NAME

       tracefs_trace_is_on, tracefs_trace_on, tracefs_trace_off, tracefs_trace_on_get_fd, tracefs_trace_on_fd,
       tracefs_trace_off_fd - Functions to enable or disable tracing.

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 descriptor 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[1]>
           Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>

REPORTING BUGS

       Report bugs to <linux-trace-devel@vger.kernel.org[3]>

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) 2021 VMware, 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. tz.stoyanov@gmail.com
           mailto:tz.stoyanov@gmail.com

        3. linux-trace-devel@vger.kernel.org
           mailto:linux-trace-devel@vger.kernel.org

libtracefs 1.8.0                                   04/16/2024                                      LIBTRACEFS(3)