tracefs_event_get_file(3) — Linux manual page

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

LIBTRACEFS(3)               libtracefs Manual              LIBTRACEFS(3)

NAME         top

       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.

SYNOPSIS         top

       #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);
       int tracefs_event_file_write(struct tracefs_instance *instance, const char *system, const char *event,
                                    const char *file, const char *str);
       int tracefs_event_file_append(struct tracefs_instance *instance, const char *system, const char *event,
                                     const char *file, const char *str);
       int tracefs_event_file_clear(struct tracefs_instance *instance, const char *system, const char *event,
                                    const char *file);
       bool tracefs_event_file_exists(struct tracefs_instance *instance, const char *system, const char *event,
                                      const char *file)

DESCRIPTION         top

       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.

       The tracefs_event_get_file() returns the full path of the file
       for the given system and event that is within the given instance.
       If instance is NULL, then the file for the event 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 the tracefs_instance_get_file(3), but is to
       be used to get to event files if the system and event are already
       known.

       The tracefs_event_file_read() reads the content for the event
       file for the given instance or the top level instance if instance
       is NULL. The content of the file is returned and psize is set to
       the amount of data that was read. The returned content must be
       freed with free(3). This acts similar to the
       tracefs_instance_file_read(3), but is to be used to read the
       event file if the system and event are already known.

       The tracefs_event_file_write() writes str to the event file. It
       will truncate anything that is already in that file. This acts
       similar to the tracefs_instance_file_write(3), but is to be used
       to read the event file if the system and event are already known.

       The tracefs_event_file_append() appends str to the event file. It
       will not clear out the file as it writes sting. This acts similar
       to the tracefs_instance_file_append(3), but is to be used to read
       the event file if the system and event are already known.

       The tracefs_event_file_clear() clears the content of the event
       file. This acts similar to the tracefs_instance_file_clear(3),
       but is to be used to read the event file if the system and event
       are already known.

       The tracefs_event_file_exists() returns true if the event file
       exists, and false otherwise. This acts similar to the
       tracefs_instance_file_exists(3), but is to be used to read the
       event file if the system and event are already known.

RETURN VALUE         top

       tracefs_event_get_file() returns the path of the given
       system/event file on success and NULL on error. The return value
       must be freed with tracefs_put_tracing_file(3).

       tracefs_event_file_read() reads the content of the system/event
       file or NULL on error. The return pointer must be freed with
       free(3).

       tracefs_event_file_write() and tracefs_event_file_append()
       returns the number of bytes written to the system/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 the system/event file
       exists for the given instance (or top level if instance is NULL)
       or false otherwise.

EXAMPLE         top

           #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);
           }

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 <rostedt@goodmis.org[1]>

REPORTING BUGS         top

       Report bugs to <linux-trace-devel@vger.kernel.org[2]>

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) 2022 Google, Inc. Free use of this software is
       granted under the terms of the GNU Public License (GPL).

NOTES         top

        1. rostedt@goodmis.org
           mailto:rostedt@goodmis.org

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

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 man-pages@man7.org

libtracefs 1.7.0               12/22/2023                  LIBTRACEFS(3)

Pages that refer to this page: tracefs_synth_create(3)