// VolumeAttachmentSpec is the specification of a VolumeAttachment request.
message VolumeAttachmentSpec {
  // attacher indicates the name of the volume driver that MUST handle this
  // request. This is the name returned by GetPluginName().
  optional string attacher = 1;

  // source represents the volume that should be attached.
  optional VolumeAttachmentSource source = 2;