xref: /aosp_15_r20/external/libtracefs/Documentation/libtracefs-utils.txt (revision 287e80b3a36113050663245e7f2c00d274188f18)

libtracefs(3)
=============

NAME
----
tracefs_tracers, tracefs_tracer_available, tracefs_get_clock, tracefs_list_free,
tracefs_list_add, tracefs_list_size - Helper functions for working with trace file system.

SYNOPSIS
--------
[verse]
--
*#include <tracefs.h>*

char pass:[*]pass:[*]*tracefs_tracers*(const char pass:[*]_tracing_dir_);
bool *tracefs_tracer_available*(const char pass:[*]_tracing_dir_, const char pass:[*]_tracer_);
char pass:[*]*tracefs_get_clock*(struct tracefs_instance pass:[*]_instance_);
void *tracefs_list_free*(char pass:[*]pass:[*]_list_);
char pass:[**]*tracefs_list_add*(char **_list_, const char *_string_);
int *tracefs_list_size*(char pass:[**]_list_);
--

DESCRIPTION
-----------
Various useful functions for working with trace file system.

The *tracefs_tracers()* function returns array of strings with the
names of supported tracer plugins, located in the given _tracing_dir_
directory. This could be NULL or the location of the tracefs mount point
for the trace systems of the local machine, or it may be a path to a copy
of the tracefs directory from another machine. The last entry in the array
as a NULL pointer. The array must be freed with *tracefs_list_free()* API.

The *tracefs_tracer_available()* returns true if the _tracer_ is available
in the given _tracing_dir_director_, and false otherwise.

The *tracefs_get_clock()* function returns name of the current trace clock,
used in the given _instance_. If _instance_ is NULL, the clock of the main
trace instance is returned. The returned string must be freed with free().

The *tracefs_list_free()* function frees an array of strings, returned by
*tracefs_event_systems()*, *tracefs_system_events()* and *tracefs_tracers()*
APIs.

The *tracefs_list_add()* function adds _string_ to the string _list_. If
_list_ is NULL, then a new list is created with the first element a copy
of _string_, and the second element will be a NULL pointer.  If _list_ is
not NULL, then it is reallocated to include a new element and a NULL terminator,
and the new allocated array is returned. The list passed in should be ignored,
as it wil be freed if a new one was allocated.

The *tracefs_list_size()* is a fast way to find out the number of elements
in a string array that is to be freed with *tracefs_list_free()*. Note, this
depends on meta data that is created for these lists and will not work on
normal string arrays like argv.

RETURN VALUE
------------
The *tracefs_tracers()* returns array of strings. The last element in that
array is a NULL pointer. The array must be freed with *tracefs_list_free()* API.
In case of an error, NULL is returned.

The *tracefs_tracer_available()* returns true if the _tracer_ is available,
and false otherwise.

The *tracefs_get_clock()* returns string, that must be freed with free(), or NULL
in case of an error.

The *tracefs_list_add()* returns an allocated string array that must be freed
with *tracefs_list_free()* on success or NULL on error. If NULL is returned,
then the passed in _list_ is untouched. Thus, *tracefs_list_add()* should be
treated similarly to *realloc*(3).

The *tracefs_list_size()* returns the number of strings in the _list_. The
passed in list must be one that is to be freed with *tracefs_list_free()*
as the list has meta data that is used to determine the size and this does
not work on any normal string array like argv.

EXAMPLE
-------
[source,c]
--
#include <tracefs.h>

char **tracers = tracefs_tracers(NULL);

	if (tracers) {
		/* Got tracer plugins from the top trace instance */
		...
		tracefs_list_free(tracers);
	}
....
char *clock = tracefs_get_clock(NULL);

	if (clock) {
		/* Got current trace clock of the top trace instance */
		...
		free(clock);
	}
--
FILES
-----
[verse]
--
*tracefs.h*
	Header file to include in order to have access to the library APIs.
*-ltracefs*
	Linker switch to add when building a program that uses the library.
--

SEE ALSO
--------
*libtracefs*(3),
*libtraceevent*(3),
*trace-cmd*(1)

AUTHOR
------
[verse]
--
*Steven Rostedt* <[email protected]>
*Tzvetomir Stoyanov* <[email protected]>
--
REPORTING BUGS
--------------
Report bugs to  <[email protected]>

LICENSE
-------
libtracefs is Free Software licensed under the GNU LGPL 2.1

RESOURCES
---------
https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/

COPYING
-------
Copyright \(C) 2020 VMware, Inc. Free use of this software is granted under
the terms of the GNU Public License (GPL).