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

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

NAME
----
tracefs_instance_get_name, tracefs_instance_get_trace_dir, tracefs_instances_walk, tracefs_instance_exists,
tracefs_instance_get_buffer_size, tracefs_instance_set_buffer_size - Helper functions for working with tracing instances.

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

const char pass:[*]*tracefs_instance_get_name*(struct tracefs_instance pass:[*]_instance_);
const char pass:[*]*tracefs_instance_get_trace_dir*(struct tracefs_instance pass:[*]_instance_);
int *tracefs_instances_walk*(int (pass:[*]_callback_)(const char pass:[*], void pass:[*]), void pass:[*]_context)_;
bool *tracefs_instance_exists*(const char pass:[*]_name_);
size_t *tracefs_instance_get_buffer_size*(struct tracefs_instance pass:[*]_instance_, int _cpu_);
int *tracefs_instance_set_buffer_size*(struct tracefs_instance pass:[*]_instance_, size_t _size_, int _cpu_);
--

DESCRIPTION
-----------
Helper functions for working with trace instances.

The *tracefs_instance_get_name()* function returns the name of the given _instance_.
Note that the top instance has no name, the function returns NULL for it.

The *tracefs_instance_get_trace_dir()* function returns the tracing directory, where
the given _instance_ is configured.

The *tracefs_instances_walk()* function walks through all configured tracing
instances in the system and calls _callback_ for each one of them. The _context_
argument is passed to the _callback_, together with the instance name. If the
_callback_ returns non-zero, the iteration stops. Note, the _callback_ is not
called for the top top instance.

The *tracefs_instance_exists()* function checks if an instance with the given
_name_ exists in the system.

The *tracefs_instace_get_buffer_size()* returns the size of the ring buffer. If _cpu_
is negative, it returns the total size of all the per CPU ring buffers, otherwise
it returns the size of the per CPU ring buffer for _cpu_.

The *tracefs_instance_set_buffer_size()* function sets the size of the ring buffer.
If _cpu_ is negative, then it sets all the per CPU ring buffers to _size_ (note
the total size is the number of CPUs * _size_). If _cpu_ is specified, then it only
sets the size of the per CPU ring buffer.

RETURN VALUE
------------
The *tracefs_instance_get_name()* returns a string or NULL in case of the top
instance. The returned string must _not_ be freed.

The *tracefs_instance_get_trace_dir()* returns a string or NULL in case of an error.
The returned string must _not_ be freed.

The *tracefs_instances_walk()* function returns 0, if all instances were iterated, 1
if the iteration was stopped by the _callback_, or -1 in case of an error.

The *tracefs_instance_exists()* returns true if an instance with the given _name_
exists in the system or false otherwise.

The *tracefs_instance_get_buffer_size()* returns the size of the ring buffer depending on
the _cpu_ value passed in, or -1 on error.

The *tracefs_instance_set_buffer_size()* returns zero on success and -1 on error.

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

struct tracefs_instance *inst;
....
char *name = tracefs_instance_get_name(inst);
	if(name) {
		/* Got name of the instance */
	}
char *dir = tracefs_instance_get_trace_dir(inst);
	if(dir) {
		/* Got tracing directory of the instance */
	}
...
static int instance_walk(char *name, void *context)
{
	/* Got instance with name */
	return 0;
}
...
	if (tracefs_instances_walk(instance_walk, NULL) < 0) {
		/* Error walking through the instances */
	}
...
	if (tracefs_instance_exists("foo")) {
		/* There is instance with name foo in the system */
	} else {
		/* There is no instance with name foo in the system */
	}
--
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).