'\" t
.\"     Title: libtracefs
.\"    Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 10/08/2022
.\"    Manual: libtracefs Manual
.\"    Source: libtracefs 1.5.0
.\"  Language: English
.\"
.TH "LIBTRACEFS" "3" "10/08/2022" "libtracefs 1\&.5\&.0" "libtracefs Manual"
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.nh
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.SH "NAME"
tracefs_print_init, tracefs_print_close, tracefs_printf, tracefs_vprintf \- Open, close and write formated strings in the trace buffer\&.
.SH "SYNOPSIS"
.sp
.nf
\fB#include <tracefs\&.h>\fR

int \fBtracefs_print_init\fR(struct tracefs_instance *\fIinstance\fR);
int \fBtracefs_printf\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIfmt\fR, \fI\&...\fR);
int \fBtracefs_vprintf\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIfmt\fR, va_list \fIap\fR);
void \fBtracefs_print_close\fR(struct tracefs_instance *\fIinstance\fR);
.fi
.SH "DESCRIPTION"
.sp
Set of functions to write formated strings in the trace buffer\&. See Documentation/trace/ftrace\&.rst from the Linux kernel tree for more information about writing data from user space in the trace buffer\&. All these APIs have \fIinstance\fR as a first argument\&. If NULL is passed as \fIinstance\fR, the top trace instance is used\&.
.sp
The \fBtracefs_print_init()\fR function initializes the library for writing into the trace buffer of the selected \fIinstance\fR\&. It is not mandatory to call this API before writing strings, any of the printf APIs will call it automatically, if the library is not yet initialized\&. But calling \fBtracefs_print_init()\fR in advance will speed up the writing\&.
.sp
The \fBtracefs_printf()\fR function writes a formatted string in the trace buffer of the selected \fIinstance\fR\&. The \fIfmt\fR argument is a string in printf format, followed by variable arguments \fI\&...\fR\&.
.sp
The \fBtracefs_vprintf()\fR function writes a formatted string in the trace buffer of the selected \fIinstance\fR\&. The \fIfmt\fR argument is a string in printf format, followed by list \fIap\fR of arguments\&.
.sp
The \fBtracefs_print_close()\fR function closes the resources, used by the library for writing in the trace buffer of the selected instance\&.
.SH "RETURN VALUE"
.sp
The \fBtracefs_print_init()\fR, \fBtracefs_printf()\fR, and \fBtracefs_vprintf()\fR functions return 0 if the operation is successful, or \-1 in case of an error\&.
.SH "EXAMPLE"
.sp
.if n \{\
.RS 4
.\}
.nf
#include <tracefs\&.h>

if (tracefs_print_init(NULL) < 0) {
 /* Failed to initialize the library for writing in the trace buffer of the top trace instance */
}

void foo_print(char *format, \&.\&.\&.)
{
        va_list ap;
        va_start(ap, format);
        if (tracefs_vprintf(NULL, format, ap) < 0) {
                /* Failed to print in the trace buffer */
        }
        va_end(ap);
}

void foo_print_string(char *message)
{
        if (tracefs_printf(NULL, "Message from user space: %s", message) < 0) {
                /* Failed to print in the trace buffer */
        }
}

tracefs_print_close();
.fi
.if n \{\
.RE
.\}
.SH "FILES"
.sp
.if n \{\
.RS 4
.\}
.nf
\fBtracefs\&.h\fR
        Header file to include in order to have access to the library APIs\&.
\fB\-ltracefs\fR
        Linker switch to add when building a program that uses the library\&.
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.sp
\fBlibtracefs\fR(3), \fBlibtraceevent\fR(3), \fBtrace\-cmd\fR(1), Documentation/trace/ftrace\&.rst from the Linux kernel tree
.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
libtracefs is Free Software licensed under the GNU LGPL 2\&.1
.SH "RESOURCES"
.sp
\m[blue]\fBhttps://git\&.kernel\&.org/pub/scm/libs/libtrace/libtracefs\&.git/\fR\m[]
.SH "COPYING"
.sp
Copyright (C) 2021 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