'\" t
.\"     Title: libtracefs
.\"    Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 10/08/2022
.\"    Manual: libtracefs Manual
.\"    Source: libtracefs 1.5.0
.\"  Language: English
.\"
.TH "LIBTRACEFS" "3" "10/08/2022" "libtracefs 1\&.5\&.0" "libtracefs Manual"
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.SH "NAME"
tracefs_error_last, tracefs_error_all, tracefs_error_clear \- functions to read and clear the tracefs error log\&.
.SH "SYNOPSIS"
.sp
.nf
\fB#include <tracefs\&.h>\fR

char *\fBtracefs_error_last\fR(struct tracefs_instance *\fIinstance\fR);
char *\fBtracefs_error_all\fR(struct tracefs_instance *\fIinstance\fR);
int \fBtracefs_error_clear\fR(struct tracefs_instance *\fIinstance\fR);
.fi
.SH "DESCRIPTION"
.sp
The \fBtracefs_error_last\fR() 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\&.
.sp
The \fBtracefs_error_all\fR() 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\&.
.sp
The \fBtracefs_error_clear\fR() will clear the error log\&.
.SH "RETURN VALUE"
.sp
Both \fBtracefs_error_last\fR() and \fBtracefs_error_all\fR() 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\&.
.sp
\fBtracefs_error_clear\fR() returns 0 on success or \-1 on error\&.
.SH "EXAMPLE"
.sp
.if n \{\
.RS 4
.\}
.nf
#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\en", 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\en", err);
                else if (errno)
                        perror("Failed reading error log");
                free(err);
        }

        exit(ret);
}
.fi
.if n \{\
.RE
.\}
.SH "FILES"
.sp
.if n \{\
.RS 4
.\}
.nf
\fBtracefs\&.h\fR
        Header file to include in order to have access to the library APIs\&.
\fB\-ltracefs\fR
        Linker switch to add when building a program that uses the library\&.
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.sp
\fBlibtracefs\fR(3), \fBlibtraceevent\fR(3), \fBtrace\-cmd\fR(1)
.SH "AUTHOR"
.sp
.if n \{\
.RS 4
.\}
.nf
\fBSteven Rostedt\fR <\m[blue]\fBrostedt@goodmis\&.org\fR\m[]\&\s-2\u[1]\d\s+2>
\fBTzvetomir Stoyanov\fR <\m[blue]\fBtz\&.stoyanov@gmail\&.com\fR\m[]\&\s-2\u[2]\d\s+2>
.fi
.if n \{\
.RE
.\}
.SH "REPORTING BUGS"
.sp
Report bugs to <\m[blue]\fBlinux\-trace\-devel@vger\&.kernel\&.org\fR\m[]\&\s-2\u[3]\d\s+2>
.SH "LICENSE"
.sp
libtracefs is Free Software licensed under the GNU LGPL 2\&.1
.SH "RESOURCES"
.sp
\m[blue]\fBhttps://git\&.kernel\&.org/pub/scm/libs/libtrace/libtracefs\&.git/\fR\m[]
.SH "COPYING"
.sp
Copyright (C) 2020 VMware, Inc\&. Free use of this software is granted under the terms of the GNU Public License (GPL)\&.
.SH "NOTES"
.IP " 1." 4
rostedt@goodmis.org
.RS 4
\%mailto:rostedt@goodmis.org
.RE
.IP " 2." 4
tz.stoyanov@gmail.com
.RS 4
\%mailto:tz.stoyanov@gmail.com
.RE
.IP " 3." 4
linux-trace-devel@vger.kernel.org
.RS 4
\%mailto:linux-trace-devel@vger.kernel.org
.RE