# libtracefs(3) Manual Page

## NAME

tracefs_tracers, tracefs_tracer_available, tracefs_get_clock, tracefs_list_free, tracefs_list_add, tracefs_list_size - Helper functions for working with trace file system.

## SYNOPSIS

    #include <tracefs.h>

    char **tracefs_tracers(const char *tracing_dir);
    bool tracefs_tracer_available(const char *tracing_dir, const char *tracer);
    char *tracefs_get_clock(struct tracefs_instance *instance);
    void tracefs_list_free(char **list);
    char **tracefs_list_add(char *list, const char *string);
    int *tracefs_list_size(char **list);

## DESCRIPTION

Various useful functions for working with trace file system.

The tracefs_tracers() function returns array of strings with the names of supported tracer plugins, located in the given tracing_dir directory. This could be NULL or the location of the tracefs mount point for the trace systems of the local machine, or it may be a path to a copy of the tracefs directory from another machine. The last entry in the array as a NULL pointer. The array must be freed with tracefs_list_free() API.

The tracefs_tracer_available() returns true if the tracer is available in the given tracing_dir_director, and false otherwise.

The tracefs_get_clock() function returns name of the current trace clock, used in the given instance. If instance is NULL, the clock of the main trace instance is returned. The returned string must be freed with free().

The tracefs_list_free() function frees an array of strings, returned by tracefs_event_systems(), tracefs_system_events() and tracefs_tracers() APIs.

The tracefs_list_add() function adds string to the string list. If list is NULL, then a new list is created with the first element a copy of string, and the second element will be a NULL pointer. If list is not NULL, then it is reallocated to include a new element and a NULL terminator, and the new allocated array is returned. The list passed in should be ignored, as it wil be freed if a new one was allocated.

The tracefs_list_size() is a fast way to find out the number of elements in a string array that is to be freed with tracefs_list_free(). Note, this depends on meta data that is created for these lists and will not work on normal string arrays like argv.

## RETURN VALUE

The tracefs_tracers() returns array of strings. The last element in that array is a NULL pointer. The array must be freed with tracefs_list_free() API. In case of an error, NULL is returned.

The tracefs_tracer_available() returns true if the tracer is available, and false otherwise.

The tracefs_get_clock() returns string, that must be freed with free(), or NULL in case of an error.

The tracefs_list_add() returns an allocated string array that must be freed with tracefs_list_free() on success or NULL on error. If NULL is returned, then the passed in list is untouched. Thus, tracefs_list_add() should be treated similarly to realloc(3).

The tracefs_list_size() returns the number of strings in the list. The passed in list must be one that is to be freed with tracefs_list_free() as the list has meta data that is used to determine the size and this does not work on any normal string array like argv.

## EXAMPLE

## 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)

## AUTHOR

    Steven Rostedt <rostedt@goodmis.org>
    Tzvetomir Stoyanov <tz.stoyanov@gmail.com>

## REPORTING BUGS

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

## 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) 2020 VMware, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL).