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

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

NAME
----
tracefs_options_get_supported, tracefs_option_is_supported, tracefs_options_get_enabled,
tracefs_option_is_enabled, tracefs_option_mask_is_set, tracefs_option_id
- Get and check ftrace options.

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

const struct tracefs_options_mask pass:[*]*tracefs_options_get_supported*(struct tracefs_instance pass:[*]_instance_);
bool *tracefs_option_is_supported*(struct tracefs_instance pass:[*]_instance_, enum tracefs_option_id _id_);
const struct tracefs_options_mask pass:[*]*tracefs_options_get_enabled*(struct tracefs_instance pass:[*]_instance_);
bool *tracefs_option_is_enabled*(struct tracefs_instance pass:[*]_instance_, enum tracefs_option_id _id_);
bool *tracefs_option_mask_is_set*(const struct tracefs_options_mask *options, enum tracefs_option_id id);
enum tracefs_option_id *tracefs_option_id*(const char pass:[*]_name_);
--

DESCRIPTION
-----------
This set of APIs can be used to get and check current ftrace options. Supported ftrace options may
depend on the kernel version and the kernel configuration.

The *tracefs_options_get_supported()* function gets all ftrace options supported by the system in
the given _instance_. If _instance_ is NULL, supported options of the top trace instance are
returned. The set of supported options is the same in all created trace instances, but may be different
than the top trace instance.

The *tracefs_option_is_supported()/ function checks if the option with given _id_ is supported by
the system in the given _instance_. If _instance_ is NULL, the top trace instance is used. If an
option is supported at the top trace instance, it it may not be supported in a created trace instance.

The *tracefs_options_get_enabled()* function gets all ftrace options, currently enabled in
the given _instance_. If _instance_ is NULL, enabled options of the top trace instance are returned.

The *tracefs_option_is_enabled()* function checks if the option with given _id_ is enabled in the
given _instance_. If _instance_ is NULL, the top trace instance is used.

The *tracefs_option_mask_is_set()* function checks if the bit, corresponding to the option with _id_ is
set in the _options_ bitmask returned from *tracefs_option_get_enabled()* and *tracefs_option_is_supported()*.

The *tracefs_option_id()* converts an option _name_ into its corresponding id, if it is found.
This allows to find the option _id_ to use in the other functions if only the _name_ is known.

RETURN VALUE
------------
The *tracefs_options_get_supported()* and *tracefs_options_get_enabled()* functions, on success,
return a pointer to the bitmask within the instance, or a global bitmask for the top level,
or NULL in case of an error. As the returned bitmask is part of the instance structure (or a
global variable) and must not be freed or modified.

The *tracefs_option_is_supported()* and *tracefs_option_is_enabled()* functions return true if the
option in supported / enabled, or false otherwise.

The *tracefs_option_mask_is_set()* returns true if the corresponding option is set in the mask
or false otherwise.

The *tracefs_option_id()* returns the corresponding id defined by *tracefs_options*(3) from
the given _name_. If the _name_ can not be found, then TRACEFS_OPTION_INVALID is returned.

EXAMPLE
-------
[source,c]
--
#include <tracefs.h>
...
const struct tracefs_options_mask *options;
...
options = tracefs_options_get_supported(NULL);
if (!options) {
	/* Failed to get supported options */
} else {
	...
}
...
options = tracefs_options_get_enabled(NULL);
if (!options) {
	/* Failed to get options, enabled in the top instance */
} else {
	...
}
if (tracefs_options_mask_is_set(options, TRACEFS_OPTION_LATENCY_FORMAT)) {
	...
}
...

if (tracefs_option_is_supported(NULL, TRACEFS_OPTION_LATENCY_FORMAT)) {
	/* Latency format option is supprted */
}

...

if (tracefs_option_is_enabled(NULL, TRACEFS_OPTION_STACKTRACE)) {
	/* Stacktrace option is enabled in the top instance */
}

--
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).