152 lines
4.0 KiB
Plaintext
152 lines
4.0 KiB
Plaintext
libtracefs(3)
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=============
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NAME
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----
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tracefs_trace_is_on, tracefs_trace_on, tracefs_trace_off, tracefs_trace_on_get_fd,
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tracefs_trace_on_fd, tracefs_trace_off_fd - Functions to enable or disable tracing.
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SYNOPSIS
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--------
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[verse]
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--
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*#include <tracefs.h>*
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int *tracefs_trace_is_on*(struct tracefs_instance pass:[*]_instance_);
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int *tracefs_trace_on*(struct tracefs_instance pass:[*]_instance_);
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int *tracefs_trace_off*(struct tracefs_instance pass:[*]_instance_);
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int *tracefs_trace_on_get_fd*(struct tracefs_instance pass:[*]_instance_);
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int *tracefs_trace_on_fd*(int _fd_);
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int *tracefs_trace_off_fd*(int _fd_);
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--
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DESCRIPTION
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-----------
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This set of functions can be used to check, enable or disable writing to the ring buffer in
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the given trace instance. The tracing is enabled when writing to the ring buffer is enabled.
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The *tracefs_trace_is_on()* function checks if tracing is enabled for the given _instance_. If
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_instance_ is NULL, the top instance is used.
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The *tracefs_trace_on()* and *tracefs_trace_off()* functions set the tracing in the _instance_
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to enable or disable state. If _instance_ is NULL, the top instance is used.
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The *tracefs_trace_on_get_fd()* function returns a file descriptor to the "tracing_on" file from
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the given _instance_. If _instance_ is NULL, the top trace instance is used. The returned descriptor
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can be used for fast enabling or disabling the tracing of the instance.
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The *tracefs_trace_on_fd()* and *tracefs_trace_off_fd()* functions set the tracing state to enable
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or disable using the given _fd_. This file descriptor must be opened for writing with
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*tracefs_trace_on_get_fd*(3) of the desired trace instance. These functions are faster than
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*tracefs_trace_on* and *tracefs_trace_off*.
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RETURN VALUE
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------------
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The *tracefs_trace_is_on()* function returns 0 if tracing is disable, 1 if it is enabled or
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-1 in case of an error.
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The *tracefs_trace_on_get_fd()* function returns a file descriptor to "tracing_on"
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file for reading and writing, which must be closed wuth close(). In case of an error -1 is returned.
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The *tracefs_trace_on()*, *tracefs_trace_off()*, *tracefs_trace_on_fd()* and
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*tracefs_trace_off_fd()* functions return -1 in case of an error or 0 otherwise.
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EXAMPLE
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-------
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[source,c]
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--
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#include <tracefs.h>
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int ret;
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ret = tracefs_trace_is_on(NULL);
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if (ret == 0) {
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/* Tracing is disabled in the top instance */
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} else if (ret == 1) {
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/* Tracing is enabled in the top instance */
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} else {
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/* Error getting tracing state of the top instance */
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}
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...
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if (!tracefs_trace_on(NULL)) {
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/* Enabled tracing in the top instance */
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...
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if (!tracefs_trace_off(NULL)) {
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/* Disabled tracing in the top instance */
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} else {
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/* Error disabling tracing in the top instance */
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}
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} else {
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/* Error enabling tracing in the top instance */
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}
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...
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int fd = tracefs_trace_on_get_fd(NULL);
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if (fd < 0) {
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/* Error opening tracing_on file */
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}
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...
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if (!tracefs_trace_on_fd(fd)) {
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/* Enabled tracing in the top instance */
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...
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if (!tracefs_trace_off_fd(fd)) {
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/* Disabled tracing in the top instance */
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} else {
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/* Error disabling tracing in the top instance */
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}
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} else {
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/* Error enabling tracing in the top instance */
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}
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...
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close(fd);
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--
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FILES
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-----
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[verse]
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--
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*tracefs.h*
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Header file to include in order to have access to the library APIs.
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*-ltracefs*
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Linker switch to add when building a program that uses the library.
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--
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SEE ALSO
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--------
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*libtracefs*(3),
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*libtraceevent*(3),
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*trace-cmd*(1)
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AUTHOR
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------
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[verse]
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--
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*Steven Rostedt* <rostedt@goodmis.org>
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*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>
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--
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REPORTING BUGS
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--------------
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Report bugs to <linux-trace-devel@vger.kernel.org>
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LICENSE
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-------
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libtracefs is Free Software licensed under the GNU LGPL 2.1
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RESOURCES
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---------
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https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
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COPYING
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-------
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Copyright \(C) 2021 VMware, Inc. Free use of this software is granted under
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the terms of the GNU Public License (GPL).
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