1LIBTRACECMD(3) libtracefs Manual LIBTRACECMD(3)
2
6 tracecmd_open, tracecmd_open_fd, tracecmd_open_head,
7 tracecmd_init_data, tracecmd_close - Open and close a trace file.
8
10 #include <trace-cmd.h>
11 struct tracecmd_input *tracecmd_open(const char *file, int flags);
13 struct tracecmd_input *tracecmd_open_fd(int fd, int flags);
14 struct tracecmd_input *tracecmd_open_head(const char *file, int flags);
15 int tracecmd_init_data(struct tracecmd_input *handle);
16 void tracecmd_close(struct tracecmd_input *handle);
17
19 This set of APIs can be used to open and close a trace file recorded by
20 trace-cmd(1) and containing tracing information from ftrace, the
21 official Linux kernel tracer. The opened file is represented by a
22 tracecmd_input structure, all other library APIs that work with the
23 file require a pointer to the structure. The APIs for opening a trace
24 file have a flag input parameter, which controls how the file will be
25 opened and parsed. The flag is a combination of these options:
26 TRACECMD_FL_LOAD_NO_PLUGINS - Do not load any plugins
28 TRACECMD_FL_LOAD_NO_SYSTEM_PLUGINS - Do not load system wide plugins, load only "local only"
29 plugins from user's home directory.
30 The tracecmd_open() function opens a given trace file, parses the
32 metadata headers from the file, allocates and initializes а
33 tracecmd_input handler structure representing the file. It also
34 initializes the handler for reading trace data from the file. The
35 returned handler is ready to be used with tracecmd_read_ APIs.
36 The tracecmd_open_fd() function does the same as tracecmd_open(), but
38 works with a file descriptor to a trace file, opened for reading.
39 The tracecmd_open_head() function is the same as tracecmd_open(), but
41 does not initialize the handler for reading trace data. It reads and
42 parses the metadata headers only. The tracecmd_init_data() should be
43 used before using the tracecmd_read_ APIs.
44 The tracecmd_init_data() function initializes a handle, allocated with
46 tracecmd_open_head(), for reading trace data from the file associated
47 with it. This API must be called before any of the tracecmd_read_ APIs.
48 The tracecmd_close() function frees a handle, pointer to tracecmd_input
50 structure, previously allocated with tracecmd_open(),
51 tracecmd_open_fd() or tracecmd_open_head() APIs.
52
54 The tracecmd_open(), tracecmd_open_fd() and tracecmd_open_head()
55 functions return a pointer to tracecmd_input structure or NULL in case
56 of an error. The returned structure must be free with tracecmd_close().
57 Note that if tracecmd_open_fd() is used to allocate a tracecmd_input
58 handler, when tracecmd_close() is called to close it, that fd will be
59 closed also.
60 The tracecmd_init_data() function returns -1 in case of an error or 0
62 otherwise.
63
65 The are two different use patterns for opening and reading trace data from
66 a trace file, which can be used depending on the use case.
67 1. Open and initialise the trace file in а single step:
69 #include <trace-cmd.h>
71 ...
72 struct tracecmd_input *handle = tracecmd_open("trace.dat");
73 if (!handle) {
74 /* Failed to open trace.dat file */
75 }
76 ...
77 /* Read tracing data from the file, using the handle */
78 ...
79 tracecmd_close(handle);
80 ...
81 int fd;
82 fd = = open("trace.dat", O_RDONLY);
83 if (fd < 0) {
84 /* Failed to open trace file for reading */
85 }
86 handle = tracecmd_open_fd(fd);
87 if (!handle) {
88 close(fd);
89 /* Failed to initialise handler for reading the trace file */
90 }
91 ...
92 /* Read tracing data from the file, using the handle */
93 ...
94 tracecmd_close(handle);
95 ...
96 2. Open and initialise the trace file in two steps. This allows to perform
98 some processing based on metadata, read from the file, before initialising
99 the trace data for reading. Example for such use case is when opening multiple
100 trace files recorded in a same trace session. In that case timestamps of all
101 trace events must be adjusted based on the information from the file's metadata
102 and before reading the trace data.
103 #include <trace-cmd.h>
105 ...
106 struct tracecmd_input *handle = tracecmd_open_head("trace.dat");
107 if (!handle) {
108 /* Failed to open trace.dat file */
109 }
110 ...
111 /* do some processing, before initialising the trace data for reading */
112 ...
113 if (tracecmd_init_data(handle) < 0) {
114 /* Failed to initialize hadle for reading the trace data */
115 }
116 ...
117 /* Read tracing data from the file, using the handle */
118 ...
119 tracecmd_close(handle);
120 ...
121
123 trace-cmd.h
124 Header file to include in order to have access to the library APIs.
125 -ltracecmd
126 Linker switch to add when building a program that uses the library.
127
129 libtracefs(3), libtraceevent(3), trace-cmd(1) trace-cmd.dat(5)
130
132 Steven Rostedt <rostedt@goodmis.org[1]>
133 Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>
134
136 Report bugs to <linux-trace-devel@vger.kernel.org[3]>
137
139 libtracecmd is Free Software licensed under the GNU LGPL 2.1
140
142 https://git.kernel.org/pub/scm/utils/trace-cmd/trace-cmd.git/
143
145 Copyright (C) 2020 VMware, Inc. Free use of this software is granted
146 under the terms of the GNU Public License (GPL).
147
149 1. rostedt@goodmis.org
150 mailto:rostedt@goodmis.org
151 2. tz.stoyanov@gmail.com
153 mailto:tz.stoyanov@gmail.com
154 3. linux-trace-devel@vger.kernel.org
156 mailto:linux-trace-devel@vger.kernel.org
157libtracefs 03/29/2021 LIBTRACECMD(3)