'\" t
.\" Title: libtracecmd
.\" Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot
.\" Date: 02/10/2024
.\" Manual: libtracefs Manual
.\" Source: libtracefs
.\" Language: English
.\"
.TH "LIBTRACECMD" "3" "02/10/2024" "libtracefs" "libtracefs Manual"
.\" -----------------------------------------------------------------
.\" * Define some portability stuff
.\" -----------------------------------------------------------------
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.\" http://bugs.debian.org/507673
.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.ie \n(.g .ds Aq \(aq
.el .ds Aq '
.\" -----------------------------------------------------------------
.\" * set default formatting
.\" -----------------------------------------------------------------
.\" disable hyphenation
.nh
.\" disable justification (adjust text to left margin only)
.ad l
.\" -----------------------------------------------------------------
.\" * MAIN CONTENT STARTS HERE *
.\" -----------------------------------------------------------------
.SH "NAME"
tracecmd_open, tracecmd_open_fd, tracecmd_open_head, tracecmd_init_data, tracecmd_close, tracecmd_set_private, tracecmd_get_private \- 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);
void \fBtracecmd_set_private\fR(struct tracecmd_input *\fIhandle\fR, void *\fIdata\fR);
void *\fBtracecmd_get_private\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 \fBtrace\-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 \fBtracecmd_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 \fBtracecmd_open_fd()\fR function does the same as \fBtracecmd_open()\fR, but works with a file descriptor to a trace file, opened for reading\&.
.sp
The \fBtracecmd_open_head()\fR function is the same as \fBtracecmd_open()\fR, but does not initialize the handler for reading trace data\&. It reads and parses the metadata headers only\&. The \fBtracecmd_init_data()\fR should be used before using the \fItracecmd_read_\fR APIs\&.
.sp
The \fBtracecmd_init_data()\fR function initializes a \fIhandle\fR, allocated with \fBtracecmd_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 \fBtracecmd_close()\fR function frees a \fIhandle\fR, pointer to tracecmd_input structure, previously allocated with \fBtracecmd_open()\fR, \fBtracecmd_open_fd()\fR or \fBtracecmd_open_head()\fR APIs\&.
.sp
The \fBtracecmd_set_private()\fR function allows to add specific \fIdata\fR to the \fIhandle\fR that can be retrieved later\&.
.sp
The \fBtracecmd_get_private()\fR function will retrieve the \fIdata\fR set by \fBtracecmd_set_private()\fR for the given \fIhandle\fR\&.
.SH "RETURN VALUE"
.sp
The \fBtracecmd_open()\fR, \fBtracecmd_open_fd()\fR and \fBtracecmd_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 \fBtracecmd_close()\fR\&. Note that if \fBtracecmd_open_fd()\fR is used to allocate a tracecmd_input handler, when \fBtracecmd_close()\fR is called to close it, that fd will be closed also\&.
.sp
The \fBtracecmd_init_data()\fR function returns \-1 in case of an error or 0 otherwise\&.
.sp
The \fBtracecmd_get_private()\fR returns the \fIdata\fR set by \fBtracecmd_set_private()\fR\&.
.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
#include
static int print_events(struct tracecmd_input *handle, struct tep_record *record, int cpu, void *data)
{
static struct trace_seq seq;
struct tep_handle *tep = tracecmd_get_tep(handle);
const char *file = tracecmd_get_private(handle);
if (!seq\&.buffer)
trace_seq_init(&seq);
trace_seq_reset(&seq);
trace_seq_printf(&seq, "%s: ", file);
tep_print_event(tep, &seq, record, "%6\&.1000d [%03d] %s\-%d %s: %s\en",
TEP_PRINT_TIME, TEP_PRINT_CPU, TEP_PRINT_COMM, TEP_PRINT_PID,
TEP_PRINT_NAME, TEP_PRINT_INFO);
trace_seq_terminate(&seq);
trace_seq_do_printf(&seq);
return 0;
}
int main(int argc, char **argv)
{
struct tracecmd_input *handle;
if (argc < 2) {
printf("usage: %s trace\&.dat\en", argv[0]);
exit(\-1);
}
handle = tracecmd_open(argv[i], 0);
if (!handle)
exit(\-1);
tracecmd_set_private(handles[nr_handles], argv[i]);
tracecmd_iterate_events(handles, NULL, 0, print_events, NULL);
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
\fBlibtracefs(3)\fR, \fBlibtraceevent(3)\fR, \fBtrace\-cmd(1)\fR \fBtrace\-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