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NAME | SYNOPSIS | DESCRIPTION | TRACEFS_TRACER ENUMS | RETURN VALUE | ERRORS | EXAMPLE | FILES | SEE ALSO | AUTHOR | REPORTING BUGS | LICENSE | RESOURCES | COPYING | NOTES | COLOPHON |
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LIBTRACEFS(3) libtracefs Manual LIBTRACEFS(3)
tracefs_instance_tracers, tracefs_tracer_set, tracefs_tracer_clear
- Enable or disable a tracer in an instance or the top level
#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);
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.
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.
Returns 0 on success, or -1 on error.
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.
#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);
}
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.
libtracefs(3), libtraceevent(3), trace-cmd(1)
Steven Rostedt <rostedt@goodmis.org[1]>
Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>
sameeruddin shaik <sameeruddin.shaik8@gmail.com[3]>
Report bugs to <linux-trace-devel@vger.kernel.org[4]>
libtracefs is Free Software licensed under the GNU LGPL 2.1
https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
Copyright (C) 2020 VMware, Inc. Free use of this software is
granted under the terms of the GNU Public License (GPL).
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
This page is part of the libtracefs (Linux kernel trace file
system library) project. Information about the project can be
found at ⟨https://www.trace-cmd.org/⟩. If you have a bug report
for this manual page, see ⟨https://www.trace-cmd.org/⟩. This page
was obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-06-02.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
libtracefs 1.7.0 12/22/2023 LIBTRACEFS(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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