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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | EXAMPLE | FILES | SEE ALSO | AUTHOR | REPORTING BUGS | LICENSE | RESOURCES | COPYING | NOTES | COLOPHON |
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LIBTRACEFS(3) libtracefs Manual LIBTRACEFS(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);
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);
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.
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.
#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 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
2025-02-02. (At that time, the date of the most recent commit
that was found in the repository was 2024-11-22.) 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 1.8.1 01/02/2025 LIBTRACEFS(3)
Pages that refer to this page: tracefs_synth_create(3)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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