Add logging message for debug/error

This changes adds logging message:debug and error. fmt.Errorf() is
wrapped by logging.Errorf() hence all error message is also put to
log file. logging.Debugf() is called at almost function call, so
we could track the code by logging message.

logging/logging.go

@@ -35,8 +35,9 @@ const (
 )
 
 var loggingStderr bool
-var loggingFp	*os.File
+var loggingFp *os.File
 var loggingLevel Level
+
 const defaultTimestampFormat = time.RFC3339
 
 func (l Level) String() string {
@@ -75,8 +76,9 @@ func Debugf(format string, a ...interface{}) {
 	Printf(DebugLevel, format, a...)
 }
 
-func Errorf(format string, a ...interface{}) {
+func Errorf(format string, a ...interface{}) error {
 	Printf(ErrorLevel, format, a...)
+	return fmt.Errorf(format, a...)
 }
 
 func Panicf(format string, a ...interface{}) {
@@ -86,7 +88,7 @@ func Panicf(format string, a ...interface{}) {
 	Printf(PanicLevel, "========= Stack trace output end ========")
 }
 
-func GetLoggingLevel (levelStr string) Level {
+func GetLoggingLevel(levelStr string) Level {
 	switch strings.ToLower(levelStr) {
 	case "debug":
 		return DebugLevel
@@ -99,18 +101,18 @@ func GetLoggingLevel (levelStr string) Level {
 	return UnknownLevel
 }
 
-func SetLogLevel (levelStr string) {
+func SetLogLevel(levelStr string) {
 	level := GetLoggingLevel(levelStr)
 	if level < MaxLevel {
 		loggingLevel = level
 	}
 }
 
-func SetLogStderr (enable bool) {
+func SetLogStderr(enable bool) {
 	loggingStderr = enable
 }
 
-func SetLogFile (filename string) {
+func SetLogFile(filename string) {
 	if filename == "" {
 		return
 	}