fs: make sure config is persisted to the config file when using config.Mapper

fs/config.go

@@ -4,6 +4,8 @@ import (
 	"net"
 	"strings"
 	"time"
+
+	"github.com/pkg/errors"
 )
 
 // Global
@@ -17,12 +19,12 @@ var (
 	// implementation from the fs
 	ConfigFileGet = func(section, key string) (string, bool) { return "", false }
 
-	// Set a value into the config file
+	// Set a value into the config file and persist it
 	//
 	// This is a function pointer to decouple the config
 	// implementation from the fs
-	ConfigFileSet = func(section, key, value string) {
-		Errorf(nil, "No config handler to set %q = %q in section %q of the config file", key, value, section)
+	ConfigFileSet = func(section, key, value string) (err error) {
+		return errors.New("no config file set handler")
 	}
 
 	// CountError counts an error.  If any errors have been

fs/config/config.go

@@ -93,7 +93,7 @@ var (
 func init() {
 	// Set the function pointers up in fs
 	fs.ConfigFileGet = FileGetFlag
-	fs.ConfigFileSet = FileSet
+	fs.ConfigFileSet = SetValueAndSave
 }
 
 func getConfigData() *goconfig.ConfigFile {

fs/fs.go

@@ -1150,7 +1150,10 @@ type setConfigFile string
 // Set a config item into the config file
 func (section setConfigFile) Set(key, value string) {
 	Debugf(nil, "Saving config %q = %q in section %q of the config file", key, value, section)
-	ConfigFileSet(string(section), key, value)
+	err := ConfigFileSet(string(section), key, value)
+	if err != nil {
+		Errorf(nil, "Failed saving config %q = %q in section %q of the config file: %v", key, value, section, err)
+	}
 }
 
 // A configmap.Getter to read from the config file