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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_event_get_file, tracefs_event_file_read, tracefs_event_file_write, tracefs_event_file_append, tracefs_event_file_clear, tracefs_event_file_exists - Work with trace event files.
#include <tracefs.h> char *tracefs_event_get_file(struct tracefs_instance *instance, const char *system, const char *event, const char *file); char *tracefs_event_file_read(struct tracefs_instance *instance, const char *system, const char *event, const char *file, int *psize); inttracefs_event_file_write(struct tracefs_instance *instance, const char *system, const char *event, const char *file, const char *str); inttracefs_event_file_append(struct tracefs_instance *instance, const char *system, const char *event, const char *file, const char *str); inttracefs_event_file_clear(struct tracefs_instance *instance, const char *system, const char *event, const char *file); booltracefs_event_file_exists(struct tracefs_instance *instance, const char *system, const char *event, const char *file);
These are functions for accessing tracefs event specific files. These functions act similar to the tracefs instance file functions but are easier to get to if the system and events are known before hand. Thetracefs_event_get_file()returns the full path of thefile for the givensystem andevent that is within the giveninstance. Ifinstance is NULL, then the file for theevent for the top level instance is returned. Note, there is no check to see if the file actually exists or even if the system and event exist. It only creates the path name for such an event if it did exist. This acts similar to thetracefs_instance_get_file(3), but is to be used to get to event files if thesystem andevent are already known. Thetracefs_event_file_read()reads the content for theevent file for the giveninstance or the top level instance ifinstance is NULL. The content of the file is returned andpsize is set to the amount of data that was read. The returned content must be freed withfree(3). This acts similar to thetracefs_instance_file_read(3), but is to be used to read the event file if thesystem andevent are already known. Thetracefs_event_file_write()writesstr to theevent file. It will truncate anything that is already in that file. This acts similar to thetracefs_instance_file_write(3), but is to be used to read the event file if thesystem andevent are already known. Thetracefs_event_file_append()appendsstr to theevent file. It will not clear out the file as it writessting. This acts similar to thetracefs_instance_file_append(3), but is to be used to read the event file if thesystem andevent are already known. Thetracefs_event_file_clear()clears the content of theeventfile. This acts similar to thetracefs_instance_file_clear(3), but is to be used to read the event file if thesystem andevent are already known. Thetracefs_event_file_exists()returns true if theevent file exists, and false otherwise. This acts similar to thetracefs_instance_file_exists(3), but is to be used to read the event file if thesystem andevent are already known.
tracefs_event_get_file()returns the path of the givensystem/event file on success and NULL on error. The return value must be freed withtracefs_put_tracing_file(3).tracefs_event_file_read()reads the content of thesystem/eventfile or NULL on error. The return pointer must be freed withfree(3).tracefs_event_file_write()andtracefs_event_file_append()returns the number of bytes written to thesystem/event file or negative on error.tracefs_event_file_clear()returns zero on success and -1 on error.tracefs_event_file_exists()returns true if thesystem/event file exists for the giveninstance (or top level ifinstance is NULL) or false otherwise.
#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <tracefs.h> int main(int argc, char **argv) { char *system; char *event; char *file; char *cmd = NULL; char *buf; char *str; char ch = 'r'; int size; if (argc < 4) { printf("usage: %s sytem event file [(-a|-w) write | -c]\n" " reads the system/event file or writes if [write is supplied]\n", argv[0]); exit(0); } system = argv[1]; event = argv[2]; file = argv[3]; if (argc > 4) cmd = argv[4]; if (!tracefs_event_file_exists(NULL, system, event, file)) { fprintf(stderr, "File %s/%s/%s does not exist\n", system, event, file); exit(-1); } if (cmd) { if (cmd[0] != '-') ch = cmd[0]; else ch = cmd[1]; if (!ch) ch = 'c'; } switch (ch) { case 'r': buf = tracefs_event_file_read(NULL, system, event, file, &size); if (buf) printf("%s", buf); else fprintf(stderr, "Failed to read %s/%s/%s\n", system, event, file); free(buf); break; case 'w': case 'a': if (argc < 6) { fprintf(stderr, "%s command requires something to write\n", ch == 'w' ? "write" : "append"); exit(-1); } if (ch == 'w') size = tracefs_event_file_write(NULL, system, event, file, argv[5]); else size = tracefs_event_file_append(NULL, system, event, file, argv[5]); if (size < 0) { fprintf(stderr, "Failed to write '%s' to %s/%s/%s\n", argv[5], system, event, file); exit(-1); } break; case 'c': if (tracefs_event_file_clear(NULL, system, event, file) < 0) { fprintf(stderr, "Failed to clear %s/%s/%s\n", system, event, file); exit(-1); } break; default: fprintf(stderr, "Unknown command '%c'\n", ch); exit(-1); } 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]>
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) 2022 Google, 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. 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_synth_create(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. | |