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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 | |
LIBTRACEFS(3) libtracefs ManualLIBTRACEFS(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); inttracefs_tracer_set(struct tracefs_instance *instance, enum tracefs_tracerstracer); inttracefs_tracer_set(struct tracefs_instance *instance, enum tracefs_tracerstracer, const char *name); inttracefs_tracer_clear(struct tracefs_instance *instance);
tracefs_instance_tracerswill return a list of available tracers for a giveninstance (note, an instance may not have the same set of available tracers as the top level). Ifinstance is NULL, then the list of available tracers returned will be for the top level.tracefs_tracer_setenables a tracer in the given instance, defined by theinstance parameter. Ifinstance is NULL, then the top level instance is changed. Iftracer is set toTRACFES_TRACER_CUSTOM then aname 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_cleardisables the tracer for the given instance defined by theinstance variable, or the top level instance if it is NULL. This is the same as callingtracefs_tracer_setwith TRACEFS_TRACER_NOP as thetracer 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 andtracefs_tracer_set()will return an error with errno set to ENODEV, if the kernel does not support thetracer 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:EINVALThetracer parameter is outside the scope of what is defined.ENOMEMMemory allocation error.ENOENTTracers are not supported on the running kernel.ENODEVThe 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 thelibtracefs (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 isnot part of the original manual page), send a mail to man-pages@man7.orglibtracefs 1.7.0 12/22/2023LIBTRACEFS(3)HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |