Provided by: libtracefs-doc_1.7.0-1_all bug

NAME

       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

       #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

       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

       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

           #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

           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)

AUTHOR

           Steven Rostedt <rostedt@goodmis.org[1]>

REPORTING BUGS

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

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) 2022 Google, 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. linux-trace-devel@vger.kernel.org
           mailto:linux-trace-devel@vger.kernel.org