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NAME | SYNOPSIS | DESCRIPTION | EXAMPLE | LIMITATIONS | BUGS | RESOURCES | COPYRIGHTS | THANKS | AUTHORS | SEE ALSO | COLOPHON |
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LTTNG_UST_TRACELOG(3) LTTng Manual LTTNG_UST_TRACELOG(3)
lttng_ust_tracelog, lttng_ust_vtracelog - LTTng-UST
printf(3)-like interface with a log level
#include <lttng/tracelog.h>
#define lttng_ust_tracelog(level, fmt, ...)
#define lttng_ust_vtracelog(level, fmt, ap)
Link with:
• -llttng-ust
• If you define _LGPL_SOURCE before including
<lttng/tracelog.h> (directly or indirectly): -llttng-ust-
common
The LTTng-UST lttng_ust_tracelog() and lttng_ust_vtracelog() API
allows you to trace your application with the help of simple
printf(3)-like and vprintf(3)-like macros, with an additional
parameter for the desired log level.
The fmt argument is passed directly as the fmt parameter of
vasprintf(3), as well as:
For lttng_ust_tracelog()
The optional parameters following fmt.
For lttng_ust_vtracelog()
The ap parameter as the ap parameter of vasprintf(3) (va_list
type).
The purpose of lttng_ust_tracelog() and lttng_ust_vtracelog() is
to ease the migration from logging to tracing.
The available values for the level parameter are:
LTTNG_UST_TRACEPOINT_LOGLEVEL_EMERG
System is unusable.
LTTNG_UST_TRACEPOINT_LOGLEVEL_ALERT
Action must be taken immediately.
LTTNG_UST_TRACEPOINT_LOGLEVEL_CRIT
Critical conditions.
LTTNG_UST_TRACEPOINT_LOGLEVEL_ERR
Error conditions.
LTTNG_UST_TRACEPOINT_LOGLEVEL_WARNING
Warning conditions.
LTTNG_UST_TRACEPOINT_LOGLEVEL_NOTICE
Normal, but significant, condition.
LTTNG_UST_TRACEPOINT_LOGLEVEL_INFO
Informational message.
LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_SYSTEM
Debug information with system-level scope (set of programs).
LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_PROGRAM
Debug information with program-level scope (set of
processes).
LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_PROCESS
Debug information with process-level scope (set of modules).
LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_MODULE
Debug information with module (executable/library) scope (set
of units).
LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_UNIT
Debug information with compilation unit scope (set of
functions).
LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_FUNCTION
Debug information with function-level scope.
LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_LINE
Debug information with line-level scope (default log level).
LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG
Debug-level message.
To use lttng_ust_tracelog() or lttng_ust_vtracelog(), include
<lttng/tracelog.h> where you need it, and link your application
with liblttng-ust and liblttng-ust-common. See the EXAMPLE
section below for a complete usage example.
Once your application is instrumented with lttng_ust_tracelog()
and/or lttng_ust_vtracelog() calls and ready to run, use
lttng-enable-event(1) to enable the lttng_ust_tracelog:* event.
You can isolate specific log levels with the --loglevel and
--loglevel-only options of this command.
The lttng_ust_tracelog() and lttng_ust_vtracelog() events contain
the following fields:
┌────────────┬──────────────────────────┐
│ Field name │ Description │
├────────────┼──────────────────────────┤
│ │ │
│ line │ Line in source file │
│ │ where │
│ │ lttng_ust_tracelog() was │
│ │ called. │
├────────────┼──────────────────────────┤
│ │ │
│ file │ Source file from which │
│ │ lttng_ust_tracelog() was │
│ │ called. │
├────────────┼──────────────────────────┤
│ │ │
│ func │ Function name from which │
│ │ lttng_ust_tracelog() was │
│ │ called. │
├────────────┼──────────────────────────┤
│ │ │
│ msg │ Formatted string output. │
└────────────┴──────────────────────────┘
If you do not need to attach a specific log level to a
lttng_ust_tracelog()/lttng_ust_vtracelog() call, use
lttng_ust_tracef(3) instead.
See also the LIMITATIONS section below for important limitations
to consider when using lttng_ust_tracelog() or
lttng_ust_vtracelog().
Here’s a usage example of lttng_ust_tracelog():
#include <stdlib.h>
#include <lttng/tracelog.h>
int main(int argc, char *argv[])
{
int i;
if (argc < 2) {
lttng_ust_tracelog(LTTNG_UST_TRACEPOINT_LOGLEVEL_CRIT,
"Not enough arguments: %d", argc);
return EXIT_FAILURE;
}
lttng_ust_tracelog(LTTNG_UST_TRACEPOINT_LOGLEVEL_INFO,
"Starting app with %d arguments", argc);
for (i = 0; i < argc; i++) {
lttng_ust_tracelog(LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG,
"Argument %d: %s", i, argv[i]);
}
lttng_ust_tracelog(LTTNG_UST_TRACEPOINT_LOGLEVEL_INFO,
"Exiting app");
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 -llttng-ust-common
You can create an LTTng tracing session, enable all the
lttng_ust_tracelog() events, and start the created tracing
session like this:
$ lttng create my-session
$ lttng enable-event --userspace 'lttng_ust_tracelog:*'
$ lttng start
Or you can enable lttng_ust_tracelog() events matching a log
level at least as severe as a given log level:
$ lttng enable-event --userspace 'lttng_ust_tracelog:*' \
--loglevel=INFO
Next, start the program to be traced:
$ ./app a few arguments passed to this application
Finally, stop the tracing session, and inspect the recorded
events:
$ lttng stop
$ lttng view
The lttng_ust_tracelog() and lttng_ust_vtracelog() utility macros
were 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 lttng_ust_tracelog() and lttng_ust_vtracelog() use C
standard library’s vasprintf(3) function in the background to
format the strings at run time, their 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, lttng_ust_tracelog()/lttng_ust_vtracelog() are useful for
quick prototyping and debugging, but should not be considered for
any permanent/serious application instrumentation.
lttng_ust_vtracelog() does not have a STAP_PROBEV() call, because
STAP_PROBEV() does not support va_list. If you need it, you
should emit this call yourself.
See lttng-ust(3) to learn more about custom tracepoint providers.
If you encounter any issue or usability problem, please report it
on the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-
ust>.
• 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: [email protected]
• IRC channel <irc://irc.oftc.net/lttng>: #lttng on
irc.oftc.net
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/v2.14/COPYING> file for
more details.
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.
LTTng-UST was originally written by Mathieu Desnoyers, with
additional contributions from various other people. It is
currently maintained by Mathieu Desnoyers
<mailto:[email protected]>.
lttng_ust_tracef(3), lttng_ust_vtracef(3), lttng-ust(3),
lttng(1), printf(3)
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 [email protected].
This page was obtained from the tarball fetched from
⟨https://lttng.org/files/lttng-ust/⟩ on 2024-06-14. 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 [email protected]
LTTng 2.14.0-pre 06/07/2024 LTTNG_UST_TRACELOG(3)
Pages that refer to this page: lttng-ust(3), lttng_ust_tracef(3), tracelog(3)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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