Provided by: libtracefs-doc_1.7.0-1_all 
NAME
tracefs_instance_tracers, tracefs_tracer_set, tracefs_tracer_clear - Enable or disable a
tracer in an instance or the top level
SYNOPSIS
#include <tracefs.h>
char ** tracefs_instance_tracers(struct tracefs_instance *instance);
int tracefs_tracer_set(struct tracefs_instance *instance, enum tracefs_tracers tracer);
int tracefs_tracer_set(struct tracefs_instance *instance, enum tracefs_tracers tracer, const char *name);
int tracefs_tracer_clear(struct tracefs_instance *instance);
DESCRIPTION
tracefs_instance_tracers will return a list of available tracers for a given instance
(note, an instance may not have the same set of available tracers as the top level). If
instance is NULL, then the list of available tracers returned will be for the top level.
tracefs_tracer_set enables a tracer in the given instance, defined by the instance
parameter. If instance is NULL, then the top level instance is changed. If tracer is set
to TRACFES_TRACER_CUSTOM then a name string must be passed in as the third parameter, and
that is written into the instance to enable the tracer with that name. This is useful for
newer or custom kernels that contain tracers that are not yet identified by the
tracefs_tracers enum.
tracefs_tracer_clear disables the tracer for the given instance defined by the instance
variable, or the top level instance if it is NULL. This is the same as calling
tracefs_tracer_set with TRACEFS_TRACER_NOP as the tracer parameter.
TRACEFS_TRACER ENUMS
The currently defined enums that are accepted are:
TRACEFS_TRACER_NOP : This is the idle tracer, which does nothing and is used to clear any
active tracer.
TRACEFS_TRACER_FUNCTION : Enables most functions in the kernel to be traced.
TRACEFS_TRACER_FUNCTION_GRAPH : Enables most functions in the kernel to be traced as well
as the return of the function.
TRACEFS_TRACER_IRQSOFF : Tracers the latency of interrupts disabled.
TRACEFS_TRACER_PREEMPTOFF : Tracers the latency of preemption disabled (the time in the
kernel that tasks can not be scheduled from the CPU).
TRACEFS_TRACER_PREEMPTIRQSOFF : Traces the combined total latency of when interrupts are
disabled as well as when preemption is disabled.
TRACEFS_TRACER_WAKEUP : Traces the latency of when the highest priority task takes to wake
up.
TRACEFS_TRACER_WAKEUP_RT : Traces the latency of when the highest priority real-time task
takes to wake up. All other tasks are ignored.
TRACEFS_TRACER_WAKEUP_DL : Traces the latency of when the highest priority DEADLINE task
takes to wake up. All other tasks are ignored.
TRACEFS_TRACER_MMIOTRACE : Traces the interaction of devices with the kernel.
TRACEFS_TRACER_HWLAT : Detects latency caused by the hardware that is outside the scope of
the kernel.
TRACEFS_TRACER_BRANCH : Traces when likely or unlikely branches are taken.
TRACEFS_TRACER_BLOCK : Special tracer for the block devices.
Note that the above tracers may not be available in the kernel and tracefs_tracer_set()
will return an error with errno set to ENODEV, if the kernel does not support the tracer
option, or the custom one if TRACEFS_TRACER_CUSTOM is used.
RETURN VALUE
Returns 0 on success, or -1 on error.
ERRORS
tracefs_tracer_set() can fail with the following errors:
EINVAL The tracer parameter is outside the scope of what is defined.
ENOMEM Memory allocation error.
ENOENT Tracers are not supported on the running kernel.
ENODEV The specified tracer is not supported on the running kernel.
Other errors may also happen caused by internal system calls.
EXAMPLE
#include <stdlib.h>
#include <stdio.h>
#include <getopt.h>
#include <errno.h>
#include <tracefs.h>
int main(int argc, char *argv[])
{
struct tracefs_instance *inst = NULL;
enum tracefs_tracers t = TRACEFS_TRACER_NOP;
const char *cust = NULL;
const char *buf = NULL;
char **tracers;
int ret;
int ch;
int i;
while ((ch = getopt(argc, argv, "nfgiwdc:B:")) > 0) {
switch (ch) {
case 'f': t = TRACEFS_TRACER_FUNCTION; break;
case 'g': t = TRACEFS_TRACER_FUNCTION_GRAPH; break;
case 'i': t = TRACEFS_TRACER_PREEMPTIRQSOFF; break;
case 'w': t = TRACEFS_TRACER_WAKEUP_RT; break;
case 'd': t = TRACEFS_TRACER_WAKEUP_DL; break;
case 'c':
t = TRACEFS_TRACER_CUSTOM;
cust = optarg;
break;
case 'B':
buf = optarg;
break;
case 'n':
/* nop */
break;
default:
printf("Unknow arg %c\n", ch);
exit(-1);
}
}
if (buf) {
inst = tracefs_instance_create(buf);
if (!inst) {
printf("failed to create instance\n");
exit(-1);
}
}
if (t == TRACEFS_TRACER_CUSTOM)
ret = tracefs_tracer_set(inst, t, cust);
else
ret = tracefs_tracer_set(inst, t);
if (ret < 0) {
if (errno == ENODEV) {
if (cust)
printf("Tracer '%s' not supported by kernel\n", cust);
else
printf("Tracer not supported by kernel\n");
tracers = tracefs_instance_tracers(inst);
printf("Available tracers:");
for (i = 0; tracers && tracers[i]; i++)
printf(" %s", tracers[i]);
tracefs_list_free(tracers);
printf("\n");
} else
perror("Error");
if (inst) {
tracefs_instance_destroy(inst);
tracefs_instance_free(inst);
}
exit(-1);
}
tracefs_instance_free(inst);
exit(0);
}
FILES
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
Steven Rostedt <rostedt@goodmis.org[1]>
Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>
sameeruddin shaik <sameeruddin.shaik8@gmail.com[3]>
REPORTING BUGS
Report bugs to <linux-trace-devel@vger.kernel.org[4]>
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).
NOTES
1. rostedt@goodmis.org
mailto:rostedt@goodmis.org
2. tz.stoyanov@gmail.com
mailto:tz.stoyanov@gmail.com
3. sameeruddin.shaik8@gmail.com
mailto:sameeruddin.shaik8@gmail.com
4. linux-trace-devel@vger.kernel.org
mailto:linux-trace-devel@vger.kernel.org