SYNOPSIS

#include <tracefs.h>

int tracefs_trace_is_on(struct tracefs_instance *instance);
int tracefs_trace_on(struct tracefs_instance *instance);
int tracefs_trace_off(struct tracefs_instance *instance);
int tracefs_trace_on_get_fd(struct tracefs_instance *instance);
int tracefs_trace_on_fd(int fd);
int tracefs_trace_off_fd(int fd);

DESCRIPTION

This set of functions can be used to check, enable or disable writing to the ring buffer in the given trace instance. The tracing is enabled when writing to the ring buffer is enabled.

The tracefs_trace_is_on() function checks if tracing is enabled for the given instance. If instance is NULL, the top instance is used.

The tracefs_trace_on() and tracefs_trace_off() functions set the tracing in the instance to enable or disable state. If instance is NULL, the top instance is used.

The tracefs_trace_on_get_fd() function returns a file deascriptor to the "tracing_on" file from the given instance. If instance is NULL, the top trace instance is used. The returned descriptor can be used for fast enabling or disabling the tracing of the instance.

The tracefs_trace_on_fd() and tracefs_trace_off_fd() functions set the tracing state to enable or disable using the given fd. This file descriptor must be opened for writing with tracefs_trace_on_get_fd(3) of the desired trace instance. These functions are faster than tracefs_trace_on and tracefs_trace_off.

RETURN VALUE

The tracefs_trace_is_on() function returns 0 if tracing is disable, 1 if it is enabled or -1 in case of an error.

The tracefs_trace_on_get_fd() function returns a file descriptor to "tracing_on" file for reading and writing, which must be closed wuth close(). In case of an error -1 is returned.

The tracefs_trace_on(), tracefs_trace_off(), tracefs_trace_on_fd() and tracefs_trace_off_fd() functions return -1 in case of an error or 0 otherwise.

EXAMPLE

#include <tracefs.h>

        int ret;

        ret = tracefs_trace_is_on(NULL);
        if (ret == 0) {
                /* Tracing is disabled in the top instance */
        } else if (ret == 1) {"
                /* Tracing is enabled in the top instance */
        } else {
                /* Error getting tracing state of the top instance */
        }

        ...

        if (!tracefs_trace_on(NULL)) {
            /* Enabled tracing in the top instance */

            ...

            if (!tracefs_trace_off(NULL)) {
                /* Disabled tracing in the top instance */
            } else {
                /* Error disabling tracing in the top instance */
            }
        } else {
                /* Error enabling tracing in the top instance */
        }

        ...

        int fd = tracefs_trace_on_get_fd(NULL);

        if (fd < 0) {
                /* Error opening tracing_on file */
        }
        ...
        if (!tracefs_trace_on_fd(fd)) {
            /* Enabled tracing in the top instance */

            ...

            if (!tracefs_trace_off_fd(fd)) {
                /* Disabled tracing in the top instance */
            } else {
                /* Error disabling tracing in the top instance */
            }
        } else {
                /* Error enabling tracing in the top instance */
        }

        ...

        close(fd);

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>
Tzvetomir Stoyanov <tz.stoyanov@gmail.com>

REPORTING BUGS

LICENSE

libtracefs is Free Software licensed under the GNU LGPL 2.1

RESOURCES

COPYING

Copyright (C) 2021 VMware, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL).