// all the contents of the provided bucket+prefix.
func (z *erasureServerPools) Walk(ctx context.Context, bucket, prefix string, results chan<- itemOrErr[ObjectInfo], opts WalkOptions) error {
	if err := checkListObjsArgs(ctx, bucket, prefix, ""); err != nil {
		xioutil.SafeClose(results)
		return err
	}
	parentCtx := ctx
	ctx, cancelCause := context.WithCancelCause(ctx)
	var entries []chan metaCacheEntry