xref: /aosp_15_r20/external/libtraceevent/Documentation/libtraceevent-plugins.txt (revision 436bf2bcd5202612ffffe471bbcc1f277cc8d28e)

libtraceevent(3)
================

NAME
----
tep_load_plugins, tep_unload_plugins, tep_load_plugins_hook, tep_add_plugin_path,
tep_plugin_add_option - Load / unload traceevent plugins.

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

struct tep_plugin_list pass:[*]*tep_load_plugins*(struct tep_handle pass:[*]_tep_);
void *tep_unload_plugins*(struct tep_plugin_list pass:[*]_plugin_list_, struct tep_handle pass:[*]_tep_);
void *tep_load_plugins_hook*(struct tep_handle pass:[*]_tep_, const char pass:[*]_suffix_,
			   void (pass:[*]_load_plugin_)(struct tep_handle pass:[*]tep,
					       const char pass:[*]path,
					       const char pass:[*]name,
					       void pass:[*]data),
			   void pass:[*]_data_);
int *tep_add_plugin_path*(struct tep_handle pass:[*]tep, char pass:[*]path,
			  enum tep_plugin_load_priority prio);
int *tep_plugin_add_option*(const char pass:[*]_name_, const char pass:[*]_val_);
--

DESCRIPTION
-----------
The *tep_load_plugins()* function loads all plugins, located in the plugin
directories. The _tep_ argument is trace event parser context.
The plugin directories are :
[verse]
--
	- Directories, specified in _tep_->plugins_dir with priority TEP_PLUGIN_FIRST
	- System's plugin directory, defined at the library compile time. It
	  depends on the library installation prefix and usually is
	  _(install_preffix)/lib/traceevent/plugins_
	- Directory, defined by the environment variable _TRACEEVENT_PLUGIN_DIR_
	- User's plugin directory, located at _~/.local/lib/traceevent/plugins_
	- Directories, specified in _tep_->plugins_dir with priority TEP_PLUGIN_LAST
--
Loading of plugins can be controlled by the _tep_flags_, using the
*tep_set_flag()* API:
[verse]
--
	_TEP_DISABLE_SYS_PLUGINS_	- do not load plugins, located in
					the system's plugin directory.
	_TEP_DISABLE_PLUGINS_		- do not load any plugins.
--
The *tep_set_flag()* API needs to be called before *tep_load_plugins()*, if
loading of all plugins is not the desired case.

The *tep_unload_plugins()* function unloads the plugins, previously loaded by
*tep_load_plugins()*. The _tep_ argument is trace event parser context. The
_plugin_list_ is the list of loaded plugins, returned by
the *tep_load_plugins()* function.

The *tep_load_plugins_hook()* function walks through all directories with plugins
and calls user specified *load_plugin()* hook for each plugin file. Only files
with given _suffix_ are considered to be plugins. The _data_ is a user specified
context, passed to *load_plugin()*. Directories and the walk order are the same
as in *tep_load_plugins()* API.

The *tep_add_plugin_path()* functions adds additional directories with plugins in
the _tep_->plugins_dir list. It must be called before *tep_load_plugins()* in order
for the plugins from the new directories to be loaded. The _tep_ argument is
the trace event parser context. The _path_ is the full path to the new plugin
directory. The _prio_ argument specifies the loading priority order for the
new directory of plugins. The loading priority is important in case of different
versions of the same plugin located in multiple plugin directories.The last loaded
plugin wins. The priority can be:
[verse]
--
	_TEP_PLUGIN_FIRST_	- Load plugins from this directory first
	_TEP_PLUGIN_LAST_	- Load plugins from this directory last
--
Where the plugins in TEP_PLUGIN_LAST" will take precedence over the
plugins in the other directories.

The *tep_plugin_add_option()* sets options defined by a plugin. The _name_ is the
name of the option to set to _val_. Plugins can add options to change its behavior
and *tep_plugin_add_option()* is used by the application to make those modifications.


RETURN VALUE
------------
The *tep_load_plugins()* function returns a list of successfully loaded plugins,
or NULL in case no plugins are loaded.
The *tep_add_plugin_path()* function returns -1 in case of an error, 0 otherwise.

EXAMPLE
-------
[source,c]
--
#include <event-parse.h>
...
struct tep_handle *tep = tep_alloc();
...
tep_add_plugin_path(tep, "~/dev_plugins", TEP_PLUGIN_LAST);
...
struct tep_plugin_list *plugins = tep_load_plugins(tep);
if (plugins == NULL) {
	/* no plugins are loaded */
}
...
tep_unload_plugins(plugins, tep);
...
void print_plugin(struct tep_handle *tep, const char *path,
		  const char *name, void *data)
{
	pritnf("Found libtraceevent plugin %s/%s\n", path, name);
}
...
tep_load_plugins_hook(tep, ".so", print_plugin, NULL);
...
--

FILES
-----
[verse]
--
*event-parse.h*
	Header file to include in order to have access to the library APIs.
*-ltraceevent*
	Linker switch to add when building a program that uses the library.
--

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

AUTHOR
------
[verse]
--
*Steven Rostedt* <[email protected]>, author of *libtraceevent*.
*Tzvetomir Stoyanov* <[email protected]>, author of this man page.
--
REPORTING BUGS
--------------
Report bugs to  <[email protected]>

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

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