fix bug that gen layer tar contains duplicated files

Signed-off-by: frankyang <[email protected]>

cache/blobs_linux.go

@@ -43,8 +43,17 @@ func (sr *immutableRef) tryComputeOverlayBlob(ctx context.Context, lower, upper
 	if err != nil {
 		return emptyDesc, false, errors.Wrap(err, "failed to open writer")
 	}
+	cw.Truncate(0)
 	defer func() {
 		if cw != nil {
+			// after commit success cw will be set to nil, if cw isn't nil, error
+			// happened before commit, we should abort this ingest, and because the
+			// error may incured by ctx cancel, use a new context here. And since
+			// cm.Close will unlock this ref in the content store, we invoke abort
+			// to remove the ingest root in advance.
+			if aerr := sr.cm.ContentStore.Abort(context.Background(), ref); aerr != nil {
+				bklog.G(ctx).WithError(aerr).Warnf("failed to abort writer %q", ref)
+			}
 			if cerr := cw.Close(); cerr != nil {
 				bklog.G(ctx).WithError(cerr).Warnf("failed to close writer %q", ref)
 			}