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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_snapshot_snap, tracefs_snapshot_clear, tracefs_snapshot_free - API to create, clear and read snapshots
#include <tracefs.h> inttracefs_snapshot_snap(struct tracefs_instance *instance); inttracefs_snapshot_clear(struct tracefs_instance *instance); inttracefs_snapshot_free(struct tracefs_instance *instance);
The Linux kernel tracing provides a "snapshot" feature. The kernel has two ring buffers. One that is written to by the tracing system and another one that is the "snapshot" buffer. When a snapshot happens, the two buffers are swapped, and the current snapshot buffer becomes the one being written to, and the buffer that was being written to becomes the saved snapshot. Note, the snapshot buffer is allocated the first time it is taken, so it is best to take a snapshot at the start before one is needed so that it is allocated and a snapshot is ready, then the snapshot will happen immediately. Thetracefs_snapshot_snap()will allocate (if not already allocated) the snapshot buffer and then take a "snapshot" (swap the main buffer that’s being written to with the allocated snapshot buffer). It will do this to the giveninstance buffer or the top instance ifinstance is NULL. Thetracefs_snapshot_clear()will erase the content of the snapshot buffer for the giveninstance or the top level instance ifinstance is NULL. Thetracefs_snapshot_free()will free the allocated snapshot for the giveninstance or the top level instance ifinstance is NULL. That is, if another call totracefs_snapshot_snap()is done after this, then it will need to allocate the snapshot buffer again before it can take a snapshot. This function should be used to free up the kernel memory used by hte snapshot buffer when no longer in use.
Thetracefs_snapshot_snap(),tracefs_snapshot_clear()and thetracefs_snapshot_free()all return 0 on success and -1 on failure.
#include <stdlib.h> #include <stdio.h> #include <tracefs.h> static int callback(struct tep_event *event, struct tep_record *record, int cpu, void *data) { static struct trace_seq seq; struct tep_handle *tep = event->tep; if (!seq.buffer) trace_seq_init(&seq); trace_seq_reset(&seq); tep_print_event(tep, &seq, record, "[%03d] %s-%d %6.1000d\t%s: %s\n", TEP_PRINT_CPU, TEP_PRINT_COMM, TEP_PRINT_PID, TEP_PRINT_TIME, TEP_PRINT_NAME, TEP_PRINT_INFO); trace_seq_do_printf(&seq); return 0; } int main (int argc, char **argv) { struct tracefs_instance *instance; struct tep_handle *tep; char *line = NULL; size_t len = 0; int ret; instance = tracefs_instance_create("my_snapshots"); if (!instance) { perror("creating instance"); exit(-1); } tep = tracefs_local_events(NULL); if (!tep) { perror("reading event formats"); goto out; } /* Make sure the snapshot buffer is allocated */ ret = tracefs_snapshot_snap(instance); if (ret < 0) goto out; ret = tracefs_event_enable(instance, "sched", NULL); if (ret < 0) { perror("enabling event"); goto out; } for (;;) { printf("Hit enter without text to take snapshot!\n"); printf("Enter any text to display the snapshot\n"); printf("Enter 'quit' to exit\n"); getline(&line, &len, stdin); ret = tracefs_snapshot_snap(instance); if (ret < 0) { perror("taking snapshot"); goto out; } if (!line) break; if (strlen(line) < 2) continue; if (strncmp(line, "quit", 4) == 0) break; tracefs_iterate_snapshot_events(tep, instance, NULL, 0, callback, NULL); } free(line); tracefs_instance_clear(instance); out: tracefs_snapshot_free(instance); tracefs_event_disable(instance, "sched", NULL); tracefs_instance_destroy(instance); tracefs_instance_free(instance); 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.
tracefs_iterate_snapshot_events(3)libtracefs(3),libtraceevent(3),trace-cmd(1)
Steven Rostedt<rostedt@goodmis.org[1]>
Report bugs to <linux-trace-devel@vger.kernel.org[2]>
libtracefs is Free Software licensed under the GNU LGPL 2.1
https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
Copyright (C) 2023 Google, LLC. 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. 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_cpu_open(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. | |