Provided by: libtracefs-doc_1.4.2-1_all 
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