X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;ds=sidebyside;f=doc%2Fman%2Flttng-ust.3.txt;h=21f60984a3295e131c757eaaf2e66455ff96bd27;hb=c7667bfebfa1d054ad8d54fd98ada3c86184e327;hp=8ecda775b3477f363a8c234109e4d9a95802f67d;hpb=d1194248c71fd4767382b4ea40dfa1cea3db1fd7;p=lttng-ust.git diff --git a/doc/man/lttng-ust.3.txt b/doc/man/lttng-ust.3.txt index 8ecda775..21f60984 100644 --- a/doc/man/lttng-ust.3.txt +++ b/doc/man/lttng-ust.3.txt @@ -605,9 +605,9 @@ source: Create the tracepoint provider object file: [role="term"] --------------- -cc -c -I. tp.c --------------- +---- +$ cc -c -I. tp.c +---- NOTE: Although an application instrumented with LTTng-UST tracepoints can be compiled with a C++ compiler, tracepoint probes should be @@ -618,9 +618,9 @@ possibly with other object files of your application or with other tracepoint provider object files, as a static library: [role="term"] ---------------- -ar rc tp.a tp.o ---------------- +---- +$ ar rc tp.a tp.o +---- Using a static library does have the advantage of centralising the tracepoint providers objects so they can be shared between multiple @@ -635,9 +635,9 @@ library containing it) and with `liblttng-ust` and `libdl` (`libc` on a BSD system): [role="term"] -------------------------------------- -cc -o app tp.o app.o -llttng-ust -ldl -------------------------------------- +---- +$ cc -o app tp.o app.o -llttng-ust -ldl +---- [[build-dynamic]] @@ -678,16 +678,16 @@ built like it is using the static linking method, but with the nloption:-fpic option: [role="term"] --------------------- -cc -c -fpic -I. tp.c --------------------- +---- +$ cc -c -fpic -I. tp.c +---- It is then linked as a shared library like this: [role="term"] -------------------------------------------------------- -cc -shared -Wl,--no-as-needed -o tp.so tp.o -llttng-ust -------------------------------------------------------- +---- +$ cc -shared -Wl,--no-as-needed -o tp.so tp.o -llttng-ust +---- This tracepoint provider shared object isn't linked with the user application: it must be loaded manually. This is why the application is @@ -695,9 +695,9 @@ built with no mention of this tracepoint provider, but still needs libdl: [role="term"] --------------------------------- -cc -o app app.o tp-define.o -ldl --------------------------------- +---- +$ cc -o app app.o tp-define.o -ldl +---- There are two ways to dynamically load the tracepoint provider shared object: @@ -738,6 +738,12 @@ without a following man:exec(3) family system call. The library application with the `LD_PRELOAD` environment variable (see man:ld.so(8)). +To use `liblttng-ust` with a daemon application which closes file +descriptors that were not opened by it, preload the `liblttng-ust-fd.so` +library before you start the application. Typical use cases include +daemons closing all file descriptors after man:fork(2), and buggy +applications doing ``double-closes''. + Context information ~~~~~~~~~~~~~~~~~~~ @@ -763,12 +769,16 @@ information about event filtering. reverse-lookup the source location that caused the event to be emitted. -+perf:thread:COUNTER+:: +`perf:thread:COUNTER`:: perf counter named 'COUNTER'. Use `lttng add-context --list` to list the available perf counters. + Only available on IA-32 and x86-64 architectures. +`perf:thread:raw:rN:NAME`:: + perf counter with raw ID 'N' and custom name 'NAME'. See + man:lttng-add-context(1) for more details. + `pthread_id`:: POSIX thread identifier. Can be used on architectures where `pthread_t` maps nicely to an `unsigned long` type. @@ -981,6 +991,33 @@ Fields: |=== +Detect if LTTng-UST is loaded +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +To detect if `liblttng-ust` is loaded from an application: + +. Define the `lttng_ust_loaded` weak symbol globally: ++ +------------------------------------------------------------------------ +int lttng_ust_loaded __attribute__((weak)); +------------------------------------------------------------------------ ++ +This weak symbol is set by the constructor of `liblttng-ust`. + +. Test `lttng_ust_loaded` where needed: ++ +------------------------------------------------------------------------ +/* ... */ + +if (lttng_ust_loaded) { + /* LTTng-UST is loaded */ +} else { + /* LTTng-UST is NOT loaded */ +} + +/* ... */ +------------------------------------------------------------------------ + + [[example]] EXAMPLE ------- @@ -996,44 +1033,44 @@ You can compile the source files and link them together statically like this: [role="term"] -------------------------------------- -cc -c -I. tp.c -cc -c app.c -cc -o app tp.o app.o -llttng-ust -ldl -------------------------------------- +---- +$ cc -c -I. tp.c +$ cc -c app.c +$ cc -o app tp.o app.o -llttng-ust -ldl +---- Using the man:lttng(1) tool, create an LTTng tracing session, enable all the events of this tracepoint provider, and start tracing: [role="term"] ----------------------------------------------- -lttng create my-session -lttng enable-event --userspace 'my_provider:*' -lttng start ----------------------------------------------- +---- +$ lttng create my-session +$ lttng enable-event --userspace 'my_provider:*' +$ lttng start +---- You may also enable specific events: [role="term"] ----------------------------------------------------------- -lttng enable-event --userspace my_provider:big_event -lttng enable-event --userspace my_provider:event_instance2 ----------------------------------------------------------- +---- +$ lttng enable-event --userspace my_provider:big_event +$ lttng enable-event --userspace my_provider:event_instance2 +---- Run the application: [role="term"] --------------------- -./app some arguments --------------------- +---- +$ ./app some arguments +---- Stop the current tracing session and inspect the recorded events: [role="term"] ----------- -lttng stop -lttng view ----------- +---- +$ lttng stop +$ lttng view +---- Tracepoint provider header file @@ -1260,7 +1297,7 @@ are located in a specific directory under `$LTTNG_HOME` (or `$HOME` if there's no space left for the event record in the sub-buffer. + -- -`0` (default):: +`0`:: Never block the application. Positive value:: @@ -1272,6 +1309,8 @@ Negative value:: Block the application until there's space left for the event record. -- + +Default: {lttng_ust_blocking_retry_timeout}. ++ This option can be useful in workloads generating very large trace data throughput, where blocking the application is an acceptable trade-off to prevent discarding event records. @@ -1304,24 +1343,6 @@ with time constraints on the process startup time. + Default: {lttng_ust_register_timeout}. -`LTTNG_UST_BLOCKING_RETRY_TIMEOUT`:: - Maximum time during which event tracing retry is attempted on buffer - full condition (millliseconds). Setting this environment to non-zero - value effectively blocks the application on buffer full condition. - Setting this environment variable to non-zero values may - significantly affect application timings. Setting this to a negative - value may block the application indefinitely if there is no consumer - emptying the ring buffer. The delay between retry attempts is the - minimum between the specified timeout value and 100ms. This option - can be useful in workloads generating very large trace data - throughput, where blocking the application is an acceptable - trade-off to not discard events. _Use with caution_. -+ -The value `0` means _do not retry_. The value `-1` means _retry forever_. -Value > `0` means a maximum timeout of the given value. -+ -Default: {lttng_ust_blocking_retry_timeout}. - `LTTNG_UST_WITHOUT_BADDR_STATEDUMP`:: Prevents `liblttng-ust` from performing a base address state dump (see the <> section above) if