# libtracefs(3) Manual Page

## NAME

tracefs_instance_create, tracefs_instance_destroy, tracefs_instance_alloc, tracefs_instance_free, tracefs_instance_is_new, tracefs_instances, tracefs_instance_clear, tracefs_instance_reset - Manage trace instances.

## SYNOPSIS

    #include <tracefs.h>

    struct tracefs_instance *tracefs_instance_create(const char *name);
    int tracefs_instance_destroy(struct tracefs_instance *instance);
    struct tracefs_instance *tracefs_instance_alloc(const char *tracing_dir, const char *name);
    void tracefs_instance_free(struct tracefs_instance *instance);
    bool tracefs_instance_is_new(struct tracefs_instance *instance);
    char **tracefs_instances(const char *regex);
    void tracefs_instance_clear(struct tracefs_instance *instance);
    void tracefs_instance_reset(struct tracefs_instance *instance);

## DESCRIPTION

This set of functions can be used to manage trace instances. A trace instance is a sub buffer used by the Linux tracing system. Given a unique name, the events enabled in an instance do not affect the main tracing system, nor other instances, as events enabled in the main tracing system or other instances do not affect the given instance.

The tracefs_instance_create() function allocates and initializes a new tracefs_instance structure and returns it. If the instance with name does not yet exist in the system, it will be created. The name could be NULL, then the new tracefs_instance structure is initialized for the top instance. Note that the top instance cannot be created in the system, if it does not exist.

The tracefs_instance_destroy() removes the instance from the system, but does not free the structure. tracefs_instance_free() must still be called on instance.

The tracefs_instance_alloc() function allocates a new tracefs_instance structure for existing trace instance. If the instance does not exist in the system, the function fails. The tracing_dir parameter points to the system trace directory. It can be NULL, then default system trace directory is used. This parameter is useful to allocate instances to trace directories, copied from another machine. The name is the name of the instance, or NULL for the top instance in the given tracing_dir.

The tracefs_instance_free() function frees the tracefs_instance structure, without removing the trace instance from the system.

The tracefs_instance_is_new() function checks if the given instance is newly created by tracefs_instance_create(), or it has been in the system before that.

The tracefs_instances() function returns a list of instances that exist in the system that match the regular expression regex. If regex is NULL, then it will match all instances that exist. The returned list must be freed with tracefs_list_free(3). Note, if no instances are found an empty list is returned and that too needs to be free with tracefs_list_free(3).

The tracefs_instance_clear() function clears the ring buffer of the given instance or the top level ring buffer if instance is NULL.

The tracefs_instance_reset() function resets the given instance to its default state.

## RETURN VALUE

The tracefs_instance_create() and tracefs_instance_alloc() functions return a pointer to a newly allocated tracefs_instance structure. It must be freed with tracefs_instance_free().

The tracefs_instance_destroy() function returns 0 if it succeeds to remove the instance, otherwise it returns -1 if the instance does not exist or it fails to remove it.

The tracefs_instance_is_new() function returns true if the tracefs_instance_create() that allocated instance also created the trace instance in the system, or false if the trace instance already existed in the system when instance was allocated by tracefs_instance_create() or tracefs_instance_alloc().

The tracefs_instances() returns a list of instance names that exist on the system. The list must be freed with tracefs_list_free(3). An empty list is returned if no instance exists that matches regex, and this needs to be freed with tracefs_list_free(3) as well. NULL is returned on error.

The tracefs_instance_clear() returns 0 if it successfully cleared the ring buffer, or -1 on error.

## 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).