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