NAME

       tracefs_instance_get_name, tracefs_instance_get_trace_dir, tracefs_instances_walk,
       tracefs_instance_exists, tracefs_instance_get_buffer_size,
       tracefs_instance_set_buffer_size, tracefs_instance_get_buffer_percent,
       tracefs_instance_set_buffer_percent - Helper functions for working with tracing instances.

SYNOPSIS

       #include <tracefs.h>

       const char *tracefs_instance_get_name(struct tracefs_instance *instance);
       const char *tracefs_instance_get_trace_dir(struct tracefs_instance *instance);
       int tracefs_instances_walk(int (*callback)(const char *, void *), void *context);
       bool tracefs_instance_exists(const char *name);
       size_t tracefs_instance_get_buffer_size(struct tracefs_instance *instance, int cpu);
       int tracefs_instance_set_buffer_size(struct tracefs_instance *instance, size_t size, int cpu);
       int tracefs_instance_get_buffer_percent(struct tracefs_instance *instance);
       int tracefs_instance_set_buffer_percent(struct tracefs_instance *instance, int val);

DESCRIPTION

       Helper functions for working with trace instances.

       The tracefs_instance_get_name() function returns the name of the given instance. Note that
       the top instance has no name, the function returns NULL for it.

       The tracefs_instance_get_trace_dir() function returns the tracing directory, where the
       given instance is configured.

       The tracefs_instances_walk() function walks through all configured tracing instances in
       the system and calls callback for each one of them. The context argument is passed to the
       callback, together with the instance name. If the callback returns non-zero, the iteration
       stops. Note, the callback is not called for the top top instance.

       The tracefs_instance_exists() function checks if an instance with the given name exists in
       the system.

       The tracefs_instace_get_buffer_size() returns the size of the ring buffer. If cpu is
       negative, it returns the total size of all the per CPU ring buffers, otherwise it returns
       the size of the per CPU ring buffer for cpu.

       The tracefs_instance_set_buffer_size() function sets the size of the ring buffer. If cpu
       is negative, then it sets all the per CPU ring buffers to size (note the total size is the
       number of CPUs * size). If cpu is specified, then it only sets the size of the per CPU
       ring buffer.

       The tracefs_instance_set_buffer_percent() sets the buffer percent value of the tracing
       ring buffer for instance or the top level buffer if instance is NULL. The buffer percent
       decides when readers on tracefs_cpu_read(3), tracefs_cpu_buffered_read(3),
       tracefs_cpu_write(3) and tracefs_cpu_pipe(3) will block when O_NONBLOCK is not set. The
       value of val must be between 0 and 100, where:

             0   - block until there’s any data in the ring buffer
             1   - block until 1% of the ring buffer sub-buffers are filled
             50  - block until 50% of the ring buffer sub-buffers are filled
             100 - block until the entire ring buffer is filled

       Note, any number from 0 to 100 can be used where it is the percentage of the ring buffer
       that must be filled before a blocked reader will be notified that there’s data to be
       retrieved.

       The tracefs_instance_get_buffer_percent() retrieves the current buffer percent setting of
       the tracing ring buffer for instance or the top level buffer if instance is NULL.

RETURN VALUE

       The tracefs_instance_get_name() returns a string or NULL in case of the top instance. The
       returned string must not be freed.

       The tracefs_instance_get_trace_dir() returns a string or NULL in case of an error. The
       returned string must not be freed.

       The tracefs_instances_walk() function returns 0, if all instances were iterated, 1 if the
       iteration was stopped by the callback, or -1 in case of an error.

       The tracefs_instance_exists() returns true if an instance with the given name exists in
       the system or false otherwise.

       The tracefs_instance_get_buffer_size() returns the size of the ring buffer depending on
       the cpu value passed in, or -1 on error.

       The tracefs_instance_set_buffer_size() returns zero on success and -1 on error.

EXAMPLE

           #include <tracefs.h>

           struct tracefs_instance *inst;
           ....
           char *name = tracefs_instance_get_name(inst);
                   if(name) {
                           /* Got name of the instance */
                   }
           char *dir = tracefs_instance_get_trace_dir(inst);
                   if(dir) {
                           /* Got tracing directory of the instance */
                   }
           ...
           static int instance_walk(char *name, void *context)
           {
                   /* Got instance with name */
                   return 0;
           }
           ...
                   if (tracefs_instances_walk(instance_walk, NULL) < 0) {
                           /* Error walking through the instances */
                   }
           ...
                   if (tracefs_instance_exists("foo")) {
                           /* There is instance with name foo in the system */
                   } else {
                           /* There is no instance with name foo in the system */
                   }

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[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) 2020 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