preliminary EROFS support for local turboOCI convertion

This is a very basic support for EROFS local OCI convertion.

Unlike EXT4, EROFS doesn't need a `--import` and `export` pair to
generate modified tar headers first since erofs-utils just needs to
parse tar streams once.

Even for parallel convertion, erofs-utils will use EROFS layer blobs
directly.

Also, EROFS doesn't have an explicit `--mkfs` step since `mkfs.erofs`
can handle layer imports directly.

Signed-off-by: Hongzhen Luo <hongzhen.lhz@linux.alibaba.com>

Author: Hongzhen Luo

pkg/snapshot/storage.go

@@ -534,20 +534,32 @@ func (o *snapshotter) constructOverlayBDSpec(ctx context.Context, key string, wr
 		// 1. generate tar meta for oci layer blob
 		// 2. convert local layer.tarmeta to overlaybd
 		// 3. create layer's config
-		log.G(ctx).Infof("generate metadata of layer blob (sn: %s)", id)
-		if err := utils.GenerateTarMeta(ctx, o.overlaybdOCILayerPath(id), o.overlaybdOCILayerMeta(id)); err != nil {
-			log.G(ctx).Errorf("generate tar metadata failed. (sn: %s)", id)
-			return err
-		}
-		opt := &utils.ConvertOption{
-			TarMetaPath:    o.overlaybdOCILayerMeta(id),
-			Workdir:        o.convertTempdir(id),
-			Ext4FSMetaPath: o.magicFilePath(id), // overlaybd.commit
-			Config:         configJSON,
+		var opt *utils.ConvertOption
+		rootfs_type := o.defaultFsType
+		if rootfs_type == "erofs" {
+			opt = &utils.ConvertOption{
+				TarMetaPath:    o.overlaybdOCILayerPath(id),
+				Workdir:        o.convertTempdir(id),
+				Ext4FSMetaPath: o.magicFilePath(id), // overlaybd.commit
+				Config:         configJSON,
+			}
+		} else {
+			log.G(ctx).Infof("generate metadata of layer blob (sn: %s)", id)
+			if err := utils.GenerateTarMeta(ctx, o.overlaybdOCILayerPath(id), o.overlaybdOCILayerMeta(id)); err != nil {
+				log.G(ctx).Errorf("generate tar metadata failed. (sn: %s)", id)
+				return err
+			}
+
+			opt = &utils.ConvertOption{
+				TarMetaPath:    o.overlaybdOCILayerMeta(id),
+				Workdir:        o.convertTempdir(id),
+				Ext4FSMetaPath: o.magicFilePath(id), // overlaybd.commit
+				Config:         configJSON,
+			}
 		}
 		log.G(ctx).Infof("convert layer to turboOCI (sn: %s)", id)
 
-		if err := utils.ConvertLayer(ctx, opt); err != nil {
+		if err := utils.ConvertLayer(ctx, opt, rootfs_type); err != nil {
 			log.G(ctx).Error(err.Error())
 			os.RemoveAll(opt.Workdir)
 			os.Remove(opt.Ext4FSMetaPath)

pkg/utils/cmd.go

@@ -182,7 +182,7 @@ func GenerateTarMeta(ctx context.Context, srcTarFile string, dstTarMeta string)
 }
 
 // ConvertLayer produce a turbooci layer, target is path of ext4.fs.meta
-func ConvertLayer(ctx context.Context, opt *ConvertOption) error {
+func ConvertLayer(ctx context.Context, opt *ConvertOption, fs_type string) error {
 	if opt.Workdir == "" {
 		opt.Workdir = "tmp_conv"
 	}
@@ -199,7 +199,7 @@ func ConvertLayer(ctx context.Context, opt *ConvertOption) error {
 
 	// overlaybd-create
 	args := []string{pathWritableData, pathWritableIndex, "256", "-s", "--turboOCI"}
-	if len(opt.Config.Lowers) == 0 {
+	if fs_type != "erofs" && len(opt.Config.Lowers) == 0 {
 		args = append(args, "--mkfs")
 	}
 	if out, err := exec.CommandContext(ctx, obdBinCreate, args...).CombinedOutput(); err != nil {
@@ -231,9 +231,13 @@ func ConvertLayer(ctx context.Context, opt *ConvertOption) error {
 	}
 	args = []string{
 		opt.TarMetaPath, pathConfig,
-		"--import",
 		"--service_config_path", pathService,
+		"--fstype", fs_type,
 	}
+	if fs_type != "erofs" {
+		args = append(args, "--import")
+	}
+
 	log.G(ctx).Debugf("%s %s", obdBinTurboOCIApply, strings.Join(args, " "))
 	if out, err := exec.CommandContext(ctx, obdBinTurboOCIApply,
 		args...,