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

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

NAME
----
tracefs_local_events, tracefs_local_events_system, tracefs_fill_local_events,
tracefs_load_cmdlines -
Initialize a tep handler with trace events from the local system.

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

struct tep_handle pass:[*]*tracefs_local_events*(const char pass:[*]_tracing_dir_);
struct tep_handle pass:[*]*tracefs_local_events_system*(const char pass:[*]_tracing_dir_, const char pass:[*] const pass:[*]_sys_names_);
int *tracefs_fill_local_events*(const char pass:[*]_tracing_dir_, struct tep_handle pass:[*]_tep_, int pass:[*]_parsing_failures_);
int *tracefs_load_cmdlines*(const char pass:[*]_tracing_dir_, struct tep_handle pass:[*]_tep_);
--

DESCRIPTION
-----------
Functions for initializing a tep handler with trace events from the local system.

The *tracefs_local_events()* function allocates a new _tep_ handler and
initializes it with events from all trace systems, 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 *tracefs_local_events_system()* function allocates a new _tep_ handler
and initializes it with events from specified trace systems _sys_names_,
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 _sys_names_ argument is an array of trace system names, that
will be used for _tep_ handler initialization. The last element in that
array must be a NULL pointer.

The *tracefs_fill_local_events()* function initializes already allocated _tep_
handler with events from all trace systems, 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 _tep_ argument must be
a pointer to already allocated tep handler, that is going to be initialized.
The _parsing_failures_ argument could be NULL or a pointer to an integer,
where the number of failures while parsing the event files are returned.

The above functions will also load the mappings between pids and the process
command line names. In some cases the _tep_ handle is created with one
of the above before tracing begins. As the mappings get updated during the
trace, there may be a need to read the mappings again after the trace.
The *tracefs_load_cmdlines()* does just that. The _tracing_dir_ is
the directory of the mount point to load from, or NULL to use the
mount point of the tracefs file system.

RETURN VALUE
------------
The *tracefs_local_events()* and *tracefs_local_events_system()* functions
return pointer to allocated and initialized _tep_ handler, or NULL in
case of an error. The returned _tep_ handler must be freed with *tep_free*(3).

The *tracefs_fill_local_events()* function returns -1 in case of an error or
0 otherwise.

The *tracefs_load_cmdlines()* function returns -1 in case of an error, or
0 otherwise.

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

struct tep_handle *tep;
...
	tep = tracefs_local_events(NULL);
	if (!tep) {
		/* Failed to initialise tep handler with local events from top instance */
		...
	}
...
	tep_free(tep);
...
	const char *systems[] = {"ftrace", "irq", NULL};
	tep = tracefs_local_events_system(NULL, systems);
	if (!tep) {
		/* Failed to initialise tep handler with local events from
		 * ftrace and irq systems in top instance.
		 */
		...
	}
...
	tep_free(tep);
...
	int parsing_failures;
	tep = tep_alloc();
	if (!tep) {
		/* Failed to allocate a tep handler */
		...
	}
	if (tracefs_fill_local_events(NULL, tep, &parsing_failures) < 0) {
		/* Failed to initialise tep handler with local events from top instance */
	}
	tracefs_load_cmdlines(NULL, tep);
...
	tep_free(tep);
--
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).