NAME

       tracefs_error_last, tracefs_error_all, tracefs_error_clear - functions to read and clear
       the tracefs error log.

SYNOPSIS

       #include <tracefs.h>

       char *tracefs_error_last(struct tracefs_instance *instance);
       char *tracefs_error_all(struct tracefs_instance *instance);
       int tracefs_error_clear(struct tracefs_instance *instance);

DESCRIPTION

       The tracefs_error_last() returns the last error message in the tracefs error log. Several
       actions that require proper syntax written into the tracefs file system may produce error
       messages in the error log. This function will show the most recent error in the error log.

       The tracefs_error_all() returns all messages saved in the error log. Note, this may not be
       all messages that were ever produced, as the kernel only keeps a limited amount of
       messages, and older ones may be discarded by the kernel.

       The tracefs_error_clear() will clear the error log.

RETURN VALUE

       Both tracefs_error_last() and tracefs_error_all() will return an allocated string an error
       exists in the log, otherwise NULL is returned. If an error occurs, errno will be set,
       otherwise if there is no error messages to display then errno is not touched.

       tracefs_error_clear() returns 0 on success or -1 on error.

EXAMPLE

           #include <stdlib.h>
           #include <unistd.h>
           #include <errno.h>

           #include <tracefs.h>

           int main (int argc, char **argv, char **env)
           {
                   struct tracefs_dynevent *kevent;
                   char *system = NULL;
                   char *kprobe;
                   char *format;
                   char *addr;
                   int arg = 1;
                   int ret;

                   if (argc < 4) {
                           printf("usage: %s [system] kprobe addr fmt\n", argv[0]);
                           exit(-1);
                   }

                   if (argc > 5)
                           system = argv[arg++];

                   kprobe = argv[arg++];
                   addr = argv[arg++];
                   format = argv[arg++];

                   tracefs_error_clear(NULL);
                   kevent = tracefs_dynevent_get(TRACEFS_DYNEVENT_KPROBE, system, kprobe);
                   if (kevent) {
                           tracefs_dynevent_destroy(kevent, true);
                           tracefs_dynevent_free(kevent);
                   }

                   ret = tracefs_kprobe_raw(system, kprobe, addr, format);
                   if (ret < 0) {
                           char *err;

                           perror("Failed creating kprobe");
                           errno = 0;
                           err = tracefs_error_last(NULL);
                           if (err)
                                   fprintf(stderr, "%s\n", err);
                           else if (errno)
                                   perror("Failed reading error log");
                           free(err);
                   }

                   exit(ret);
           }

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