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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |EXAMPLE |FILES |SEE ALSO |AUTHOR |REPORTING BUGS |LICENSE |RESOURCES |COPYING |NOTES |COLOPHON | |
LIBTRACEFS(3) libtracefs ManualLIBTRACEFS(3)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.
#include <tracefs.h> const char *tracefs_instance_get_name(struct tracefs_instance *instance); const char *tracefs_instance_get_trace_dir(struct tracefs_instance *instance); inttracefs_instances_walk(int (*callback)(const char *, void *), void *context); booltracefs_instance_exists(const char *name); size_ttracefs_instance_get_buffer_size(struct tracefs_instance *instance, intcpu); inttracefs_instance_set_buffer_size(struct tracefs_instance *instance, size_tsize, intcpu); inttracefs_instance_get_buffer_percent(struct tracefs_instance *instance); inttracefs_instance_set_buffer_percent(struct tracefs_instance *instance, intval);
Helper functions for working with trace instances. Thetracefs_instance_get_name()function returns the name of the giveninstance. Note that the top instance has no name, the function returns NULL for it. Thetracefs_instance_get_trace_dir()function returns the tracing directory, where the giveninstance is configured. Thetracefs_instances_walk()function walks through all configured tracing instances in the system and callscallback for each one of them. Thecontext argument is passed to thecallback, together with the instance name. If thecallback returns non-zero, the iteration stops. Note, thecallback is not called for the top top instance. Thetracefs_instance_exists()function checks if an instance with the givenname exists in the system. Thetracefs_instace_get_buffer_size()returns the size of the ring buffer. Ifcpu 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 forcpu. Thetracefs_instance_set_buffer_size()function sets the size of the ring buffer. Ifcpu is negative, then it sets all the per CPU ring buffers tosize (note the total size is the number of CPUs *size). Ifcpu is specified, then it only sets the size of the per CPU ring buffer. Thetracefs_instance_set_buffer_percent()sets the buffer percent value of the tracing ring buffer forinstance or the top level buffer ifinstance is NULL. The buffer percent decides when readers ontracefs_cpu_read(3),tracefs_cpu_buffered_read(3),tracefs_cpu_write(3) andtracefs_cpu_pipe(3) will block when O_NONBLOCK is not set. The value ofval 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. Thetracefs_instance_get_buffer_percent()retrieves the current buffer percent setting of the tracing ring buffer forinstance or the top level buffer ifinstance is NULL.
Thetracefs_instance_get_name()returns a string or NULL in case of the top instance. The returned string mustnot be freed. Thetracefs_instance_get_trace_dir()returns a string or NULL in case of an error. The returned string mustnot be freed. Thetracefs_instances_walk()function returns 0, if all instances were iterated, 1 if the iteration was stopped by thecallback, or -1 in case of an error. Thetracefs_instance_exists()returns true if an instance with the givenname exists in the system or false otherwise. Thetracefs_instance_get_buffer_size()returns the size of the ring buffer depending on thecpu value passed in, or -1 on error. Thetracefs_instance_set_buffer_size()returns zero on success and -1 on error.
#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 */ }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.
libtracefs(3),libtraceevent(3),trace-cmd(1)
Steven Rostedt<rostedt@goodmis.org[1]>Tzvetomir Stoyanov<tz.stoyanov@gmail.com[2]>
Report bugs to <linux-trace-devel@vger.kernel.org[3]>
libtracefs is Free Software licensed under the GNU LGPL 2.1
https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
Copyright (C) 2020 VMware, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL).
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
This page is part of thelibtracefs (Linux kernel trace file system library) project. Information about the project can be found at ⟨https://www.trace-cmd.org/⟩. If you have a bug report for this manual page, see ⟨https://www.trace-cmd.org/⟩. This page was obtained from the project's upstream Git repository ⟨https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git⟩ on 2025-08-11. (At that time, the date of the most recent commit that was found in the repository was 2025-06-02.) If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up-to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orglibtracefs 1.8.1 01/02/2025LIBTRACEFS(3)HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |