go.mod: github.com/Microsoft/hcsshim v0.10.0-rc.7

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

vendor/github.com/Microsoft/hcsshim/pkg/ociwclayer/export.go

@@ -51,6 +51,8 @@ func ExportLayerToTar(ctx context.Context, w io.Writer, path string, parentLayer
 }
 
 func writeTarFromLayer(ctx context.Context, r wclayer.LayerReader, w io.Writer) error {
+	linkRecords := make(map[[16]byte]string)
+
 	t := tar.NewWriter(w)
 	for {
 		select {
@@ -76,6 +78,27 @@ func writeTarFromLayer(ctx context.Context, r wclayer.LayerReader, w io.Writer)
 				return err
 			}
 		} else {
+			numberOfLinks, fileIDInfo, err := r.LinkInfo()
+			if err != nil {
+				return err
+			}
+			if numberOfLinks > 1 {
+				if linkName, ok := linkRecords[fileIDInfo.FileID]; ok {
+					// We've seen this file before, by another name, so put a hardlink in the tar stream.
+					hdr := backuptar.BasicInfoHeader(name, 0, fileInfo)
+					hdr.Mode = 0644
+					hdr.Typeflag = tar.TypeLink
+					hdr.Linkname = linkName
+					if err := t.WriteHeader(hdr); err != nil {
+						return err
+					}
+					continue
+				}
+
+				// All subsequent names for this file will be hard-linked to this name
+				linkRecords[fileIDInfo.FileID] = filepath.ToSlash(name)
+			}
+
 			err = backuptar.WriteTarFileFromBackupStream(t, r, name, size, fileInfo)
 			if err != nil {
 				return err