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, tracefs_instance_get_buffer_percent,
tracefs_instance_set_buffer_percent - 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_);
int *tracefs_instance_get_buffer_percent*(struct tracefs_instance pass:[*]_instance_);
int *tracefs_instance_set_buffer_percent*(struct tracefs_instance pass:[*]_instance_, int _val_);
--

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.

The *tracefs_instance_set_buffer_percent()* sets the buffer percent value of
the tracing ring buffer for _instance_ or the top level buffer if _instance_ is
NULL. The buffer percent decides when readers on *tracefs_cpu_read*(3),
*tracefs_cpu_buffered_read*(3), *tracefs_cpu_write*(3) and *tracefs_cpu_pipe*(3)
will block when O_NONBLOCK is not set. The value of _val_ must be between 0 and
100, where:

[verse]
--
  0   - block until there's any data in the ring buffer
  1   - block until 1% of the ring buffer sub-buffers are filled
  50  - block until 50% of the ring buffer sub-buffers are filled
  100 - block until the entire ring buffer is filled
--

Note, any number from 0 to 100 can be used where it is the percentage of the
ring buffer that must be filled before a blocked reader will be notified that
there's data to be retrieved.

The *tracefs_instance_get_buffer_percent()* retrieves the current buffer percent
setting of the tracing ring buffer for _instance_ or the top level buffer
if _instance_ is NULL.

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* <rostedt@goodmis.org>
*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>
--
REPORTING BUGS
--------------
Report bugs to  <linux-trace-devel@vger.kernel.org>

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).
