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

2.

tz.stoyanov@gmail.com

3.

linux-trace-devel@vger.kernel.org