1libtracefs(3) 2============= 3 4NAME 5---- 6tracefs_trace_is_on, tracefs_trace_on, tracefs_trace_off, tracefs_trace_on_get_fd, 7tracefs_trace_on_fd, tracefs_trace_off_fd - Functions to enable or disable tracing. 8 9SYNOPSIS 10-------- 11[verse] 12-- 13*#include <tracefs.h>* 14 15int *tracefs_trace_is_on*(struct tracefs_instance pass:[*]_instance_); 16int *tracefs_trace_on*(struct tracefs_instance pass:[*]_instance_); 17int *tracefs_trace_off*(struct tracefs_instance pass:[*]_instance_); 18int *tracefs_trace_on_get_fd*(struct tracefs_instance pass:[*]_instance_); 19int *tracefs_trace_on_fd*(int _fd_); 20int *tracefs_trace_off_fd*(int _fd_); 21-- 22 23DESCRIPTION 24----------- 25This set of functions can be used to check, enable or disable writing to the ring buffer in 26the given trace instance. The tracing is enabled when writing to the ring buffer is enabled. 27 28The *tracefs_trace_is_on()* function checks if tracing is enabled for the given _instance_. If 29_instance_ is NULL, the top instance is used. 30 31The *tracefs_trace_on()* and *tracefs_trace_off()* functions set the tracing in the _instance_ 32to enable or disable state. If _instance_ is NULL, the top instance is used. 33 34The *tracefs_trace_on_get_fd()* function returns a file descriptor to the "tracing_on" file from 35the given _instance_. If _instance_ is NULL, the top trace instance is used. The returned descriptor 36can be used for fast enabling or disabling the tracing of the instance. 37 38The *tracefs_trace_on_fd()* and *tracefs_trace_off_fd()* functions set the tracing state to enable 39or disable using the given _fd_. This file descriptor must be opened for writing with 40*tracefs_trace_on_get_fd*(3) of the desired trace instance. These functions are faster than 41*tracefs_trace_on* and *tracefs_trace_off*. 42 43RETURN VALUE 44------------ 45The *tracefs_trace_is_on()* function returns 0 if tracing is disable, 1 if it is enabled or 46-1 in case of an error. 47 48The *tracefs_trace_on_get_fd()* function returns a file descriptor to "tracing_on" 49file for reading and writing, which must be closed wuth close(). In case of an error -1 is returned. 50 51The *tracefs_trace_on()*, *tracefs_trace_off()*, *tracefs_trace_on_fd()* and 52*tracefs_trace_off_fd()* functions return -1 in case of an error or 0 otherwise. 53 54EXAMPLE 55------- 56[source,c] 57-- 58#include <tracefs.h> 59 60 int ret; 61 62 ret = tracefs_trace_is_on(NULL); 63 if (ret == 0) { 64 /* Tracing is disabled in the top instance */ 65 } else if (ret == 1) { 66 /* Tracing is enabled in the top instance */ 67 } else { 68 /* Error getting tracing state of the top instance */ 69 } 70 71 ... 72 73 if (!tracefs_trace_on(NULL)) { 74 /* Enabled tracing in the top instance */ 75 76 ... 77 78 if (!tracefs_trace_off(NULL)) { 79 /* Disabled tracing in the top instance */ 80 } else { 81 /* Error disabling tracing in the top instance */ 82 } 83 } else { 84 /* Error enabling tracing in the top instance */ 85 } 86 87 ... 88 89 int fd = tracefs_trace_on_get_fd(NULL); 90 91 if (fd < 0) { 92 /* Error opening tracing_on file */ 93 } 94 ... 95 if (!tracefs_trace_on_fd(fd)) { 96 /* Enabled tracing in the top instance */ 97 98 ... 99 100 if (!tracefs_trace_off_fd(fd)) { 101 /* Disabled tracing in the top instance */ 102 } else { 103 /* Error disabling tracing in the top instance */ 104 } 105 } else { 106 /* Error enabling tracing in the top instance */ 107 } 108 109 ... 110 111 close(fd); 112-- 113FILES 114----- 115[verse] 116-- 117*tracefs.h* 118 Header file to include in order to have access to the library APIs. 119*-ltracefs* 120 Linker switch to add when building a program that uses the library. 121-- 122 123SEE ALSO 124-------- 125*libtracefs*(3), 126*libtraceevent*(3), 127*trace-cmd*(1) 128 129AUTHOR 130------ 131[verse] 132-- 133*Steven Rostedt* <[email protected]> 134*Tzvetomir Stoyanov* <[email protected]> 135-- 136REPORTING BUGS 137-------------- 138Report bugs to <[email protected]> 139 140LICENSE 141------- 142libtracefs is Free Software licensed under the GNU LGPL 2.1 143 144RESOURCES 145--------- 146https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/ 147 148COPYING 149------- 150Copyright \(C) 2021 VMware, Inc. Free use of this software is granted under 151the terms of the GNU Public License (GPL). 152