LIBTRACEFS(3)

📦
version 1.8.4 · 13 versions
, in arch rolling

💖 LIBTRACEFS(3) — the libtracefs manual, bestie edition 💖

okay so you found the libtracefs page, welcome, grab a snack 🍓 — this is the one about systems and events, and honestly it's giving backstage-pass energy. iykyk.

✨ NAME ✨

tracefs_event_systems, tracefs_system_events, tracefs_event_enable, tracefs_event_disable, tracefs_event_is_enabled — literally the whole friend group that handles trace systems and events 💅

🌸 SYNOPSIS 🌸

#include <tracefs.h>

enum tracefs_event_state {
        TRACEFS_ERROR = -1,
        TRACEFS_ALL_DISABLED = 0,
        TRACEFS_ALL_ENABLED = 1,
        TRACEFS_SOME_ENABLED = 2,
};

char **tracefs_event_systems(const char *tracing_dir);
char **tracefs_system_events(const char *tracing_dir, const char *system);
int tracefs_event_enable(struct tracefs_instance *instance, const char *system,
                           const char *event);
int tracefs_event_disable(struct tracefs_instance *instance, const char *system,
                            const char *event);
enum tracefs_enable_state tracefs_event_is_enabled(struct tracefs_instance *instance,
                         const char *system, const char *event);
ngl, peep that the synopsis declares tracefs_event_is_enabled as returning enum tracefs_enable_state while the enum above it is named tracefs_event_state — that's exactly what the page says, so i'm not touching it. copy it as-is and you're golden 🫶

🦋 DESCRIPTION 🦋

hiii so this is the trace systems and events related APIs. all of them. the whole squad.

💜 tracefs_event_systems()

tracefs_event_systems() returns an array of strings with the names of all registered trace systems, located in the given tracing_dir directory. tracing_dir could be NULL or the location of the tracefs mount point for the trace systems of the local machine, or it may be a path to a copy of the tracefs directory from another machine. the last entry in the array is a NULL pointer. and bestie, you must free that array with the tracefs_list_free() API — no leaking, periodt 🎀

🌈 tracefs_system_events()

tracefs_system_events() returns an array of strings with the names of all registered trace events for the given trace system specified by system, located in the given tracing_dir directory. same deal: tracing_dir could be NULL or the location of the tracefs mount point for the trace systems of the local machine, or it may be a path to a copy of the tracefs directory from another machine. the last entry in the array is a NULL pointer. must be freed with tracefs_list_free() API too. iconic behavior, honestly ✨

🔥 tracefs_event_enable()

tracefs_event_enable() enables a given event based on the system and event passed in for the given instance. the rules, laid out cute:

  • if instance is NULL, then the top level tracing directory is used.
  • if system and event are both NULL, then all events are enabled for the instance.
  • if event is NULL then all events within the system are enabled.
  • if system is NULL, then all systems are searched and any event within a system that matches event is enabled.

both system and event may be regular expressions as defined by regex(3). yes regex, she's invited too 💅

🧚 tracefs_event_disable()

tracefs_event_disable() disables the events that match the system and event parameters for the given instance. what events get disabled follows the same rules as tracefs_event_enable() for matching events. that is: if instance is NULL, then the top level tracing directory is used. if both system and event are NULL then all events are disabled for the given instance, and so on. chain reaction, love that for us 🦋

👑 tracefs_event_is_enabled()

tracefs_event_is_enabled() returns if an event is enabled, a set of events are enabled, a system is enabled, or all events are enabled. the vibes:

  • if both system and event are NULL, then it returns the enable state of all events.
  • if system is not NULL and event is NULL, then it will check if all the events in all the systems that system and return the enable state of those events.
  • if system is NULL and event is not NULL, then it will match all the events in all systems that match event and return their enabled state.
  • if both system and event are not NULL, then it will return the enabled state of all matching events.

the enabled state is defined as:

TRACEFS_ERROR — An error occurred including no event were matched.

TRACEFS_ALL_DISABLED — All matching events are disabled.

TRACEFS_ALL_ENABLED — All matching events are enabled.

TRACEFS_SOME_ENABLED — Some matching events were enabled while others were not. (the messy middle. we've all been there 😭)

⭐ RETURN VALUE ⭐

tracefs_event_systems() and tracefs_system_events() return an array of strings. the last element in that array is a NULL pointer. the array must be freed with tracefs_list_free() API. in case of an error, NULL is returned. no cap.

both tracefs_event_enable() and tracefs_event_disable() return 0 if they found any matching events — and heads up, it does not check the previous status of the event. so if tracefs_event_enable() finds an event that is already enabled, and there are no other errors, then it will return 0. if an error occurs, even if other events were found, it will return -1 and errno will be set. if no errors occur, but no events are found that match the system and event parameters, then -1 is returned and errno is not set. sneaky little distinction, don't sleep on it 🙈

tracefs_event_is_enabled() returns the enabled status of the matching events or TRACEFS_ERROR on error.

🎀 EXAMPLE 🎀

#include <tracefs.h>

char **systems = tracefs_event_systems(NULL);

        if (systems) {
                int i = 0;
                /* Got registered trace systems from the top trace instance */
                while (systems[i]) {
                        char **events = tracefs_system_events(NULL, systems[i]);
                        if (events) {
                                /* Got registered events in system[i] from the top trace instance */
                                int j = 0;

                                while (events[j]) {
                                        /* Got event[j] in system[i] from the top trace instance */
                                        j++;
                                }
                                tracefs_list_free(events);
                        }
                        i++;
                }
                tracefs_list_free(systems);
        }
....
static int records_walk(struct tep_event *tep, struct tep_record *record, int cpu, void *context)
{
        /* Got recorded event on cpu */
        return 0;
}
...
struct tep_handle *tep = tracefs_local_events(NULL);

        if (!tep) {
                /* Failed to initialise tep handler with local events */
                ...
        }

        errno = 0;
        ret = tracefs_event_enable(NULL, "sched", NULL);
        if (ret < 0 && !errno)
                printf("Could not find 'sched' events\n");
        tracefs_event_enable(NULL, "irq", "irq_handler_\(enter\|exit\)");

        if (tracefs_iterate_raw_events(tep, NULL, NULL, 0, records_walk, NULL) < 0) {
                /* Error walking through the recorded raw events */
        }

        /* Disable all events */
        tracefs_event_disable(NULL, NULL, NULL);
        tep_free(tep);

see how it all comes together? main character code fr fr 🔥

🍓 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)

the whole extended universe, go read 'em 💜

🌸 AUTHOR 🌸

  • Steven Rostedt <rostedt@goodmis.org<sup>1</sup>>
  • Tzvetomir Stoyanov <tz.stoyanov@gmail.com<sup>2</sup>>

legends, both of them 👑

🫶 REPORTING BUGS 🫶

Report bugs to <linux-trace-devel@vger.kernel.org<sup>3</sup>>

pls do, we love a bug report that's actually useful 💖

🧚 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. linux-trace-devel@vger.kernel.org mailto:linux-trace-devel@vger.kernel.org

okay that's the whole page, you ate that 🎀✨ this little diva is libtracefs 1.8.4, all dated 10/21/2026 — stay slay, stay tracing, and free your arrays bestie 💖🦋

📦 where this page comes from