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

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

NAME
----
tracefs_trace_is_on, tracefs_trace_on, tracefs_trace_off, tracefs_trace_on_get_fd,
tracefs_trace_on_fd, tracefs_trace_off_fd - Functions to enable or disable tracing.

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

int *tracefs_trace_is_on*(struct tracefs_instance pass:[*]_instance_);
int *tracefs_trace_on*(struct tracefs_instance pass:[*]_instance_);
int *tracefs_trace_off*(struct tracefs_instance pass:[*]_instance_);
int *tracefs_trace_on_get_fd*(struct tracefs_instance pass:[*]_instance_);
int *tracefs_trace_on_fd*(int _fd_);
int *tracefs_trace_off_fd*(int _fd_);
--

DESCRIPTION
-----------
This set of functions can be used to check, enable or disable writing to the ring buffer in
the given trace instance. The tracing is enabled when writing to the ring buffer is enabled.

The *tracefs_trace_is_on()* function checks if tracing is enabled for the given _instance_. If
_instance_ is NULL, the top instance is used.

The *tracefs_trace_on()* and *tracefs_trace_off()* functions set the tracing in the _instance_
to enable or disable state. If _instance_ is NULL, the top instance is used.

The *tracefs_trace_on_get_fd()* function returns a file descriptor to the "tracing_on" file from
the given _instance_. If _instance_ is NULL, the top trace instance is used. The returned descriptor
can be used for fast enabling or disabling the tracing of the instance.

The *tracefs_trace_on_fd()* and *tracefs_trace_off_fd()* functions set the tracing state to enable
or disable using the given _fd_. This file descriptor must be opened for writing with
*tracefs_trace_on_get_fd*(3) of the desired trace instance. These functions are faster than
*tracefs_trace_on* and *tracefs_trace_off*.

RETURN VALUE
------------
The *tracefs_trace_is_on()* function returns 0 if tracing is disable, 1 if it is enabled or
-1 in case of an error.

The *tracefs_trace_on_get_fd()* function returns a file descriptor to "tracing_on"
file for reading and writing, which must be closed wuth close(). In case of an error -1 is returned.

The *tracefs_trace_on()*, *tracefs_trace_off()*, *tracefs_trace_on_fd()* and
*tracefs_trace_off_fd()* functions return -1 in case of an error or 0 otherwise.

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

	int ret;

	ret = tracefs_trace_is_on(NULL);
	if (ret == 0) {
		/* Tracing is disabled in the top instance */
	} else if (ret == 1) {
		/* Tracing is enabled in the top instance */
	} else {
		/* Error getting tracing state of the top instance */
	}

	...

	if (!tracefs_trace_on(NULL)) {
	    /* Enabled tracing in the top instance */

	    ...

	    if (!tracefs_trace_off(NULL)) {
	    	/* Disabled tracing in the top instance */
	    } else {
	    	/* Error disabling tracing in the top instance */
	    }
	} else {
		/* Error enabling tracing in the top instance */
	}

	...

	int fd = tracefs_trace_on_get_fd(NULL);

	if (fd < 0) {
		/* Error opening tracing_on file */
	}
	...
	if (!tracefs_trace_on_fd(fd)) {
	    /* Enabled tracing in the top instance */

	    ...

	    if (!tracefs_trace_off_fd(fd)) {
	    	/* Disabled tracing in the top instance */
	    } else {
	    	/* Error disabling tracing in the top instance */
	    }
	} else {
		/* Error enabling tracing in the top instance */
	}

	...

	close(fd);
--
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) 2021 VMware, Inc. Free use of this software is granted under
the terms of the GNU Public License (GPL).