log: define OutputFormat type

Strong-type the format.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit dd67240)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cmd/containerd/command/main.go

@@ -352,7 +352,7 @@ func setLogLevel(context *cli.Context, config *srvconfig.Config) error {
 }
 
 func setLogFormat(config *srvconfig.Config) error {
-	f := config.Debug.Format
+	f := log.OutputFormat(config.Debug.Format)
 	if f == "" {
 		f = log.TextFormat
 	}

log/context.go

@@ -96,17 +96,20 @@ func GetLevel() Level {
 	return logrus.GetLevel()
 }
 
+// OutputFormat specifies a log output format.
+type OutputFormat string
+
 // Supported log output formats.
 const (
 	// TextFormat represents the text logging format.
-	TextFormat = "text"
+	TextFormat OutputFormat = "text"
 
 	// JSONFormat represents the JSON logging format.
-	JSONFormat = "json"
+	JSONFormat OutputFormat = "json"
 )
 
 // SetFormat sets the log output format ([TextFormat] or [JSONFormat]).
-func SetFormat(format string) error {
+func SetFormat(format OutputFormat) error {
 	switch format {
 	case TextFormat:
 		logrus.SetFormatter(&logrus.TextFormatter{