NAME | SYNOPSIS | DESCRIPTION | EXAMPLE | LIMITATIONS | BUGS | RESOURCES | COPYRIGHTS | THANKS | AUTHORS | SEE ALSO | COLOPHON

TRACEF(3)                       LTTng Manual                       TRACEF(3)

NAME         top

       tracef - LTTng-UST printf(3)-like interface

SYNOPSIS         top

       #include <lttng/tracef.h>

       #define tracef(fmt, ...)

       Link with -llttng-ust.

DESCRIPTION         top

       The LTTng-UST tracef() API allows you to trace your application with
       the help of a simple printf(3)-like macro. The fmt argument is passed
       directly to the fmt parameter of vasprintf(3), as well as the
       optional parameters following fmt.

       To use tracef(), include <lttng/tracef.h> where you need it, and link
       your application with liblttng-ust. See the EXAMPLE section below for
       a complete usage example.

       Once your application is instrumented with tracef() calls and ready
       to run, use lttng-enable-event(1) to enable the lttng_ust_tracef:*
       event.

       The tracef() events contain a single field, named msg, which is the
       formatted string output.

       If you need to attach a specific log level to a tracef() call, use
       tracelog(3) instead.

       See also the LIMITATIONS section below for important limitations to
       consider when using tracef().

EXAMPLE         top

       Here’s a usage example of tracef():

           #include <stdlib.h>
           #include <lttng/tracef.h>

           int main(void)
           {
               int i;

               for (i = 0; i < 25; i++) {
                   tracef("my message: %s, this integer: %d", "a message", i);
               }

               return EXIT_SUCCESS;
           }

       This C source file, saved as app.c, can be compiled into a program
       like this:

           $ cc -o app app.c -llttng-ust

       You can create an LTTng tracing session, enable the tracef() events,
       and start the created tracing session like this:

           $ lttng create my-session
           $ lttng enable-event --userspace 'lttng_ust_tracef:*'
           $ lttng start

       Next, start the program to be traced:

           $ ./app

       Finally, stop the tracing session, and inspect the recorded events:

           $ lttng stop
           $ lttng view

LIMITATIONS         top

       The tracef() utility macro was developed to make user space tracing
       super simple, albeit with notable disadvantages compared to custom,
       full-fledged tracepoint providers:

       ·   All generated events have the same provider/event names.

       ·   There’s no static type checking.

       ·   The only event field with user data you actually get, named msg,
           is a string potentially containing the values you passed to the
           macro using your own format. This also means that you cannot use
           filtering using a custom expression at run time because there are
           no isolated fields.

       ·   Since tracef() uses C standard library’s vasprintf(3) function in
           the background to format the strings at run time, its expected
           performance is lower than using custom tracepoint providers with
           typed fields, which do not require a conversion to a string.

       ·   Generally, a string containing the textual representation of the
           user data fields is not as compact as binary fields in the
           resulting trace.

       Thus, tracef() is useful for quick prototyping and debugging, but
       should not be considered for any permanent/serious application
       instrumentation.

       See lttng-ust(3) to learn more about custom tracepoint providers.

BUGS         top

       If you encounter any issue or usability problem, please report it on
       the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-ust>.

RESOURCES         top

       ·   LTTng project website <http://lttng.org>

       ·   LTTng documentation <http://lttng.org/docs>

       ·   Git repositories <http://git.lttng.org>

       ·   GitHub organization <http://github.com/lttng>

       ·   Continuous integration <http://ci.lttng.org/>

       ·   Mailing list <http://lists.lttng.org> for support and
           development: lttng-dev@lists.lttng.org

       ·   IRC channel <irc://irc.oftc.net/lttng>: #lttng on irc.oftc.net

COPYRIGHTS         top

       This macro is part of the LTTng-UST project.

       This macro is distributed under the GNU Lesser General Public
       License, version 2.1 <http://www.gnu.org/licenses/old-
       licenses/lgpl-2.1.en.html>. See the COPYING
       <https://github.com/lttng/lttng-ust/blob/master/COPYING> file for
       more details.

THANKS         top

       Thanks to Ericsson for funding this work, providing real-life use
       cases, and testing.

       Special thanks to Michel Dagenais and the DORSAL laboratory
       <http://www.dorsal.polymtl.ca/> at École Polytechnique de Montréal
       for the LTTng journey.

AUTHORS         top

       LTTng-UST was originally written by Mathieu Desnoyers, with
       additional contributions from various other people. It is currently
       maintained by Mathieu Desnoyers
       <mailto:mathieu.desnoyers@efficios.com>.

SEE ALSO         top

       tracelog(3), lttng-ust(3), lttng(1), printf(3)

COLOPHON         top

       This page is part of the LTTng-UST (    LTTng Userspace Tracer)
       project.  Information about the project can be found at 
       ⟨http://lttng.org/⟩.  It is not known how to report bugs for this man
       page; if you know, please send a mail to man-pages@man7.org.  This
       page was obtained from the project's upstream Git repository 
       ⟨git://git.lttng.org/lttng-ust.git⟩ on 2017-07-05.  If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail
       to man-pages@man7.org

LTTng 2.9.0-rc1                  04/24/2017                        TRACEF(3)

Pages that refer to this page: lttng-ust(3)tracelog(3)