lib/config: Sanity checks on MaxConcurrentWrites (ref #7064) (#7069)

lib/config/folderconfiguration.go

@@ -26,7 +26,11 @@ var (
 	ErrMarkerMissing    = errors.New("folder marker missing (this indicates potential data loss, search docs/forum to get information about how to proceed)")
 )
 
-const DefaultMarkerName = ".stfolder"
+const (
+	DefaultMarkerName          = ".stfolder"
+	maxConcurrentWritesDefault = 2
+	maxConcurrentWritesLimit   = 64
+)
 
 func NewFolderConfiguration(myID protocol.DeviceID, id, label string, fsType fs.FilesystemType, path string) FolderConfiguration {
 	f := FolderConfiguration{
@@ -206,6 +210,12 @@ func (f *FolderConfiguration) prepare() {
 	if f.MarkerName == "" {
 		f.MarkerName = DefaultMarkerName
 	}
+
+	if f.MaxConcurrentWrites <= 0 {
+		f.MaxConcurrentWrites = maxConcurrentWritesDefault
+	} else if f.MaxConcurrentWrites > maxConcurrentWritesLimit {
+		f.MaxConcurrentWrites = maxConcurrentWritesLimit
+	}
 }
 
 // RequiresRestartOnly returns a copy with only the attributes that require