoint_enabled(my_provider, my_tracepoint)) { | |
2588 | stuff = prepare_stuff(); | |
2589 | } | |
2590 | ||
2591 | tracepoint(my_provider, my_tracepoint, stuff); | |
2592 | ---- | |
2593 | ||
2594 | If the tracepoint is enabled after the condition, then `stuff` is not | |
2595 | prepared: the emitted event will either contain wrong data, or the whole | |
2596 | application could crash (segmentation fault, for example). | |
2597 | ||
2598 | NOTE: Neither `tracepoint_enabled()` nor `do_tracepoint()` have an | |
2599 | `STAP_PROBEV()` call. If you need it, you must emit | |
2600 | this call yourself. | |
2601 | ||
2602 | ||
2603 | [[building-tracepoint-providers-and-user-application]] | |
2604 | ==== Build and link a tracepoint provider package and an application | |
2605 | ||
2606 | Once you have one or more <<tpp-header,tracepoint provider header | |
2607 | files>> and a <<tpp-source,tracepoint provider package source file>>, | |
2608 | you can create the tracepoint provider package by compiling its source | |
2609 | file. From here, multiple build and run scenarios are possible. The | |
2610 | following table shows common application and library configurations | |
2611 | along with the required command lines to achieve them. | |
2612 | ||
2613 | In the following diagrams, we use the following file names: | |
2614 | ||
2615 | `app`:: | |
2616 | Executable application. | |
2617 | ||
2618 | `app.o`:: | |
2619 | Application's object file. | |
2620 | ||
2621 | `tpp.o`:: | |
2622 | Tracepoint provider package object file. | |
2623 | ||
2624 | `tpp.a`:: | |
2625 | Tracepoint provider package archive file. | |
2626 | ||
2627 | `libtpp.so`:: | |
2628 | Tracepoint provider package shared object file. | |
2629 | ||
2630 | `emon.o`:: | |
2631 | User library object file. | |
2632 | ||
2633 | `libemon.so`:: | |
2634 | User library shared object file. | |
2635 | ||
2636 | We use the following symbols in the diagrams of table below: | |
2637 | ||
2638 | [role="img-100"] | |
2639 | .Symbols used in the build scenario diagrams. | |
2640 | image::ust-sit-symbols.png[] | |
2641 | ||
2642 | We assume that path:{.} is part of the env:LD_LIBRARY_PATH environment | |
2643 | variable in the following instructions. | |
2644 | ||
2645 | [role="growable ust-scenarios",cols="asciidoc,asciidoc"] | |
2646 | .Common tracepoint provider package scenarios. | |
2647 | |==== | |
2648 | |Scenario |Instructions | |
2649 | ||
2650 | | | |
2651 | The instrumented application is statically linked with | |
2652 | the tracepoint provider package object. | |
2653 | ||
2654 | image::ust-sit+app-linked-with-tp-o+app-instrumented.png[] | |
2655 | ||
2656 | | | |
2657 | include::../common/ust-sit-step-tp-o.txt[] | |
2658 | ||
2659 | To build the instrumented application: | |
2660 | ||
2661 | . In path:{app.c}, before including path:{tpp.h}, add the following line: | |
2662 | + | |
2663 | -- | |
2664 | [source,c] | |
2665 | ---- | |
2666 | #define TRACEPOINT_DEFINE | |
2667 | ---- | |
2668 | -- | |
2669 | ||
2670 | . Compile the application source file: | |
2671 | + | |
2672 | -- | |
2673 | [role="term"] | |
2674 | ---- | |
2675 | $ gcc -c app.c | |
2676 | ---- | |
2677 | -- | |
2678 | ||
2679 | . Build the application: | |
2680 | + | |
2681 | -- | |
2682 | [role="term"] | |
2683 | ---- | |
2684 | $ gcc -o app app.o tpp.o -llttng-ust -ldl | |
2685 | ---- | |
2686 | -- | |
2687 | ||
2688 | To run the instrumented application: | |
2689 | ||
2690 | * Start the application: | |
2691 | + | |
2692 | -- | |
2693 | [role="term"] | |
2694 | ---- | |
2695 | $ ./app | |
2696 | ---- | |
2697 | -- | |
2698 | ||
2699 | | | |
2700 | The instrumented application is statically linked with the | |
2701 | tracepoint provider package archive file. | |
2702 | ||
2703 | image::ust-sit+app-linked-with-tp-a+app-instrumented.png[] | |
2704 | ||
2705 | | | |
2706 | To create the tracepoint provider package archive file: | |
2707 | ||
2708 | . Compile the <<tpp-source,tracepoint provider package source file>>: | |
2709 | + | |
2710 | -- | |
2711 | [role="term"] | |
2712 | ---- | |
2713 | $ gcc -I. -c tpp.c | |
2714 | ---- | |
2715 | -- | |
2716 | ||
2717 | . Create the tracepoint provider package archive file: | |
2718 | + | |
2719 | -- | |
2720 | [role="term"] | |
2721 | ---- | |
2722 | $ ar rcs tpp.a tpp.o | |
2723 | ---- | |
2724 | -- | |
2725 | ||
2726 | To build the instrumented application: | |
2727 | ||
2728 | . In path:{app.c}, before including path:{tpp.h}, add the following line: | |
2729 | + | |
2730 | -- | |
2731 | [source,c] | |
2732 | ---- | |
2733 | #define TRACEPOINT_DEFINE | |
2734 | ---- | |
2735 | -- | |
2736 | ||
2737 | . Compile the application source file: | |
2738 | + | |
2739 | -- | |
2740 | [role="term"] | |
2741 | ---- | |
2742 | $ gcc -c app.c | |
2743 | ---- | |
2744 | -- | |
2745 | ||
2746 | . Build the application: | |
2747 | + | |
2748 | -- | |
2749 | [role="term"] | |
2750 | ---- | |
2751 | $ gcc -o app app.o tpp.a -llttng-ust -ldl | |
2752 | ---- | |
2753 | -- | |
2754 | ||
2755 | To run the instrumented application: | |
2756 | ||
2757 | * Start the application: | |
2758 | + | |
2759 | -- | |
2760 | [role="term"] | |
2761 | ---- | |
2762 | $ ./app | |
2763 | ---- | |
2764 | -- | |
2765 | ||
2766 | | | |
2767 | The instrumented application is linked with the tracepoint provider | |
2768 | package shared object. | |
2769 | ||
2770 | image::ust-sit+app-linked-with-tp-so+app-instrumented.png[] | |
2771 | ||
2772 | | | |
2773 | include::../common/ust-sit-step-tp-so.txt[] | |
2774 | ||
2775 | To build the instrumented application: | |
2776 | ||
2777 | . In path:{app.c}, before including path:{tpp.h}, add the following line: | |
2778 | + | |
2779 | -- | |
2780 | [source,c] | |
2781 | ---- | |
2782 | #define TRACEPOINT_DEFINE | |
2783 | ---- | |
2784 | -- | |
2785 | ||
2786 | . Compile the application source file: | |
2787 | + | |
2788 | -- | |
2789 | [role="term"] | |
2790 | ---- | |
2791 | $ gcc -c app.c | |
2792 | ---- | |
2793 | -- | |
2794 | ||
2795 | . Build the application: | |
2796 | + | |
2797 | -- | |
2798 | [role="term"] | |
2799 | ---- | |
2800 | $ gcc -o app app.o -ldl -L. -ltpp | |
2801 | ---- | |
2802 | -- | |
2803 | ||
2804 | To run the instrumented application: | |
2805 | ||
2806 | * Start the application: | |
2807 | + | |
2808 | -- | |
2809 | [role="term"] | |
2810 | ---- | |
2811 | $ ./app | |
2812 | ---- | |
2813 | -- | |
2814 | ||
2815 | | | |
2816 | The tracepoint provider package shared object is preloaded before the | |
2817 | instrumented application starts. | |
2818 | ||
2819 | image::ust-sit+tp-so-preloaded+app-instrumented.png[] | |
2820 | ||
2821 | | | |
2822 | include::../common/ust-sit-step-tp-so.txt[] | |
2823 | ||
2824 | To build the instrumented application: | |
2825 | ||
2826 | . In path:{app.c}, before including path:{tpp.h}, add the | |
2827 | following lines: | |
2828 | + | |
2829 | -- | |
2830 | [source,c] | |
2831 | ---- | |
2832 | #define TRACEPOINT_DEFINE | |
2833 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
2834 | ---- | |
2835 | -- | |
2836 | ||
2837 | . Compile the application source file: | |
2838 | + | |
2839 | -- | |
2840 | [role="term"] | |
2841 | ---- | |
2842 | $ gcc -c app.c | |
2843 | ---- | |
2844 | -- | |
2845 | ||
2846 | . Build the application: | |
2847 | + | |
2848 | -- | |
2849 | [role="term"] | |
2850 | ---- | |
2851 | $ gcc -o app app.o -ldl | |
2852 | ---- | |
2853 | -- | |
2854 | ||
2855 | To run the instrumented application with tracing support: | |
2856 | ||
2857 | * Preload the tracepoint provider package shared object and | |
2858 | start the application: | |
2859 | + | |
2860 | -- | |
2861 | [role="term"] | |
2862 | ---- | |
2863 | $ LD_PRELOAD=./libtpp.so ./app | |
2864 | ---- | |
2865 | -- | |
2866 | ||
2867 | To run the instrumented application without tracing support: | |
2868 | ||
2869 | * Start the application: | |
2870 | + | |
2871 | -- | |
2872 | [role="term"] | |
2873 | ---- | |
2874 | $ ./app | |
2875 | ---- | |
2876 | -- | |
2877 | ||
2878 | | | |
2879 | The instrumented application dynamically loads the tracepoint provider | |
2880 | package shared object. | |
2881 | ||
2882 | See the <<dlclose-warning,warning about `dlclose()`>>. | |
2883 | ||
2884 | image::ust-sit+app-dlopens-tp-so+app-instrumented.png[] | |
2885 | ||
2886 | | | |
2887 | include::../common/ust-sit-step-tp-so.txt[] | |
2888 | ||
2889 | To build the instrumented application: | |
2890 | ||
2891 | . In path:{app.c}, before including path:{tpp.h}, add the | |
2892 | following lines: | |
2893 | + | |
2894 | -- | |
2895 | [source,c] | |
2896 | ---- | |
2897 | #define TRACEPOINT_DEFINE | |
2898 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
2899 | ---- | |
2900 | -- | |
2901 | ||
2902 | . Compile the application source file: | |
2903 | + | |
2904 | -- | |
2905 | [role="term"] | |
2906 | ---- | |
2907 | $ gcc -c app.c | |
2908 | ---- | |
2909 | -- | |
2910 | ||
2911 | . Build the application: | |
2912 | + | |
2913 | -- | |
2914 | [role="term"] | |
2915 | ---- | |
2916 | $ gcc -o app app.o -ldl | |
2917 | ---- | |
2918 | -- | |
2919 | ||
2920 | To run the instrumented application: | |
2921 | ||
2922 | * Start the application: | |
2923 | + | |
2924 | -- | |
2925 | [role="term"] | |
2926 | ---- | |
2927 | $ ./app | |
2928 | ---- | |
2929 | -- | |
2930 | ||
2931 | | | |
2932 | The application is linked with the instrumented user library. | |
2933 | ||
2934 | The instrumented user library is statically linked with the tracepoint | |
2935 | provider package object file. | |
2936 | ||
2937 | image::ust-sit+app-linked-with-lib+lib-linked-with-tp-o+lib-instrumented.png[] | |
2938 | ||
2939 | | | |
2940 | include::../common/ust-sit-step-tp-o-fpic.txt[] | |
2941 | ||
2942 | To build the instrumented user library: | |
2943 | ||
2944 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
2945 | following line: | |
2946 | + | |
2947 | -- | |
2948 | [source,c] | |
2949 | ---- | |
2950 | #define TRACEPOINT_DEFINE | |
2951 | ---- | |
2952 | -- | |
2953 | ||
2954 | . Compile the user library source file: | |
2955 | + | |
2956 | -- | |
2957 | [role="term"] | |
2958 | ---- | |
2959 | $ gcc -I. -fpic -c emon.c | |
2960 | ---- | |
2961 | -- | |
2962 | ||
2963 | . Build the user library shared object: | |
2964 | + | |
2965 | -- | |
2966 | [role="term"] | |
2967 | ---- | |
2968 | $ gcc -shared -o libemon.so emon.o tpp.o -llttng-ust -ldl | |
2969 | ---- | |
2970 | -- | |
2971 | ||
2972 | To build the application: | |
2973 | ||
2974 | . Compile the application source file: | |
2975 | + | |
2976 | -- | |
2977 | [role="term"] | |
2978 | ---- | |
2979 | $ gcc -c app.c | |
2980 | ---- | |
2981 | -- | |
2982 | ||
2983 | . Build the application: | |
2984 | + | |
2985 | -- | |
2986 | [role="term"] | |
2987 | ---- | |
2988 | $ gcc -o app app.o -L. -lemon | |
2989 | ---- | |
2990 | -- | |
2991 | ||
2992 | To run the application: | |
2993 | ||
2994 | * Start the application: | |
2995 | + | |
2996 | -- | |
2997 | [role="term"] | |
2998 | ---- | |
2999 | $ ./app | |
3000 | ---- | |
3001 | -- | |
3002 | ||
3003 | | | |
3004 | The application is linked with the instrumented user library. | |
3005 | ||
3006 | The instrumented user library is linked with the tracepoint provider | |
3007 | package shared object. | |
3008 | ||
3009 | image::ust-sit+app-linked-with-lib+lib-linked-with-tp-so+lib-instrumented.png[] | |
3010 | ||
3011 | | | |
3012 | include::../common/ust-sit-step-tp-so.txt[] | |
3013 | ||
3014 | To build the instrumented user library: | |
3015 | ||
3016 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
3017 | following line: | |
3018 | + | |
3019 | -- | |
3020 | [source,c] | |
3021 | ---- | |
3022 | #define TRACEPOINT_DEFINE | |
3023 | ---- | |
3024 | -- | |
3025 | ||
3026 | . Compile the user library source file: | |
3027 | + | |
3028 | -- | |
3029 | [role="term"] | |
3030 | ---- | |
3031 | $ gcc -I. -fpic -c emon.c | |
3032 | ---- | |
3033 | -- | |
3034 | ||
3035 | . Build the user library shared object: | |
3036 | + | |
3037 | -- | |
3038 | [role="term"] | |
3039 | ---- | |
3040 | $ gcc -shared -o libemon.so emon.o -ldl -L. -ltpp | |
3041 | ---- | |
3042 | -- | |
3043 | ||
3044 | To build the application: | |
3045 | ||
3046 | . Compile the application source file: | |
3047 | + | |
3048 | -- | |
3049 | [role="term"] | |
3050 | ---- | |
3051 | $ gcc -c app.c | |
3052 | ---- | |
3053 | -- | |
3054 | ||
3055 | . Build the application: | |
3056 | + | |
3057 | -- | |
3058 | [role="term"] | |
3059 | ---- | |
3060 | $ gcc -o app app.o -L. -lemon | |
3061 | ---- | |
3062 | -- | |
3063 | ||
3064 | To run the application: | |
3065 | ||
3066 | * Start the application: | |
3067 | + | |
3068 | -- | |
3069 | [role="term"] | |
3070 | ---- | |
3071 | $ ./app | |
3072 | ---- | |
3073 | -- | |
3074 | ||
3075 | | | |
3076 | The tracepoint provider package shared object is preloaded before the | |
3077 | application starts. | |
3078 | ||
3079 | The application is linked with the instrumented user library. | |
3080 | ||
3081 | image::ust-sit+tp-so-preloaded+app-linked-with-lib+lib-instrumented.png[] | |
3082 | ||
3083 | | | |
3084 | include::../common/ust-sit-step-tp-so.txt[] | |
3085 | ||
3086 | To build the instrumented user library: | |
3087 | ||
3088 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
3089 | following lines: | |
3090 | + | |
3091 | -- | |
3092 | [source,c] | |
3093 | ---- | |
3094 | #define TRACEPOINT_DEFINE | |
3095 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
3096 | ---- | |
3097 | -- | |
3098 | ||
3099 | . Compile the user library source file: | |
3100 | + | |
3101 | -- | |
3102 | [role="term"] | |
3103 | ---- | |
3104 | $ gcc -I. -fpic -c emon.c | |
3105 | ---- | |
3106 | -- | |
3107 | ||
3108 | . Build the user library shared object: | |
3109 | + | |
3110 | -- | |
3111 | [role="term"] | |
3112 | ---- | |
3113 | $ gcc -shared -o libemon.so emon.o -ldl | |
3114 | ---- | |
3115 | -- | |
3116 | ||
3117 | To build the application: | |
3118 | ||
3119 | . Compile the application source file: | |
3120 | + | |
3121 | -- | |
3122 | [role="term"] | |
3123 | ---- | |
3124 | $ gcc -c app.c | |
3125 | ---- | |
3126 | -- | |
3127 | ||
3128 | . Build the application: | |
3129 | + | |
3130 | -- | |
3131 | [role="term"] | |
3132 | ---- | |
3133 | $ gcc -o app app.o -L. -lemon | |
3134 | ---- | |
3135 | -- | |
3136 | ||
3137 | To run the application with tracing support: | |
3138 | ||
3139 | * Preload the tracepoint provider package shared object and | |
3140 | start the application: | |
3141 | + | |
3142 | -- | |
3143 | [role="term"] | |
3144 | ---- | |
3145 | $ LD_PRELOAD=./libtpp.so ./app | |
3146 | ---- | |
3147 | -- | |
3148 | ||
3149 | To run the application without tracing support: | |
3150 | ||
3151 | * Start the application: | |
3152 | + | |
3153 | -- | |
3154 | [role="term"] | |
3155 | ---- | |
3156 | $ ./app | |
3157 | ---- | |
3158 | -- | |
3159 | ||
3160 | | | |
3161 | The application is linked with the instrumented user library. | |
3162 | ||
3163 | The instrumented user library dynamically loads the tracepoint provider | |
3164 | package shared object. | |
3165 | ||
3166 | See the <<dlclose-warning,warning about `dlclose()`>>. | |
3167 | ||
3168 | image::ust-sit+app-linked-with-lib+lib-dlopens-tp-so+lib-instrumented.png[] | |
3169 | ||
3170 | | | |
3171 | include::../common/ust-sit-step-tp-so.txt[] | |
3172 | ||
3173 | To build the instrumented user library: | |
3174 | ||
3175 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
3176 | following lines: | |
3177 | + | |
3178 | -- | |
3179 | [source,c] | |
3180 | ---- | |
3181 | #define TRACEPOINT_DEFINE | |
3182 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
3183 | ---- | |
3184 | -- | |
3185 | ||
3186 | . Compile the user library source file: | |
3187 | + | |
3188 | -- | |
3189 | [role="term"] | |
3190 | ---- | |
3191 | $ gcc -I. -fpic -c emon.c | |
3192 | ---- | |
3193 | -- | |
3194 | ||
3195 | . Build the user library shared object: | |
3196 | + | |
3197 | -- | |
3198 | [role="term"] | |
3199 | ---- | |
3200 | $ gcc -shared -o libemon.so emon.o -ldl | |
3201 | ---- | |
3202 | -- | |
3203 | ||
3204 | To build the application: | |
3205 | ||
3206 | . Compile the application source file: | |
3207 | + | |
3208 | -- | |
3209 | [role="term"] | |
3210 | ---- | |
3211 | $ gcc -c app.c | |
3212 | ---- | |
3213 | -- | |
3214 | ||
3215 | . Build the application: | |
3216 | + | |
3217 | -- | |
3218 | [role="term"] | |
3219 | ---- | |
3220 | $ gcc -o app app.o -L. -lemon | |
3221 | ---- | |
3222 | -- | |
3223 | ||
3224 | To run the application: | |
3225 | ||
3226 | * Start the application: | |
3227 | + | |
3228 | -- | |
3229 | [role="term"] | |
3230 | ---- | |
3231 | $ ./app | |
3232 | ---- | |
3233 | -- | |
3234 | ||
3235 | | | |
3236 | The application dynamically loads the instrumented user library. | |
3237 | ||
3238 | The instrumented user library is linked with the tracepoint provider | |
3239 | package shared object. | |
3240 | ||
3241 | See the <<dlclose-warning,warning about `dlclose()`>>. | |
3242 | ||
3243 | image::ust-sit+app-dlopens-lib+lib-linked-with-tp-so+lib-instrumented.png[] | |
3244 | ||
3245 | | | |
3246 | include::../common/ust-sit-step-tp-so.txt[] | |
3247 | ||
3248 | To build the instrumented user library: | |
3249 | ||
3250 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
3251 | following line: | |
3252 | + | |
3253 | -- | |
3254 | [source,c] | |
3255 | ---- | |
3256 | #define TRACEPOINT_DEFINE | |
3257 | ---- | |
3258 | -- | |
3259 | ||
3260 | . Compile the user library source file: | |
3261 | + | |
3262 | -- | |
3263 | [role="term"] | |
3264 | ---- | |
3265 | $ gcc -I. -fpic -c emon.c | |
3266 | ---- | |
3267 | -- | |
3268 | ||
3269 | . Build the user library shared object: | |
3270 | + | |
3271 | -- | |
3272 | [role="term"] | |
3273 | ---- | |
3274 | $ gcc -shared -o libemon.so emon.o -ldl -L. -ltpp | |
3275 | ---- | |
3276 | -- | |
3277 | ||
3278 | To build the application: | |
3279 | ||
3280 | . Compile the application source file: | |
3281 | + | |
3282 | -- | |
3283 | [role="term"] | |
3284 | ---- | |
3285 | $ gcc -c app.c | |
3286 | ---- | |
3287 | -- | |
3288 | ||
3289 | . Build the application: | |
3290 | + | |
3291 | -- | |
3292 | [role="term"] | |
3293 | ---- | |
3294 | $ gcc -o app app.o -ldl -L. -lemon | |
3295 | ---- | |
3296 | -- | |
3297 | ||
3298 | To run the application: | |
3299 | ||
3300 | * Start the application: | |
3301 | + | |
3302 | -- | |
3303 | [role="term"] | |
3304 | ---- | |
3305 | $ ./app | |
3306 | ---- | |
3307 | -- | |
3308 | ||
3309 | | | |
3310 | The application dynamically loads the instrumented user library. | |
3311 | ||
3312 | The instrumented user library dynamically loads the tracepoint provider | |
3313 | package shared object. | |
3314 | ||
3315 | See the <<dlclose-warning,warning about `dlclose()`>>. | |
3316 | ||
3317 | image::ust-sit+app-dlopens-lib+lib-dlopens-tp-so+lib-instrumented.png[] | |
3318 | ||
3319 | | | |
3320 | include::../common/ust-sit-step-tp-so.txt[] | |
3321 | ||
3322 | To build the instrumented user library: | |
3323 | ||
3324 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
3325 | following lines: | |
3326 | + | |
3327 | -- | |
3328 | [source,c] | |
3329 | ---- | |
3330 | #define TRACEPOINT_DEFINE | |
3331 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
3332 | ---- | |
3333 | -- | |
3334 | ||
3335 | . Compile the user library source file: | |
3336 | + | |
3337 | -- | |
3338 | [role="term"] | |
3339 | ---- | |
3340 | $ gcc -I. -fpic -c emon.c | |
3341 | ---- | |
3342 | -- | |
3343 | ||
3344 | . Build the user library shared object: | |
3345 | + | |
3346 | -- | |
3347 | [role="term"] | |
3348 | ---- | |
3349 | $ gcc -shared -o libemon.so emon.o -ldl | |
3350 | ---- | |
3351 | -- | |
3352 | ||
3353 | To build the application: | |
3354 | ||
3355 | . Compile the application source file: | |
3356 | + | |
3357 | -- | |
3358 | [role="term"] | |
3359 | ---- | |
3360 | $ gcc -c app.c | |
3361 | ---- | |
3362 | -- | |
3363 | ||
3364 | . Build the application: | |
3365 | + | |
3366 | -- | |
3367 | [role="term"] | |
3368 | ---- | |
3369 | $ gcc -o app app.o -ldl -L. -lemon | |
3370 | ---- | |
3371 | -- | |
3372 | ||
3373 | To run the application: | |
3374 | ||
3375 | * Start the application: | |
3376 | + | |
3377 | -- | |
3378 | [role="term"] | |
3379 | ---- | |
3380 | $ ./app | |
3381 | ---- | |
3382 | -- | |
3383 | ||
3384 | | | |
3385 | The tracepoint provider package shared object is preloaded before the | |
3386 | application starts. | |
3387 | ||
3388 | The application dynamically loads the instrumented user library. | |
3389 | ||
3390 | image::ust-sit+tp-so-preloaded+app-dlopens-lib+lib-instrumented.png[] | |
3391 | ||
3392 | | | |
3393 | include::../common/ust-sit-step-tp-so.txt[] | |
3394 | ||
3395 | To build the instrumented user library: | |
3396 | ||
3397 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
3398 | following lines: | |
3399 | + | |
3400 | -- | |
3401 | [source,c] | |
3402 | ---- | |
3403 | #define TRACEPOINT_DEFINE | |
3404 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE | |
3405 | ---- | |
3406 | -- | |
3407 | ||
3408 | . Compile the user library source file: | |
3409 | + | |
3410 | -- | |
3411 | [role="term"] | |
3412 | ---- | |
3413 | $ gcc -I. -fpic -c emon.c | |
3414 | ---- | |
3415 | -- | |
3416 | ||
3417 | . Build the user library shared object: | |
3418 | + | |
3419 | -- | |
3420 | [role="term"] | |
3421 | ---- | |
3422 | $ gcc -shared -o libemon.so emon.o -ldl | |
3423 | ---- | |
3424 | -- | |
3425 | ||
3426 | To build the application: | |
3427 | ||
3428 | . Compile the application source file: | |
3429 | + | |
3430 | -- | |
3431 | [role="term"] | |
3432 | ---- | |
3433 | $ gcc -c app.c | |
3434 | ---- | |
3435 | -- | |
3436 | ||
3437 | . Build the application: | |
3438 | + | |
3439 | -- | |
3440 | [role="term"] | |
3441 | ---- | |
3442 | $ gcc -o app app.o -L. -lemon | |
3443 | ---- | |
3444 | -- | |
3445 | ||
3446 | To run the application with tracing support: | |
3447 | ||
3448 | * Preload the tracepoint provider package shared object and | |
3449 | start the application: | |
3450 | + | |
3451 | -- | |
3452 | [role="term"] | |
3453 | ---- | |
3454 | $ LD_PRELOAD=./libtpp.so ./app | |
3455 | ---- | |
3456 | -- | |
3457 | ||
3458 | To run the application without tracing support: | |
3459 | ||
3460 | * Start the application: | |
3461 | + | |
3462 | -- | |
3463 | [role="term"] | |
3464 | ---- | |
3465 | $ ./app | |
3466 | ---- | |
3467 | -- | |
3468 | ||
3469 | | | |
3470 | The application is statically linked with the tracepoint provider | |
3471 | package object file. | |
3472 | ||
3473 | The application is linked with the instrumented user library. | |
3474 | ||
3475 | image::ust-sit+app-linked-with-tp-o+app-linked-with-lib+lib-instrumented.png[] | |
3476 | ||
3477 | | | |
3478 | include::../common/ust-sit-step-tp-o.txt[] | |
3479 | ||
3480 | To build the instrumented user library: | |
3481 | ||
3482 | . In path:{emon.c}, before including path:{tpp.h}, add the | |
3483 | following line: | |
3484 | + | |
3485 | -- | |
3486 | [source,c] | |
3487 | ---- | |
3488 | #define TRACEPOINT_DEFINE | |
3489 | ---- | |
3490 | -- | |
3491 | ||
3492 | . Compile the user library source file: | |
3493 | + | |
3494 | -- | |
3495 | [role="term"] | |
3496 | ---- | |
3497 | $ gcc -I. -fpic -c emon.c | |
3498 | ---- | |
3499 | -- | |
3500 | ||
3501 | . Build the user library shared object: | |
3502 | + | |
3503 | -- | |
3504 | [role="term"] | |
3505 | ---- | |
3506 | $ gcc -shared -o libemon.so emon.o | |
3507 | ---- | |
3508 | -- | |
3509 | ||
3510 | To build the application: | |
3511 | ||
3512 | . Compile the application source file: | |
3513 | + | |
3514 | -- | |
3515 | [role="term"] | |
3516 | ---- | |
3517 | $ gcc -c app.c | |
3518 | ---- | |
3519 | -- | |
3520 | ||
3521 | . Build the application: | |
3522 | + | |
3523 | -- | |
3524 | [role="term"] | |
3525 | ---- | |
3526 | $ gcc -o app app.o tpp.o -llttng-ust -ldl -L. -lemon | |
3527 | ---- | |
3528 | -- | |
3529 | ||
3530 | To run the instrumented application: | |
3531 | ||
3532 | * Start the application: | |
3533 | + | |
3534 | -- | |
3535 | [role="term"] | |
3536 | ---- | |
3537 | $ ./app | |
3538 | ---- | |
3539 | -- | |
3540 | ||
3541 | | | |
3542 | The application is statically linked with the tracepoint provider | |
3543 | package object file. | |
3544 | ||
3545 | The application dynamically loads the instrumented user library. | |
3546 | ||
3547 | image::ust-sit+app-linked-with-tp-o+app-dlopens-lib+lib-instrumented.png[] | |
3548 | ||
3549 | | | |
3550 | include::../common/ust-sit-step-tp-o.txt[] | |
3551 | ||
3552 | To build the application: | |
3553 | ||
3554 | . In path:{app.c}, before including path:{tpp.h}, add the following line: | |
3555 | + | |
3556 | -- | |
3557 | [source,c] | |
3558 | ---- | |
3559 | #define TRACEPOINT_DEFINE | |
3560 | ---- | |
3561 | -- | |
3562 | ||
3563 | . Compile the application source file: | |
3564 | + | |
3565 | -- | |
3566 | [role="term"] | |
3567 | ---- | |
3568 | $ gcc -c app.c | |
3569 | ---- | |
3570 | -- | |
3571 | ||
3572 | . Build the application: | |
3573 | + | |
3574 | -- | |
3575 | [role="term"] | |
3576 | ---- | |
3577 | $ gcc -Wl,--export-dynamic -o app app.o tpp.o \ | |
3578 | -llttng-ust -ldl | |
3579 | ---- | |
3580 | -- | |
3581 | + | |
3582 | The `--export-dynamic` option passed to the linker is necessary for the | |
3583 | dynamically loaded library to ``see'' the tracepoint symbols defined in | |
3584 | the application. | |
3585 | ||
3586 | To build the instrumented user library: | |
3587 | ||
3588 | . Compile the user library source file: | |
3589 | + | |
3590 | -- | |
3591 | [role="term"] | |
3592 | ---- | |
3593 | $ gcc -I. -fpic -c emon.c | |
3594 | ---- | |
3595 | -- | |
3596 | ||
3597 | . Build the user library shared object: | |
3598 | + | |
3599 | -- | |
3600 | [role="term"] | |
3601 | ---- | |
3602 | $ gcc -shared -o libemon.so emon.o | |
3603 | ---- | |
3604 | -- | |
3605 | ||
3606 | To run the application: | |
3607 | ||
3608 | * Start the application: | |
3609 | + | |
3610 | -- | |
3611 | [role="term"] | |
3612 | ---- | |
3613 | $ ./app | |
3614 | ---- | |
3615 | -- | |
3616 | |==== | |
3617 | ||
3618 | [[dlclose-warning]] | |
3619 | [IMPORTANT] | |
3620 | .Do not use man:dlclose(3) on a tracepoint provider package | |
3621 | ==== | |
3622 | Never use man:dlclose(3) on any shared object which: | |
3623 | ||
3624 | * Is linked with, statically or dynamically, a tracepoint provider | |
3625 | package. | |
3626 | * Calls man:dlopen(3) itself to dynamically open a tracepoint provider | |
3627 | package shared object. | |
3628 | ||
3629 | This is currently considered **unsafe** due to a lack of reference | |
3630 | counting from LTTng-UST to the shared object. | |
3631 | ||
3632 | A known workaround (available since glibc 2.2) is to use the | |
3633 | `RTLD_NODELETE` flag when calling man:dlopen(3) initially. This has the | |
3634 | effect of not unloading the loaded shared object, even if man:dlclose(3) | |
3635 | is called. | |
3636 | ||
3637 | You can also preload the tracepoint provider package shared object with | |
3638 | the env:LD_PRELOAD environment variable to overcome this limitation. | |
3639 | ==== | |
3640 | ||
3641 | ||
3642 | [[using-lttng-ust-with-daemons]] | |
3643 | ===== Use noch:{LTTng-UST} with daemons | |
3644 | ||
3645 | If your instrumented application calls man:fork(2), man:clone(2), | |
3646 | or BSD's man:rfork(2), without a following man:exec(3)-family | |
3647 | system call, you must preload the path:{liblttng-ust-fork.so} shared | |
3648 | object when you start the application. | |
3649 | ||
3650 | [role="term"] | |
3651 | ---- | |
3652 | $ LD_PRELOAD=liblttng-ust-fork.so ./my-app | |
3653 | ---- | |
3654 | ||
3655 | If your tracepoint provider package is | |
3656 | a shared library which you also preload, you must put both | |
3657 | shared objects in env:LD_PRELOAD: | |
3658 | ||
3659 | [role="term"] | |
3660 | ---- | |
3661 | $ LD_PRELOAD=liblttng-ust-fork.so:/path/to/tp.so ./my-app | |
3662 | ---- | |
3663 | ||
3664 | ||
3665 | [role="since-2.9"] | |
3666 | [[liblttng-ust-fd]] | |
3667 | ===== Use noch:{LTTng-UST} with applications which close file descriptors that don't belong to them | |
3668 | ||
3669 | If your instrumented application closes one or more file descriptors | |
3670 | which it did not open itself, you must preload the | |
3671 | path:{liblttng-ust-fd.so} shared object when you start the application: | |
3672 | ||
3673 | [role="term"] | |
3674 | ---- | |
3675 | $ LD_PRELOAD=liblttng-ust-fd.so ./my-app | |
3676 | ---- | |
3677 | ||
3678 | Typical use cases include closing all the file descriptors after | |
3679 | man:fork(2) or man:rfork(2) and buggy applications doing | |
3680 | ``double closes''. | |
3681 | ||
3682 | ||
3683 | [[lttng-ust-pkg-config]] | |
3684 | ===== Use noch:{pkg-config} | |
3685 | ||
3686 | On some distributions, LTTng-UST ships with a | |
3687 | https://www.freedesktop.org/wiki/Software/pkg-config/[pkg-config] | |
3688 | metadata file. If this is your case, then you can use cmd:pkg-config to | |
3689 | build an application on the command line: | |
3690 | ||
3691 | [role="term"] | |
3692 | ---- | |
3693 | $ gcc -o my-app my-app.o tp.o $(pkg-config --cflags --libs lttng-ust) | |
3694 | ---- | |
3695 | ||
3696 | ||
3697 | [[instrumenting-32-bit-app-on-64-bit-system]] | |
3698 | ===== [[advanced-instrumenting-techniques]]Build a 32-bit instrumented application for a 64-bit target system | |
3699 | ||
3700 | In order to trace a 32-bit application running on a 64-bit system, | |
3701 | LTTng must use a dedicated 32-bit | |
3702 | <<lttng-consumerd,consumer daemon>>. | |
3703 | ||
3704 | The following steps show how to build and install a 32-bit consumer | |
3705 | daemon, which is _not_ part of the default 64-bit LTTng build, how to | |
3706 | build and install the 32-bit LTTng-UST libraries, and how to build and | |
3707 | link an instrumented 32-bit application in that context. | |
3708 | ||
3709 | To build a 32-bit instrumented application for a 64-bit target system, | |
3710 | assuming you have a fresh target system with no installed Userspace RCU | |
3711 | or LTTng packages: | |
3712 | ||
3713 | . Download, build, and install a 32-bit version of Userspace RCU: | |
3714 | + | |
3715 | -- | |
3716 | [role="term"] | |
3717 | ---- | |
3718 | $ cd $(mktemp -d) && | |
3719 | wget http://lttng.org/files/urcu/userspace-rcu-latest-0.9.tar.bz2 && | |
3720 | tar -xf userspace-rcu-latest-0.9.tar.bz2 && | |
3721 | cd userspace-rcu-0.9.* && | |
3722 | ./configure --libdir=/usr/local/lib32 CFLAGS=-m32 && | |
3723 | make && | |
3724 | sudo make install && | |
3725 | sudo ldconfig | |
3726 | ---- | |
3727 | -- | |
3728 | ||
3729 | . Using your distribution's package manager, or from source, install | |
3730 | the following 32-bit versions of the following dependencies of | |
3731 | LTTng-tools and LTTng-UST: | |
3732 | + | |
3733 | -- | |
3734 | * https://sourceforge.net/projects/libuuid/[libuuid] | |
3735 | * http://directory.fsf.org/wiki/Popt[popt] | |
3736 | * http://www.xmlsoft.org/[libxml2] | |
3737 | -- | |
3738 | ||
3739 | . Download, build, and install a 32-bit version of the latest | |
3740 | LTTng-UST{nbsp}{revision}: | |
3741 | + | |
3742 | -- | |
3743 | [role="term"] | |
3744 | ---- | |
3745 | $ cd $(mktemp -d) && | |
3746 | wget http://lttng.org/files/lttng-ust/lttng-ust-latest-2.10.tar.bz2 && | |
3747 | tar -xf lttng-ust-latest-2.10.tar.bz2 && | |
3748 | cd lttng-ust-2.10.* && | |
3749 | ./configure --libdir=/usr/local/lib32 \ | |
3750 | CFLAGS=-m32 CXXFLAGS=-m32 \ | |
3751 | LDFLAGS='-L/usr/local/lib32 -L/usr/lib32' && | |
3752 | make && | |
3753 | sudo make install && | |
3754 | sudo ldconfig | |
3755 | ---- | |
3756 | -- | |
3757 | + | |
3758 | [NOTE] | |
3759 | ==== | |
3760 | Depending on your distribution, | |
3761 | 32-bit libraries could be installed at a different location than | |
3762 | `/usr/lib32`. For example, Debian is known to install | |
3763 | some 32-bit libraries in `/usr/lib/i386-linux-gnu`. | |
3764 | ||
3765 | In this case, make sure to set `LDFLAGS` to all the | |
3766 | relevant 32-bit library paths, for example: | |
3767 | ||
3768 | [role="term"] | |
3769 | ---- | |
3770 | $ LDFLAGS='-L/usr/lib/i386-linux-gnu -L/usr/lib32' | |
3771 | ---- | |
3772 | ==== | |
3773 | ||
3774 | . Download the latest LTTng-tools{nbsp}{revision}, build, and install | |
3775 | the 32-bit consumer daemon: | |
3776 | + | |
3777 | -- | |
3778 | [role="term"] | |
3779 | ---- | |
3780 | $ cd $(mktemp -d) && | |
3781 | wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.10.tar.bz2 && | |
3782 | tar -xf lttng-tools-latest-2.10.tar.bz2 && | |
3783 | cd lttng-tools-2.10.* && | |
3784 | ./configure --libdir=/usr/local/lib32 CFLAGS=-m32 CXXFLAGS=-m32 \ | |
3785 | LDFLAGS='-L/usr/local/lib32 -L/usr/lib32' \ | |
3786 | --disable-bin-lttng --disable-bin-lttng-crash \ | |
3787 | --disable-bin-lttng-relayd --disable-bin-lttng-sessiond && | |
3788 | make && | |
3789 | cd src/bin/lttng-consumerd && | |
3790 | sudo make install && | |
3791 | sudo ldconfig | |
3792 | ---- | |
3793 | -- | |
3794 | ||
3795 | . From your distribution or from source, | |
3796 | <<installing-lttng,install>> the 64-bit versions of | |
3797 | LTTng-UST and Userspace RCU. | |
3798 | . Download, build, and install the 64-bit version of the | |
3799 | latest LTTng-tools{nbsp}{revision}: | |
3800 | + | |
3801 | -- | |
3802 | [role="term"] | |
3803 | ---- | |
3804 | $ cd $(mktemp -d) && | |
3805 | wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.10.tar.bz2 && | |
3806 | tar -xf lttng-tools-latest-2.10.tar.bz2 && | |
3807 | cd lttng-tools-2.10.* && | |
3808 | ./configure --with-consumerd32-libdir=/usr/local/lib32 \ | |
3809 | --with-consumerd32-bin=/usr/local/lib32/lttng/libexec/lttng-consumerd && | |
3810 | make && | |
3811 | sudo make install && | |
3812 | sudo ldconfig | |
3813 | ---- | |
3814 | -- | |
3815 | ||
3816 | . Pass the following options to man:gcc(1), man:g++(1), or man:clang(1) | |
3817 | when linking your 32-bit application: | |
3818 | + | |
3819 | ---- | |
3820 | -m32 -L/usr/lib32 -L/usr/local/lib32 \ | |
3821 | -Wl,-rpath,/usr/lib32,-rpath,/usr/local/lib32 | |
3822 | ---- | |
3823 | + | |
3824 | For example, let's rebuild the quick start example in | |
3825 | <<tracing-your-own-user-application,Trace a user application>> as an | |
3826 | instrumented 32-bit application: | |
3827 | + | |
3828 | -- | |
3829 | [role="term"] | |
3830 | ---- | |
3831 | $ gcc -m32 -c -I. hello-tp.c | |
3832 | $ gcc -m32 -c hello.c | |
3833 | $ gcc -m32 -o hello hello.o hello-tp.o \ | |
3834 | -L/usr/lib32 -L/usr/local/lib32 \ | |
3835 | -Wl,-rpath,/usr/lib32,-rpath,/usr/local/lib32 \ | |
3836 | -llttng-ust -ldl | |
3837 | ---- | |
3838 | -- | |
3839 | ||
3840 | No special action is required to execute the 32-bit application and | |
3841 | to trace it: use the command-line man:lttng(1) tool as usual. | |
3842 | ||
3843 | ||
3844 | [role="since-2.5"] | |
3845 | [[tracef]] | |
3846 | ==== Use `tracef()` | |
3847 | ||
3848 | man:tracef(3) is a small LTTng-UST API designed for quick, | |
3849 | man:printf(3)-like instrumentation without the burden of | |
3850 | <<tracepoint-provider,creating>> and | |
3851 | <<building-tracepoint-providers-and-user-application,building>> | |
3852 | a tracepoint provider package. | |
3853 | ||
3854 | To use `tracef()` in your application: | |
3855 | ||
3856 | . In the C or C++ source files where you need to use `tracef()`, | |
3857 | include `<lttng/tracef.h>`: | |
3858 | + | |
3859 | -- | |
3860 | [source,c] | |
3861 | ---- | |
3862 | #include <lttng/tracef.h> | |
3863 | ---- | |
3864 | -- | |
3865 | ||
3866 | . In the application's source code, use `tracef()` like you would use | |
3867 | man:printf(3): | |
3868 | + | |
3869 | -- | |
3870 | [source,c] | |
3871 | ---- | |
3872 | /* ... */ | |
3873 | ||
3874 | tracef("my message: %d (%s)", my_integer, my_string); | |
3875 | ||
3876 | /* ... */ | |
3877 | ---- | |
3878 | -- | |
3879 | ||
3880 | . Link your application with `liblttng-ust`: | |
3881 | + | |
3882 | -- | |
3883 | [role="term"] | |
3884 | ---- | |
3885 | $ gcc -o app app.c -llttng-ust | |
3886 | ---- | |
3887 | -- | |
3888 | ||
3889 | To trace the events that `tracef()` calls emit: | |
3890 | ||
3891 | * <<enabling-disabling-events,Create an event rule>> which matches the | |
3892 | `lttng_ust_tracef:*` event name: | |
3893 | + | |
3894 | -- | |
3895 | [role="term"] | |
3896 | ---- | |
3897 | $ lttng enable-event --userspace 'lttng_ust_tracef:*' | |
3898 | ---- | |
3899 | -- | |
3900 | ||
3901 | [IMPORTANT] | |
3902 | .Limitations of `tracef()` | |
3903 | ==== | |
3904 | The `tracef()` utility function was developed to make user space tracing | |
3905 | super simple, albeit with notable disadvantages compared to | |
3906 | <<defining-tracepoints,user-defined tracepoints>>: | |
3907 | ||
3908 | * All the emitted events have the same tracepoint provider and | |
3909 | tracepoint names, respectively `lttng_ust_tracef` and `event`. | |
3910 | * There is no static type checking. | |
3911 | * The only event record field you actually get, named `msg`, is a string | |
3912 | potentially containing the values you passed to `tracef()` | |
3913 | using your own format string. This also means that you cannot filter | |
3914 | events with a custom expression at run time because there are no | |
3915 | isolated fields. | |
3916 | * Since `tracef()` uses the C standard library's man:vasprintf(3) | |
3917 | function behind the scenes to format the strings at run time, its | |
3918 | expected performance is lower than with user-defined tracepoints, | |
3919 | which do not require a conversion to a string. | |
3920 | ||
3921 | Taking this into consideration, `tracef()` is useful for some quick | |
3922 | prototyping and debugging, but you should not consider it for any | |
3923 | permanent and serious applicative instrumentation. | |
3924 | ==== | |
3925 | ||
3926 | ||
3927 | [role="since-2.7"] | |
3928 | [[tracelog]] | |
3929 | ==== Use `tracelog()` | |
3930 | ||
3931 | The man:tracelog(3) API is very similar to <<tracef,`tracef()`>>, with | |
3932 | the difference that it accepts an additional log level parameter. | |
3933 | ||
3934 | The goal of `tracelog()` is to ease the migration from logging to | |
3935 | tracing. | |
3936 | ||
3937 | To use `tracelog()` in your application: | |
3938 | ||
3939 | . In the C or C++ source files where you need to use `tracelog()`, | |
3940 | include `<lttng/tracelog.h>`: | |
3941 | + | |
3942 | -- | |
3943 | [source,c] | |
3944 | ---- | |
3945 | #include <lttng/tracelog.h> | |
3946 | ---- | |
3947 | -- | |
3948 | ||
3949 | . In the application's source code, use `tracelog()` like you would use | |
3950 | man:printf(3), except for the first parameter which is the log | |
3951 | level: | |
3952 | + | |
3953 | -- | |
3954 | [source,c] | |
3955 | ---- | |
3956 | /* ... */ | |
3957 | ||
3958 | tracelog(TRACE_WARNING, "my message: %d (%s)", | |
3959 | my_integer, my_string); | |
3960 | ||
3961 | /* ... */ | |
3962 | ---- | |
3963 | -- | |
3964 | + | |
3965 | See man:lttng-ust(3) for a list of available log level names. | |
3966 | ||
3967 | . Link your application with `liblttng-ust`: | |
3968 | + | |
3969 | -- | |
3970 | [role="term"] | |
3971 | ---- | |
3972 | $ gcc -o app app.c -llttng-ust | |
3973 | ---- | |
3974 | -- | |
3975 | ||
3976 | To trace the events that `tracelog()` calls emit with a log level | |
3977 | _as severe as_ a specific log level: | |
3978 | ||
3979 | * <<enabling-disabling-events,Create an event rule>> which matches the | |
3980 | `lttng_ust_tracelog:*` event name and a minimum level | |
3981 | of severity: | |
3982 | + | |
3983 | -- | |
3984 | [role="term"] | |
3985 | ---- | |
3986 | $ lttng enable-event --userspace 'lttng_ust_tracelog:*' | |
3987 | --loglevel=TRACE_WARNING | |
3988 | ---- | |
3989 | -- | |
3990 | ||
3991 | To trace the events that `tracelog()` calls emit with a | |
3992 | _specific log level_: | |
3993 | ||
3994 | * Create an event rule which matches the `lttng_ust_tracelog:*` | |
3995 | event name and a specific log level: | |
3996 | + | |
3997 | -- | |
3998 | [role="term"] | |
3999 | ---- | |
4000 | $ lttng enable-event --userspace 'lttng_ust_tracelog:*' | |
4001 | --loglevel-only=TRACE_INFO | |
4002 | ---- | |
4003 | -- | |
4004 | ||
4005 | ||
4006 | [[prebuilt-ust-helpers]] | |
4007 | === Prebuilt user space tracing helpers | |
4008 | ||
4009 | The LTTng-UST package provides a few helpers in the form or preloadable | |
4010 | shared objects which automatically instrument system functions and | |
4011 | calls. | |
4012 | ||
4013 | The helper shared objects are normally found in dir:{/usr/lib}. If you | |
4014 | built LTTng-UST <<building-from-source,from source>>, they are probably | |
4015 | located in dir:{/usr/local/lib}. | |
4016 | ||
4017 | The installed user space tracing helpers in LTTng-UST{nbsp}{revision} | |
4018 | are: | |
4019 | ||
4020 | path:{liblttng-ust-libc-wrapper.so}:: | |
4021 | path:{liblttng-ust-pthread-wrapper.so}:: | |
4022 | <<liblttng-ust-libc-pthread-wrapper,C{nbsp}standard library | |
4023 | memory and POSIX threads function tracing>>. | |
4024 | ||
4025 | path:{liblttng-ust-cyg-profile.so}:: | |
4026 | path:{liblttng-ust-cyg-profile-fast.so}:: | |
4027 | <<liblttng-ust-cyg-profile,Function entry and exit tracing>>. | |
4028 | ||
4029 | path:{liblttng-ust-dl.so}:: | |
4030 | <<liblttng-ust-dl,Dynamic linker tracing>>. | |
4031 | ||
4032 | To use a user space tracing helper with any user application: | |
4033 | ||
4034 | * Preload the helper shared object when you start the application: | |
4035 | + | |
4036 | -- | |
4037 | [role="term"] | |
4038 | ---- | |
4039 | $ LD_PRELOAD=liblttng-ust-libc-wrapper.so my-app | |
4040 | ---- | |
4041 | -- | |
4042 | + | |
4043 | You can preload more than one helper: | |
4044 | + | |
4045 | -- | |
4046 | [role="term"] | |
4047 | ---- | |
4048 | $ LD_PRELOAD=liblttng-ust-libc-wrapper.so:liblttng-ust-dl.so my-app | |
4049 | ---- | |
4050 | -- | |
4051 | ||
4052 | ||
4053 | [role="since-2.3"] | |
4054 | [[liblttng-ust-libc-pthread-wrapper]] | |
4055 | ==== Instrument C standard library memory and POSIX threads functions | |
4056 | ||
4057 | The path:{liblttng-ust-libc-wrapper.so} and | |
4058 | path:{liblttng-ust-pthread-wrapper.so} helpers | |
4059 | add instrumentation to some C standard library and POSIX | |
4060 | threads functions. | |
4061 | ||
4062 | [role="growable"] | |
4063 | .Functions instrumented by preloading path:{liblttng-ust-libc-wrapper.so}. | |
4064 | |==== | |
4065 | |TP provider name |TP name |Instrumented function | |
4066 | ||
4067 | .6+|`lttng_ust_libc` |`malloc` |man:malloc(3) | |
4068 | |`calloc` |man:calloc(3) | |
4069 | |`realloc` |man:realloc(3) | |
4070 | |`free` |man:free(3) | |
4071 | |`memalign` |man:memalign(3) | |
4072 | |`posix_memalign` |man:posix_memalign(3) | |
4073 | |==== | |
4074 | ||
4075 | [role="growable"] | |
4076 | .Functions instrumented by preloading path:{liblttng-ust-pthread-wrapper.so}. | |
4077 | |==== | |
4078 | |TP provider name |TP name |Instrumented function | |
4079 | ||
4080 | .4+|`lttng_ust_pthread` |`pthread_mutex_lock_req` |man:pthread_mutex_lock(3p) (request time) | |
4081 | |`pthread_mutex_lock_acq` |man:pthread_mutex_lock(3p) (acquire time) | |
4082 | |`pthread_mutex_trylock` |man:pthread_mutex_trylock(3p) | |
4083 | |`pthread_mutex_unlock` |man:pthread_mutex_unlock(3p) | |
4084 | |==== | |
4085 | ||
4086 | When you preload the shared object, it replaces the functions listed | |
4087 | in the previous tables by wrappers which contain tracepoints and call | |
4088 | the replaced functions. | |
4089 | ||
4090 | ||
4091 | [[liblttng-ust-cyg-profile]] | |
4092 | ==== Instrument function entry and exit | |
4093 | ||
4094 | The path:{liblttng-ust-cyg-profile*.so} helpers can add instrumentation | |
4095 | to the entry and exit points of functions. | |
4096 | ||
4097 | man:gcc(1) and man:clang(1) have an option named | |
4098 | https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html[`-finstrument-functions`] | |
4099 | which generates instrumentation calls for entry and exit to functions. | |
4100 | The LTTng-UST function tracing helpers, | |
4101 | path:{liblttng-ust-cyg-profile.so} and | |
4102 | path:{liblttng-ust-cyg-profile-fast.so}, take advantage of this feature | |
4103 | to add tracepoints to the two generated functions (which contain | |
4104 | `cyg_profile` in their names, hence the helper's name). | |
4105 | ||
4106 | To use the LTTng-UST function tracing helper, the source files to | |
4107 | instrument must be built using the `-finstrument-functions` compiler | |
4108 | flag. | |
4109 | ||
4110 | There are two versions of the LTTng-UST function tracing helper: | |
4111 | ||
4112 | * **path:{liblttng-ust-cyg-profile-fast.so}** is a lightweight variant | |
4113 | that you should only use when it can be _guaranteed_ that the | |
4114 | complete event stream is recorded without any lost event record. | |
4115 | Any kind of duplicate information is left out. | |
4116 | + | |
4117 | Assuming no event record is lost, having only the function addresses on | |
4118 | entry is enough to create a call graph, since an event record always | |
4119 | contains the ID of the CPU that generated it. | |
4120 | + | |
4121 | You can use a tool like man:addr2line(1) to convert function addresses | |
4122 | back to source file names and line numbers. | |
4123 | ||
4124 | * **path:{liblttng-ust-cyg-profile.so}** is a more robust variant | |
4125 | which also works in use cases where event records might get discarded or | |
4126 | not recorded from application startup. | |
4127 | In these cases, the trace analyzer needs more information to be | |
4128 | able to reconstruct the program flow. | |
4129 | ||
4130 | See man:lttng-ust-cyg-profile(3) to learn more about the instrumentation | |
4131 | points of this helper. | |
4132 | ||
4133 | All the tracepoints that this helper provides have the | |
4134 | log level `TRACE_DEBUG_FUNCTION` (see man:lttng-ust(3)). | |
4135 | ||
4136 | TIP: It's sometimes a good idea to limit the number of source files that | |
4137 | you compile with the `-finstrument-functions` option to prevent LTTng | |
4138 | from writing an excessive amount of trace data at run time. When using | |
4139 | man:gcc(1), you can use the | |
4140 | `-finstrument-functions-exclude-function-list` option to avoid | |
4141 | instrument entries and exits of specific function names. | |
4142 | ||
4143 | ||
4144 | [role="since-2.4"] | |
4145 | [[liblttng-ust-dl]] | |
4146 | ==== Instrument the dynamic linker | |
4147 | ||
4148 | The path:{liblttng-ust-dl.so} helper adds instrumentation to the | |
4149 | man:dlopen(3) and man:dlclose(3) function calls. | |
4150 | ||
4151 | See man:lttng-ust-dl(3) to learn more about the instrumentation points | |
4152 | of this helper. | |
4153 | ||
4154 | ||
4155 | [role="since-2.4"] | |
4156 | [[java-application]] | |
4157 | === User space Java agent | |
4158 | ||
4159 | You can instrument any Java application which uses one of the following | |
4160 | logging frameworks: | |
4161 | ||
4162 | * The https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[**`java.util.logging`**] | |
4163 | (JUL) core logging facilities. | |
4164 | * http://logging.apache.org/log4j/1.2/[**Apache log4j 1.2**], since | |
4165 | LTTng 2.6. Note that Apache Log4j{nbsp}2 is not supported. | |
4166 | ||
4167 | [role="img-100"] | |
4168 | .LTTng-UST Java agent imported by a Java application. | |
4169 | image::java-app.png[] | |
4170 | ||
4171 | Note that the methods described below are new in LTTng{nbsp}{revision}. | |
4172 | Previous LTTng versions use another technique. | |
4173 | ||
4174 | NOTE: We use http://openjdk.java.net/[OpenJDK]{nbsp}8 for development | |
4175 | and https://ci.lttng.org/[continuous integration], thus this version is | |
4176 | directly supported. However, the LTTng-UST Java agent is also tested | |
4177 | with OpenJDK{nbsp}7. | |
4178 | ||
4179 | ||
4180 | [role="since-2.8"] | |
4181 | [[jul]] | |
4182 | ==== Use the LTTng-UST Java agent for `java.util.logging` | |
4183 | ||
4184 | To use the LTTng-UST Java agent in a Java application which uses | |
4185 | `java.util.logging` (JUL): | |
4186 | ||
4187 | . In the Java application's source code, import the LTTng-UST | |
4188 | log handler package for `java.util.logging`: | |
4189 | + | |
4190 | -- | |
4191 | [source,java] | |
4192 | ---- | |
4193 | import org.lttng.ust.agent.jul.LttngLogHandler; | |
4194 | ---- | |
4195 | -- | |
4196 | ||
4197 | . Create an LTTng-UST JUL log handler: | |
4198 | + | |
4199 | -- | |
4200 | [source,java] | |
4201 | ---- | |
4202 | Handler lttngUstLogHandler = new LttngLogHandler(); | |
4203 | ---- | |
4204 | -- | |
4205 | ||
4206 | . Add this handler to the JUL loggers which should emit LTTng events: | |
4207 | + | |
4208 | -- | |
4209 | [source,java] | |
4210 | ---- | |
4211 | Logger myLogger = Logger.getLogger("some-logger"); | |
4212 | ||
4213 | myLogger.addHandler(lttngUstLogHandler); | |
4214 | ---- | |
4215 | -- | |
4216 | ||
4217 | . Use `java.util.logging` log statements and configuration as usual. | |
4218 | The loggers with an attached LTTng-UST log handler can emit | |
4219 | LTTng events. | |
4220 | ||
4221 | . Before exiting the application, remove the LTTng-UST log handler from | |
4222 | the loggers attached to it and call its `close()` method: | |
4223 | + | |
4224 | -- | |
4225 | [source,java] | |
4226 | ---- | |
4227 | myLogger.removeHandler(lttngUstLogHandler); | |
4228 | lttngUstLogHandler.close(); | |
4229 | ---- | |
4230 | -- | |
4231 | + | |
4232 | This is not strictly necessary, but it is recommended for a clean | |
4233 | disposal of the handler's resources. | |
4234 | ||
4235 | . Include the LTTng-UST Java agent's common and JUL-specific JAR files, | |
4236 | path:{lttng-ust-agent-common.jar} and path:{lttng-ust-agent-jul.jar}, | |
4237 | in the | |
4238 | https://docs.oracle.com/javase/tutorial/essential/environment/paths.html[class | |
4239 | path] when you build the Java application. | |
4240 | + | |
4241 | The JAR files are typically located in dir:{/usr/share/java}. | |
4242 | + | |
4243 | IMPORTANT: The LTTng-UST Java agent must be | |
4244 | <<installing-lttng,installed>> for the logging framework your | |
4245 | application uses. | |
4246 | ||
4247 | .Use the LTTng-UST Java agent for `java.util.logging`. | |
4248 | ==== | |
4249 | [source,java] | |
4250 | .path:{Test.java} | |
4251 | ---- | |
4252 | import java.io.IOException; | |
4253 | import java.util.logging.Handler; | |
4254 | import java.util.logging.Logger; | |
4255 | import org.lttng.ust.agent.jul.LttngLogHandler; | |
4256 | ||
4257 | public class Test | |
4258 | { | |
4259 | private static final int answer = 42; | |
4260 | ||
4261 | public static void main(String[] argv) throws Exception | |
4262 | { | |
4263 | // Create a logger | |
4264 | Logger logger = Logger.getLogger("jello"); | |
4265 | ||
4266 | // Create an LTTng-UST log handler | |
4267 | Handler lttngUstLogHandler = new LttngLogHandler(); | |
4268 | ||
4269 | // Add the LTTng-UST log handler to our logger | |
4270 | logger.addHandler(lttngUstLogHandler); | |
4271 | ||
4272 | // Log at will! | |
4273 | logger.info("some info"); | |
4274 | logger.warning("some warning"); | |
4275 | Thread.sleep(500); | |
4276 | logger.finer("finer information; the answer is " + answer); | |
4277 | Thread.sleep(123); | |
4278 | logger.severe("error!"); | |
4279 | ||
4280 | // Not mandatory, but cleaner | |
4281 | logger.removeHandler(lttngUstLogHandler); | |
4282 | lttngUstLogHandler.close(); | |
4283 | } | |
4284 | } | |
4285 | ---- | |
4286 | ||
4287 | Build this example: | |
4288 | ||
4289 | [role="term"] | |
4290 | ---- | |
4291 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar Test.java | |
4292 | ---- | |
4293 | ||
4294 | <<creating-destroying-tracing-sessions,Create a tracing session>>, | |
4295 | <<enabling-disabling-events,create an event rule>> matching the | |
4296 | `jello` JUL logger, and <<basic-tracing-session-control,start tracing>>: | |
4297 | ||
4298 | [role="term"] | |
4299 | ---- | |
4300 | $ lttng create | |
4301 | $ lttng enable-event --jul jello | |
4302 | $ lttng start | |
4303 | ---- | |
4304 | ||
4305 | Run the compiled class: | |
4306 | ||
4307 | [role="term"] | |
4308 | ---- | |
4309 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar:. Test | |
4310 | ---- | |
4311 | ||
4312 | <<basic-tracing-session-control,Stop tracing>> and inspect the | |
4313 | recorded events: | |
4314 | ||
4315 | [role="term"] | |
4316 | ---- | |
4317 | $ lttng stop | |
4318 | $ lttng view | |
4319 | ---- | |
4320 | ==== | |
4321 | ||
4322 | In the resulting trace, an <<event,event record>> generated by a Java | |
4323 | application using `java.util.logging` is named `lttng_jul:event` and | |
4324 | has the following fields: | |
4325 | ||
4326 | `msg`:: | |
4327 | Log record's message. | |
4328 | ||
4329 | `logger_name`:: | |
4330 | Logger name. | |
4331 | ||
4332 | `class_name`:: | |
4333 | Name of the class in which the log statement was executed. | |
4334 | ||
4335 | `method_name`:: | |
4336 | Name of the method in which the log statement was executed. | |
4337 | ||
4338 | `long_millis`:: | |
4339 | Logging time (timestamp in milliseconds). | |
4340 | ||
4341 | `int_loglevel`:: | |
4342 | Log level integer value. | |
4343 | ||
4344 | `int_threadid`:: | |
4345 | ID of the thread in which the log statement was executed. | |
4346 | ||
4347 | You can use the opt:lttng-enable-event(1):--loglevel or | |
4348 | opt:lttng-enable-event(1):--loglevel-only option of the | |
4349 | man:lttng-enable-event(1) command to target a range of JUL log levels | |
4350 | or a specific JUL log level. | |
4351 | ||
4352 | ||
4353 | [role="since-2.8"] | |
4354 | [[log4j]] | |
4355 | ==== Use the LTTng-UST Java agent for Apache log4j | |
4356 | ||
4357 | To use the LTTng-UST Java agent in a Java application which uses | |
4358 | Apache log4j 1.2: | |
4359 | ||
4360 | . In the Java application's source code, import the LTTng-UST | |
4361 | log appender package for Apache log4j: | |
4362 | + | |
4363 | -- | |
4364 | [source,java] | |
4365 | ---- | |
4366 | import org.lttng.ust.agent.log4j.LttngLogAppender; | |
4367 | ---- | |
4368 | -- | |
4369 | ||
4370 | . Create an LTTng-UST log4j log appender: | |
4371 | + | |
4372 | -- | |
4373 | [source,java] | |
4374 | ---- | |
4375 | Appender lttngUstLogAppender = new LttngLogAppender(); | |
4376 | ---- | |
4377 | -- | |
4378 | ||
4379 | . Add this appender to the log4j loggers which should emit LTTng events: | |
4380 | + | |
4381 | -- | |
4382 | [source,java] | |
4383 | ---- | |
4384 | Logger myLogger = Logger.getLogger("some-logger"); | |
4385 | ||
4386 | myLogger.addAppender(lttngUstLogAppender); | |
4387 | ---- | |
4388 | -- | |
4389 | ||
4390 | . Use Apache log4j log statements and configuration as usual. The | |
4391 | loggers with an attached LTTng-UST log appender can emit LTTng events. | |
4392 | ||
4393 | . Before exiting the application, remove the LTTng-UST log appender from | |
4394 | the loggers attached to it and call its `close()` method: | |
4395 | + | |
4396 | -- | |
4397 | [source,java] | |
4398 | ---- | |
4399 | myLogger.removeAppender(lttngUstLogAppender); | |
4400 | lttngUstLogAppender.close(); | |
4401 | ---- | |
4402 | -- | |
4403 | + | |
4404 | This is not strictly necessary, but it is recommended for a clean | |
4405 | disposal of the appender's resources. | |
4406 | ||
4407 | . Include the LTTng-UST Java agent's common and log4j-specific JAR | |
4408 | files, path:{lttng-ust-agent-common.jar} and | |
4409 | path:{lttng-ust-agent-log4j.jar}, in the | |
4410 | https://docs.oracle.com/javase/tutorial/essential/environment/paths.html[class | |
4411 | path] when you build the Java application. | |
4412 | + | |
4413 | The JAR files are typically located in dir:{/usr/share/java}. | |
4414 | + | |
4415 | IMPORTANT: The LTTng-UST Java agent must be | |
4416 | <<installing-lttng,installed>> for the logging framework your | |
4417 | application uses. | |
4418 | ||
4419 | .Use the LTTng-UST Java agent for Apache log4j. | |
4420 | ==== | |
4421 | [source,java] | |
4422 | .path:{Test.java} | |
4423 | ---- | |
4424 | import org.apache.log4j.Appender; | |
4425 | import org.apache.log4j.Logger; | |
4426 | import org.lttng.ust.agent.log4j.LttngLogAppender; | |
4427 | ||
4428 | public class Test | |
4429 | { | |
4430 | private static final int answer = 42; | |
4431 | ||
4432 | public static void main(String[] argv) throws Exception | |
4433 | { | |
4434 | // Create a logger | |
4435 | Logger logger = Logger.getLogger("jello"); | |
4436 | ||
4437 | // Create an LTTng-UST log appender | |
4438 | Appender lttngUstLogAppender = new LttngLogAppender(); | |
4439 | ||
4440 | // Add the LTTng-UST log appender to our logger | |
4441 | logger.addAppender(lttngUstLogAppender); | |
4442 | ||
4443 | // Log at will! | |
4444 | logger.info("some info"); | |
4445 | logger.warn("some warning"); | |
4446 | Thread.sleep(500); | |
4447 | logger.debug("debug information; the answer is " + answer); | |
4448 | Thread.sleep(123); | |
4449 | logger.fatal("error!"); | |
4450 | ||
4451 | // Not mandatory, but cleaner | |
4452 | logger.removeAppender(lttngUstLogAppender); | |
4453 | lttngUstLogAppender.close(); | |
4454 | } | |
4455 | } | |
4456 | ||
4457 | ---- | |
4458 | ||
4459 | Build this example (`$LOG4JPATH` is the path to the Apache log4j JAR | |
4460 | file): | |
4461 | ||
4462 | [role="term"] | |
4463 | ---- | |
4464 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-log4j.jar:$LOG4JPATH Test.java | |
4465 | ---- | |
4466 | ||
4467 | <<creating-destroying-tracing-sessions,Create a tracing session>>, | |
4468 | <<enabling-disabling-events,create an event rule>> matching the | |
4469 | `jello` log4j logger, and <<basic-tracing-session-control,start tracing>>: | |
4470 | ||
4471 | [role="term"] | |
4472 | ---- | |
4473 | $ lttng create | |
4474 | $ lttng enable-event --log4j jello | |
4475 | $ lttng start | |
4476 | ---- | |
4477 | ||
4478 | Run the compiled class: | |
4479 | ||
4480 | [role="term"] | |
4481 | ---- | |
4482 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-log4j.jar:$LOG4JPATH:. Test | |
4483 | ---- | |
4484 | ||
4485 | <<basic-tracing-session-control,Stop tracing>> and inspect the | |
4486 | recorded events: | |
4487 | ||
4488 | [role="term"] | |
4489 | ---- | |
4490 | $ lttng stop | |
4491 | $ lttng view | |
4492 | ---- | |
4493 | ==== | |
4494 | ||
4495 | In the resulting trace, an <<event,event record>> generated by a Java | |
4496 | application using log4j is named `lttng_log4j:event` and | |
4497 | has the following fields: | |
4498 | ||
4499 | `msg`:: | |
4500 | Log record's message. | |
4501 | ||
4502 | `logger_name`:: | |
4503 | Logger name. | |
4504 | ||
4505 | `class_name`:: | |
4506 | Name of the class in which the log statement was executed. | |
4507 | ||
4508 | `method_name`:: | |
4509 | Name of the method in which the log statement was executed. | |
4510 | ||
4511 | `filename`:: | |
4512 | Name of the file in which the executed log statement is located. | |
4513 | ||
4514 | `line_number`:: | |
4515 | Line number at which the log statement was executed. | |
4516 | ||
4517 | `timestamp`:: | |
4518 | Logging timestamp. | |
4519 | ||
4520 | `int_loglevel`:: | |
4521 | Log level integer value. | |
4522 | ||
4523 | `thread_name`:: | |
4524 | Name of the Java thread in which the log statement was executed. | |
4525 | ||
4526 | You can use the opt:lttng-enable-event(1):--loglevel or | |
4527 | opt:lttng-enable-event(1):--loglevel-only option of the | |
4528 | man:lttng-enable-event(1) command to target a range of Apache log4j log levels | |
4529 | or a specific log4j log level. | |
4530 | ||
4531 | ||
4532 | [role="since-2.8"] | |
4533 | [[java-application-context]] | |
4534 | ==== Provide application-specific context fields in a Java application | |
4535 | ||
4536 | A Java application-specific context field is a piece of state provided | |
4537 | by the application which <<adding-context,you can add>>, using the | |
4538 | man:lttng-add-context(1) command, to each <<event,event record>> | |
4539 | produced by the log statements of this application. | |
4540 | ||
4541 | For example, a given object might have a current request ID variable. | |
4542 | You can create a context information retriever for this object and | |
4543 | assign a name to this current request ID. You can then, using the | |
4544 | man:lttng-add-context(1) command, add this context field by name to | |
4545 | the JUL or log4j <<channel,channel>>. | |
4546 | ||
4547 | To provide application-specific context fields in a Java application: | |
4548 | ||
4549 | . In the Java application's source code, import the LTTng-UST | |
4550 | Java agent context classes and interfaces: | |
4551 | + | |
4552 | -- | |
4553 | [source,java] | |
4554 | ---- | |
4555 | import org.lttng.ust.agent.context.ContextInfoManager; | |
4556 | import org.lttng.ust.agent.context.IContextInfoRetriever; | |
4557 | ---- | |
4558 | -- | |
4559 | ||
4560 | . Create a context information retriever class, that is, a class which | |
4561 | implements the `IContextInfoRetriever` interface: | |
4562 | + | |
4563 | -- | |
4564 | [source,java] | |
4565 | ---- | |
4566 | class MyContextInfoRetriever implements IContextInfoRetriever | |
4567 | { | |
4568 | @Override | |
4569 | public Object retrieveContextInfo(String key) | |
4570 | { | |
4571 | if (key.equals("intCtx")) { | |
4572 | return (short) 17; | |
4573 | } else if (key.equals("strContext")) { | |
4574 | return "context value!"; | |
4575 | } else { | |
4576 | return null; | |
4577 | } | |
4578 | } | |
4579 | } | |
4580 | ---- | |
4581 | -- | |
4582 | + | |
4583 | This `retrieveContextInfo()` method is the only member of the | |
4584 | `IContextInfoRetriever` interface. Its role is to return the current | |
4585 | value of a state by name to create a context field. The names of the | |
4586 | context fields and which state variables they return depends on your | |
4587 | specific scenario. | |
4588 | + | |
4589 | All primitive types and objects are supported as context fields. | |
4590 | When `retrieveContextInfo()` returns an object, the context field | |
4591 | serializer calls its `toString()` method to add a string field to | |
4592 | event records. The method can also return `null`, which means that | |
4593 | no context field is available for the required name. | |
4594 | ||
4595 | . Register an instance of your context information retriever class to | |
4596 | the context information manager singleton: | |
4597 | + | |
4598 | -- | |
4599 | [source,java] | |
4600 | ---- | |
4601 | IContextInfoRetriever cir = new MyContextInfoRetriever(); | |
4602 | ContextInfoManager cim = ContextInfoManager.getInstance(); | |
4603 | cim.registerContextInfoRetriever("retrieverName", cir); | |
4604 | ---- | |
4605 | -- | |
4606 | ||
4607 | . Before exiting the application, remove your context information | |
4608 | retriever from the context information manager singleton: | |
4609 | + | |
4610 | -- | |
4611 | [source,java] | |
4612 | ---- | |
4613 | ContextInfoManager cim = ContextInfoManager.getInstance(); | |
4614 | cim.unregisterContextInfoRetriever("retrieverName"); | |
4615 | ---- | |
4616 | -- | |
4617 | + | |
4618 | This is not strictly necessary, but it is recommended for a clean | |
4619 | disposal of some manager's resources. | |
4620 | ||
4621 | . Build your Java application with LTTng-UST Java agent support as | |
4622 | usual, following the procedure for either the <<jul,JUL>> or | |
4623 | <<log4j,Apache log4j>> framework. | |
4624 | ||
4625 | ||
4626 | .Provide application-specific context fields in a Java application. | |
4627 | ==== | |
4628 | [source,java] | |
4629 | .path:{Test.java} | |
4630 | ---- | |
4631 | import java.util.logging.Handler; | |
4632 | import java.util.logging.Logger; | |
4633 | import org.lttng.ust.agent.jul.LttngLogHandler; | |
4634 | import org.lttng.ust.agent.context.ContextInfoManager; | |
4635 | import org.lttng.ust.agent.context.IContextInfoRetriever; | |
4636 | ||
4637 | public class Test | |
4638 | { | |
4639 | // Our context information retriever class | |
4640 | private static class MyContextInfoRetriever | |
4641 | implements IContextInfoRetriever | |
4642 | { | |
4643 | @Override | |
4644 | public Object retrieveContextInfo(String key) { | |
4645 | if (key.equals("intCtx")) { | |
4646 | return (short) 17; | |
4647 | } else if (key.equals("strContext")) { | |
4648 | return "context value!"; | |
4649 | } else { | |
4650 | return null; | |
4651 | } | |
4652 | } | |
4653 | } | |
4654 | ||
4655 | private static final int answer = 42; | |
4656 | ||
4657 | public static void main(String args[]) throws Exception | |
4658 | { | |
4659 | // Get the context information manager instance | |
4660 | ContextInfoManager cim = ContextInfoManager.getInstance(); | |
4661 | ||
4662 | // Create and register our context information retriever | |
4663 | IContextInfoRetriever cir = new MyContextInfoRetriever(); | |
4664 | cim.registerContextInfoRetriever("myRetriever", cir); | |
4665 | ||
4666 | // Create a logger | |
4667 | Logger logger = Logger.getLogger("jello"); | |
4668 | ||
4669 | // Create an LTTng-UST log handler | |
4670 | Handler lttngUstLogHandler = new LttngLogHandler(); | |
4671 | ||
4672 | // Add the LTTng-UST log handler to our logger | |
4673 | logger.addHandler(lttngUstLogHandler); | |
4674 | ||
4675 | // Log at will! | |
4676 | logger.info("some info"); | |
4677 | logger.warning("some warning"); | |
4678 | Thread.sleep(500); | |
4679 | logger.finer("finer information; the answer is " + answer); | |
4680 | Thread.sleep(123); | |
4681 | logger.severe("error!"); | |
4682 | ||
4683 | // Not mandatory, but cleaner | |
4684 | logger.removeHandler(lttngUstLogHandler); | |
4685 | lttngUstLogHandler.close(); | |
4686 | cim.unregisterContextInfoRetriever("myRetriever"); | |
4687 | } | |
4688 | } | |
4689 | ---- | |
4690 | ||
4691 | Build this example: | |
4692 | ||
4693 | [role="term"] | |
4694 | ---- | |
4695 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar Test.java | |
4696 | ---- | |
4697 | ||
4698 | <<creating-destroying-tracing-sessions,Create a tracing session>> | |
4699 | and <<enabling-disabling-events,create an event rule>> matching the | |
4700 | `jello` JUL logger: | |
4701 | ||
4702 | [role="term"] | |
4703 | ---- | |
4704 | $ lttng create | |
4705 | $ lttng enable-event --jul jello | |
4706 | ---- | |
4707 | ||
4708 | <<adding-context,Add the application-specific context fields>> to the | |
4709 | JUL channel: | |
4710 | ||
4711 | [role="term"] | |
4712 | ---- | |
4713 | $ lttng add-context --jul --type='$app.myRetriever:intCtx' | |
4714 | $ lttng add-context --jul --type='$app.myRetriever:strContext' | |
4715 | ---- | |
4716 | ||
4717 | <<basic-tracing-session-control,Start tracing>>: | |
4718 | ||
4719 | [role="term"] | |
4720 | ---- | |
4721 | $ lttng start | |
4722 | ---- | |
4723 | ||
4724 | Run the compiled class: | |
4725 | ||
4726 | [role="term"] | |
4727 | ---- | |
4728 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar:. Test | |
4729 | ---- | |
4730 | ||
4731 | <<basic-tracing-session-control,Stop tracing>> and inspect the | |
4732 | recorded events: | |
4733 | ||
4734 | [role="term"] | |
4735 | ---- | |
4736 | $ lttng stop | |
4737 | $ lttng view | |
4738 | ---- | |
4739 | ==== | |
4740 | ||
4741 | ||
4742 | [role="since-2.7"] | |
4743 | [[python-application]] | |
4744 | === User space Python agent | |
4745 | ||
4746 | You can instrument a Python 2 or Python 3 application which uses the | |
4747 | standard https://docs.python.org/3/library/logging.html[`logging`] | |
4748 | package. | |
4749 | ||
4750 | Each log statement emits an LTTng event once the | |
4751 | application module imports the | |
4752 | <<lttng-ust-agents,LTTng-UST Python agent>> package. | |
4753 | ||
4754 | [role="img-100"] | |
4755 | .A Python application importing the LTTng-UST Python agent. | |
4756 | image::python-app.png[] | |
4757 | ||
4758 | To use the LTTng-UST Python agent: | |
4759 | ||
4760 | . In the Python application's source code, import the LTTng-UST Python | |
4761 | agent: | |
4762 | + | |
4763 | -- | |
4764 | [source,python] | |
4765 | ---- | |
4766 | import lttngust | |
4767 | ---- | |
4768 | -- | |
4769 | + | |
4770 | The LTTng-UST Python agent automatically adds its logging handler to the | |
4771 | root logger at import time. | |
4772 | + | |
4773 | Any log statement that the application executes before this import does | |
4774 | not emit an LTTng event. | |
4775 | + | |
4776 | IMPORTANT: The LTTng-UST Python agent must be | |
4777 | <<installing-lttng,installed>>. | |
4778 | ||
4779 | . Use log statements and logging configuration as usual. | |
4780 | Since the LTTng-UST Python agent adds a handler to the _root_ | |
4781 | logger, you can trace any log statement from any logger. | |
4782 | ||
4783 | .Use the LTTng-UST Python agent. | |
4784 | ==== | |
4785 | [source,python] | |
4786 | .path:{test.py} | |
4787 | ---- | |
4788 | import lttngust | |
4789 | import logging | |
4790 | import time | |
4791 | ||
4792 | ||
4793 | def example(): | |
4794 | logging.basicConfig() | |
4795 | logger = logging.getLogger('my-logger') | |
4796 | ||
4797 | while True: | |
4798 | logger.debug('debug message') | |
4799 | logger.info('info message') | |
4800 | logger.warn('warn message') | |
4801 | logger.error('error message') | |
4802 | logger.critical('critical message') | |
4803 | time.sleep(1) | |
4804 | ||
4805 | ||
4806 | if __name__ == '__main__': | |
4807 | example() | |
4808 | ---- | |
4809 | ||
4810 | NOTE: `logging.basicConfig()`, which adds to the root logger a basic | |
4811 | logging handler which prints to the standard error stream, is not | |
4812 | strictly required for LTTng-UST tracing to work, but in versions of | |
4813 | Python preceding 3.2, you could see a warning message which indicates | |
4814 | that no handler exists for the logger `my-logger`. | |
4815 | ||
4816 | <<creating-destroying-tracing-sessions,Create a tracing session>>, | |
4817 | <<enabling-disabling-events,create an event rule>> matching the | |
4818 | `my-logger` Python logger, and <<basic-tracing-session-control,start | |
4819 | tracing>>: | |
4820 | ||
4821 | [role="term"] | |
4822 | ---- | |
4823 | $ lttng create | |
4824 | $ lttng enable-event --python my-logger | |
4825 | $ lttng start | |
4826 | ---- | |
4827 | ||
4828 | Run the Python script: | |
4829 | ||
4830 | [role="term"] | |
4831 | ---- | |
4832 | $ python test.py | |
4833 | ---- | |
4834 | ||
4835 | <<basic-tracing-session-control,Stop tracing>> and inspect the recorded | |
4836 | events: | |
4837 | ||
4838 | [role="term"] | |
4839 | ---- | |
4840 | $ lttng stop | |
4841 | $ lttng view | |
4842 | ---- | |
4843 | ==== | |
4844 | ||
4845 | In the resulting trace, an <<event,event record>> generated by a Python | |
4846 | application is named `lttng_python:event` and has the following fields: | |
4847 | ||
4848 | `asctime`:: | |
4849 | Logging time (string). | |
4850 | ||
4851 | `msg`:: | |
4852 | Log record's message. | |
4853 | ||
4854 | `logger_name`:: | |
4855 | Logger name. | |
4856 | ||
4857 | `funcName`:: | |
4858 | Name of the function in which the log statement was executed. | |
4859 | ||
4860 | `lineno`:: | |
4861 | Line number at which the log statement was executed. | |
4862 | ||
4863 | `int_loglevel`:: | |
4864 | Log level integer value. | |
4865 | ||
4866 | `thread`:: | |
4867 | ID of the Python thread in which the log statement was executed. | |
4868 | ||
4869 | `threadName`:: | |
4870 | Name of the Python thread in which the log statement was executed. | |
4871 | ||
4872 | You can use the opt:lttng-enable-event(1):--loglevel or | |
4873 | opt:lttng-enable-event(1):--loglevel-only option of the | |
4874 | man:lttng-enable-event(1) command to target a range of Python log levels | |
4875 | or a specific Python log level. | |
4876 | ||
4877 | When an application imports the LTTng-UST Python agent, the agent tries | |
4878 | to register to a <<lttng-sessiond,session daemon>>. Note that you must | |
4879 | <<start-sessiond,start the session daemon>> _before_ you run the Python | |
4880 | application. If a session daemon is found, the agent tries to register | |
4881 | to it during 5{nbsp}seconds, after which the application continues | |
4882 | without LTTng tracing support. You can override this timeout value with | |
4883 | the env:LTTNG_UST_PYTHON_REGISTER_TIMEOUT environment variable | |
4884 | (milliseconds). | |
4885 | ||
4886 | If the session daemon stops while a Python application with an imported | |
4887 | LTTng-UST Python agent runs, the agent retries to connect and to | |
4888 | register to a session daemon every 3{nbsp}seconds. You can override this | |
4889 | delay with the env:LTTNG_UST_PYTHON_REGISTER_RETRY_DELAY environment | |
4890 | variable. | |
4891 | ||
4892 | ||
4893 | [role="since-2.5"] | |
4894 | [[proc-lttng-logger-abi]] | |
4895 | === LTTng logger | |
4896 | ||
4897 | The `lttng-tracer` Linux kernel module, part of | |
4898 | <<lttng-modules,LTTng-modules>>, creates the special LTTng logger file | |
4899 | path:{/proc/lttng-logger} when it's loaded. Any application can write | |
4900 | text data to this file to emit an LTTng event. | |
4901 | ||
4902 | [role="img-100"] | |
4903 | .An application writes to the LTTng logger file to emit an LTTng event. | |
4904 | image::lttng-logger.png[] | |
4905 | ||
4906 | The LTTng logger is the quickest method--not the most efficient, | |
4907 | however--to add instrumentation to an application. It is designed | |
4908 | mostly to instrument shell scripts: | |
4909 | ||
4910 | [role="term"] | |
4911 | ---- | |
4912 | $ echo "Some message, some $variable" > /proc/lttng-logger | |
4913 | ---- | |
4914 | ||
4915 | Any event that the LTTng logger emits is named `lttng_logger` and | |
4916 | belongs to the Linux kernel <<domain,tracing domain>>. However, unlike | |
4917 | other instrumentation points in the kernel tracing domain, **any Unix | |
4918 | user** can <<enabling-disabling-events,create an event rule>> which | |
4919 | matches its event name, not only the root user or users in the | |
4920 | <<tracing-group,tracing group>>. | |
4921 | ||
4922 | To use the LTTng logger: | |
4923 | ||
4924 | * From any application, write text data to the path:{/proc/lttng-logger} | |
4925 | file. | |
4926 | ||
4927 | The `msg` field of `lttng_logger` event records contains the | |
4928 | recorded message. | |
4929 | ||
4930 | NOTE: The maximum message length of an LTTng logger event is | |
4931 | 1024{nbsp}bytes. Writing more than this makes the LTTng logger emit more | |
4932 | than one event to contain the remaining data. | |
4933 | ||
4934 | You should not use the LTTng logger to trace a user application which | |
4935 | can be instrumented in a more efficient way, namely: | |
4936 | ||
4937 | * <<c-application,C and $$C++$$ applications>>. | |
4938 | * <<java-application,Java applications>>. | |
4939 | * <<python-application,Python applications>>. | |
4940 | ||
4941 | .Use the LTTng logger. | |
4942 | ==== | |
4943 | [source,bash] | |
4944 | .path:{test.bash} | |
4945 | ---- | |
4946 | echo 'Hello, World!' > /proc/lttng-logger | |
4947 | sleep 2 | |
4948 | df --human-readable --print-type / > /proc/lttng-logger | |
4949 | ---- | |
4950 | ||
4951 | <<creating-destroying-tracing-sessions,Create a tracing session>>, | |
4952 | <<enabling-disabling-events,create an event rule>> matching the | |
4953 | `lttng_logger` Linux kernel tracepoint, and | |
4954 | <<basic-tracing-session-control,start tracing>>: | |
4955 | ||
4956 | [role="term"] | |
4957 | ---- | |
4958 | $ lttng create | |
4959 | $ lttng enable-event --kernel lttng_logger | |
4960 | $ lttng start | |
4961 | ---- | |
4962 | ||
4963 | Run the Bash script: | |
4964 | ||
4965 | [role="term"] | |
4966 | ---- | |
4967 | $ bash test.bash | |
4968 | ---- | |
4969 | ||
4970 | <<basic-tracing-session-control,Stop tracing>> and inspect the recorded | |
4971 | events: | |
4972 | ||
4973 | [role="term"] | |
4974 | ---- | |
4975 | $ lttng stop | |
4976 | $ lttng view | |
4977 | ---- | |
4978 | ==== | |
4979 | ||
4980 | ||
4981 | [[instrumenting-linux-kernel]] | |
4982 | === LTTng kernel tracepoints | |
4983 | ||
4984 | NOTE: This section shows how to _add_ instrumentation points to the | |
4985 | Linux kernel. The kernel's subsystems are already thoroughly | |
4986 | instrumented at strategic places for LTTng when you | |
4987 | <<installing-lttng,install>> the <<lttng-modules,LTTng-modules>> | |
4988 | package. | |
4989 | ||
4990 | //// | |
4991 | There are two methods to instrument the Linux kernel: | |
4992 | ||
4993 | . <<linux-add-lttng-layer,Add an LTTng layer>> over an existing ftrace | |
4994 | tracepoint which uses the `TRACE_EVENT()` API. | |
4995 | + | |
4996 | Choose this if you want to instrumentation a Linux kernel tree with an | |
4997 | instrumentation point compatible with ftrace, perf, and SystemTap. | |
4998 | ||
4999 | . Use an <<linux-lttng-tracepoint-event,LTTng-only approach>> to | |
5000 | instrument an out-of-tree kernel module. | |
5001 | + | |
5002 | Choose this if you don't need ftrace, perf, or SystemTap support. | |
5003 | //// | |
5004 | ||
5005 | ||
5006 | [[linux-add-lttng-layer]] | |
5007 | ==== [[instrumenting-linux-kernel-itself]][[mainline-trace-event]][[lttng-adaptation-layer]]Add an LTTng layer to an existing ftrace tracepoint | |
5008 | ||
5009 | This section shows how to add an LTTng layer to existing ftrace | |
5010 | instrumentation using the `TRACE_EVENT()` API. | |
5011 | ||
5012 | This section does not document the `TRACE_EVENT()` macro. You can | |
5013 | read the following articles to learn more about this API: | |
5014 | ||
5015 | * http://lwn.net/Articles/379903/[Using the TRACE_EVENT() macro (Part 1)] | |
5016 | * http://lwn.net/Articles/381064/[Using the TRACE_EVENT() macro (Part 2)] | |
5017 | * http://lwn.net/Articles/383362/[Using the TRACE_EVENT() macro (Part 3)] | |
5018 | ||
5019 | The following procedure assumes that your ftrace tracepoints are | |
5020 | correctly defined in their own header and that they are created in | |
5021 | one source file using the `CREATE_TRACE_POINTS` definition. | |
5022 | ||
5023 | To add an LTTng layer over an existing ftrace tracepoint: | |
5024 | ||
5025 | . Make sure the following kernel configuration options are | |
5026 | enabled: | |
5027 | + | |
5028 | -- | |
5029 | * `CONFIG_MODULES` | |
5030 | * `CONFIG_KALLSYMS` | |
5031 | * `CONFIG_HIGH_RES_TIMERS` | |
5032 | * `CONFIG_TRACEPOINTS` | |
5033 | -- | |
5034 | ||
5035 | . Build the Linux source tree with your custom ftrace tracepoints. | |
5036 | . Boot the resulting Linux image on your target system. | |
5037 | + | |
5038 | Confirm that the tracepoints exist by looking for their names in the | |
5039 | dir:{/sys/kernel/debug/tracing/events/subsys} directory, where `subsys` | |
5040 | is your subsystem's name. | |
5041 | ||
5042 | . Get a copy of the latest LTTng-modules{nbsp}{revision}: | |
5043 | + | |
5044 | -- | |
5045 | [role="term"] | |
5046 | ---- | |
5047 | $ cd $(mktemp -d) && | |
5048 | wget http://lttng.org/files/lttng-modules/lttng-modules-latest-2.10.tar.bz2 && | |
5049 | tar -xf lttng-modules-latest-2.10.tar.bz2 && | |
5050 | cd lttng-modules-2.10.* | |
5051 | ---- | |
5052 | -- | |
5053 | ||
5054 | . In dir:{instrumentation/events/lttng-module}, relative to the root | |
5055 | of the LTTng-modules source tree, create a header file named | |
5056 | +__subsys__.h+ for your custom subsystem +__subsys__+ and write your | |
5057 | LTTng-modules tracepoint definitions using the LTTng-modules | |
5058 | macros in it. | |
5059 | + | |
5060 | Start with this template: | |
5061 | + | |
5062 | -- | |
5063 | [source,c] | |
5064 | .path:{instrumentation/events/lttng-module/my_subsys.h} | |
5065 | ---- | |
5066 | #undef TRACE_SYSTEM | |
5067 | #define TRACE_SYSTEM my_subsys | |
5068 | ||
5069 | #if !defined(_LTTNG_MY_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) | |
5070 | #define _LTTNG_MY_SUBSYS_H | |
5071 | ||
5072 | #include "../../../probes/lttng-tracepoint-event.h" | |
5073 | #include <linux/tracepoint.h> | |
5074 | ||
5075 | LTTNG_TRACEPOINT_EVENT( | |
5076 | /* | |
5077 | * Format is identical to TRACE_EVENT()'s version for the three | |
5078 | * following macro parameters: | |
5079 | */ | |
5080 | my_subsys_my_event, | |
5081 | TP_PROTO(int my_int, const char *my_string), | |
5082 | TP_ARGS(my_int, my_string), | |
5083 | ||
5084 | /* LTTng-modules specific macros */ | |
5085 | TP_FIELDS( | |
5086 | ctf_integer(int, my_int_field, my_int) | |
5087 | ctf_string(my_bar_field, my_bar) | |
5088 | ) | |
5089 | ) | |
5090 | ||
5091 | #endif /* !defined(_LTTNG_MY_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) */ | |
5092 | ||
5093 | #include "../../../probes/define_trace.h" | |
5094 | ---- | |
5095 | -- | |
5096 | + | |
5097 | The entries in the `TP_FIELDS()` section are the list of fields for the | |
5098 | LTTng tracepoint. This is similar to the `TP_STRUCT__entry()` part of | |
5099 | ftrace's `TRACE_EVENT()` macro. | |
5100 | + | |
5101 | See <<lttng-modules-tp-fields,Tracepoint fields macros>> for a | |
5102 | complete description of the available `ctf_*()` macros. | |
5103 | ||
5104 | . Create the LTTng-modules probe's kernel module C source file, | |
5105 | +probes/lttng-probe-__subsys__.c+, where +__subsys__+ is your | |
5106 | subsystem name: | |
5107 | + | |
5108 | -- | |
5109 | [source,c] | |
5110 | .path:{probes/lttng-probe-my-subsys.c} | |
5111 | ---- | |
5112 | #include <linux/module.h> | |
5113 | #include "../lttng-tracer.h" | |
5114 | ||
5115 | /* | |
5116 | * Build-time verification of mismatch between mainline | |
5117 | * TRACE_EVENT() arguments and the LTTng-modules adaptation | |
5118 | * layer LTTNG_TRACEPOINT_EVENT() arguments. | |
5119 | */ | |
5120 | #include <trace/events/my_subsys.h> | |
5121 | ||
5122 | /* Create LTTng tracepoint probes */ | |
5123 | #define LTTNG_PACKAGE_BUILD | |
5124 | #define CREATE_TRACE_POINTS | |
5125 | #define TRACE_INCLUDE_PATH ../instrumentation/events/lttng-module | |
5126 | ||
5127 | #include "../instrumentation/events/lttng-module/my_subsys.h" | |
5128 | ||
5129 | MODULE_LICENSE("GPL and additional rights"); | |
5130 | MODULE_AUTHOR("Your name <your-email>"); | |
5131 | MODULE_DESCRIPTION("LTTng my_subsys probes"); | |
5132 | MODULE_VERSION(__stringify(LTTNG_MODULES_MAJOR_VERSION) "." | |
5133 | __stringify(LTTNG_MODULES_MINOR_VERSION) "." | |
5134 | __stringify(LTTNG_MODULES_PATCHLEVEL_VERSION) | |
5135 | LTTNG_MODULES_EXTRAVERSION); | |
5136 | ---- | |
5137 | -- | |
5138 | ||
5139 | . Edit path:{probes/KBuild} and add your new kernel module object | |
5140 | next to the existing ones: | |
5141 | + | |
5142 | -- | |
5143 | [source,make] | |
5144 | .path:{probes/KBuild} | |
5145 | ---- | |
5146 | # ... | |
5147 | ||
5148 | obj-m += lttng-probe-module.o | |
5149 | obj-m += lttng-probe-power.o | |
5150 | ||
5151 | obj-m += lttng-probe-my-subsys.o | |
5152 | ||
5153 | # ... | |
5154 | ---- | |
5155 | -- | |
5156 | ||
5157 | . Build and install the LTTng kernel modules: | |
5158 | + | |
5159 | -- | |
5160 | [role="term"] | |
5161 | ---- | |
5162 | $ make KERNELDIR=/path/to/linux | |
5163 | # make modules_install && depmod -a | |
5164 | ---- | |
5165 | -- | |
5166 | + | |
5167 | Replace `/path/to/linux` with the path to the Linux source tree where | |
5168 | you defined and used tracepoints with ftrace's `TRACE_EVENT()` macro. | |
5169 | ||
5170 | Note that you can also use the | |
5171 | <<lttng-tracepoint-event-code,`LTTNG_TRACEPOINT_EVENT_CODE()` macro>> | |
5172 | instead of `LTTNG_TRACEPOINT_EVENT()` to use custom local variables and | |
5173 | C code that need to be executed before the event fields are recorded. | |
5174 | ||
5175 | The best way to learn how to use the previous LTTng-modules macros is to | |
5176 | inspect the existing LTTng-modules tracepoint definitions in the | |
5177 | dir:{instrumentation/events/lttng-module} header files. Compare them | |
5178 | with the Linux kernel mainline versions in the | |
5179 | dir:{include/trace/events} directory of the Linux source tree. | |
5180 | ||
5181 | ||
5182 | [role="since-2.7"] | |
5183 | [[lttng-tracepoint-event-code]] | |
5184 | ===== Use custom C code to access the data for tracepoint fields | |
5185 | ||
5186 | Although we recommended to always use the | |
5187 | <<lttng-adaptation-layer,`LTTNG_TRACEPOINT_EVENT()`>> macro to describe | |
5188 | the arguments and fields of an LTTng-modules tracepoint when possible, | |
5189 | sometimes you need a more complex process to access the data that the | |
5190 | tracer records as event record fields. In other words, you need local | |
5191 | variables and multiple C{nbsp}statements instead of simple | |
5192 | argument-based expressions that you pass to the | |
5193 | <<lttng-modules-tp-fields,`ctf_*()` macros of `TP_FIELDS()`>>. | |
5194 | ||
5195 | You can use the `LTTNG_TRACEPOINT_EVENT_CODE()` macro instead of | |
5196 | `LTTNG_TRACEPOINT_EVENT()` to declare custom local variables and define | |
5197 | a block of C{nbsp}code to be executed before LTTng records the fields. | |
5198 | The structure of this macro is: | |
5199 | ||
5200 | [source,c] | |
5201 | .`LTTNG_TRACEPOINT_EVENT_CODE()` macro syntax. | |
5202 | ---- | |
5203 | LTTNG_TRACEPOINT_EVENT_CODE( | |
5204 | /* | |
5205 | * Format identical to the LTTNG_TRACEPOINT_EVENT() | |
5206 | * version for the following three macro parameters: | |
5207 | */ | |
5208 | my_subsys_my_event, | |
5209 | TP_PROTO(int my_int, const char *my_string), | |
5210 | TP_ARGS(my_int, my_string), | |
5211 | ||
5212 | /* Declarations of custom local variables */ | |
5213 | TP_locvar( | |
5214 | int a = 0; | |
5215 | unsigned long b = 0; | |
5216 | const char *name = "(undefined)"; | |
5217 | struct my_struct *my_struct; | |
5218 | ), | |
5219 | ||
5220 | /* | |
5221 | * Custom code which uses both tracepoint arguments | |
5222 | * (in TP_ARGS()) and local variables (in TP_locvar()). | |
5223 | * | |
5224 | * Local variables are actually members of a structure pointed | |
5225 | * to by the special variable tp_locvar. | |
5226 | */ | |
5227 | TP_code( | |
5228 | if (my_int) { | |
5229 | tp_locvar->a = my_int + 17; | |
5230 | tp_locvar->my_struct = get_my_struct_at(tp_locvar->a); | |
5231 | tp_locvar->b = my_struct_compute_b(tp_locvar->my_struct); | |
5232 | tp_locvar->name = my_struct_get_name(tp_locvar->my_struct); | |
5233 | put_my_struct(tp_locvar->my_struct); | |
5234 | ||
5235 | if (tp_locvar->b) { | |
5236 | tp_locvar->a = 1; | |
5237 | } | |
5238 | } | |
5239 | ), | |
5240 | ||
5241 | /* | |
5242 | * Format identical to the LTTNG_TRACEPOINT_EVENT() | |
5243 | * version for this, except that tp_locvar members can be | |
5244 | * used in the argument expression parameters of | |
5245 | * the ctf_*() macros. | |
5246 | */ | |
5247 | TP_FIELDS( | |
5248 | ctf_integer(unsigned long, my_struct_b, tp_locvar->b) | |
5249 | ctf_integer(int, my_struct_a, tp_locvar->a) | |
5250 | ctf_string(my_string_field, my_string) | |
5251 | ctf_string(my_struct_name, tp_locvar->name) | |
5252 | ) | |
5253 | ) | |
5254 | ---- | |
5255 | ||
5256 | IMPORTANT: The C code defined in `TP_code()` must not have any side | |
5257 | effects when executed. In particular, the code must not allocate | |
5258 | memory or get resources without deallocating this memory or putting | |
5259 | those resources afterwards. | |
5260 | ||
5261 | ||
5262 | [[instrumenting-linux-kernel-tracing]] | |
5263 | ==== Load and unload a custom probe kernel module | |
5264 | ||
5265 | You must load a <<lttng-adaptation-layer,created LTTng-modules probe | |
5266 | kernel module>> in the kernel before it can emit LTTng events. | |
5267 | ||
5268 | To load the default probe kernel modules and a custom probe kernel | |
5269 | module: | |
5270 | ||
5271 | * Use the opt:lttng-sessiond(8):--extra-kmod-probes option to give extra | |
5272 | probe modules to load when starting a root <<lttng-sessiond,session | |
5273 | daemon>>: | |
5274 | + | |
5275 | -- | |
5276 | .Load the `my_subsys`, `usb`, and the default probe modules. | |
5277 | ==== | |
5278 | [role="term"] | |
5279 | ---- | |
5280 | # lttng-sessiond --extra-kmod-probes=my_subsys,usb | |
5281 | ---- | |
5282 | ==== | |
5283 | -- | |
5284 | + | |
5285 | You only need to pass the subsystem name, not the whole kernel module | |
5286 | name. | |
5287 | ||
5288 | To load _only_ a given custom probe kernel module: | |
5289 | ||
5290 | * Use the opt:lttng-sessiond(8):--kmod-probes option to give the probe | |
5291 | modules to load when starting a root session daemon: | |
5292 | + | |
5293 | -- | |
5294 | .Load only the `my_subsys` and `usb` probe modules. | |
5295 | ==== | |
5296 | [role="term"] | |
5297 | ---- | |
5298 | # lttng-sessiond --kmod-probes=my_subsys,usb | |
5299 | ---- | |
5300 | ==== | |
5301 | -- | |
5302 | ||
5303 | To confirm that a probe module is loaded: | |
5304 | ||
5305 | * Use man:lsmod(8): | |
5306 | + | |
5307 | -- | |
5308 | [role="term"] | |
5309 | ---- | |
5310 | $ lsmod | grep lttng_probe_usb | |
5311 | ---- | |
5312 | -- | |
5313 | ||
5314 | To unload the loaded probe modules: | |
5315 | ||
5316 | * Kill the session daemon with `SIGTERM`: | |
5317 | + | |
5318 | -- | |
5319 | [role="term"] | |
5320 | ---- | |
5321 | # pkill lttng-sessiond | |
5322 | ---- | |
5323 | -- | |
5324 | + | |
5325 | You can also use man:modprobe(8)'s `--remove` option if the session | |
5326 | daemon terminates abnormally. | |
5327 | ||
5328 | ||
5329 | [[controlling-tracing]] | |
5330 | == Tracing control | |
5331 | ||
5332 | Once an application or a Linux kernel is | |
5333 | <<instrumenting,instrumented>> for LTTng tracing, | |
5334 | you can _trace_ it. | |
5335 | ||
5336 | This section is divided in topics on how to use the various | |
5337 | <<plumbing,components of LTTng>>, in particular the <<lttng-cli,cmd:lttng | |
5338 | command-line tool>>, to _control_ the LTTng daemons and tracers. | |
5339 | ||
5340 | NOTE: In the following subsections, we refer to an man:lttng(1) command | |
5341 | using its man page name. For example, instead of _Run the `create` | |
5342 | command to..._, we use _Run the man:lttng-create(1) command to..._. | |
5343 | ||
5344 | ||
5345 | [[start-sessiond]] | |
5346 | === Start a session daemon | |
5347 | ||
5348 | In some situations, you need to run a <<lttng-sessiond,session daemon>> | |
5349 | (man:lttng-sessiond(8)) _before_ you can use the man:lttng(1) | |
5350 | command-line tool. | |
5351 | ||
5352 | You will see the following error when you run a command while no session | |
5353 | daemon is running: | |
5354 | ||
5355 | ---- | |
5356 | Error: No session daemon is available | |
5357 | ---- | |
5358 | ||
5359 | The only command that automatically runs a session daemon is | |
5360 | man:lttng-create(1), which you use to | |
5361 | <<creating-destroying-tracing-sessions,create a tracing session>>. While | |
5362 | this is most of the time the first operation that you do, sometimes it's | |
5363 | not. Some examples are: | |
5364 | ||
5365 | * <<list-instrumentation-points,List the available instrumentation points>>. | |
5366 | * <<saving-loading-tracing-session,Load a tracing session configuration>>. | |
5367 | ||
5368 | [[tracing-group]] Each Unix user must have its own running session | |
5369 | daemon to trace user applications. The session daemon that the root user | |
5370 | starts is the only one allowed to control the LTTng kernel tracer. Users | |
5371 | that are part of the _tracing group_ can control the root session | |
5372 | daemon. The default tracing group name is `tracing`; you can set it to | |
5373 | something else with the opt:lttng-sessiond(8):--group option when you | |
5374 | start the root session daemon. | |
5375 | ||
5376 | To start a user session daemon: | |
5377 | ||
5378 | * Run man:lttng-sessiond(8): | |
5379 | + | |
5380 | -- | |
5381 | [role="term"] | |
5382 | ---- | |
5383 | $ lttng-sessiond --daemonize | |
5384 | ---- | |
5385 | -- | |
5386 | ||
5387 | To start the root session daemon: | |
5388 | ||
5389 | * Run man:lttng-sessiond(8) as the root user: | |
5390 | + | |
5391 | -- | |
5392 | [role="term"] | |
5393 | ---- | |
5394 | # lttng-sessiond --daemonize | |
5395 | ---- | |
5396 | -- | |
5397 | ||
5398 | In both cases, remove the opt:lttng-sessiond(8):--daemonize option to | |
5399 | start the session daemon in foreground. | |
5400 | ||
5401 | To stop a session daemon, use man:kill(1) on its process ID (standard | |
5402 | `TERM` signal). | |
5403 | ||
5404 | Note that some Linux distributions could manage the LTTng session daemon | |
5405 | as a service. In this case, you should use the service manager to | |
5406 | start, restart, and stop session daemons. | |
5407 | ||
5408 | ||
5409 | [[creating-destroying-tracing-sessions]] | |
5410 | === Create and destroy a tracing session | |
5411 | ||
5412 | Almost all the LTTng control operations happen in the scope of | |
5413 | a <<tracing-session,tracing session>>, which is the dialogue between the | |
5414 | <<lttng-sessiond,session daemon>> and you. | |
5415 | ||
5416 | To create a tracing session with a generated name: | |
5417 | ||
5418 | * Use the man:lttng-create(1) command: | |
5419 | + | |
5420 | -- | |
5421 | [role="term"] | |
5422 | ---- | |
5423 | $ lttng create | |
5424 | ---- | |
5425 | -- | |
5426 | ||
5427 | The created tracing session's name is `auto` followed by the | |
5428 | creation date. | |
5429 | ||
5430 | To create a tracing session with a specific name: | |
5431 | ||
5432 | * Use the optional argument of the man:lttng-create(1) command: | |
5433 | + | |
5434 | -- | |
5435 | [role="term"] | |
5436 | ---- | |
5437 | $ lttng create my-session | |
5438 | ---- | |
5439 | -- | |
5440 | + | |
5441 | Replace `my-session` with the specific tracing session name. | |
5442 | ||
5443 | LTTng appends the creation date to the created tracing session's name. | |
5444 | ||
5445 | LTTng writes the traces of a tracing session in | |
5446 | +$LTTNG_HOME/lttng-trace/__name__+ by default, where +__name__+ is the | |
5447 | name of the tracing session. Note that the env:LTTNG_HOME environment | |
5448 | variable defaults to `$HOME` if not set. | |
5449 | ||
5450 | To output LTTng traces to a non-default location: | |
5451 | ||
5452 | * Use the opt:lttng-create(1):--output option of the man:lttng-create(1) command: | |
5453 | + | |
5454 | -- | |
5455 | [role="term"] | |
5456 | ---- | |
5457 | $ lttng create my-session --output=/tmp/some-directory | |
5458 | ---- | |
5459 | -- | |
5460 | ||
5461 | You may create as many tracing sessions as you wish. | |
5462 | ||
5463 | To list all the existing tracing sessions for your Unix user: | |
5464 | ||
5465 | * Use the man:lttng-list(1) command: | |
5466 | + | |
5467 | -- | |
5468 | [role="term"] | |
5469 | ---- | |
5470 | $ lttng list | |
5471 | ---- | |
5472 | -- | |
5473 | ||
5474 | When you create a tracing session, it is set as the _current tracing | |
5475 | session_. The following man:lttng(1) commands operate on the current | |
5476 | tracing session when you don't specify one: | |
5477 | ||
5478 | [role="list-3-cols"] | |
5479 | * `add-context` | |
5480 | * `destroy` | |
5481 | * `disable-channel` | |
5482 | * `disable-event` | |
5483 | * `enable-channel` | |
5484 | * `enable-event` | |
5485 | * `load` | |
5486 | * `regenerate` | |
5487 | * `save` | |
5488 | * `snapshot` | |
5489 | * `start` | |
5490 | * `stop` | |
5491 | * `track` | |
5492 | * `untrack` | |
5493 | * `view` | |
5494 | ||
5495 | To change the current tracing session: | |
5496 | ||
5497 | * Use the man:lttng-set-session(1) command: | |
5498 | + | |
5499 | -- | |
5500 | [role="term"] | |
5501 | ---- | |
5502 | $ lttng set-session new-session | |
5503 | ---- | |
5504 | -- | |
5505 | + | |
5506 | Replace `new-session` by the name of the new current tracing session. | |
5507 | ||
5508 | When you are done tracing in a given tracing session, you can destroy | |
5509 | it. This operation frees the resources taken by the tracing session | |
5510 | to destroy; it does not destroy the trace data that LTTng wrote for | |
5511 | this tracing session. | |
5512 | ||
5513 | To destroy the current tracing session: | |
5514 | ||
5515 | * Use the man:lttng-destroy(1) command: | |
5516 | + | |
5517 | -- | |
5518 | [role="term"] | |
5519 | ---- | |
5520 | $ lttng destroy | |
5521 | ---- | |
5522 | -- | |
5523 | ||
5524 | ||
5525 | [[list-instrumentation-points]] | |
5526 | === List the available instrumentation points | |
5527 | ||
5528 | The <<lttng-sessiond,session daemon>> can query the running instrumented | |
5529 | user applications and the Linux kernel to get a list of available | |
5530 | instrumentation points. For the Linux kernel <<domain,tracing domain>>, | |
5531 | they are tracepoints and system calls. For the user space tracing | |
5532 | domain, they are tracepoints. For the other tracing domains, they are | |
5533 | logger names. | |
5534 | ||
5535 | To list the available instrumentation points: | |
5536 | ||
5537 | * Use the man:lttng-list(1) command with the requested tracing domain's | |
5538 | option amongst: | |
5539 | + | |
5540 | -- | |
5541 | * opt:lttng-list(1):--kernel: Linux kernel tracepoints (your Unix user | |
5542 | must be a root user, or it must be a member of the | |
5543 | <<tracing-group,tracing group>>). | |
5544 | * opt:lttng-list(1):--kernel with opt:lttng-list(1):--syscall: Linux | |
5545 | kernel system calls (your Unix user must be a root user, or it must be | |
5546 | a member of the tracing group). | |
5547 | * opt:lttng-list(1):--userspace: user space tracepoints. | |
5548 | * opt:lttng-list(1):--jul: `java.util.logging` loggers. | |
5549 | * opt:lttng-list(1):--log4j: Apache log4j loggers. | |
5550 | * opt:lttng-list(1):--python: Python loggers. | |
5551 | -- | |
5552 | ||
5553 | .List the available user space tracepoints. | |
5554 | ==== | |
5555 | [role="term"] | |
5556 | ---- | |
5557 | $ lttng list --userspace | |
5558 | ---- | |
5559 | ==== | |
5560 | ||
5561 | .List the available Linux kernel system call tracepoints. | |
5562 | ==== | |
5563 | [role="term"] | |
5564 | ---- | |
5565 | $ lttng list --kernel --syscall | |
5566 | ---- | |
5567 | ==== | |
5568 | ||
5569 | ||
5570 | [[enabling-disabling-events]] | |
5571 | === Create and enable an event rule | |
5572 | ||
5573 | Once you <<creating-destroying-tracing-sessions,create a tracing | |
5574 | session>>, you can create <<event,event rules>> with the | |
5575 | man:lttng-enable-event(1) command. | |
5576 | ||
5577 | You specify each condition with a command-line option. The available | |
5578 | condition options are shown in the following table. | |
5579 | ||
5580 | [role="growable",cols="asciidoc,asciidoc,default"] | |
5581 | .Condition command-line options for the man:lttng-enable-event(1) command. | |
5582 | |==== | |
5583 | |Option |Description |Applicable tracing domains | |
5584 | ||
5585 | | | |
5586 | One of: | |
5587 | ||
5588 | . `--syscall` | |
5589 | . +--probe=__ADDR__+ | |
5590 | . +--function=__ADDR__+ | |
5591 | ||
5592 | | | |
5593 | Instead of using the default _tracepoint_ instrumentation type, use: | |
5594 | ||
5595 | . A Linux system call. | |
5596 | . A Linux https://lwn.net/Articles/132196/[KProbe] (symbol or address). | |
5597 | . The entry and return points of a Linux function (symbol or address). | |
5598 | ||
5599 | |Linux kernel. | |
5600 | ||
5601 | |First positional argument. | |
5602 | ||
5603 | | | |
5604 | Tracepoint or system call name. In the case of a Linux KProbe or | |
5605 | function, this is a custom name given to the event rule. With the | |
5606 | JUL, log4j, and Python domains, this is a logger name. | |
5607 | ||
5608 | With a tracepoint, logger, or system call name, the last character | |
5609 | can be `*` to match anything that remains. | |
5610 | ||
5611 | |All. | |
5612 | ||
5613 | | | |
5614 | One of: | |
5615 | ||
5616 | . +--loglevel=__LEVEL__+ | |
5617 | . +--loglevel-only=__LEVEL__+ | |
5618 | ||
5619 | | | |
5620 | . Match only tracepoints or log statements with a logging level at | |
5621 | least as severe as +__LEVEL__+. | |
5622 | . Match only tracepoints or log statements with a logging level | |
5623 | equal to +__LEVEL__+. | |
5624 | ||
5625 | See man:lttng-enable-event(1) for the list of available logging level | |
5626 | names. | |
5627 | ||
5628 | |User space, JUL, log4j, and Python. | |
5629 | ||
5630 | |+--exclude=__EXCLUSIONS__+ | |
5631 | ||
5632 | | | |
5633 | When you use a `*` character at the end of the tracepoint or logger | |
5634 | name (first positional argument), exclude the specific names in the | |
5635 | comma-delimited list +__EXCLUSIONS__+. | |
5636 | ||
5637 | | | |
5638 | User space, JUL, log4j, and Python. | |
5639 | ||
5640 | |+--filter=__EXPR__+ | |
5641 | ||
5642 | | | |
5643 | Match only events which satisfy the expression +__EXPR__+. | |
5644 | ||
5645 | See man:lttng-enable-event(1) to learn more about the syntax of a | |
5646 | filter expression. | |
5647 | ||
5648 | |All. | |
5649 | ||
5650 | |==== | |
5651 | ||
5652 | You attach an event rule to a <<channel,channel>> on creation. If you do | |
5653 | not specify the channel with the opt:lttng-enable-event(1):--channel | |
5654 | option, and if the event rule to create is the first in its | |
5655 | <<domain,tracing domain>> for a given tracing session, then LTTng | |
5656 | creates a _default channel_ for you. This default channel is reused in | |
5657 | subsequent invocations of the man:lttng-enable-event(1) command for the | |
5658 | same tracing domain. | |
5659 | ||
5660 | An event rule is always enabled at creation time. | |
5661 | ||
5662 | The following examples show how you can combine the previous | |
5663 | command-line options to create simple to more complex event rules. | |
5664 | ||
5665 | .Create an event rule targetting a Linux kernel tracepoint (default channel). | |
5666 | ==== | |
5667 | [role="term"] | |
5668 | ---- | |
5669 | $ lttng enable-event --kernel sched_switch | |
5670 | ---- | |
5671 | ==== | |
5672 | ||
5673 | .Create an event rule matching four Linux kernel system calls (default channel). | |
5674 | ==== | |
5675 | [role="term"] | |
5676 | ---- | |
5677 | $ lttng enable-event --kernel --syscall open,write,read,close | |
5678 | ---- | |
5679 | ==== | |
5680 | ||
5681 | .Create event rules matching tracepoints with filter expressions (default channel). | |
5682 | ==== | |
5683 | [role="term"] | |
5684 | ---- | |
5685 | $ lttng enable-event --kernel sched_switch --filter='prev_comm == "bash"' | |
5686 | ---- | |
5687 | ||
5688 | [role="term"] | |
5689 | ---- | |
5690 | $ lttng enable-event --kernel --all \ | |
5691 | --filter='$ctx.tid == 1988 || $ctx.tid == 1534' | |
5692 | ---- | |
5693 | ||
5694 | [role="term"] | |
5695 | ---- | |
5696 | $ lttng enable-event --jul my_logger \ | |
5697 | --filter='$app.retriever:cur_msg_id > 3' | |
5698 | ---- | |
5699 | ||
5700 | IMPORTANT: Make sure to always quote the filter string when you | |
5701 | use man:lttng(1) from a shell. | |
5702 | ==== | |
5703 | ||
5704 | .Create an event rule matching any user space tracepoint of a given tracepoint provider with a log level range (default channel). | |
5705 | ==== | |
5706 | [role="term"] | |
5707 | ---- | |
5708 | $ lttng enable-event --userspace my_app:'*' --loglevel=TRACE_INFO | |
5709 | ---- | |
5710 | ||
5711 | IMPORTANT: Make sure to always quote the wildcard character when you | |
5712 | use man:lttng(1) from a shell. | |
5713 | ==== | |
5714 | ||
5715 | .Create an event rule matching multiple Python loggers with a wildcard and with exclusions (default channel). | |
5716 | ==== | |
5717 | [role="term"] | |
5718 | ---- | |
5719 | $ lttng enable-event --python my-app.'*' \ | |
5720 | --exclude='my-app.module,my-app.hello' | |
5721 | ---- | |
5722 | ==== | |
5723 | ||
5724 | .Create an event rule matching any Apache log4j logger with a specific log level (default channel). | |
5725 | ==== | |
5726 | [role="term"] | |
5727 | ---- | |
5728 | $ lttng enable-event --log4j --all --loglevel-only=LOG4J_WARN | |
5729 | ---- | |
5730 | ==== | |
5731 | ||
5732 | .Create an event rule attached to a specific channel matching a specific user space tracepoint provider and tracepoint. | |
5733 | ==== | |
5734 | [role="term"] | |
5735 | ---- | |
5736 | $ lttng enable-event --userspace my_app:my_tracepoint --channel=my-channel | |
5737 | ---- | |
5738 | ==== | |
5739 | ||
5740 | The event rules of a given channel form a whitelist: as soon as an | |
5741 | emitted event passes one of them, LTTng can record the event. For | |
5742 | example, an event named `my_app:my_tracepoint` emitted from a user space | |
5743 | tracepoint with a `TRACE_ERROR` log level passes both of the following | |
5744 | rules: | |
5745 | ||
5746 | [role="term"] | |
5747 | ---- | |
5748 | $ lttng enable-event --userspace my_app:my_tracepoint | |
5749 | $ lttng enable-event --userspace my_app:my_tracepoint \ | |
5750 | --loglevel=TRACE_INFO | |
5751 | ---- | |
5752 | ||
5753 | The second event rule is redundant: the first one includes | |
5754 | the second one. | |
5755 | ||
5756 | ||
5757 | [[disable-event-rule]] | |
5758 | === Disable an event rule | |
5759 | ||
5760 | To disable an event rule that you <<enabling-disabling-events,created>> | |
5761 | previously, use the man:lttng-disable-event(1) command. This command | |
5762 | disables _all_ the event rules (of a given tracing domain and channel) | |
5763 | which match an instrumentation point. The other conditions are not | |
5764 | supported as of LTTng{nbsp}{revision}. | |
5765 | ||
5766 | The LTTng tracer does not record an emitted event which passes | |
5767 | a _disabled_ event rule. | |
5768 | ||
5769 | .Disable an event rule matching a Python logger (default channel). | |
5770 | ==== | |
5771 | [role="term"] | |
5772 | ---- | |
5773 | $ lttng disable-event --python my-logger | |
5774 | ---- | |
5775 | ==== | |
5776 | ||
5777 | .Disable an event rule matching all `java.util.logging` loggers (default channel). | |
5778 | ==== | |
5779 | [role="term"] | |
5780 | ---- | |
5781 | $ lttng disable-event --jul '*' | |
5782 | ---- | |
5783 | ==== | |
5784 | ||
5785 | .Disable _all_ the event rules of the default channel. | |
5786 | ==== | |
5787 | The opt:lttng-disable-event(1):--all-events option is not, like the | |
5788 | opt:lttng-enable-event(1):--all option of man:lttng-enable-event(1), the | |
5789 | equivalent of the event name `*` (wildcard): it disables _all_ the event | |
5790 | rules of a given channel. | |
5791 | ||
5792 | [role="term"] | |
5793 | ---- | |
5794 | $ lttng disable-event --jul --all-events | |
5795 | ---- | |
5796 | ==== | |
5797 | ||
5798 | NOTE: You cannot delete an event rule once you create it. | |
5799 | ||
5800 | ||
5801 | [[status]] | |
5802 | === Get the status of a tracing session | |
5803 | ||
5804 | To get the status of the current tracing session, that is, its | |
5805 | parameters, its channels, event rules, and their attributes: | |
5806 | ||
5807 | * Use the man:lttng-status(1) command: | |
5808 | + | |
5809 | -- | |
5810 | [role="term"] | |
5811 | ---- | |
5812 | $ lttng status | |
5813 | ---- | |
5814 | -- | |
5815 | + | |
5816 | ||
5817 | To get the status of any tracing session: | |
5818 | ||
5819 | * Use the man:lttng-list(1) command with the tracing session's name: | |
5820 | + | |
5821 | -- | |
5822 | [role="term"] | |
5823 | ---- | |
5824 | $ lttng list my-session | |
5825 | ---- | |
5826 | -- | |
5827 | + | |
5828 | Replace `my-session` with the desired tracing session's name. | |
5829 | ||
5830 | ||
5831 | [[basic-tracing-session-control]] | |
5832 | === Start and stop a tracing session | |
5833 | ||
5834 | Once you <<creating-destroying-tracing-sessions,create a tracing | |
5835 | session>> and | |
5836 | <<enabling-disabling-events,create one or more event rules>>, | |
5837 | you can start and stop the tracers for this tracing session. | |
5838 | ||
5839 | To start tracing in the current tracing session: | |
5840 | ||
5841 | * Use the man:lttng-start(1) command: | |
5842 | + | |
5843 | -- | |
5844 | [role="term"] | |
5845 | ---- | |
5846 | $ lttng start | |
5847 | ---- | |
5848 | -- | |
5849 | ||
5850 | LTTng is very flexible: you can launch user applications before | |
5851 | or after the you start the tracers. The tracers only record the events | |
5852 | if they pass enabled event rules and if they occur while the tracers are | |
5853 | started. | |
5854 | ||
5855 | To stop tracing in the current tracing session: | |
5856 | ||
5857 | * Use the man:lttng-stop(1) command: | |
5858 | + | |
5859 | -- | |
5860 | [role="term"] | |
5861 | ---- | |
5862 | $ lttng stop | |
5863 | ---- | |
5864 | -- | |
5865 | + | |
5866 | If there were <<channel-overwrite-mode-vs-discard-mode,lost event | |
5867 | records>> or lost sub-buffers since the last time you ran | |
5868 | man:lttng-start(1), warnings are printed when you run the | |
5869 | man:lttng-stop(1) command. | |
5870 | ||
5871 | ||
5872 | [[enabling-disabling-channels]] | |
5873 | === Create a channel | |
5874 | ||
5875 | Once you create a tracing session, you can create a <<channel,channel>> | |
5876 | with the man:lttng-enable-channel(1) command. | |
5877 | ||
5878 | Note that LTTng automatically creates a default channel when, for a | |
5879 | given <<domain,tracing domain>>, no channels exist and you | |
5880 | <<enabling-disabling-events,create>> the first event rule. This default | |
5881 | channel is named `channel0` and its attributes are set to reasonable | |
5882 | values. Therefore, you only need to create a channel when you need | |
5883 | non-default attributes. | |
5884 | ||
5885 | You specify each non-default channel attribute with a command-line | |
5886 | option when you use the man:lttng-enable-channel(1) command. The | |
5887 | available command-line options are: | |
5888 | ||
5889 | [role="growable",cols="asciidoc,asciidoc"] | |
5890 | .Command-line options for the man:lttng-enable-channel(1) command. | |
5891 | |==== | |
5892 | |Option |Description | |
5893 | ||
5894 | |`--overwrite` | |
5895 | ||
5896 | | | |
5897 | Use the _overwrite_ | |
5898 | <<channel-overwrite-mode-vs-discard-mode,event loss mode>> instead of | |
5899 | the default _discard_ mode. | |
5900 | ||
5901 | |`--buffers-pid` (user space tracing domain only) | |
5902 | ||
5903 | | | |
5904 | Use the per-process <<channel-buffering-schemes,buffering scheme>> | |
5905 | instead of the default per-user buffering scheme. | |
5906 | ||
5907 | |+--subbuf-size=__SIZE__+ | |
5908 | ||
5909 | | | |
5910 | Allocate sub-buffers of +__SIZE__+ bytes (power of two), for each CPU, | |
5911 | either for each Unix user (default), or for each instrumented process. | |
5912 | ||
5913 | See <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>>. | |
5914 | ||
5915 | |+--num-subbuf=__COUNT__+ | |
5916 | ||
5917 | | | |
5918 | Allocate +__COUNT__+ sub-buffers (power of two), for each CPU, either | |
5919 | for each Unix user (default), or for each instrumented process. | |
5920 | ||
5921 | See <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>>. | |
5922 | ||
5923 | |+--tracefile-size=__SIZE__+ | |
5924 | ||
5925 | | | |
5926 | Set the maximum size of each trace file that this channel writes within | |
5927 | a stream to +__SIZE__+ bytes instead of no maximum. | |
5928 | ||
5929 | See <<tracefile-rotation,Trace file count and size>>. | |
5930 | ||
5931 | |+--tracefile-count=__COUNT__+ | |
5932 | ||
5933 | | | |
5934 | Limit the number of trace files that this channel creates to | |
5935 | +__COUNT__+ channels instead of no limit. | |
5936 | ||
5937 | See <<tracefile-rotation,Trace file count and size>>. | |
5938 | ||
5939 | |+--switch-timer=__PERIODUS__+ | |
5940 | ||
5941 | | | |
5942 | Set the <<channel-switch-timer,switch timer period>> | |
5943 | to +__PERIODUS__+{nbsp}µs. | |
5944 | ||
5945 | |+--read-timer=__PERIODUS__+ | |
5946 | ||
5947 | | | |
5948 | Set the <<channel-read-timer,read timer period>> | |
5949 | to +__PERIODUS__+{nbsp}µs. | |
5950 | ||
5951 | |[[opt-blocking-timeout]]+--blocking-timeout=__TIMEOUTUS__+ | |
5952 | ||
5953 | | | |
5954 | Set the timeout of user space applications which load LTTng-UST | |
5955 | in blocking mode to +__TIMEOUTUS__+: | |
5956 | ||
5957 | 0 (default):: | |
5958 | Never block (non-blocking mode). | |
5959 | ||
000f69a6 | 5960 | `inf`:: |
85c29972 PP |
5961 | Block forever until space is available in a sub-buffer to record |
5962 | the event. | |
5963 | ||
5964 | __n__, a positive value:: | |
5965 | Wait for at most __n__ µs when trying to write into a sub-buffer. | |
5966 | ||
5967 | Note that, for this option to have any effect on an instrumented | |
5968 | user space application, you need to run the application with a set | |
5969 | env:LTTNG_UST_ALLOW_BLOCKING environment variable. | |
5970 | ||
5971 | |+--output=__TYPE__+ (Linux kernel tracing domain only) | |
5972 | ||
5973 | | | |
5974 | Set the channel's output type to +__TYPE__+, either `mmap` or `splice`. | |
5975 | ||
5976 | |==== | |
5977 | ||
5978 | You can only create a channel in the Linux kernel and user space | |
5979 | <<domain,tracing domains>>: other tracing domains have their own channel | |
5980 | created on the fly when <<enabling-disabling-events,creating event | |
5981 | rules>>. | |
5982 | ||
5983 | [IMPORTANT] | |
5984 | ==== | |
5985 | Because of a current LTTng limitation, you must create all channels | |
5986 | _before_ you <<basic-tracing-session-control,start tracing>> in a given | |
5987 | tracing session, that is, before the first time you run | |
5988 | man:lttng-start(1). | |
5989 | ||
5990 | Since LTTng automatically creates a default channel when you use the | |
5991 | man:lttng-enable-event(1) command with a specific tracing domain, you | |
5992 | cannot, for example, create a Linux kernel event rule, start tracing, | |
5993 | and then create a user space event rule, because no user space channel | |
5994 | exists yet and it's too late to create one. | |
5995 | ||
5996 | For this reason, make sure to configure your channels properly | |
5997 | before starting the tracers for the first time! | |
5998 | ==== | |
5999 | ||
6000 | The following examples show how you can combine the previous | |
6001 | command-line options to create simple to more complex channels. | |
6002 | ||
6003 | .Create a Linux kernel channel with default attributes. | |
6004 | ==== | |
6005 | [role="term"] | |
6006 | ---- | |
6007 | $ lttng enable-channel --kernel my-channel | |
6008 | ---- | |
6009 | ==== | |
6010 | ||
6011 | .Create a user space channel with 4 sub-buffers or 1{nbsp}MiB each, per CPU, per instrumented process. | |
6012 | ==== | |
6013 | [role="term"] | |
6014 | ---- | |
6015 | $ lttng enable-channel --userspace --num-subbuf=4 --subbuf-size=1M \ | |
6016 | --buffers-pid my-channel | |
6017 | ---- | |
6018 | ==== | |
6019 | ||
71b643ed | 6020 | .[[blocking-timeout-example]]Create a default user space channel with an infinite blocking timeout. |
85c29972 PP |
6021 | ==== |
6022 | <<creating-destroying-tracing-sessions,Create a tracing-session>>, | |
6023 | create the channel, <<enabling-disabling-events,create an event rule>>, | |
6024 | and <<basic-tracing-session-control,start tracing>>: | |
6025 | ||
6026 | [role="term"] | |
6027 | ---- | |
6028 | $ lttng create | |
000f69a6 | 6029 | $ lttng enable-channel --userspace --blocking-timeout=inf blocking-channel |
85c29972 PP |
6030 | $ lttng enable-event --userspace --channel=blocking-channel --all |
6031 | $ lttng start | |
6032 | ---- | |
6033 | ||
6034 | Run an application instrumented with LTTng-UST and allow it to block: | |
6035 | ||
6036 | [role="term"] | |
6037 | ---- | |
6038 | $ LTTNG_UST_ALLOW_BLOCKING=1 my-app | |
6039 | ---- | |
6040 | ==== | |
6041 | ||
6042 | .Create a Linux kernel channel which rotates 8 trace files of 4{nbsp}MiB each for each stream | |
6043 | ==== | |
6044 | [role="term"] | |
6045 | ---- | |
6046 | $ lttng enable-channel --kernel --tracefile-count=8 \ | |
6047 | --tracefile-size=4194304 my-channel | |
6048 | ---- | |
6049 | ==== | |
6050 | ||
6051 | .Create a user space channel in overwrite (or _flight recorder_) mode. | |
6052 | ==== | |
6053 | [role="term"] | |
6054 | ---- | |
6055 | $ lttng enable-channel --userspace --overwrite my-channel | |
6056 | ---- | |
6057 | ==== | |
6058 | ||
6059 | You can <<enabling-disabling-events,create>> the same event rule in | |
6060 | two different channels: | |
6061 | ||
6062 | [role="term"] | |
6063 | ---- | |
6064 | $ lttng enable-event --userspace --channel=my-channel app:tp | |
6065 | $ lttng enable-event --userspace --channel=other-channel app:tp | |
6066 | ---- | |
6067 | ||
6068 | If both channels are enabled, when a tracepoint named `app:tp` is | |
6069 | reached, LTTng records two events, one for each channel. | |
6070 | ||
6071 | ||
6072 | [[disable-channel]] | |
6073 | === Disable a channel | |
6074 | ||
6075 | To disable a specific channel that you <<enabling-disabling-channels,created>> | |
6076 | previously, use the man:lttng-disable-channel(1) command. | |
6077 | ||
6078 | .Disable a specific Linux kernel channel. | |
6079 | ==== | |
6080 | [role="term"] | |
6081 | ---- | |
6082 | $ lttng disable-channel --kernel my-channel | |
6083 | ---- | |
6084 | ==== | |
6085 | ||
6086 | The state of a channel precedes the individual states of event rules | |
6087 | attached to it: event rules which belong to a disabled channel, even if | |
6088 | they are enabled, are also considered disabled. | |
6089 | ||
6090 | ||
6091 | [[adding-context]] | |
6092 | === Add context fields to a channel | |
6093 | ||
6094 | Event record fields in trace files provide important information about | |
6095 | events that occured previously, but sometimes some external context may | |
6096 | help you solve a problem faster. Examples of context fields are: | |
6097 | ||
6098 | * The **process ID**, **thread ID**, **process name**, and | |
6099 | **process priority** of the thread in which the event occurs. | |
6100 | * The **hostname** of the system on which the event occurs. | |
6101 | * The current values of many possible **performance counters** using | |
6102 | perf, for example: | |
6103 | ** CPU cycles, stalled cycles, idle cycles, and the other cycle types. | |
6104 | ** Cache misses. | |
6105 | ** Branch instructions, misses, and loads. | |
6106 | ** CPU faults. | |
6107 | * Any context defined at the application level (supported for the | |
6108 | JUL and log4j <<domain,tracing domains>>). | |
6109 | ||
6110 | To get the full list of available context fields, see | |
6111 | `lttng add-context --list`. Some context fields are reserved for a | |
6112 | specific <<domain,tracing domain>> (Linux kernel or user space). | |
6113 | ||
6114 | You add context fields to <<channel,channels>>. All the events | |
6115 | that a channel with added context fields records contain those fields. | |
6116 | ||
6117 | To add context fields to one or all the channels of a given tracing | |
6118 | session: | |
6119 | ||
6120 | * Use the man:lttng-add-context(1) command. | |
6121 | ||
6122 | .Add context fields to all the channels of the current tracing session. | |
6123 | ==== | |
6124 | The following command line adds the virtual process identifier and | |
6125 | the per-thread CPU cycles count fields to all the user space channels | |
6126 | of the current tracing session. | |
6127 | ||
6128 | [role="term"] | |
6129 | ---- | |
6130 | $ lttng add-context --userspace --type=vpid --type=perf:thread:cpu-cycles | |
6131 | ---- | |
6132 | ==== | |
6133 | ||
6134 | .Add performance counter context fields by raw ID | |
6135 | ==== | |
6136 | See man:lttng-add-context(1) for the exact format of the context field | |
6137 | type, which is partly compatible with the format used in | |
6138 | man:perf-record(1). | |
6139 | ||
6140 | [role="term"] | |
6141 | ---- | |
6142 | $ lttng add-context --userspace --type=perf:thread:raw:r0110:test | |
6143 | $ lttng add-context --kernel --type=perf:cpu:raw:r0013c:x86unhalted | |
6144 | ---- | |
6145 | ==== | |
6146 | ||
6147 | .Add a context field to a specific channel. | |
6148 | ==== | |
6149 | The following command line adds the thread identifier context field | |
6150 | to the Linux kernel channel named `my-channel` in the current | |
6151 | tracing session. | |
6152 | ||
6153 | [role="term"] | |
6154 | ---- | |
6155 | $ lttng add-context --kernel --channel=my-channel --type=tid | |
6156 | ---- | |
6157 | ==== | |
6158 | ||
6159 | .Add an application-specific context field to a specific channel. | |
6160 | ==== | |
6161 | The following command line adds the `cur_msg_id` context field of the | |
6162 | `retriever` context retriever for all the instrumented | |
6163 | <<java-application,Java applications>> recording <<event,event records>> | |
6164 | in the channel named `my-channel`: | |
6165 | ||
6166 | [role="term"] | |
6167 | ---- | |
6168 | $ lttng add-context --kernel --channel=my-channel \ | |
6169 | --type='$app:retriever:cur_msg_id' | |
6170 | ---- | |
6171 | ||
6172 | IMPORTANT: Make sure to always quote the `$` character when you | |
6173 | use man:lttng-add-context(1) from a shell. | |
6174 | ==== | |
6175 | ||
6176 | NOTE: You cannot remove context fields from a channel once you add it. | |
6177 | ||
6178 | ||
6179 | [role="since-2.7"] | |
6180 | [[pid-tracking]] | |
6181 | === Track process IDs | |
6182 | ||
6183 | It's often useful to allow only specific process IDs (PIDs) to emit | |
6184 | events. For example, you may wish to record all the system calls made by | |
6185 | a given process (Ă la http://linux.die.net/man/1/strace[strace]). | |
6186 | ||
6187 | The man:lttng-track(1) and man:lttng-untrack(1) commands serve this | |
6188 | purpose. Both commands operate on a whitelist of process IDs. You _add_ | |
6189 | entries to this whitelist with the man:lttng-track(1) command and remove | |
6190 | entries with the man:lttng-untrack(1) command. Any process which has one | |
6191 | of the PIDs in the whitelist is allowed to emit LTTng events which pass | |
6192 | an enabled <<event,event rule>>. | |
6193 | ||
6194 | NOTE: The PID tracker tracks the _numeric process IDs_. Should a | |
6195 | process with a given tracked ID exit and another process be given this | |
6196 | ID, then the latter would also be allowed to emit events. | |
6197 | ||
6198 | .Track and untrack process IDs. | |
6199 | ==== | |
6200 | For the sake of the following example, assume the target system has 16 | |
6201 | possible PIDs. | |
6202 | ||
6203 | When you | |
6204 | <<creating-destroying-tracing-sessions,create a tracing session>>, | |
6205 | the whitelist contains all the possible PIDs: | |
6206 | ||
6207 | [role="img-100"] | |
6208 | .All PIDs are tracked. | |
6209 | image::track-all.png[] | |
6210 | ||
6211 | When the whitelist is full and you use the man:lttng-track(1) command to | |
6212 | specify some PIDs to track, LTTng first clears the whitelist, then it | |
6213 | tracks the specific PIDs. After: | |
6214 | ||
6215 | [role="term"] | |
6216 | ---- | |
6217 | $ lttng track --pid=3,4,7,10,13 | |
6218 | ---- | |
6219 | ||
6220 | the whitelist is: | |
6221 | ||
6222 | [role="img-100"] | |
6223 | .PIDs 3, 4, 7, 10, and 13 are tracked. | |
6224 | image::track-3-4-7-10-13.png[] | |
6225 | ||
6226 | You can add more PIDs to the whitelist afterwards: | |
6227 | ||
6228 | [role="term"] | |
6229 | ---- | |
6230 | $ lttng track --pid=1,15,16 | |
6231 | ---- | |
6232 | ||
6233 | The result is: | |
6234 | ||
6235 | [role="img-100"] | |
6236 | .PIDs 1, 15, and 16 are added to the whitelist. | |
6237 | image::track-1-3-4-7-10-13-15-16.png[] | |
6238 | ||
6239 | The man:lttng-untrack(1) command removes entries from the PID tracker's | |
6240 | whitelist. Given the previous example, the following command: | |
6241 | ||
6242 | [role="term"] | |
6243 | ---- | |
6244 | $ lttng untrack --pid=3,7,10,13 | |
6245 | ---- | |
6246 | ||
6247 | leads to this whitelist: | |
6248 | ||
6249 | [role="img-100"] | |
6250 | .PIDs 3, 7, 10, and 13 are removed from the whitelist. | |
6251 | image::track-1-4-15-16.png[] | |
6252 | ||
6253 | LTTng can track all possible PIDs again using the opt:track(1):--all | |
6254 | option: | |
6255 | ||
6256 | [role="term"] | |
6257 | ---- | |
6258 | $ lttng track --pid --all | |
6259 | ---- | |
6260 | ||
6261 | The result is, again: | |
6262 | ||
6263 | [role="img-100"] | |
6264 | .All PIDs are tracked. | |
6265 | image::track-all.png[] | |
6266 | ==== | |
6267 | ||
6268 | .Track only specific PIDs | |
6269 | ==== | |
6270 | A very typical use case with PID tracking is to start with an empty | |
6271 | whitelist, then <<basic-tracing-session-control,start the tracers>>, and | |
6272 | then add PIDs manually while tracers are active. You can accomplish this | |
6273 | by using the opt:lttng-untrack(1):--all option of the | |
6274 | man:lttng-untrack(1) command to clear the whitelist after you | |
6275 | <<creating-destroying-tracing-sessions,create a tracing session>>: | |
6276 | ||
6277 | [role="term"] | |
6278 | ---- | |
6279 | $ lttng untrack --pid --all | |
6280 | ---- | |
6281 | ||
6282 | gives: | |
6283 | ||
6284 | [role="img-100"] | |
6285 | .No PIDs are tracked. | |
6286 | image::untrack-all.png[] | |
6287 | ||
6288 | If you trace with this whitelist configuration, the tracer records no | |
6289 | events for this <<domain,tracing domain>> because no processes are | |
6290 | tracked. You can use the man:lttng-track(1) command as usual to track | |
6291 | specific PIDs, for example: | |
6292 | ||
6293 | [role="term"] | |
6294 | ---- | |
6295 | $ lttng track --pid=6,11 | |
6296 | ---- | |
6297 | ||
6298 | Result: | |
6299 | ||
6300 | [role="img-100"] | |
6301 | .PIDs 6 and 11 are tracked. | |
6302 | image::track-6-11.png[] | |
6303 | ==== | |
6304 | ||
6305 | ||
6306 | [role="since-2.5"] | |
6307 | [[saving-loading-tracing-session]] | |
6308 | === Save and load tracing session configurations | |
6309 | ||
6310 | Configuring a <<tracing-session,tracing session>> can be long. Some of | |
6311 | the tasks involved are: | |
6312 | ||
6313 | * <<enabling-disabling-channels,Create channels>> with | |
6314 | specific attributes. | |
6315 | * <<adding-context,Add context fields>> to specific channels. | |
6316 | * <<enabling-disabling-events,Create event rules>> with specific log | |
6317 | level and filter conditions. | |
6318 | ||
6319 | If you use LTTng to solve real world problems, chances are you have to | |
6320 | record events using the same tracing session setup over and over, | |
6321 | modifying a few variables each time in your instrumented program | |
6322 | or environment. To avoid constant tracing session reconfiguration, | |
6323 | the man:lttng(1) command-line tool can save and load tracing session | |
6324 | configurations to/from XML files. | |
6325 | ||
6326 | To save a given tracing session configuration: | |
6327 | ||
6328 | * Use the man:lttng-save(1) command: | |
6329 | + | |
6330 | -- | |
6331 | [role="term"] | |
6332 | ---- | |
6333 | $ lttng save my-session | |
6334 | ---- | |
6335 | -- | |
6336 | + | |
6337 | Replace `my-session` with the name of the tracing session to save. | |
6338 | ||
6339 | LTTng saves tracing session configurations to | |
6340 | dir:{$LTTNG_HOME/.lttng/sessions} by default. Note that the | |
6341 | env:LTTNG_HOME environment variable defaults to `$HOME` if not set. Use | |
6342 | the opt:lttng-save(1):--output-path option to change this destination | |
6343 | directory. | |
6344 | ||
6345 | LTTng saves all configuration parameters, for example: | |
6346 | ||
6347 | * The tracing session name. | |
6348 | * The trace data output path. | |
6349 | * The channels with their state and all their attributes. | |
6350 | * The context fields you added to channels. | |
6351 | * The event rules with their state, log level and filter conditions. | |
6352 | ||
6353 | To load a tracing session: | |
6354 | ||
6355 | * Use the man:lttng-load(1) command: | |
6356 | + | |
6357 | -- | |
6358 | [role="term"] | |
6359 | ---- | |
6360 | $ lttng load my-session | |
6361 | ---- | |
6362 | -- | |
6363 | + | |
6364 | Replace `my-session` with the name of the tracing session to load. | |
6365 | ||
6366 | When LTTng loads a configuration, it restores your saved tracing session | |
6367 | as if you just configured it manually. | |
6368 | ||
6369 | See man:lttng(1) for the complete list of command-line options. You | |
6370 | can also save and load all many sessions at a time, and decide in which | |
6371 | directory to output the XML files. | |
6372 | ||
6373 | ||
6374 | [[sending-trace-data-over-the-network]] | |
6375 | === Send trace data over the network | |
6376 | ||
6377 | LTTng can send the recorded trace data to a remote system over the | |
6378 | network instead of writing it to the local file system. | |
6379 | ||
6380 | To send the trace data over the network: | |
6381 | ||
6382 | . On the _remote_ system (which can also be the target system), | |
6383 | start an LTTng <<lttng-relayd,relay daemon>> (man:lttng-relayd(8)): | |
6384 | + | |
6385 | -- | |
6386 | [role="term"] | |
6387 | ---- | |
6388 | $ lttng-relayd | |
6389 | ---- | |
6390 | -- | |
6391 | ||
6392 | . On the _target_ system, create a tracing session configured to | |
6393 | send trace data over the network: | |
6394 | + | |
6395 | -- | |
6396 | [role="term"] | |
6397 | ---- | |
6398 | $ lttng create my-session --set-url=net://remote-system | |
6399 | ---- | |
6400 | -- | |
6401 | + | |
6402 | Replace `remote-system` by the host name or IP address of the | |
6403 | remote system. See man:lttng-create(1) for the exact URL format. | |
6404 | ||
6405 | . On the target system, use the man:lttng(1) command-line tool as usual. | |
6406 | When tracing is active, the target's consumer daemon sends sub-buffers | |
6407 | to the relay daemon running on the remote system instead of flushing | |
6408 | them to the local file system. The relay daemon writes the received | |
6409 | packets to the local file system. | |
6410 | ||
6411 | The relay daemon writes trace files to | |
6412 | +$LTTNG_HOME/lttng-traces/__hostname__/__session__+ by default, where | |
6413 | +__hostname__+ is the host name of the target system and +__session__+ | |
6414 | is the tracing session name. Note that the env:LTTNG_HOME environment | |
6415 | variable defaults to `$HOME` if not set. Use the | |
6416 | opt:lttng-relayd(8):--output option of man:lttng-relayd(8) to write | |
6417 | trace files to another base directory. | |
6418 | ||
6419 | ||
6420 | [role="since-2.4"] | |
6421 | [[lttng-live]] | |
6422 | === View events as LTTng emits them (noch:{LTTng} live) | |
6423 | ||
6424 | LTTng live is a network protocol implemented by the <<lttng-relayd,relay | |
6425 | daemon>> (man:lttng-relayd(8)) to allow compatible trace viewers to | |
6426 | display events as LTTng emits them on the target system while tracing is | |
6427 | active. | |
6428 | ||
6429 | The relay daemon creates a _tee_: it forwards the trace data to both | |
6430 | the local file system and to connected live viewers: | |
6431 | ||
6432 | [role="img-90"] | |
6433 | .The relay daemon creates a _tee_, forwarding the trace data to both trace files and a connected live viewer. | |
6434 | image::live.png[] | |
6435 | ||
6436 | To use LTTng live: | |
6437 | ||
6438 | . On the _target system_, create a <<tracing-session,tracing session>> | |
6439 | in _live mode_: | |
6440 | + | |
6441 | -- | |
6442 | [role="term"] | |
6443 | ---- | |
6444 | $ lttng create my-session --live | |
6445 | ---- | |
6446 | -- | |
6447 | + | |
6448 | This spawns a local relay daemon. | |
6449 | ||
6450 | . Start the live viewer and configure it to connect to the relay | |
6451 | daemon. For example, with http://diamon.org/babeltrace[Babeltrace]: | |
6452 | + | |
6453 | -- | |
6454 | [role="term"] | |
6455 | ---- | |
6456 | $ babeltrace --input-format=lttng-live \ | |
6457 | net://localhost/host/hostname/my-session | |
6458 | ---- | |
6459 | -- | |
6460 | + | |
6461 | Replace: | |
6462 | + | |
6463 | -- | |
6464 | * `hostname` with the host name of the target system. | |
6465 | * `my-session` with the name of the tracing session to view. | |
6466 | -- | |
6467 | ||
6468 | . Configure the tracing session as usual with the man:lttng(1) | |
6469 | command-line tool, and <<basic-tracing-session-control,start tracing>>. | |
6470 | ||
6471 | You can list the available live tracing sessions with Babeltrace: | |
6472 | ||
6473 | [role="term"] | |
6474 | ---- | |
6475 | $ babeltrace --input-format=lttng-live net://localhost | |
6476 | ---- | |
6477 | ||
6478 | You can start the relay daemon on another system. In this case, you need | |
6479 | to specify the relay daemon's URL when you create the tracing session | |
6480 | with the opt:lttng-create(1):--set-url option. You also need to replace | |
6481 | `localhost` in the procedure above with the host name of the system on | |
6482 | which the relay daemon is running. | |
6483 | ||
6484 | See man:lttng-create(1) and man:lttng-relayd(8) for the complete list of | |
6485 | command-line options. | |
6486 | ||
6487 | ||
6488 | [role="since-2.3"] | |
6489 | [[taking-a-snapshot]] | |
6490 | === Take a snapshot of the current sub-buffers of a tracing session | |
6491 | ||
6492 | The normal behavior of LTTng is to append full sub-buffers to growing | |
6493 | trace data files. This is ideal to keep a full history of the events | |
6494 | that occurred on the target system, but it can | |
6495 | represent too much data in some situations. For example, you may wish | |
6496 | to trace your application continuously until some critical situation | |
6497 | happens, in which case you only need the latest few recorded | |
6498 | events to perform the desired analysis, not multi-gigabyte trace files. | |
6499 | ||
6500 | With the man:lttng-snapshot(1) command, you can take a snapshot of the | |
6501 | current sub-buffers of a given <<tracing-session,tracing session>>. | |
6502 | LTTng can write the snapshot to the local file system or send it over | |
6503 | the network. | |
6504 | ||
6505 | To take a snapshot: | |
6506 | ||
6507 | . Create a tracing session in _snapshot mode_: | |
6508 | + | |
6509 | -- | |
6510 | [role="term"] | |
6511 | ---- | |
6512 | $ lttng create my-session --snapshot | |
6513 | ---- | |
6514 | -- | |
6515 | + | |
6516 | The <<channel-overwrite-mode-vs-discard-mode,event loss mode>> of | |
6517 | <<channel,channels>> created in this mode is automatically set to | |
6518 | _overwrite_ (flight recorder mode). | |
6519 | ||
6520 | . Configure the tracing session as usual with the man:lttng(1) | |
6521 | command-line tool, and <<basic-tracing-session-control,start tracing>>. | |
6522 | ||
6523 | . **Optional**: When you need to take a snapshot, | |
6524 | <<basic-tracing-session-control,stop tracing>>. | |
6525 | + | |
6526 | You can take a snapshot when the tracers are active, but if you stop | |
6527 | them first, you are sure that the data in the sub-buffers does not | |
6528 | change before you actually take the snapshot. | |
6529 | ||
6530 | . Take a snapshot: | |
6531 | + | |
6532 | -- | |
6533 | [role="term"] | |
6534 | ---- | |
6535 | $ lttng snapshot record --name=my-first-snapshot | |
6536 | ---- | |
6537 | -- | |
6538 | + | |
6539 | LTTng writes the current sub-buffers of all the current tracing | |
6540 | session's channels to trace files on the local file system. Those trace | |
6541 | files have `my-first-snapshot` in their name. | |
6542 | ||
6543 | There is no difference between the format of a normal trace file and the | |
6544 | format of a snapshot: viewers of LTTng traces also support LTTng | |
6545 | snapshots. | |
6546 | ||
6547 | By default, LTTng writes snapshot files to the path shown by | |
6548 | `lttng snapshot list-output`. You can change this path or decide to send | |
6549 | snapshots over the network using either: | |
6550 | ||
6551 | . An output path or URL that you specify when you create the | |
6552 | tracing session. | |
6553 | . An snapshot output path or URL that you add using | |
6554 | `lttng snapshot add-output` | |
6555 | . An output path or URL that you provide directly to the | |
6556 | `lttng snapshot record` command. | |
6557 | ||
6558 | Method 3 overrides method 2, which overrides method 1. When you | |
6559 | specify a URL, a relay daemon must listen on a remote system (see | |
6560 | <<sending-trace-data-over-the-network,Send trace data over the network>>). | |
6561 | ||
6562 | ||
6563 | [role="since-2.6"] | |
6564 | [[mi]] | |
6565 | === Use the machine interface | |
6566 | ||
6567 | With any command of the man:lttng(1) command-line tool, you can set the | |
6568 | opt:lttng(1):--mi option to `xml` (before the command name) to get an | |
6569 | XML machine interface output, for example: | |
6570 | ||
6571 | [role="term"] | |
6572 | ---- | |
6573 | $ lttng --mi=xml enable-event --kernel --syscall open | |
6574 | ---- | |
6575 | ||
6576 | A schema definition (XSD) is | |
6577 | https://github.com/lttng/lttng-tools/blob/stable-2.10/src/common/mi-lttng-3.0.xsd[available] | |
6578 | to ease the integration with external tools as much as possible. | |
6579 | ||
6580 | ||
6581 | [role="since-2.8"] | |
6582 | [[metadata-regenerate]] | |
6583 | === Regenerate the metadata of an LTTng trace | |
6584 | ||
6585 | An LTTng trace, which is a http://diamon.org/ctf[CTF] trace, has both | |
6586 | data stream files and a metadata file. This metadata file contains, | |
6587 | amongst other things, information about the offset of the clock sources | |
6588 | used to timestamp <<event,event records>> when tracing. | |
6589 | ||
6590 | If, once a <<tracing-session,tracing session>> is | |
6591 | <<basic-tracing-session-control,started>>, a major | |
6592 | https://en.wikipedia.org/wiki/Network_Time_Protocol[NTP] correction | |
6593 | happens, the trace's clock offset also needs to be updated. You | |
6594 | can use the `metadata` item of the man:lttng-regenerate(1) command | |
6595 | to do so. | |
6596 | ||
6597 | The main use case of this command is to allow a system to boot with | |
6598 | an incorrect wall time and trace it with LTTng before its wall time | |
6599 | is corrected. Once the system is known to be in a state where its | |
6600 | wall time is correct, it can run `lttng regenerate metadata`. | |
6601 | ||
6602 | To regenerate the metadata of an LTTng trace: | |
6603 | ||
6604 | * Use the `metadata` item of the man:lttng-regenerate(1) command: | |
6605 | + | |
6606 | -- | |
6607 | [role="term"] | |
6608 | ---- | |
6609 | $ lttng regenerate metadata | |
6610 | ---- | |
6611 | -- | |
6612 | ||
6613 | [IMPORTANT] | |
6614 | ==== | |
6615 | `lttng regenerate metadata` has the following limitations: | |
6616 | ||
6617 | * Tracing session <<creating-destroying-tracing-sessions,created>> | |
6618 | in non-live mode. | |
6619 | * User space <<channel,channels>>, if any, are using | |
6620 | <<channel-buffering-schemes,per-user buffering>>. | |
6621 | ==== | |
6622 | ||
6623 | ||
6624 | [role="since-2.9"] | |
6625 | [[regenerate-statedump]] | |
6626 | === Regenerate the state dump of a tracing session | |
6627 | ||
6628 | The LTTng kernel and user space tracers generate state dump | |
6629 | <<event,event records>> when the application starts or when you | |
6630 | <<basic-tracing-session-control,start a tracing session>>. An analysis | |
6631 | can use the state dump event records to set an initial state before it | |
6632 | builds the rest of the state from the following event records. | |
6633 | http://tracecompass.org/[Trace Compass] is a notable example of an | |
6634 | application which uses the state dump of an LTTng trace. | |
6635 | ||
6636 | When you <<taking-a-snapshot,take a snapshot>>, it's possible that the | |
6637 | state dump event records are not included in the snapshot because they | |
6638 | were recorded to a sub-buffer that has been consumed or overwritten | |
6639 | already. | |
6640 | ||
6641 | You can use the `lttng regenerate statedump` command to emit the state | |
6642 | dump event records again. | |
6643 | ||
6644 | To regenerate the state dump of the current tracing session, provided | |
6645 | create it in snapshot mode, before you take a snapshot: | |
6646 | ||
6647 | . Use the `statedump` item of the man:lttng-regenerate(1) command: | |
6648 | + | |
6649 | -- | |
6650 | [role="term"] | |
6651 | ---- | |
6652 | $ lttng regenerate statedump | |
6653 | ---- | |
6654 | -- | |
6655 | ||
6656 | . <<basic-tracing-session-control,Stop the tracing session>>: | |
6657 | + | |
6658 | -- | |
6659 | [role="term"] | |
6660 | ---- | |
6661 | $ lttng stop | |
6662 | ---- | |
6663 | -- | |
6664 | ||
6665 | . <<taking-a-snapshot,Take a snapshot>>: | |
6666 | + | |
6667 | -- | |
6668 | [role="term"] | |
6669 | ---- | |
6670 | $ lttng snapshot record --name=my-snapshot | |
6671 | ---- | |
6672 | -- | |
6673 | ||
6674 | Depending on the event throughput, you should run steps 1 and 2 | |
6675 | as closely as possible. | |
6676 | ||
6677 | NOTE: To record the state dump events, you need to | |
6678 | <<enabling-disabling-events,create event rules>> which enable them. | |
6679 | LTTng-UST state dump tracepoints start with `lttng_ust_statedump:`. | |
6680 | LTTng-modules state dump tracepoints start with `lttng_statedump_`. | |
6681 | ||
6682 | ||
6683 | [role="since-2.7"] | |
6684 | [[persistent-memory-file-systems]] | |
6685 | === Record trace data on persistent memory file systems | |
6686 | ||
6687 | https://en.wikipedia.org/wiki/Non-volatile_random-access_memory[Non-volatile random-access memory] | |
6688 | (NVRAM) is random-access memory that retains its information when power | |
6689 | is turned off (non-volatile). Systems with such memory can store data | |
6690 | structures in RAM and retrieve them after a reboot, without flushing | |
6691 | to typical _storage_. | |
6692 | ||
6693 | Linux supports NVRAM file systems thanks to either | |
6694 | http://pramfs.sourceforge.net/[PRAMFS] or | |
6695 | https://www.kernel.org/doc/Documentation/filesystems/dax.txt[DAX]{nbsp}+{nbsp}http://lkml.iu.edu/hypermail/linux/kernel/1504.1/03463.html[pmem] | |
6696 | (requires Linux 4.1+). | |
6697 | ||
6698 | This section does not describe how to operate such file systems; | |
6699 | we assume that you have a working persistent memory file system. | |
6700 | ||
6701 | When you create a <<tracing-session,tracing session>>, you can specify | |
6702 | the path of the shared memory holding the sub-buffers. If you specify a | |
6703 | location on an NVRAM file system, then you can retrieve the latest | |
6704 | recorded trace data when the system reboots after a crash. | |
6705 | ||
6706 | To record trace data on a persistent memory file system and retrieve the | |
6707 | trace data after a system crash: | |
6708 | ||
6709 | . Create a tracing session with a sub-buffer shared memory path located | |
6710 | on an NVRAM file system: | |
6711 | + | |
6712 | -- | |
6713 | [role="term"] | |
6714 | ---- | |
6715 | $ lttng create my-session --shm-path=/path/to/shm | |
6716 | ---- | |
6717 | -- | |
6718 | ||
6719 | . Configure the tracing session as usual with the man:lttng(1) | |
6720 | command-line tool, and <<basic-tracing-session-control,start tracing>>. | |
6721 | ||
6722 | . After a system crash, use the man:lttng-crash(1) command-line tool to | |
6723 | view the trace data recorded on the NVRAM file system: | |
6724 | + | |
6725 | -- | |
6726 | [role="term"] | |
6727 | ---- | |
6728 | $ lttng-crash /path/to/shm | |
6729 | ---- | |
6730 | -- | |
6731 | ||
6732 | The binary layout of the ring buffer files is not exactly the same as | |
6733 | the trace files layout. This is why you need to use man:lttng-crash(1) | |
6734 | instead of your preferred trace viewer directly. | |
6735 | ||
6736 | To convert the ring buffer files to LTTng trace files: | |
6737 | ||
6738 | * Use the opt:lttng-crash(1):--extract option of man:lttng-crash(1): | |
6739 | + | |
6740 | -- | |
6741 | [role="term"] | |
6742 | ---- | |
6743 | $ lttng-crash --extract=/path/to/trace /path/to/shm | |
6744 | ---- | |
6745 | -- | |
6746 | ||
6747 | ||
90c4e38a PP |
6748 | [role="since-2.10"] |
6749 | [[notif-trigger-api]] | |
6750 | === Get notified when a channel's buffer usage is too high or too low | |
6751 | ||
6752 | With LTTng's $$C/C++$$ notification and trigger API, your user | |
6753 | application can get notified when the buffer usage of one or more | |
6754 | <<channel,channels>> becomes too low or too high. You can use this API | |
6755 | and enable or disable <<event,event rules>> during tracing to avoid | |
6756 | <<channel-overwrite-mode-vs-discard-mode,discarded event records>>. | |
6757 | ||
6758 | .Have a user application get notified when an LTTng channel's buffer usage is too high. | |
6759 | ==== | |
6760 | In this example, we create and build an application which gets notified | |
6761 | when the buffer usage of a specific LTTng channel is higher than | |
6762 | 75{nbsp}%. We only print that it is the case in the example, but we | |
6763 | could as well use the API of <<liblttng-ctl-lttng,`liblttng-ctl`>> to | |
6764 | disable event rules when this happens. | |
6765 | ||
6766 | . Create the application's C source file: | |
6767 | + | |
6768 | -- | |
6769 | [source,c] | |
6770 | .path:{notif-app.c} | |
6771 | ---- | |
6772 | #include <stdio.h> | |
6773 | #include <assert.h> | |
6774 | #include <lttng/domain.h> | |
6775 | #include <lttng/action/action.h> | |
6776 | #include <lttng/action/notify.h> | |
6777 | #include <lttng/condition/condition.h> | |
6778 | #include <lttng/condition/buffer-usage.h> | |
6779 | #include <lttng/condition/evaluation.h> | |
6780 | #include <lttng/notification/channel.h> | |
6781 | #include <lttng/notification/notification.h> | |
6782 | #include <lttng/trigger/trigger.h> | |
6783 | #include <lttng/endpoint.h> | |
6784 | ||
6785 | int main(int argc, char *argv[]) | |
6786 | { | |
d2a86fb9 PP |
6787 | int exit_status = 0; |
6788 | struct lttng_notification_channel *notification_channel; | |
6789 | struct lttng_condition *condition; | |
6790 | struct lttng_action *action; | |
6791 | struct lttng_trigger *trigger; | |
6792 | const char *tracing_session_name; | |
6793 | const char *channel_name; | |
6794 | ||
6795 | assert(argc >= 3); | |
6796 | tracing_session_name = argv[1]; | |
6797 | channel_name = argv[2]; | |
90c4e38a PP |
6798 | |
6799 | /* | |
d2a86fb9 PP |
6800 | * Create a notification channel. A notification channel |
6801 | * connects the user application to the LTTng session daemon. | |
7568806b | 6802 | * This notification channel can be used to listen to various |
d2a86fb9 PP |
6803 | * types of notifications. |
6804 | */ | |
6805 | notification_channel = lttng_notification_channel_create( | |
6806 | lttng_session_daemon_notification_endpoint); | |
6807 | ||
6808 | /* | |
6809 | * Create a "high buffer usage" condition. In this case, the | |
6810 | * condition is reached when the buffer usage is greater than or | |
7568806b PP |
6811 | * equal to 75 %. We create the condition for a specific tracing |
6812 | * session name, channel name, and for the user space tracing | |
6813 | * domain. | |
90c4e38a | 6814 | * |
d2a86fb9 PP |
6815 | * The "low buffer usage" condition type also exists. |
6816 | */ | |
6817 | condition = lttng_condition_buffer_usage_high_create(); | |
6818 | lttng_condition_buffer_usage_set_threshold_ratio(condition, .75); | |
6819 | lttng_condition_buffer_usage_set_session_name( | |
6820 | condition, tracing_session_name); | |
6821 | lttng_condition_buffer_usage_set_channel_name(condition, | |
6822 | channel_name); | |
6823 | lttng_condition_buffer_usage_set_domain_type(condition, | |
6824 | LTTNG_DOMAIN_UST); | |
6825 | ||
6826 | /* | |
6827 | * Create an action (get a notification) to take when the | |
6828 | * condition created above is reached. | |
6829 | */ | |
6830 | action = lttng_action_notify_create(); | |
6831 | ||
6832 | /* | |
6833 | * Create a trigger. A trigger associates a condition to an | |
6834 | * action: the action is executed when the condition is reached. | |
90c4e38a | 6835 | */ |
d2a86fb9 | 6836 | trigger = lttng_trigger_create(condition, action); |
90c4e38a | 6837 | |
d2a86fb9 PP |
6838 | /* Register the trigger to LTTng. */ |
6839 | lttng_register_trigger(trigger); | |
90c4e38a PP |
6840 | |
6841 | /* | |
d2a86fb9 PP |
6842 | * Now that we have registered a trigger, a notification will be |
6843 | * emitted everytime its condition is met. To receive this | |
6844 | * notification, we must subscribe to notifications that match | |
6845 | * the same condition. | |
90c4e38a | 6846 | */ |
7568806b PP |
6847 | lttng_notification_channel_subscribe(notification_channel, |
6848 | condition); | |
90c4e38a PP |
6849 | |
6850 | /* | |
7568806b PP |
6851 | * Notification loop. You can put this in a dedicated thread to |
6852 | * avoid blocking the main thread. | |
90c4e38a | 6853 | */ |
d2a86fb9 PP |
6854 | for (;;) { |
6855 | struct lttng_notification *notification; | |
6856 | enum lttng_notification_channel_status status; | |
6857 | const struct lttng_evaluation *notification_evaluation; | |
6858 | const struct lttng_condition *notification_condition; | |
6859 | double buffer_usage; | |
6860 | ||
6861 | /* Receive the next notification. */ | |
6862 | status = lttng_notification_channel_get_next_notification( | |
7568806b | 6863 | notification_channel, ¬ification); |
d2a86fb9 PP |
6864 | |
6865 | switch (status) { | |
6866 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_OK: | |
6867 | break; | |
6868 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_NOTIFICATIONS_DROPPED: | |
6869 | /* | |
6870 | * The session daemon can drop notifications if | |
6871 | * a monitoring application is not consuming the | |
6872 | * notifications fast enough. | |
6873 | */ | |
6874 | continue; | |
6875 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_CLOSED: | |
6876 | /* | |
6877 | * The notification channel has been closed by the | |
6878 | * session daemon. This is typically caused by a session | |
6879 | * daemon shutting down. | |
6880 | */ | |
6881 | goto end; | |
6882 | default: | |
6883 | /* Unhandled conditions or errors. */ | |
6884 | exit_status = 1; | |
6885 | goto end; | |
6886 | } | |
6887 | ||
6888 | /* | |
6889 | * A notification provides, amongst other things: | |
6890 | * | |
6891 | * * The condition that caused this notification to be | |
6892 | * emitted. | |
6893 | * * The condition evaluation, which provides more | |
6894 | * specific information on the evaluation of the | |
6895 | * condition. | |
6896 | * | |
6897 | * The condition evaluation provides the buffer usage | |
7568806b | 6898 | * value at the moment the condition was reached. |
d2a86fb9 PP |
6899 | */ |
6900 | notification_condition = lttng_notification_get_condition( | |
6901 | notification); | |
6902 | notification_evaluation = lttng_notification_get_evaluation( | |
6903 | notification); | |
6904 | ||
6905 | /* We're subscribed to only one condition. */ | |
6906 | assert(lttng_condition_get_type(notification_condition) == | |
6907 | LTTNG_CONDITION_TYPE_BUFFER_USAGE_HIGH); | |
6908 | ||
6909 | /* | |
6910 | * Get the exact sampled buffer usage from the | |
6911 | * condition evaluation. | |
6912 | */ | |
6913 | lttng_evaluation_buffer_usage_get_usage_ratio( | |
6914 | notification_evaluation, &buffer_usage); | |
6915 | ||
6916 | /* | |
6917 | * At this point, instead of printing a message, we | |
6918 | * could do something to reduce the channel's buffer | |
6919 | * usage, like disable specific events. | |
6920 | */ | |
6921 | printf("Buffer usage is %f %% in tracing session \"%s\", " | |
7568806b PP |
6922 | "user space channel \"%s\".\n", buffer_usage * 100, |
6923 | tracing_session_name, channel_name); | |
d2a86fb9 PP |
6924 | lttng_notification_destroy(notification); |
6925 | } | |
90c4e38a PP |
6926 | |
6927 | end: | |
d2a86fb9 PP |
6928 | lttng_action_destroy(action); |
6929 | lttng_condition_destroy(condition); | |
6930 | lttng_trigger_destroy(trigger); | |
6931 | lttng_notification_channel_destroy(notification_channel); | |
6932 | return exit_status; | |
90c4e38a PP |
6933 | } |
6934 | ---- | |
6935 | -- | |
6936 | ||
6937 | . Build the `notif-app` application, linking it to `liblttng-ctl`: | |
6938 | + | |
6939 | -- | |
6940 | [role="term"] | |
6941 | ---- | |
6942 | $ gcc -o notif-app notif-app.c -llttng-ctl | |
6943 | ---- | |
6944 | -- | |
6945 | ||
6946 | . <<creating-destroying-tracing-sessions,Create a tracing session>>, | |
6947 | <<enabling-disabling-events,create an event rule>> matching all the | |
6948 | user space tracepoints, and | |
6949 | <<basic-tracing-session-control,start tracing>>: | |
6950 | + | |
6951 | -- | |
6952 | [role="term"] | |
6953 | ---- | |
6954 | $ lttng create my-session | |
6955 | $ lttng enable-event --userspace --all | |
6956 | $ lttng start | |
6957 | ---- | |
6958 | -- | |
6959 | + | |
6960 | If you create the channel manually with the man:lttng-enable-channel(1) | |
6961 | command, you can control how frequently are the current values of the | |
6962 | channel's properties sampled to evaluate user conditions with the | |
6963 | opt:lttng-enable-channel(1):--monitor-timer option. | |
6964 | ||
6965 | . Run the `notif-app` application. This program accepts the | |
6966 | <<tracing-session,tracing session>> name and the user space channel | |
6967 | name as its two first arguments. The channel which LTTng automatically | |
6968 | creates with the man:lttng-enable-event(1) command above is named | |
6969 | `channel0`: | |
6970 | + | |
6971 | -- | |
6972 | [role="term"] | |
6973 | ---- | |
6974 | $ ./notif-app my-session channel0 | |
6975 | ---- | |
6976 | -- | |
6977 | ||
6978 | . In another terminal, run an application with a very high event | |
6979 | throughput so that the 75{nbsp}% buffer usage condition is reached. | |
6980 | + | |
6981 | In the first terminal, the application should print lines like this: | |
6982 | + | |
6983 | ---- | |
6984 | Buffer usage is 81.45197 % in tracing session "my-session", user space | |
6985 | channel "channel0". | |
6986 | ---- | |
6987 | + | |
6988 | If you don't see anything, try modifying the condition in | |
6989 | path:{notif-app.c} to a lower value (0.1, for example), rebuilding it | |
6990 | (step 2) and running it again (step 4). | |
6991 | ==== | |
6992 | ||
6993 | ||
85c29972 PP |
6994 | [[reference]] |
6995 | == Reference | |
6996 | ||
6997 | [[lttng-modules-ref]] | |
6998 | === noch:{LTTng-modules} | |
6999 | ||
7000 | ||
7001 | [role="since-2.9"] | |
7002 | [[lttng-tracepoint-enum]] | |
7003 | ==== `LTTNG_TRACEPOINT_ENUM()` usage | |
7004 | ||
7005 | Use the `LTTNG_TRACEPOINT_ENUM()` macro to define an enumeration: | |
7006 | ||
7007 | [source,c] | |
7008 | ---- | |
7009 | LTTNG_TRACEPOINT_ENUM(name, TP_ENUM_VALUES(entries)) | |
7010 | ---- | |
7011 | ||
7012 | Replace: | |
7013 | ||
7014 | * `name` with the name of the enumeration (C identifier, unique | |
7015 | amongst all the defined enumerations). | |
7016 | * `entries` with a list of enumeration entries. | |
7017 | ||
7018 | The available enumeration entry macros are: | |
7019 | ||
7020 | +ctf_enum_value(__name__, __value__)+:: | |
7021 | Entry named +__name__+ mapped to the integral value +__value__+. | |
7022 | ||
7023 | +ctf_enum_range(__name__, __begin__, __end__)+:: | |
7024 | Entry named +__name__+ mapped to the range of integral values between | |
7025 | +__begin__+ (included) and +__end__+ (included). | |
7026 | ||
7027 | +ctf_enum_auto(__name__)+:: | |
7028 | Entry named +__name__+ mapped to the integral value following the | |
7029 | last mapping's value. | |
7030 | + | |
7031 | The last value of a `ctf_enum_value()` entry is its +__value__+ | |
7032 | parameter. | |
7033 | + | |
7034 | The last value of a `ctf_enum_range()` entry is its +__end__+ parameter. | |
7035 | + | |
7036 | If `ctf_enum_auto()` is the first entry in the list, its integral | |
7037 | value is 0. | |
7038 | ||
7039 | Use the `ctf_enum()` <<lttng-modules-tp-fields,field definition macro>> | |
7040 | to use a defined enumeration as a tracepoint field. | |
7041 | ||
7042 | .Define an enumeration with `LTTNG_TRACEPOINT_ENUM()`. | |
7043 | ==== | |
7044 | [source,c] | |
7045 | ---- | |
7046 | LTTNG_TRACEPOINT_ENUM( | |
7047 | my_enum, | |
7048 | TP_ENUM_VALUES( | |
7049 | ctf_enum_auto("AUTO: EXPECT 0") | |
7050 | ctf_enum_value("VALUE: 23", 23) | |
7051 | ctf_enum_value("VALUE: 27", 27) | |
7052 | ctf_enum_auto("AUTO: EXPECT 28") | |
7053 | ctf_enum_range("RANGE: 101 TO 303", 101, 303) | |
7054 | ctf_enum_auto("AUTO: EXPECT 304") | |
7055 | ) | |
7056 | ) | |
7057 | ---- | |
7058 | ==== | |
7059 | ||
7060 | ||
7061 | [role="since-2.7"] | |
7062 | [[lttng-modules-tp-fields]] | |
7063 | ==== Tracepoint fields macros (for `TP_FIELDS()`) | |
7064 | ||
7065 | [[tp-fast-assign]][[tp-struct-entry]]The available macros to define | |
7066 | tracepoint fields, which must be listed within `TP_FIELDS()` in | |
7067 | `LTTNG_TRACEPOINT_EVENT()`, are: | |
7068 | ||
7069 | [role="func-desc growable",cols="asciidoc,asciidoc"] | |
7070 | .Available macros to define LTTng-modules tracepoint fields | |
7071 | |==== | |
7072 | |Macro |Description and parameters | |
7073 | ||
7074 | | | |
7075 | +ctf_integer(__t__, __n__, __e__)+ | |
7076 | ||
7077 | +ctf_integer_nowrite(__t__, __n__, __e__)+ | |
7078 | ||
7079 | +ctf_user_integer(__t__, __n__, __e__)+ | |
7080 | ||
7081 | +ctf_user_integer_nowrite(__t__, __n__, __e__)+ | |
7082 | | | |
7083 | Standard integer, displayed in base 10. | |
7084 | ||
7085 | +__t__+:: | |
7086 | Integer C type (`int`, `long`, `size_t`, ...). | |
7087 | ||
7088 | +__n__+:: | |
7089 | Field name. | |
7090 | ||
7091 | +__e__+:: | |
7092 | Argument expression. | |
7093 | ||
7094 | | | |
7095 | +ctf_integer_hex(__t__, __n__, __e__)+ | |
7096 | ||
7097 | +ctf_user_integer_hex(__t__, __n__, __e__)+ | |
7098 | | | |
7099 | Standard integer, displayed in base 16. | |
7100 | ||
7101 | +__t__+:: | |
7102 | Integer C type. | |
7103 | ||
7104 | +__n__+:: | |
7105 | Field name. | |
7106 | ||
7107 | +__e__+:: | |
7108 | Argument expression. | |
7109 | ||
7110 | |+ctf_integer_oct(__t__, __n__, __e__)+ | |
7111 | | | |
7112 | Standard integer, displayed in base 8. | |
7113 | ||
7114 | +__t__+:: | |
7115 | Integer C type. | |
7116 | ||
7117 | +__n__+:: | |
7118 | Field name. | |
7119 | ||
7120 | +__e__+:: | |
7121 | Argument expression. | |
7122 | ||
7123 | | | |
7124 | +ctf_integer_network(__t__, __n__, __e__)+ | |
7125 | ||
7126 | +ctf_user_integer_network(__t__, __n__, __e__)+ | |
7127 | | | |
7128 | Integer in network byte order (big-endian), displayed in base 10. | |
7129 | ||
7130 | +__t__+:: | |
7131 | Integer C type. | |
7132 | ||
7133 | +__n__+:: | |
7134 | Field name. | |
7135 | ||
7136 | +__e__+:: | |
7137 | Argument expression. | |
7138 | ||
7139 | | | |
7140 | +ctf_integer_network_hex(__t__, __n__, __e__)+ | |
7141 | ||
7142 | +ctf_user_integer_network_hex(__t__, __n__, __e__)+ | |
7143 | | | |
7144 | Integer in network byte order, displayed in base 16. | |
7145 | ||
7146 | +__t__+:: | |
7147 | Integer C type. | |
7148 | ||
7149 | +__n__+:: | |
7150 | Field name. | |
7151 | ||
7152 | +__e__+:: | |
7153 | Argument expression. | |
7154 | ||
7155 | | | |
7156 | +ctf_enum(__N__, __t__, __n__, __e__)+ | |
7157 | ||
7158 | +ctf_enum_nowrite(__N__, __t__, __n__, __e__)+ | |
7159 | ||
7160 | +ctf_user_enum(__N__, __t__, __n__, __e__)+ | |
7161 | ||
7162 | +ctf_user_enum_nowrite(__N__, __t__, __n__, __e__)+ | |
7163 | | | |
7164 | Enumeration. | |
7165 | ||
7166 | +__N__+:: | |
7167 | Name of a <<lttng-tracepoint-enum,previously defined enumeration>>. | |
7168 | ||
7169 | +__t__+:: | |
7170 | Integer C type (`int`, `long`, `size_t`, ...). | |
7171 | ||
7172 | +__n__+:: | |
7173 | Field name. | |
7174 | ||
7175 | +__e__+:: | |
7176 | Argument expression. | |
7177 | ||
7178 | | | |
7179 | +ctf_string(__n__, __e__)+ | |
7180 | ||
7181 | +ctf_string_nowrite(__n__, __e__)+ | |
7182 | ||
7183 | +ctf_user_string(__n__, __e__)+ | |
7184 | ||
7185 | +ctf_user_string_nowrite(__n__, __e__)+ | |
7186 | | | |
7187 | Null-terminated string; undefined behavior if +__e__+ is `NULL`. | |
7188 | ||
7189 | +__n__+:: | |
7190 | Field name. | |
7191 | ||
7192 | +__e__+:: | |
7193 | Argument expression. | |
7194 | ||
7195 | | | |
7196 | +ctf_array(__t__, __n__, __e__, __s__)+ | |
7197 | ||
7198 | +ctf_array_nowrite(__t__, __n__, __e__, __s__)+ | |
7199 | ||
7200 | +ctf_user_array(__t__, __n__, __e__, __s__)+ | |
7201 | ||
7202 | +ctf_user_array_nowrite(__t__, __n__, __e__, __s__)+ | |
7203 | | | |
7204 | Statically-sized array of integers. | |
7205 | ||
7206 | +__t__+:: | |
7207 | Array element C type. | |
7208 | ||
7209 | +__n__+:: | |
7210 | Field name. | |
7211 | ||
7212 | +__e__+:: | |
7213 | Argument expression. | |
7214 | ||
7215 | +__s__+:: | |
7216 | Number of elements. | |
7217 | ||
7218 | | | |
7219 | +ctf_array_bitfield(__t__, __n__, __e__, __s__)+ | |
7220 | ||
7221 | +ctf_array_bitfield_nowrite(__t__, __n__, __e__, __s__)+ | |
7222 | ||
7223 | +ctf_user_array_bitfield(__t__, __n__, __e__, __s__)+ | |
7224 | ||
7225 | +ctf_user_array_bitfield_nowrite(__t__, __n__, __e__, __s__)+ | |
7226 | | | |
7227 | Statically-sized array of bits. | |
7228 | ||
7229 | The type of +__e__+ must be an integer type. +__s__+ is the number | |
7230 | of elements of such type in +__e__+, not the number of bits. | |
7231 | ||
7232 | +__t__+:: | |
7233 | Array element C type. | |
7234 | ||
7235 | +__n__+:: | |
7236 | Field name. | |
7237 | ||
7238 | +__e__+:: | |
7239 | Argument expression. | |
7240 | ||
7241 | +__s__+:: | |
7242 | Number of elements. | |
7243 | ||
7244 | | | |
7245 | +ctf_array_text(__t__, __n__, __e__, __s__)+ | |
7246 | ||
7247 | +ctf_array_text_nowrite(__t__, __n__, __e__, __s__)+ | |
7248 | ||
7249 | +ctf_user_array_text(__t__, __n__, __e__, __s__)+ | |
7250 | ||
7251 | +ctf_user_array_text_nowrite(__t__, __n__, __e__, __s__)+ | |
7252 | | | |
7253 | Statically-sized array, printed as text. | |
7254 | ||
7255 | The string does not need to be null-terminated. | |
7256 | ||
7257 | +__t__+:: | |
7258 | Array element C type (always `char`). | |
7259 | ||
7260 | +__n__+:: | |
7261 | Field name. | |
7262 | ||
7263 | +__e__+:: | |
7264 | Argument expression. | |
7265 | ||
7266 | +__s__+:: | |
7267 | Number of elements. | |
7268 | ||
7269 | | | |
7270 | +ctf_sequence(__t__, __n__, __e__, __T__, __E__)+ | |
7271 | ||
7272 | +ctf_sequence_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
7273 | ||
7274 | +ctf_user_sequence(__t__, __n__, __e__, __T__, __E__)+ | |
7275 | ||
7276 | +ctf_user_sequence_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
7277 | | | |
7278 | Dynamically-sized array of integers. | |
7279 | ||
7280 | The type of +__E__+ must be unsigned. | |
7281 | ||
7282 | +__t__+:: | |
7283 | Array element C type. | |
7284 | ||
7285 | +__n__+:: | |
7286 | Field name. | |
7287 | ||
7288 | +__e__+:: | |
7289 | Argument expression. | |
7290 | ||
7291 | +__T__+:: | |
7292 | Length expression C type. | |
7293 | ||
7294 | +__E__+:: | |
7295 | Length expression. | |
7296 | ||
7297 | | | |
7298 | +ctf_sequence_hex(__t__, __n__, __e__, __T__, __E__)+ | |
7299 | ||
7300 | +ctf_user_sequence_hex(__t__, __n__, __e__, __T__, __E__)+ | |
7301 | | | |
7302 | Dynamically-sized array of integers, displayed in base 16. | |
7303 | ||
7304 | The type of +__E__+ must be unsigned. | |
7305 | ||
7306 | +__t__+:: | |
7307 | Array element C type. | |
7308 | ||
7309 | +__n__+:: | |
7310 | Field name. | |
7311 | ||
7312 | +__e__+:: | |
7313 | Argument expression. | |
7314 | ||
7315 | +__T__+:: | |
7316 | Length expression C type. | |
7317 | ||
7318 | +__E__+:: | |
7319 | Length expression. | |
7320 | ||
7321 | |+ctf_sequence_network(__t__, __n__, __e__, __T__, __E__)+ | |
7322 | | | |
7323 | Dynamically-sized array of integers in network byte order (big-endian), | |
7324 | displayed in base 10. | |
7325 | ||
7326 | The type of +__E__+ must be unsigned. | |
7327 | ||
7328 | +__t__+:: | |
7329 | Array element C type. | |
7330 | ||
7331 | +__n__+:: | |
7332 | Field name. | |
7333 | ||
7334 | +__e__+:: | |
7335 | Argument expression. | |
7336 | ||
7337 | +__T__+:: | |
7338 | Length expression C type. | |
7339 | ||
7340 | +__E__+:: | |
7341 | Length expression. | |
7342 | ||
7343 | | | |
7344 | +ctf_sequence_bitfield(__t__, __n__, __e__, __T__, __E__)+ | |
7345 | ||
7346 | +ctf_sequence_bitfield_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
7347 | ||
7348 | +ctf_user_sequence_bitfield(__t__, __n__, __e__, __T__, __E__)+ | |
7349 | ||
7350 | +ctf_user_sequence_bitfield_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
7351 | | | |
7352 | Dynamically-sized array of bits. | |
7353 | ||
7354 | The type of +__e__+ must be an integer type. +__s__+ is the number | |
7355 | of elements of such type in +__e__+, not the number of bits. | |
7356 | ||
7357 | The type of +__E__+ must be unsigned. | |
7358 | ||
7359 | +__t__+:: | |
7360 | Array element C type. | |
7361 | ||
7362 | +__n__+:: | |
7363 | Field name. | |
7364 | ||
7365 | +__e__+:: | |
7366 | Argument expression. | |
7367 | ||
7368 | +__T__+:: | |
7369 | Length expression C type. | |
7370 | ||
7371 | +__E__+:: | |
7372 | Length expression. | |
7373 | ||
7374 | | | |
7375 | +ctf_sequence_text(__t__, __n__, __e__, __T__, __E__)+ | |
7376 | ||
7377 | +ctf_sequence_text_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
7378 | ||
7379 | +ctf_user_sequence_text(__t__, __n__, __e__, __T__, __E__)+ | |
7380 | ||
7381 | +ctf_user_sequence_text_nowrite(__t__, __n__, __e__, __T__, __E__)+ | |
7382 | | | |
7383 | Dynamically-sized array, displayed as text. | |
7384 | ||
7385 | The string does not need to be null-terminated. | |
7386 | ||
7387 | The type of +__E__+ must be unsigned. | |
7388 | ||
7389 | The behaviour is undefined if +__e__+ is `NULL`. | |
7390 | ||
7391 | +__t__+:: | |
7392 | Sequence element C type (always `char`). | |
7393 | ||
7394 | +__n__+:: | |
7395 | Field name. | |
7396 | ||
7397 | +__e__+:: | |
7398 | Argument expression. | |
7399 | ||
7400 | +__T__+:: | |
7401 | Length expression C type. | |
7402 | ||
7403 | +__E__+:: | |
7404 | Length expression. | |
7405 | |==== | |
7406 | ||
7407 | Use the `_user` versions when the argument expression, `e`, is | |
7408 | a user space address. In the cases of `ctf_user_integer*()` and | |
7409 | `ctf_user_float*()`, `&e` must be a user space address, thus `e` must | |
7410 | be addressable. | |
7411 | ||
7412 | The `_nowrite` versions omit themselves from the session trace, but are | |
7413 | otherwise identical. This means the `_nowrite` fields won't be written | |
7414 | in the recorded trace. Their primary purpose is to make some | |
7415 | of the event context available to the | |
7416 | <<enabling-disabling-events,event filters>> without having to | |
7417 | commit the data to sub-buffers. | |
7418 | ||
7419 | ||
7420 | [[glossary]] | |
7421 | == Glossary | |
7422 | ||
7423 | Terms related to LTTng and to tracing in general: | |
7424 | ||
7425 | Babeltrace:: | |
7426 | The http://diamon.org/babeltrace[Babeltrace] project, which includes | |
7427 | the cmd:babeltrace command, some libraries, and Python bindings. | |
7428 | ||
7429 | <<channel-buffering-schemes,buffering scheme>>:: | |
7430 | A layout of sub-buffers applied to a given channel. | |
7431 | ||
7432 | <<channel,channel>>:: | |
7433 | An entity which is responsible for a set of ring buffers. | |
7434 | + | |
7435 | <<event,Event rules>> are always attached to a specific channel. | |
7436 | ||
7437 | clock:: | |
7438 | A reference of time for a tracer. | |
7439 | ||
7440 | <<lttng-consumerd,consumer daemon>>:: | |
7441 | A process which is responsible for consuming the full sub-buffers | |
7442 | and write them to a file system or send them over the network. | |
7443 | ||
7444 | <<channel-overwrite-mode-vs-discard-mode,discard mode>>:: The event loss | |
7445 | mode in which the tracer _discards_ new event records when there's no | |
7446 | sub-buffer space left to store them. | |
7447 | ||
7448 | event:: | |
7449 | The consequence of the execution of an instrumentation | |
7450 | point, like a tracepoint that you manually place in some source code, | |
7451 | or a Linux kernel KProbe. | |
7452 | + | |
7453 | An event is said to _occur_ at a specific time. Different actions can | |
7454 | be taken upon the occurrence of an event, like record the event's payload | |
7455 | to a sub-buffer. | |
7456 | ||
7457 | <<channel-overwrite-mode-vs-discard-mode,event loss mode>>:: | |
7458 | The mechanism by which event records of a given channel are lost | |
7459 | (not recorded) when there is no sub-buffer space left to store them. | |
7460 | ||
7461 | [[def-event-name]]event name:: | |
7462 | The name of an event, which is also the name of the event record. | |
7463 | This is also called the _instrumentation point name_. | |
7464 | ||
7465 | event record:: | |
7466 | A record, in a trace, of the payload of an event which occured. | |
7467 | ||
7468 | <<event,event rule>>:: | |
7469 | Set of conditions which must be satisfied for one or more occuring | |
7470 | events to be recorded. | |
7471 | ||
7472 | `java.util.logging`:: | |
7473 | Java platform's | |
7474 | https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[core logging facilities]. | |
7475 | ||
7476 | <<instrumenting,instrumentation>>:: | |
7477 | The use of LTTng probes to make a piece of software traceable. | |
7478 | ||
7479 | instrumentation point:: | |
7480 | A point in the execution path of a piece of software that, when | |
7481 | reached by this execution, can emit an event. | |
7482 | ||
7483 | instrumentation point name:: | |
7484 | See _<<def-event-name,event name>>_. | |
7485 | ||
7486 | log4j:: | |
7487 | A http://logging.apache.org/log4j/1.2/[logging library] for Java | |
7488 | developed by the Apache Software Foundation. | |
7489 | ||
7490 | log level:: | |
7491 | Level of severity of a log statement or user space | |
7492 | instrumentation point. | |
7493 | ||
7494 | LTTng:: | |
7495 | The _Linux Trace Toolkit: next generation_ project. | |
7496 | ||
7497 | <<lttng-cli,cmd:lttng>>:: | |
7498 | A command-line tool provided by the LTTng-tools project which you | |
7499 | can use to send and receive control messages to and from a | |
7500 | session daemon. | |
7501 | ||
7502 | LTTng analyses:: | |
7503 | The https://github.com/lttng/lttng-analyses[LTTng analyses] project, | |
7504 | which is a set of analyzing programs that are used to obtain a | |
7505 | higher level view of an LTTng trace. | |
7506 | ||
7507 | cmd:lttng-consumerd:: | |
7508 | The name of the consumer daemon program. | |
7509 | ||
7510 | cmd:lttng-crash:: | |
7511 | A utility provided by the LTTng-tools project which can convert | |
7512 | ring buffer files (usually | |
7513 | <<persistent-memory-file-systems,saved on a persistent memory file system>>) | |
7514 | to trace files. | |
7515 | ||
7516 | LTTng Documentation:: | |
7517 | This document. | |
7518 | ||
7519 | <<lttng-live,LTTng live>>:: | |
7520 | A communication protocol between the relay daemon and live viewers | |
7521 | which makes it possible to see events "live", as they are received by | |
7522 | the relay daemon. | |
7523 | ||
7524 | <<lttng-modules,LTTng-modules>>:: | |
7525 | The https://github.com/lttng/lttng-modules[LTTng-modules] project, | |
7526 | which contains the Linux kernel modules to make the Linux kernel | |
7527 | instrumentation points available for LTTng tracing. | |
7528 | ||
7529 | cmd:lttng-relayd:: | |
7530 | The name of the relay daemon program. | |
7531 | ||
7532 | cmd:lttng-sessiond:: | |
7533 | The name of the session daemon program. | |
7534 | ||
7535 | LTTng-tools:: | |
7536 | The https://github.com/lttng/lttng-tools[LTTng-tools] project, which | |
7537 | contains the various programs and libraries used to | |
7538 | <<controlling-tracing,control tracing>>. | |
7539 | ||
7540 | <<lttng-ust,LTTng-UST>>:: | |
7541 | The https://github.com/lttng/lttng-ust[LTTng-UST] project, which | |
7542 | contains libraries to instrument user applications. | |
7543 | ||
7544 | <<lttng-ust-agents,LTTng-UST Java agent>>:: | |
7545 | A Java package provided by the LTTng-UST project to allow the | |
7546 | LTTng instrumentation of `java.util.logging` and Apache log4j 1.2 | |
7547 | logging statements. | |
7548 | ||
7549 | <<lttng-ust-agents,LTTng-UST Python agent>>:: | |
7550 | A Python package provided by the LTTng-UST project to allow the | |
7551 | LTTng instrumentation of Python logging statements. | |
7552 | ||
7553 | <<channel-overwrite-mode-vs-discard-mode,overwrite mode>>:: | |
7554 | The event loss mode in which new event records overwrite older | |
7555 | event records when there's no sub-buffer space left to store them. | |
7556 | ||
7557 | <<channel-buffering-schemes,per-process buffering>>:: | |
7558 | A buffering scheme in which each instrumented process has its own | |
7559 | sub-buffers for a given user space channel. | |
7560 | ||
7561 | <<channel-buffering-schemes,per-user buffering>>:: | |
7562 | A buffering scheme in which all the processes of a Unix user share the | |
7563 | same sub-buffer for a given user space channel. | |
7564 | ||
7565 | <<lttng-relayd,relay daemon>>:: | |
7566 | A process which is responsible for receiving the trace data sent by | |
7567 | a distant consumer daemon. | |
7568 | ||
7569 | ring buffer:: | |
7570 | A set of sub-buffers. | |
7571 | ||
7572 | <<lttng-sessiond,session daemon>>:: | |
7573 | A process which receives control commands from you and orchestrates | |
7574 | the tracers and various LTTng daemons. | |
7575 | ||
7576 | <<taking-a-snapshot,snapshot>>:: | |
7577 | A copy of the current data of all the sub-buffers of a given tracing | |
7578 | session, saved as trace files. | |
7579 | ||
7580 | sub-buffer:: | |
7581 | One part of an LTTng ring buffer which contains event records. | |
7582 | ||
7583 | timestamp:: | |
7584 | The time information attached to an event when it is emitted. | |
7585 | ||
7586 | trace (_noun_):: | |
7587 | A set of files which are the concatenations of one or more | |
7588 | flushed sub-buffers. | |
7589 | ||
7590 | trace (_verb_):: | |
7591 | The action of recording the events emitted by an application | |
7592 | or by a system, or to initiate such recording by controlling | |
7593 | a tracer. | |
7594 | ||
7595 | Trace Compass:: | |
7596 | The http://tracecompass.org[Trace Compass] project and application. | |
7597 | ||
7598 | tracepoint:: | |
7599 | An instrumentation point using the tracepoint mechanism of the Linux | |
7600 | kernel or of LTTng-UST. | |
7601 | ||
7602 | tracepoint definition:: | |
7603 | The definition of a single tracepoint. | |
7604 | ||
7605 | tracepoint name:: | |
7606 | The name of a tracepoint. | |
7607 | ||
7608 | tracepoint provider:: | |
7609 | A set of functions providing tracepoints to an instrumented user | |
7610 | application. | |
7611 | + | |
7612 | Not to be confused with a _tracepoint provider package_: many tracepoint | |
7613 | providers can exist within a tracepoint provider package. | |
7614 | ||
7615 | tracepoint provider package:: | |
7616 | One or more tracepoint providers compiled as an object file or as | |
7617 | a shared library. | |
7618 | ||
7619 | tracer:: | |
7620 | A software which records emitted events. | |
7621 | ||
7622 | <<domain,tracing domain>>:: | |
7623 | A namespace for event sources. | |
7624 | ||
7625 | <<tracing-group,tracing group>>:: | |
7626 | The Unix group in which a Unix user can be to be allowed to trace the | |
7627 | Linux kernel. | |
7628 | ||
7629 | <<tracing-session,tracing session>>:: | |
7630 | A stateful dialogue between you and a <<lttng-sessiond,session | |
7631 | daemon>>. | |
7632 | ||
7633 | user application:: | |
7634 | An application running in user space, as opposed to a Linux kernel | |
7635 | module, for example. |