Support trace level.

Signed-off-by: Lantao Liu <lantaol@google.com>

cmd/containerd/main.go

@@ -54,7 +54,7 @@ func main() {
 		},
 		cli.StringFlag{
 			Name:  "log-level,l",
-			Usage: "set the logging level [debug, info, warn, error, fatal, panic]",
+			Usage: "set the logging level [trace, debug, info, warn, error, fatal, panic]",
 		},
 		cli.StringFlag{
 			Name:  "address,a",
@@ -192,7 +192,7 @@ func setLevel(context *cli.Context, config *server.Config) error {
 		l = config.Debug.Level
 	}
 	if l != "" {
-		lvl, err := logrus.ParseLevel(l)
+		lvl, err := log.ParseLevel(l)
 		if err != nil {
 			return err
 		}

log/context.go

@@ -21,6 +21,19 @@ type (
 	loggerKey struct{}
 )
 
+// TraceLevel is the log level for tracing. Trace level is lower than debug level,
+// and is usually used to trace detailed behavior of the program.
+const TraceLevel = logrus.Level(uint32(logrus.DebugLevel + 1))
+
+// ParseLevel takes a string level and returns the Logrus log level constant.
+// It supports trace level.
+func ParseLevel(lvl string) (logrus.Level, error) {
+	if lvl == "trace" {
+		return TraceLevel, nil
+	}
+	return logrus.ParseLevel(lvl)
+}
+
 // WithLogger returns a new context with the provided logger. Use in
 // combination with logger.WithField(s) for great effect.
 func WithLogger(ctx context.Context, logger *logrus.Entry) context.Context {
@@ -38,3 +51,17 @@ func GetLogger(ctx context.Context) *logrus.Entry {
 
 	return logger.(*logrus.Entry)
 }
+
+// Trace logs a message at level Trace with the log entry passed-in.
+func Trace(e *logrus.Entry, args ...interface{}) {
+	if e.Level >= TraceLevel {
+		e.Debug(args...)
+	}
+}
+
+// Tracef logs a message at level Trace with the log entry passed-in.
+func Tracef(e *logrus.Entry, format string, args ...interface{}) {
+	if e.Level >= TraceLevel {
+		e.Debugf(format, args...)
+	}
+}