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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |EXAMPLE |FILES |SEE ALSO |AUTHOR |REPORTING BUGS |LICENSE |RESOURCES |COPYING |NOTES |COLOPHON | |
LIBTRACEFS(3) libtracefs ManualLIBTRACEFS(3)tracefs_iterate_raw_events, tracefs_iterate_stop, tracefs_follow_event, tracefs_follow_missed_events, tracefs_follow_event_clear, tracefs_follow_missed_events_clear, tracefs_iterate_snapshot_events - Iterate over events in the ring buffer
#include <tracefs.h> inttracefs_iterate_raw_events(struct tep_handle *tep, struct tracefs_instance *instance, cpu_set_t *cpus, intcpu_size, int (*callback)(struct tep_event *, struct tep_record *, int, void *), void *callback_context); voidtracefs_iterate_stop(struct tracefs_instance *instance); inttracefs_follow_event(struct tep_handle *tep, struct tracefs_instance *instance, const char *system, const char *event_name, int (*callback)(struct tep_event *, struct tep_record *, int, void *), void *callback_data); inttracefs_follow_missed_events(struct tracefs_instance *instance, int (*callback)(struct tep_event *, struct tep_record *, int, void *), void *callback_data); inttracefs_follow_event_clear(struct tracefs_instance *instance, const char *system, const char *event_name); inttracefs_follow_missed_events_clear(struct tracefs_instance *instance); inttracefs_iterate_snapshot_events(struct tep_handle *tep, struct tracefs_instance *instance, cpu_set_t *cpus, intcpu_size, int (*callback)(struct tep_event *, struct tep_record *, int, void *), void *callback_context);
Trace iterator over raw events. Thetracefs_iterate_raw_events()function will read the tracefs raw data buffers and call the specifiedcallback function for every event it encounters. Events are iterated in sorted order: oldest first. An initializedtep handler is required (Seetracefs_local_events(3)). Ifinstance is NULL, then the toplevel tracefs buffer is used, otherwise the buffer for the correspondinginstance is read. To filter only on a subset of CPUs,cpus andcpu_size may be set to only callcallback with events that occurred on the CPUs specified, otherwise ifcpus is NULL then thecallback function will be called for all events, andcpu_size is ignored. Thecallback function will be called with the following parameters: A pointer to a struct tep_event that corresponds to the type of event the record is; The record representing the event; The CPU that the event occurred on; and a pointer to user specifiedcallback_context. If thecallback returns non-zero, the iteration stops. Thetracefs_iterate_snapshot_events()works the same astracefs_iterate_raw_events()except that it works on the snapshot buffer. Usetracefs_iterate_stop()to force a executingtracefs_iterate_raw_events()to halt. This can be called from either a callback that is called by the iterator (even though a return of non-zero will stop it), or from another thread. Thetracefs_follow_event()is used withtracefs_iterate_raw_events()but intead of the callback being called for every event, it is only called for the specifiedsystem /event_name given to the function. Thecallback is the same as fortracefs_iterate_raw_events(), and the passed incallback_context will be passed to thecallback as well. Note, if it returns something other than 0, it will stop the loop before thecallback oftracefs_iterate_raw_events()is called. Thetracefs_follow_missed_events()will call thecallback when missed events are detected. It will set therecord parameter of the callback to the record that came after the missed events andevent will be of the type of eventrecord is.cpu will be set to the CPU that missed the events, andcallback_data will be the content that was passed in to the function. Thetracefs_follow_event_clear()will remove followers frominstance that matchsystem andevent_name. Ifsystem andevent_name are both NULL, then it will remove all event followers associated toinstance. If justsystem is NULL, then it will remove all followers that follow events that matchevent_name. If justevent_name is NULL, then it will remove all followers that are attached to events that are apart of a system that matchessystem. Thetracefs_follow_missed_events_clear()will remove all followers for missed events.
Thetracefs_iterate_raw_events()function returns -1 in case of an error or 0 otherwise. Bothtracefs_follow_event_clear()andtracefs_follow_missed_events_clear()return 0 on success and -1 on error, or if it found no followers that match and should be removed.
#include <unistd.h> #include <tracefs.h> #include <stdbool.h> #include <signal.h> struct my_struct { bool stopped; }; #define MAX_COUNT 500000 static int counter; static int callback(struct tep_event *event, struct tep_record *record, int cpu, void *data) { struct my_struct *my_data = data; static struct trace_seq seq; if (counter++ > MAX_COUNT) { my_data->stopped = true; return 1; } if (!seq.buffer) trace_seq_init(&seq); tep_print_event(event->tep, &seq, record, "%16s-%-5d [%03d] %6.1000d %s: %s\n", TEP_PRINT_COMM, TEP_PRINT_PID, TEP_PRINT_CPU, TEP_PRINT_TIME, TEP_PRINT_NAME, TEP_PRINT_INFO); trace_seq_terminate(&seq); trace_seq_do_printf(&seq); trace_seq_reset(&seq); return 0; } static int sched_callback(struct tep_event *event, struct tep_record *record, int cpu, void *data) { static struct tep_format_field *prev_pid; static struct tep_format_field *next_pid; unsigned long long pid; int this_pid = *(int *)data; if (!prev_pid) { prev_pid = tep_find_field(event, "prev_pid"); next_pid = tep_find_field(event, "next_pid"); if (!prev_pid || !next_pid) { fprintf(stderr, "No pid fields??\n"); return -1; } } tep_read_number_field(prev_pid, record->data, &pid); if (pid == this_pid) printf("WE ARE LEAVING!\n"); tep_read_number_field(next_pid, record->data, &pid); if (pid == this_pid) printf("WE ARE ARRIVING!\n"); return 0; } static int missed_callback(struct tep_event *event, struct tep_record *record, int cpu, void *data) { printf("OOPS! cpu %d dropped ", cpu); if (record->missed_events > 0) printf("%lld ", record->missed_events); printf("events\n"); return 0; } static struct tracefs_instance *instance; static struct my_struct my_data; static void sig(int s) { tracefs_iterate_stop(instance); my_data.stopped = true; } int main (int argc, char **argv, char **env) { struct tep_handle *tep; int this_pid = getpid(); instance = tracefs_instance_create("my-buffer"); if (!instance) return -1; signal(SIGINT, sig); tracefs_event_enable(instance, NULL, NULL); sleep(1); tracefs_event_disable(instance, NULL, NULL); tep = tracefs_local_events(NULL); tep_load_plugins(tep); tracefs_follow_missed_events(instance, missed_callback, NULL); tracefs_follow_event(tep, instance, "sched", "sched_switch", sched_callback, &this_pid); tracefs_iterate_raw_events(tep, instance, NULL, 0, callback, &my_data); /* Note, the clear here is to show how to clear all followers * in case tracefs_iterate_raw_events() is called again, but * does not want to include the followers. It's not needed * here because tracefs_instance_free() will clean them up. */ tracefs_follow_event_clear(instance, NULL, NULL); tracefs_follow_missed_events_clear(instance); tracefs_instance_destroy(instance); tracefs_instance_free(instance); if (my_data.stopped) { if (counter > MAX_COUNT) printf("Finished max count\n"); else printf("Finished via signal\n"); } return 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]>
Report bugs to <linux-trace-devel@vger.kernel.org[3]>
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. 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 1.8.1 01/02/2025LIBTRACEFS(3)Pages that refer to this page:tracefs_snapshot_snap(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. | |