Man page - tracefs_vprintf(3)

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Manual

LIBTRACEFS

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
EXAMPLE
FILES
SEE ALSO
AUTHOR
REPORTING BUGS
LICENSE
RESOURCES
COPYING
NOTES

NAME

tracefs_print_init, tracefs_print_close, tracefs_printf, tracefs_vprintf - Open, close and write formated strings in the trace buffer.

SYNOPSIS

#include <tracefs.h>

int tracefs_print_init (struct tracefs_instance * instance );
int tracefs_printf (struct tracefs_instance * instance , const char * fmt , ... );
int tracefs_vprintf (struct tracefs_instance * instance , const char * fmt , va_list ap );
void tracefs_print_close (struct tracefs_instance * instance );

DESCRIPTION

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 instance as a first argument. If NULL is passed as instance , the top trace instance is used.

The tracefs_print_init() function initializes the library for writing into the trace buffer of the selected instance . 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 tracefs_print_init() in advance will speed up the writing.

The tracefs_printf() function writes a formatted string in the trace buffer of the selected instance . The fmt argument is a string in printf format, followed by variable arguments ... .

The tracefs_vprintf() function writes a formatted string in the trace buffer of the selected instance . The fmt argument is a string in printf format, followed by list ap of arguments.

The tracefs_print_close() function closes the resources, used by the library for writing in the trace buffer of the selected instance.

RETURN VALUE

The tracefs_print_init() , tracefs_printf() , and tracefs_vprintf() functions return 0 if the operation is successful, or -1 in case of an error.

EXAMPLE

#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();

FILES

tracefs.h
Header file to include in order to have access to the library APIs.
-ltracefs
Linker switch to add when building a program that uses the library.

SEE ALSO

libtracefs (3), libtraceevent (3), trace-cmd (1), Documentation/trace/ftrace.rst from the Linux kernel tree

AUTHOR

Steven Rostedt < rostedt@goodmis.org [1] >
Tzvetomir Stoyanov < tz.stoyanov@gmail.com [2] >

REPORTING BUGS

Report bugs to < linux-trace-devel@vger.kernel.org [3] >

LICENSE

libtracefs is Free Software licensed under the GNU LGPL 2.1

RESOURCES

https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/

COPYING

Copyright (C) 2021 VMware, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL).

NOTES

1.

rostedt@goodmis.org

mailto:rostedt@goodmis.org

2.

tz.stoyanov@gmail.com

mailto:tz.stoyanov@gmail.com

3.

linux-trace-devel@vger.kernel.org

mailto:linux-trace-devel@vger.kernel.org