# tracefs_error_last

## 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.
    


## 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
    


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