tracefs_file_exists(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | EXAMPLE | FILES | SEE ALSO | AUTHOR | REPORTING BUGS | LICENSE | RESOURCES | COPYING | NOTES | COLOPHON

LIBTRACEFS(3)               libtracefs Manual              LIBTRACEFS(3)

NAME         top

       tracefs_file_exists, tracefs_dir_exists,
       tracefs_instance_get_file, tracefs_instance_get_dir - Work with
       files directories in tracing instances.

SYNOPSIS         top

       #include <tracefs.h>

       bool tracefs_file_exists(struct tracefs_instance *instance, char *name);
       bool tracefs_dir_exists(struct tracefs_instance *instance, char *name);
       char *tracefs_instance_get_file(struct tracefs_instance *instance, const char *file);
       char *tracefs_instance_get_dir(struct tracefs_instance *instance);

DESCRIPTION         top

       This set of APIs can be used to work with trace files in all
       trace instances. Each of these APIs take an instance argument,
       that can be NULL to act on the top level instance. Otherwise, it
       acts on an instance created with tracefs_insance_create(3)

       The tracefs_file_exists() function checks if a file with name
       exists in instance.

       The tracefs_dir_exists() function checks if a directory with name
       exists in instance.

       The tracefs_instance_get_file() function returns the full path of
       the file with given name in instance. Note, it does not check if
       the file exists in the instance.

       The tracefs_instance_get_dir() function returns the full path of
       the directory with given name in instance. Note, it does not
       check if the directory exists in the instance.

RETURN VALUE         top

       The tracefs_file_exists() and tracefs_dir_exists() functions
       return true if the file / directory exist in the given instance
       or false if it does not exist.

       The tracefs_instance_get_file() and tracefs_instance_get_dir()
       functions return a string or NULL in case of an error. The
       returned string must be freed with tracefs_put_tracing_file().

EXAMPLE         top

           #include <tracefs.h>

           struct tracefs_instance *inst = tracefs_instance_create("foo");
                   if (!inst) {
                           /* Error creating a new trace instance */
                           ...
                   }

                   if (tracefs_file_exists(inst,"trace_clock")) {
                           /* The instance foo supports trace clock */
                           char *path, *clock;
                           int size;

                           path =  = tracefs_instance_get_file(inst, "trace_clock")
                           if (!path) {
                                   /* Error getting the path to trace_clock file in instance foo */
                                   ...
                           }
                           ...
                           tracefs_put_tracing_file(path);

                           clock = tracefs_instance_file_read(inst, "trace_clock", &size);
                           if (!clock) {
                                   /* Failed to read trace_clock file in instance foo */
                                   ...
                           }
                           ...
                           free(clock);

                           if (tracefs_instance_file_write(inst, "trace_clock", "global") != strlen("global")) {
                                   /* Failed to set gloabl trace clock in instance foo */
                                   ...
                           }
                   } else {
                           /* The instance foo does not support trace clock */
                   }

                   if (tracefs_dir_exists(inst,"options")) {
                           /* The instance foo supports trace options */
                           char *path = tracefs_instance_get_file(inst, "options");
                           if (!path) {
                                   /* Error getting the path to options directory in instance foo */
                                   ...
                           }

                           tracefs_put_tracing_file(path);
                   } else {
                           /* The instance foo does not support trace options */
                   }

                   ...

                   if (tracefs_instance_is_new(inst))
                           tracefs_instance_destroy(inst);
                   else
                           tracefs_instance_free(inst);
                   ...

                   long long int res;
                   if (tracefs_instance_file_read_number(NULL, "tracing_on", &res) == 0) {
                           if (res == 0) {
                                   /* tracing is disabled in the top instance */
                           } else if (res == 1) {
                                   /* tracing is enabled in the top instance */
                           } else {
                                   /* Unknown tracing state of the top instance */
                           }
                   } else {
                           /* Failed to read integer from tracing_on file */
                   }

                   ...

                   int fd;
                   fd = tracefs_instance_file_open(NULL, "tracing_on", O_WRONLY);
                   if (fd >= 0) {
                           /* Got file descriptor to the tracing_on file from the top instance for writing */
                           ...
                           close(fd);
                   }

FILES         top

           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         top

       libtracefs(3), libtraceevent(3), trace-cmd(1)

AUTHOR         top

           Steven Rostedt <rostedt@goodmis.org[1]>
           Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>

REPORTING BUGS         top

       Report bugs to <linux-trace-devel@vger.kernel.org[3]>

LICENSE         top

       libtracefs is Free Software licensed under the GNU LGPL 2.1

RESOURCES         top

       https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/ 

COPYING         top

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

NOTES         top

        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

COLOPHON         top

       This page is part of the libtracefs (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
       2024-06-14.  (At that time, the date of the most recent commit
       that was found in the repository was 2024-05-17.)  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 is not part of the original
       manual page), send a mail to man-pages@man7.org

libtracefs 1.7.0               12/22/2023                  LIBTRACEFS(3)

Pages that refer to this page: kbuffer_alloc(3)tracefs_event_get_file(3)