'\" t
.\" Title: libtracecmd
.\" Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot
.\" Date: 05/12/2022
.\" Manual: libtracefs Manual
.\" Source: libtracefs
.\" Language: English
.\"
.TH "LIBTRACECMD" "3" "05/12/2022" "libtracefs" "libtracefs Manual"
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.\" * MAIN CONTENT STARTS HERE *
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.SH "NAME"
tracecmd_open, tracecmd_open_fd, tracecmd_open_head, tracecmd_init_data, tracecmd_close \- Open and close a trace file\&.
.SH "SYNOPSIS"
.sp
.nf
\fB#include \fR
struct tracecmd_input *\fBtracecmd_open\fR(const char *\fIfile\fR, int \fIflags\fR);
struct tracecmd_input *\fBtracecmd_open_fd\fR(int \fIfd\fR, int \fIflags\fR);
struct tracecmd_input *\fBtracecmd_open_head\fR(const char *\fIfile\fR, int \fIflags\fR);
int \fBtracecmd_init_data\fR(struct tracecmd_input *\fIhandle\fR);
void \fBtracecmd_close\fR(struct tracecmd_input *\fIhandle\fR);
.fi
.SH "DESCRIPTION"
.sp
This set of APIs can be used to open and close a trace file recorded by \fItrace\-cmd(1)\fR and containing tracing information from ftrace, the official Linux kernel tracer\&. The opened file is represented by a \fItracecmd_input\fR structure, all other library APIs that work with the file require a pointer to the structure\&. The APIs for opening a trace file have a \fIflag\fR input parameter, which controls how the file will be opened and parsed\&. The \fIflag\fR is a combination of these options:
.sp
.if n \{\
.RS 4
.\}
.nf
TRACECMD_FL_LOAD_NO_PLUGINS \- Do not load any plugins
TRACECMD_FL_LOAD_NO_SYSTEM_PLUGINS \- Do not load system wide plugins, load only "local only"
plugins from user\*(Aqs home directory\&.
.fi
.if n \{\
.RE
.\}
.sp
The \fItracecmd_open()\fR function opens a given trace \fIfile\fR, parses the metadata headers from the file, allocates and initializes а \fItracecmd_input\fR handler structure representing the file\&. It also initializes the handler for reading trace data from the file\&. The returned handler is ready to be used with \fItracecmd_read_\fR APIs\&.
.sp
The \fItracecmd_open_fd()\fR function does the same as \fItracecmd_open()\fR, but works with a file descriptor to a trace file, opened for reading\&.
.sp
The \fItracecmd_open_head()\fR function is the same as \fItracecmd_open()\fR, but does not initialize the handler for reading trace data\&. It reads and parses the metadata headers only\&. The \fItracecmd_init_data()\fR should be used before using the \fItracecmd_read_\fR APIs\&.
.sp
The \fItracecmd_init_data()\fR function initializes a \fIhandle\fR, allocated with \fItracecmd_open_head()\fR, for reading trace data from the file associated with it\&. This API must be called before any of the \fItracecmd_read_\fR APIs\&.
.sp
The \fItracecmd_close()\fR function frees a \fIhandle\fR, pointer to tracecmd_input structure, previously allocated with \fItracecmd_open()\fR, \fItracecmd_open_fd()\fR or \fItracecmd_open_head()\fR APIs\&.
.SH "RETURN VALUE"
.sp
The \fItracecmd_open()\fR, \fItracecmd_open_fd()\fR and \fItracecmd_open_head()\fR functions return a pointer to tracecmd_input structure or NULL in case of an error\&. The returned structure must be free with \fItracecmd_close()\fR\&. Note that if \fItracecmd_open_fd()\fR is used to allocate a tracecmd_input handler, when \fItracecmd_close()\fR is called to close it, that fd will be closed also\&.
.sp
The \fItracecmd_init_data()\fR function returns \-1 in case of an error or 0 otherwise\&.
.SH "EXAMPLE"
.sp
.if n \{\
.RS 4
.\}
.nf
The are two different use patterns for opening and reading trace data from
a trace file, which can be used depending on the use case\&.
1\&. Open and initialise the trace file in а single step:
#include
\&.\&.\&.
struct tracecmd_input *handle = tracecmd_open("trace\&.dat");
if (!handle) {
/* Failed to open trace\&.dat file */
}
\&.\&.\&.
/* Read tracing data from the file, using the handle */
\&.\&.\&.
tracecmd_close(handle);
\&.\&.\&.
int fd;
fd = = open("trace\&.dat", O_RDONLY);
if (fd < 0) {
/* Failed to open trace file for reading */
}
handle = tracecmd_open_fd(fd);
if (!handle) {
close(fd);
/* Failed to initialise handler for reading the trace file */
}
\&.\&.\&.
/* Read tracing data from the file, using the handle */
\&.\&.\&.
tracecmd_close(handle);
\&.\&.\&.
2\&. Open and initialise the trace file in two steps\&. This allows to perform
some processing based on metadata, read from the file, before initialising
the trace data for reading\&. Example for such use case is when opening multiple
trace files recorded in a same trace session\&. In that case timestamps of all
trace events must be adjusted based on the information from the file\*(Aqs metadata
and before reading the trace data\&.
#include
\&.\&.\&.
struct tracecmd_input *handle = tracecmd_open_head("trace\&.dat");
if (!handle) {
/* Failed to open trace\&.dat file */
}
\&.\&.\&.
/* do some processing, before initialising the trace data for reading */
\&.\&.\&.
if (tracecmd_init_data(handle) < 0) {
/* Failed to initialize hadle for reading the trace data */
}
\&.\&.\&.
/* Read tracing data from the file, using the handle */
\&.\&.\&.
tracecmd_close(handle);
\&.\&.\&.
.fi
.if n \{\
.RE
.\}
.SH "FILES"
.sp
.if n \{\
.RS 4
.\}
.nf
\fBtrace\-cmd\&.h\fR
Header file to include in order to have access to the library APIs\&.
\fB\-ltracecmd\fR
Linker switch to add when building a program that uses the library\&.
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.sp
\fIlibtracefs(3)\fR, \fIlibtraceevent(3)\fR, \fItrace\-cmd(1)\fR \fItrace\-cmd\&.dat(5)\fR
.SH "AUTHOR"
.sp
.if n \{\
.RS 4
.\}
.nf
\fBSteven Rostedt\fR <\m[blue]\fBrostedt@goodmis\&.org\fR\m[]\&\s-2\u[1]\d\s+2>
\fBTzvetomir Stoyanov\fR <\m[blue]\fBtz\&.stoyanov@gmail\&.com\fR\m[]\&\s-2\u[2]\d\s+2>
.fi
.if n \{\
.RE
.\}
.SH "REPORTING BUGS"
.sp
Report bugs to <\m[blue]\fBlinux\-trace\-devel@vger\&.kernel\&.org\fR\m[]\&\s-2\u[3]\d\s+2>
.SH "LICENSE"
.sp
libtracecmd is Free Software licensed under the GNU LGPL 2\&.1
.SH "RESOURCES"
.sp
\m[blue]\fBhttps://git\&.kernel\&.org/pub/scm/utils/trace\-cmd/trace\-cmd\&.git/\fR\m[]
.SH "COPYING"
.sp
Copyright (C) 2020 VMware, Inc\&. Free use of this software is granted under the terms of the GNU Public License (GPL)\&.
.SH "NOTES"
.IP " 1." 4
rostedt@goodmis.org
.RS 4
\%mailto:rostedt@goodmis.org
.RE
.IP " 2." 4
tz.stoyanov@gmail.com
.RS 4
\%mailto:tz.stoyanov@gmail.com
.RE
.IP " 3." 4
linux-trace-devel@vger.kernel.org
.RS 4
\%mailto:linux-trace-devel@vger.kernel.org
.RE