tracefs_instance_tracers(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | TRACEFS_TRACER ENUMS | RETURN VALUE | ERRORS | EXAMPLE | FILES | SEE ALSO | AUTHOR | REPORTING BUGS | LICENSE | RESOURCES | COPYING | NOTES | COLOPHON

LIBTRACEFS(3)               libtracefs Manual              LIBTRACEFS(3)

NAME         top

       tracefs_instance_tracers, tracefs_tracer_set,
       tracefs_tracer_clear - Enable or disable a tracer in an instance
       or the top level

SYNOPSIS         top

       #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         top

       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         top

       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         top

       Returns 0 on success, or -1 on error.

ERRORS         top

       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         top

           #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         top

           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         top

       libtracefs(3), libtraceevent(3), trace-cmd(1)

AUTHOR         top

           Steven Rostedt <[email protected][1]>
           Tzvetomir Stoyanov <[email protected][2]>
           sameeruddin shaik <[email protected][3]>

REPORTING BUGS         top

       Report bugs to <[email protected][4]>

LICENSE         top

       libtracefs is Free Software licensed under the GNU LGPL 2.1

RESOURCES         top

       https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/ 

COPYING         top

       Copyright (C) 2020 VMware, Inc. Free use of this software is
       granted under the terms of the GNU Public License (GPL).

NOTES         top

        1. [email protected]
           mailto:[email protected]

        2. [email protected]
           mailto:[email protected]

        3. [email protected]
           mailto:[email protected]

        4. [email protected]
           mailto:[email protected]

COLOPHON         top

       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
       2024-06-14.  (At that time, the date of the most recent commit
       that was found in the repository was 2024-05-17.)  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 [email protected]

libtracefs 1.7.0               12/22/2023                  LIBTRACEFS(3)