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

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

NAME
----
tracefs_instance_create, tracefs_instance_destroy, tracefs_instance_alloc, tracefs_instance_free,
tracefs_instance_is_new, tracefs_instances - Manage trace instances.

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

struct tracefs_instance pass:[*]*tracefs_instance_create*(const char pass:[*]_name_);
int *tracefs_instance_destroy*(struct tracefs_instance pass:[*]_instance_);
struct tracefs_instance pass:[*]*tracefs_instance_alloc*(const char pass:[*]_tracing_dir_, const char pass:[*]_name_);
void *tracefs_instance_free*(struct tracefs_instance pass:[*]_instance_);
bool *tracefs_instance_is_new*(struct tracefs_instance pass:[*]_instance_);
char pass:[**]*tracefs_instances*(const char pass:[*]_regex_);

--

DESCRIPTION
-----------
This set of functions can be used to manage trace instances. A trace
instance is a sub buffer used by the Linux tracing system. Given a unique
name, the events enabled in an instance do not affect the main tracing
system, nor other instances, as events enabled in the main tracing system
or other instances do not affect the given instance.

The *tracefs_instance_create()* function allocates and initializes a new
tracefs_instance structure and returns it. If the instance with _name_ does
not yet exist in the system, it will be created. The _name_ could be NULL,
then the new tracefs_instance structure is initialized for the top instance.
Note that the top instance cannot be created in the system, if it does not
exist.

The *tracefs_instance_destroy()* removes the instance from the system, but
does not free the structure. *tracefs_instance_free()* must still be called
on _instance_.

The tracefs_instance_alloc()* function allocates a new tracefs_instance structure
for existing trace instance. If the instance does not exist in the system, the function
fails. The _tracing_dir_ parameter points to the system trace directory. It can be
NULL, then default system trace directory is used. This parameter is useful to allocate
instances to trace directories, copied from another machine. The _name_ is the name of
the instance, or NULL for the top instance in the given _tracing_dir_.

The *tracefs_instance_free()* function frees the tracefs_instance structure,
without removing the trace instance from the system.

The *tracefs_instance_is_new()* function checks if the given _instance_ is
newly created by *tracefs_instance_create()*, or it has been in the system
before that.

The *tracefs_instances*() function returns a list of instances that exist in
the system that match the regular expression _regex_. If _regex_ is NULL, then
it will match all instances that exist. The returned list must be freed with
*tracefs_list_free*(3). Note, if no instances are found an empty list is returned
and that too needs to be free with *tracefs_list_free*(3).

RETURN VALUE
------------
The *tracefs_instance_create()* and *tracefs_instance_alloc()* functions return a pointer to
a newly allocated tracefs_instance structure. It must be freed with *tracefs_instance_free()*.

The *tracefs_instance_destroy()* function returns 0 if it succeeds to remove
the instance, otherwise it returns -1 if the instance does not exist or it
fails to remove it.

The *tracefs_instance_is_new()* function returns true if the
*tracefs_instance_create()* that allocated _instance_ also created the
trace instance in the system, or false if the trace instance already
existed in the system when _instance_ was allocated by
*tracefs_instance_create()* or *tracefs_instance_alloc()*.

The *tracefs_instances()* returns a list of instance names that exist on the system.
The list must be freed with *tracefs_list_free*(3). An empty list is returned if
no instance exists that matches _regex_, and this needs to be freed with
*tracefs_list_free*(3) as well. NULL is returned on error.

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

struct tracefs_instance *inst = tracefs_instance_create("foo");
	if (!inst) {
		/* Error creating a new trace instance */
		...
	}

	...

	if (tracefs_instance_is_new(inst))
		tracefs_instance_destroy(inst);
	tracefs_instance_free(inst);
...

struct tracefs_instance *inst = tracefs_instance_alloc(NULL, "bar");
	if (!inst) {
		/* Error allocating 'bar' trace instance */
		...
	}

	...

	tracefs_instance_free(inst);
--
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).