doc: add -llttng-ust-common to linking cmd in manpages

[lttng-ust.git] / doc / man / tracelog.3.txt

tracelog(3)
===========
:object-type: macro


NAME
----
tracelog, vtracelog - LTTng-UST printf(3)-like interface with a log level


SYNOPSIS
--------
[verse]
*#include <lttng/tracelog.h>*

[verse]
#define *tracelog*('level', 'fmt', ...)
#define *vtracelog*('level', 'fmt', 'ap')

Link with `-llttng-ust -llttng-ust-common`.


DESCRIPTION
-----------
The LTTng-UST `tracelog()` and `vtracelog()` API allows you to trace
your application with the help of simple man:printf(3)-like and
man:vprintf(3)-like macros, with an additional parameter for the desired
log level.

The 'fmt' argument is passed directly as the 'fmt' parameter of
man:vasprintf(3), as well as:

For `tracelog()`::
    The optional parameters following 'fmt'.

For `vtracelog()`::
    The 'ap' parameter as the 'ap' parameter of man:vasprintf(3)
    (`va_list` type).

The purpose of `tracelog()` and `vtracelog()` is to ease the migration
from logging to tracing.

The available values for the 'level' parameter are:

include::log-levels.txt[]

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

Once your application is instrumented with `tracelog()` and/or
`vtracelog()` calls and ready to run, use man:lttng-enable-event(1) to
enable the `lttng_ust_tracelog:*` event. You can isolate specific log
levels with the nloption:--loglevel and nloption:--loglevel-only options
of this command.

The `tracelog()` and `vtracelog()` events contain the following fields:

[options="header"]
|===
|Field name |Description

|`line`
|Line in source file where `tracelog()` was called.

|`file`
|Source file from which `tracelog()` was called.

|`func`
|Function name from which `tracelog()` was called.

|`msg`
|Formatted string output.
|===

If you do not need to attach a specific log level to a
`tracelog()`/`vtracelog()` call, use man:tracef(3) instead.

See also the <<limitations,LIMITATIONS>> section below for important
limitations to consider when using `tracelog()` or `vtracelog()`.


[[example]]
EXAMPLE
-------
Here's a usage example of `tracelog()`:

-------------------------------------------------------------------
#include <stdlib.h>
#include <lttng/tracelog.h>

int main(int argc, char *argv[])
{
    int i;

    if (argc < 2) {
        tracelog(TRACE_CRIT, "Not enough arguments: %d", argc);
        return EXIT_FAILURE;
    }

    tracelog(TRACE_INFO, "Starting app with %d arguments", argc);

    for (i = 0; i < argc; i++) {
        tracelog(TRACE_DEBUG, "Argument %d: %s", i, argv[i]);
    }

    tracelog(TRACE_INFO, "Exiting app");

    return EXIT_SUCCESS;
}
-------------------------------------------------------------------

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

[role="term"]
----
$ cc -o app app.c -llttng-ust -llttng-ust-common
----

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

[role="term"]
----
$ lttng create my-session
$ lttng enable-event --userspace 'lttng_ust_tracelog:*'
$ lttng start
----

Or you can enable `tracelog()` events matching a log level at least
as severe as a given log level:

[role="term"]
----
$ lttng enable-event --userspace 'lttng_ust_tracelog:*' \
                   --loglevel=TRACE_INFO
----

Next, start the program to be traced:

[role="term"]
----
$ ./app a few arguments passed to this application
----

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

[role="term"]
----
$ lttng stop
$ lttng view
----


[[limitations]]
LIMITATIONS
-----------
:macro-name: tracelog

include::tracef-tracelog-limitations.txt[]


include::common-footer.txt[]

include::common-copyrights.txt[]

include::common-authors.txt[]


SEE ALSO
--------
man:tracef(3),
man:vtracef(3),
man:lttng-ust(3),
man:lttng(1),
man:printf(3)