# tracefs_event_get_file

## 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.
    


## 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
    


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