code: func (m *VcenterVStorageObjectManager) statDatastoreBacking(ctx *Context, ref types.ManagedObjectReference, id *types.ID) map[types.ID]error {
  	objs := m.objects[ref] // default to checking all objects
  	if id != nil {
  		// check for a specific object
  		objs = map[types.ID]*VStorageObject{
  			*id: objs[*id],
  		}
  	}
  	res := make(map[types.ID]error, len(objs))
  	ds := ctx.Map.Get(ref).(*Datastore)
  	dc := ctx.Map.getEntityDatacenter(ds)
  	fm := ctx.Map.FileManager()
  
  	for _, obj := range objs {
  		backing := obj.Config.Backing.(*types.BaseConfigInfoDiskFileBackingInfo)
  		file, _ := fm.resolve(&dc.Self, backing.FilePath)
  		_, res[obj.Config.Id] = os.Stat(file)
  	}
  
  	return res
  }
docs: // statDatastoreBacking checks if object(s) backing file exists on the given datastore ref.