[PATCH 0/2] Documentation for new libtracefs APIs

[PATCH 0/2] Documentation for new libtracefs APIs

[Tzvetomir Stoyanov (VMware)]

Documented recently added APIs for trace instances and trace options.

Tzvetomir Stoyanov (VMware) (2):
  libtracefs: Document new instance APIs
  libtracefs: Document APIs for trace options

 Documentation/libtracefs-instances-manage.txt |  34 +++-
 Documentation/libtracefs-instances-utils.txt  |  16 +-
 Documentation/libtracefs-option-bits.txt      |  90 ++++++++++
 Documentation/libtracefs-option-get.txt       | 123 ++++++++++++++
 Documentation/libtracefs-option-misc.txt      | 100 +++++++++++
 Documentation/libtracefs-options.txt          | 159 ++++++++++++++++++
 6 files changed, 513 insertions(+), 9 deletions(-)
 create mode 100644 Documentation/libtracefs-option-bits.txt
 create mode 100644 Documentation/libtracefs-option-get.txt
 create mode 100644 Documentation/libtracefs-option-misc.txt
 create mode 100644 Documentation/libtracefs-options.txt

-- 
2.29.2

[PATCH 1/2] libtracefs: Document new instance APIs

[Tzvetomir Stoyanov (VMware)]

Added documentation for these new APIs:
 tracefs_instance_alloc()
 tracefs_instance_get_trace_dir()

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 Documentation/libtracefs-instances-manage.txt | 34 +++++++++++++++----
 Documentation/libtracefs-instances-utils.txt  | 16 +++++++--
 2 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/Documentation/libtracefs-instances-manage.txt b/Documentation/libtracefs-instances-manage.txt
index a831ef2..e7dc393 100644
--- a/Documentation/libtracefs-instances-manage.txt
+++ b/Documentation/libtracefs-instances-manage.txt
@@ -3,7 +3,7 @@ libtracefs(3)
 
 NAME
 ----
-tracefs_instance_create, tracefs_instance_destroy, tracefs_instance_free,
+tracefs_instance_create, tracefs_instance_destroy, tracefs_instance_alloc, tracefs_instance_free,
 tracefs_instance_is_new - Manage trace instances.
 
 SYNOPSIS
@@ -14,6 +14,7 @@ SYNOPSIS
 
 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_);
 
@@ -28,12 +29,22 @@ 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 does not yet
-exist in the system, it will be created.
+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 initialised for the top instance.
+Note that the top instance cannot be created in the system, if it does not
+exist.
 
 The _tracefs_instance_destroy()_ frees the _instance_ structure, and will
 also remove the trace instance from the system.
 
+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.
 
@@ -43,8 +54,8 @@ before that.
 
 RETURN VALUE
 ------------
-The _tracefs_instance_create()_ function returns a pointer to a newly allocated
-tracefs_instance structure. It must be freed with _tracefs_instance_destroy()_ or
+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_destroy()_ or
 _tracefs_instance_free()_.
 
 The _tracefs_instance_destroy()_ function returns -1 in case of an error,
@@ -54,7 +65,7 @@ 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()_.
+_tracefs_instance_create()_ or _tracefs_instance_alloc()_.
 
 EXAMPLE
 -------
@@ -74,6 +85,17 @@ struct tracefs_instance *inst = tracefs_instance_create("foo");
 		tracefs_instance_destroy(inst);
 	else
 		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
 -----
diff --git a/Documentation/libtracefs-instances-utils.txt b/Documentation/libtracefs-instances-utils.txt
index 3bd54a5..f559406 100644
--- a/Documentation/libtracefs-instances-utils.txt
+++ b/Documentation/libtracefs-instances-utils.txt
@@ -3,7 +3,8 @@ libtracefs(3)
 
 NAME
 ----
-tracefs_instance_get_name, tracefs_instances_walk, tracefs_instance_exists -
+tracefs_instance_get_name, tracefs_instance_get_trace_dir,
+tracefs_instances_walk, tracefs_instance_exists -
 Helper functions for working with tracing instances.
 
 SYNOPSIS
@@ -13,6 +14,7 @@ SYNOPSIS
 *#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_);
 
@@ -25,6 +27,9 @@ 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
@@ -39,6 +44,9 @@ 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.
 
@@ -54,11 +62,13 @@ EXAMPLE
 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)
 {
-- 
2.29.2

[PATCH 2/2] libtracefs: Document APIs for trace options

[Tzvetomir Stoyanov (VMware)]

Added documentation for libtracefs APIs realated to ftrace options:
	enum tracefs_option - short description of each option

 	tracefs_option_set()
	tracefs_option_clear()
	qtracefs_option_is_set()

	tracefs_options_get_supported()
	tracefs_option_is_supported()
	tracefs_options_get_enabled()
	qtracefs_option_is_enabled()

	tracefs_option_enable()
	tracefs_option_diasble()
	tracefs_option_name()

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 Documentation/libtracefs-option-bits.txt |  90 +++++++++++++
 Documentation/libtracefs-option-get.txt  | 123 ++++++++++++++++++
 Documentation/libtracefs-option-misc.txt | 100 ++++++++++++++
 Documentation/libtracefs-options.txt     | 159 +++++++++++++++++++++++
 4 files changed, 472 insertions(+)
 create mode 100644 Documentation/libtracefs-option-bits.txt
 create mode 100644 Documentation/libtracefs-option-get.txt
 create mode 100644 Documentation/libtracefs-option-misc.txt
 create mode 100644 Documentation/libtracefs-options.txt

diff --git a/Documentation/libtracefs-option-bits.txt b/Documentation/libtracefs-option-bits.txt
new file mode 100644
index 0000000..d713a5e
--- /dev/null
+++ b/Documentation/libtracefs-option-bits.txt
@@ -0,0 +1,90 @@
+libtracefs(3)
+=============
+
+NAME
+----
+tracefs_option_set, tracefs_option_clear, tracefs_option_is_set -
+Set, clear, check option in a bitmask.
+
+SYNOPSIS
+--------
+[verse]
+--
+*#include <tracefs.h>*
+
+void *tracefs_option_set*(struct tracefs_options_mask pass:[*]_options_, enum tracefs_option_id _id_);
+void *tracefs_option_clear*(struct tracefs_options_mask pass:[*]_options_, enum tracefs_option_id _id_);
+bool *tracefs_option_is_set*(struct tracefs_options_mask _options_, enum tracefs_option_id _id_);
+--
+
+DESCRIPTION
+-----------
+This set of APIs can be used to manipulate a bitmask with option IDs.
+
+The _tracefs_option_set()_ function sets the bit, corresponding to the option with _id_ in the
+_options_ bitmask.
+
+The _tracefs_option_clear()_ function clears the bit, corresponding to the option with _id_ in the
+_options_ bitmask.
+
+The _tracefs_option_is_set()_ function checks if the bit, corresponding to the option with _id_ is
+set in the _options_ bitmask.
+
+RETURN VALUE
+------------
+The _tracefs_option_is_set()_ function returns true if the bit is set, false otherwise.
+
+EXAMPLE
+-------
+[source,c]
+--
+#include <tracefs.h>
+...
+struct tracefs_options_mask options;
+memset(&options, 0, sizeof(options));
+...
+tracefs_option_set(&options, TRACEFS_OPTION_EVENT_FORK | TRACEFS_OPTION_FUNCTION_FORK);
+...
+if (tracefs_option_is_set(options, TRACEFS_OPTION_EVENT_FORK))
+	tracefs_option_clear(&options, TRACEFS_OPTION_EVENT_FORK);
+...
+--
+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).
diff --git a/Documentation/libtracefs-option-get.txt b/Documentation/libtracefs-option-get.txt
new file mode 100644
index 0000000..9b3cb56
--- /dev/null
+++ b/Documentation/libtracefs-option-get.txt
@@ -0,0 +1,123 @@
+libtracefs(3)
+=============
+
+NAME
+----
+tracefs_options_get_supported, tracefs_option_is_supported,
+tracefs_options_get_enabled, tracefs_option_is_enabled - Get and check ftrace options.
+
+SYNOPSIS
+--------
+[verse]
+--
+*#include <tracefs.h>*
+
+struct tracefs_options_mask pass:[*]*tracefs_options_get_supported*(struct tracefs_instance pass:[*]_instance_);
+bool *tracefs_option_is_supported*(struct tracefs_instance pass:[*]_instance_, enum tracefs_option_id _id_);
+struct tracefs_options_mask pass:[*]*tracefs_options_get_enabled*(struct tracefs_instance pass:[*]_instance_);
+bool *tracefs_option_is_enabled*(struct tracefs_instance pass:[*]_instance_, enum tracefs_option_id _id_);
+--
+
+DESCRIPTION
+-----------
+This set of APIs can be used to get and check current ftrace options. Supported ftrace options may
+depend on the kernel version and the kernel configuration.
+
+The _tracefs_options_get_supported()_ function gets all ftrace options supported by the system in
+the given _instance_. If _instance_ is NULL, supported options of the top trace instance are
+returned. The set of supported options must be the same in all trace instances.
+
+The _tracefs_option_is_supported()_ function checks if the option with given _id_ is supported by
+the system in the given _instance_. If _instance_ is NULL, the top trace instance is used. If an
+option is supported at the top trace instance, it must be supported in all trace instances also.
+
+The _tracefs_options_get_enabled()_ function gets all ftrace options, currently enabled in
+the given _instance_. If _instance_ is NULL, enabled options of the top trace instance are returned.
+
+The _tracefs_option_is_enabled()_ function checks if the option with given _id_ is enabled in the
+given _instance_. If _instance_ is NULL, the top trace instance is used.
+
+RETURN VALUE
+------------
+The _tracefs_options_get_supported()_ and _tracefs_options_get_enabled()_ functions return pointer
+to allocated bitmask with trace options, or NULL in case of an error. The returned bitmask must be
+freed with free();
+
+The _tracefs_option_is_supported()_ and _tracefs_option_is_enabled()_ functions return true if the
+option in supported / enabled, or false otherwise.
+
+EXAMPLE
+-------
+[source,c]
+--
+#include <tracefs.h>
+...
+struct tracefs_options_mask *options;
+...
+options = tracefs_options_get_supported(NULL);
+if (!options) {
+	/* Failed to get supported options */
+} else {
+	...
+	free(options);
+}
+...
+options = tracefs_options_get_enabled(NULL);
+if (!options) {
+	/* Failed to get options, enabled in the top instance */
+} else {
+	...
+	free(options);
+}
+...
+
+if (tracefs_option_is_supported(NULL, TRACEFS_OPTION_LATENCY_FORMAT)) {
+	/* Latency format option is supprted */
+}
+
+...
+
+if (tracefs_option_is_enabled(NULL, TRACEFS_OPTION_STACKTRACE)) {
+	/* Stacktrace option is enabled in the top instance */
+}
+
+--
+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).
diff --git a/Documentation/libtracefs-option-misc.txt b/Documentation/libtracefs-option-misc.txt
new file mode 100644
index 0000000..1cd7c88
--- /dev/null
+++ b/Documentation/libtracefs-option-misc.txt
@@ -0,0 +1,100 @@
+libtracefs(3)
+=============
+
+NAME
+----
+tracefs_option_enable, tracefs_option_diasble, tracefs_option_name -
+Various trace option functions.
+
+SYNOPSIS
+--------
+[verse]
+--
+*#include <tracefs.h>*
+
+int *tracefs_option_enable*(struct tracefs_instance pass:[*]_instance_, enum tracefs_option_id _id_);
+int *tracefs_option_diasble*(struct tracefs_instance pass:[*]_instance_, enum tracefs_option_id _id_);
+const char pass:[*]*tracefs_option_name*(enum tracefs_option_id _id_);
+--
+
+DESCRIPTION
+-----------
+This set of APIs can be used to enable and disable ftrace options and to get the name of an option.
+
+The _tracefs_option_enable()_ function enables the option with _id_ in the given _instance_. If
+_instance_ is NULL, the option is enabled in the top trace instance.
+
+The _tracefs_option_diasble()_ function disables the option with _id_ in the given _instance_. If
+_instance_ is NULL, the option is disabled in the top trace instance.
+
+The _tracefs_option_name()_ function returns a string, representing the option with _id_. The string
+must *not* be freed.
+
+
+RETURN VALUE
+------------
+The _tracefs_option_enable()_ and _tracefs_option_diasble()_ functions return 0 if the state of the
+option is set successfully, or -1 in case of an error.
+
+The _tracefs_option_name()_ function returns string with option name, or "unknown" in case of an
+error. The returned string must *not* be freed.
+
+EXAMPLE
+-------
+[source,c]
+--
+#include <tracefs.h>
+...
+if (tracefs_option_enable(NULL, TRACEFS_OPTION_ANNOTATE)) {
+	/* Failed to enable annotate option in top trace instance */
+}
+...
+if (tracefs_option_diasble(NULL, TRACEFS_OPTION_CONTEXT_INFO)) {
+	/* Failed to disable context info option in top trace instance */
+}
+...
+char *name = tracefs_option_name(TRACEFS_OPTION_FUNC_STACKTRACE);
+if (strcmp(name, "unknown")) {
+	/* Cannot get the name of the option */
+}
+
+--
+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).
diff --git a/Documentation/libtracefs-options.txt b/Documentation/libtracefs-options.txt
new file mode 100644
index 0000000..b8f0edf
--- /dev/null
+++ b/Documentation/libtracefs-options.txt
@@ -0,0 +1,159 @@
+libtracefs(3)
+=============
+
+NAME
+----
+tracefs_options - ftrace options, that can be controlled using tracefs library.
+
+SYNOPSIS
+--------
+[verse]
+--
+*#include <tracefs.h>*
+
+enum tracefs_option_id {
+	*TRACEFS_OPTION_INVALID*,
+	*TRACEFS_OPTION_ANNOTATE*,
+	*TRACEFS_OPTION_BIN*,
+	*TRACEFS_OPTION_BLK_CGNAME*,
+	*TRACEFS_OPTION_BLK_CGROUP*,
+	*TRACEFS_OPTION_BLK_CLASSIC*,
+	*TRACEFS_OPTION_BLOCK*,
+	*TRACEFS_OPTION_CONTEXT_INFO*,
+	*TRACEFS_OPTION_DISABLE_ON_FREE*,
+	*TRACEFS_OPTION_DISPLAY_GRAPH*,
+	*TRACEFS_OPTION_EVENT_FORK*,
+	*TRACEFS_OPTION_FGRAPH_ABSTIME*,
+	*TRACEFS_OPTION_FGRAPH_CPU*,
+	*TRACEFS_OPTION_FGRAPH_DURATION*,
+	*TRACEFS_OPTION_FGRAPH_IRQS*,
+	*TRACEFS_OPTION_FGRAPH_OVERHEAD*,
+	*TRACEFS_OPTION_FGRAPH_OVERRUN*,
+	*TRACEFS_OPTION_FGRAPH_PROC*,
+	*TRACEFS_OPTION_FGRAPH_TAIL*,
+	*TRACEFS_OPTION_FUNC_STACKTRACE*,
+	*TRACEFS_OPTION_FUNCTION_FORK*,
+	*TRACEFS_OPTION_FUNCTION_TRACE*,
+	*TRACEFS_OPTION_GRAPH_TIME*,
+	*TRACEFS_OPTION_HEX*,
+	*TRACEFS_OPTION_IRQ_INFO*,
+	*TRACEFS_OPTION_LATENCY_FORMAT*,
+	*TRACEFS_OPTION_MARKERS*,
+	*TRACEFS_OPTION_OVERWRITE*,
+	*TRACEFS_OPTION_PAUSE_ON_TRACE*,
+	*TRACEFS_OPTION_PRINTK_MSG_ONLY*,
+	*TRACEFS_OPTION_PRINT_PARENT*,
+	*TRACEFS_OPTION_RAW*,
+	*TRACEFS_OPTION_RECORD_CMD*,
+	*TRACEFS_OPTION_RECORD_TGID*,
+	*TRACEFS_OPTION_SLEEP_TIME*,
+	*TRACEFS_OPTION_STACKTRACE*,
+	*TRACEFS_OPTION_SYM_ADDR*,
+	*TRACEFS_OPTION_SYM_OFFSET*,
+	*TRACEFS_OPTION_SYM_USEROBJ*,
+	*TRACEFS_OPTION_TRACE_PRINTK*,
+	*TRACEFS_OPTION_USERSTACKTRACE*,
+	*TRACEFS_OPTION_VERBOSE*,
+};
+--
+
+DESCRIPTION
+-----------
+This enum contains all ftrace options, that can be manipulated using tracefs library. More detailed
+information about each option is available in Documentation/trace/ftrace.rst from the Linux
+kernel tree, in the trace_options section. Note that some ftrace options cannot be manipulated by
+this library, as they are intended for internal, debug purposes. These options control the tracers
+or the trace output. All options have two states - on and off, the default state is different for
+each of them.
+[verse]
+--
+Common options for all tracers:
+	*TRACEFS_OPTION_INVALID* Not a valid ftrace option, used by the API to indicate an error.
+	*TRACEFS_OPTION_ANNOTATE* Display when a new CPU buffer started.
+	*TRACEFS_OPTION_BIN* Display the formats in raw binary.
+	*TRACEFS_OPTION_CONTEXT_INFO* Show only the event data. Hides the comm, PID, timestamp, CPU, and other useful data.
+	*TRACEFS_OPTION_BLOCK* When set, reading trace_pipe will not block when polled.
+	*TRACEFS_OPTION_DISABLE_ON_FREE* When the free_buffer is closed, tracing will stop.
+	*TRACEFS_OPTION_DISPLAY_GRAPH* When set, the latency tracers will use function graph tracing instead of function tracing.
+	*TRACEFS_OPTION_EVENT_FORK* When set, tasks with PIDs listed in set_event_pid will have the PIDs of their children added to set_event_pid when those tasks fork.
+	*TRACEFS_OPTION_FUNCTION_FORK* When set, tasks with PIDs listed in set_ftrace_pid will have the PIDs of their children added to set_ftrace_pid when those tasks fork.
+	*TRACEFS_OPTION_FUNCTION_TRACE* When enabled, the latency tracers will trace functions.
+	*TRACEFS_OPTION_HEX* Display numbers in a hexadecimal format.
+	*TRACEFS_OPTION_IRQ_INFO* Display the interrupt, preempt count, need resched data.
+	*TRACEFS_OPTION_LATENCY_FORMAT* Display additional information about the latency.
+	*TRACEFS_OPTION_MARKERS* When set, the trace_marker is enabled - writable (only by root).
+	*TRACEFS_OPTION_OVERWRITE* Controls what happens when the trace buffer is full. If set, the oldest events are discarded and overwritten. If disabled, then the newest events are discarded.
+	*TRACEFS_OPTION_PAUSE_ON_TRACE* When set, opening the trace file for read, will pause writing to the ring buffer. When the file is closed, tracing will be enabled again.
+	*TRACEFS_OPTION_PRINTK_MSG_ONLY* When set, trace_printk()s will only show the format and not their parameters.
+	*TRACEFS_OPTION_PRINT_PARENT* On function traces, display the calling (parent) function as well as the function being traced.
+	*TRACEFS_OPTION_RAW* Display raw numbers.
+	*TRACEFS_OPTION_RECORD_CMD* Save a mapping with a pid and corresponding command.
+	*TRACEFS_OPTION_RECORD_TGID* Save a mapping with a pid and corresponding Thread Group IDs.
+	*TRACEFS_OPTION_STACKTRACE* Record a stack trace after any trace event.
+	*TRACEFS_OPTION_SYM_ADDR* Display the function address as well as the function name.
+	*TRACEFS_OPTION_SYM_OFFSET* Display not only the function name, but also the offset in the function.
+	*TRACEFS_OPTION_SYM_USEROBJ* When *TRACEFS_OPTION_USERSTACKTRACE* is set, look up which object the address belongs to, and print the object and a relative address.
+	*TRACEFS_OPTION_TRACE_PRINTK* Disable trace_printk() from writing into the buffer.
+	*TRACEFS_OPTION_USERSTACKTRACE* Records a stack trace of the current user space thread after each trace event.
+	*TRACEFS_OPTION_VERBOSE* When *TRACEFS_OPTION_LATENCY_FORMAT* is enabled, print more detailed information.
+
+Options, specific to function tracer:
+	*TRACEFS_OPTION_FUNC_STACKTRACE* Record a stack trace after every function.
+
+Options, specific to function_graph tracer:
+	*TRACEFS_OPTION_FGRAPH_ABSTIME* Display the timestamp at each line.
+	*TRACEFS_OPTION_FGRAPH_CPU* Display the CPU number of the CPU where the trace occurred.
+	*TRACEFS_OPTION_FGRAPH_DURATION* Display the duration of the amount of time at the end of each function, in microseconds.
+	*TRACEFS_OPTION_FGRAPH_IRQS* Trace functions that happen inside an interrupt.
+	*TRACEFS_OPTION_FGRAPH_OVERHEAD* Display a marker if a function takes longer than a certain amount of time.
+	*TRACEFS_OPTION_FGRAPH_OVERRUN* Display "overrun" of the call graph, in the case of functions missed due to big callstack.
+	*TRACEFS_OPTION_FGRAPH_PROC* Display the command of each process at every line.
+	*TRACEFS_OPTION_FGRAPH_TAIL* Display the function name on its return.
+	*TRACEFS_OPTION_SLEEP_TIME* Account time the task has been scheduled out as part of the function call.
+	*TRACEFS_OPTION_GRAPH_TIME* Display the time to call nested functions, if function profiler is enabled.
+
+Options, specific to blk tracer:
+	*TRACEFS_OPTION_BLK_CGNAME*
+	*TRACEFS_OPTION_BLK_CGROUP*
+	*TRACEFS_OPTION_BLK_CLASSIC* Display a more minimalistic output.
+--
+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)_,
+_Documentation/trace/ftrace.rst_ from the Linux kernel tree.
+
+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) 2021 VMware, Inc. Free use of this software is granted under
+the terms of the GNU Public License (GPL).
-- 
2.29.2