# tracefs_trace_is_on

## 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.
    


## 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
    


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