Merge pull request containerd#4330 from ChengyuZhu6/commit-format

commit: Add an option to nerdctl commit command for media type selection

Author: AkihiroSuda

cmd/nerdctl/container/container_commit.go

@@ -43,6 +43,7 @@ func CommitCommand() *cobra.Command {
 	cmd.Flags().StringArrayP("change", "c", nil, "Apply Dockerfile instruction to the created image (supported directives: [CMD, ENTRYPOINT])")
 	cmd.Flags().BoolP("pause", "p", true, "Pause container during commit")
 	cmd.Flags().StringP("compression", "", "gzip", "commit compression algorithm (zstd or gzip)")
+	cmd.Flags().String("format", "docker", "Format of the committed image (docker or oci)")
 	return cmd
 }
 
@@ -76,6 +77,15 @@ func commitOptions(cmd *cobra.Command) (types.ContainerCommitOptions, error) {
 	if com != string(types.Zstd) && com != string(types.Gzip) {
 		return types.ContainerCommitOptions{}, errors.New("--compression param only supports zstd or gzip")
 	}
+
+	format, err := cmd.Flags().GetString("format")
+	if err != nil {
+		return types.ContainerCommitOptions{}, err
+	}
+	if format != string(types.ImageFormatDocker) && format != string(types.ImageFormatOCI) {
+		return types.ContainerCommitOptions{}, errors.New("--format param only supports docker or oci")
+	}
+
 	return types.ContainerCommitOptions{
 		Stdout:      cmd.OutOrStdout(),
 		GOptions:    globalOptions,
@@ -84,6 +94,7 @@ func commitOptions(cmd *cobra.Command) (types.ContainerCommitOptions, error) {
 		Pause:       pause,
 		Change:      change,
 		Compression: types.CompressionType(com),
+		Format:      types.ImageFormat(format),
 	}, nil
 }
 

docs/command-reference.md

@@ -777,6 +777,7 @@ Flags:
 - :whale: `-c, --change`: Apply Dockerfile instruction to the created image (supported directives: [CMD, ENTRYPOINT])
 - :whale: `-p, --pause`: Pause container during commit (default: true)
 - :nerd_face: `--compression`: Commit compression algorithm (supported values: zstd or gzip) (default: gzip) (zstd is generally better for compression ratio but might not be as widely supported)
+- :nerd_face: `--format`: Format of the committed image (supported values: docker or oci) (default: docker) (docker uses Docker Schema2 media types for compatibility, oci uses OCI image format media types)
 
 ## Image management
 

pkg/api/types/container_types.go

@@ -140,7 +140,7 @@ type ContainerCreateOptions struct {
 	OomKillDisable bool
 	// OomScoreAdjChanged specifies whether the OOM preferences has been changed
 	OomScoreAdjChanged bool
-	// OomScoreAdj specifies the tune container’s OOM preferences (-1000 to 1000, rootless: 100 to 1000)
+	// OomScoreAdj specifies the tune container's OOM preferences (-1000 to 1000, rootless: 100 to 1000)
 	OomScoreAdj int
 	// PidsLimit specifies the tune container pids limit
 	PidsLimit int64
@@ -394,6 +394,8 @@ type ContainerCommitOptions struct {
 	Pause bool
 	// Compression is set commit compression algorithm
 	Compression CompressionType
+	// Format specifies the image format for the committed image (docker or oci)
+	Format ImageFormat
 }
 
 type CompressionType string
@@ -403,6 +405,15 @@ const (
 	Gzip CompressionType = "gzip"
 )
 
+type ImageFormat string
+
+const (
+	// ImageFormatDocker uses Docker Schema2 media types for compatibility
+	ImageFormatDocker ImageFormat = "docker"
+	// ImageFormatOCI uses OCI Image Format media types
+	ImageFormatOCI ImageFormat = "oci"
+)
+
 // ContainerDiffOptions specifies options for `nerdctl (container) diff`.
 type ContainerDiffOptions struct {
 	Stdout io.Writer

pkg/cmd/container/commit.go

@@ -50,6 +50,7 @@ func Commit(ctx context.Context, client *containerd.Client, rawRef string, req s
 		Pause:       options.Pause,
 		Changes:     changes,
 		Compression: options.Compression,
+		Format:      options.Format,
 	}
 
 	walker := &containerwalker.ContainerWalker{

pkg/imgutil/commit/commit.go

@@ -63,6 +63,7 @@ type Opts struct {
 	Pause       bool
 	Changes     Changes
 	Compression types.CompressionType
+	Format      types.ImageFormat
 }
 
 var (
@@ -177,7 +178,7 @@ func Commit(ctx context.Context, client *containerd.Client, container containerd
 	// Sync filesystem to make sure that all the data writes in container could be persisted to disk.
 	Sync()
 
-	diffLayerDesc, diffID, err := createDiff(ctx, id, sn, client.ContentStore(), differ, opts.Compression)
+	diffLayerDesc, diffID, err := createDiff(ctx, id, sn, client.ContentStore(), differ, opts.Compression, opts)
 	if err != nil {
 		return emptyDigest, fmt.Errorf("failed to export layer: %w", err)
 	}
@@ -192,7 +193,7 @@ func Commit(ctx context.Context, client *containerd.Client, container containerd
 		return emptyDigest, fmt.Errorf("failed to apply diff: %w", err)
 	}
 
-	commitManifestDesc, configDigest, err := writeContentsForImage(ctx, snName, baseImg, imageConfig, diffLayerDesc)
+	commitManifestDesc, configDigest, err := writeContentsForImage(ctx, snName, baseImg, imageConfig, diffLayerDesc, opts)
 	if err != nil {
 		return emptyDigest, err
 	}
@@ -287,14 +288,29 @@ func generateCommitImageConfig(ctx context.Context, container containerd.Contain
 }
 
 // writeContentsForImage will commit oci image config and manifest into containerd's content store.
-func writeContentsForImage(ctx context.Context, snName string, baseImg containerd.Image, newConfig ocispec.Image, diffLayerDesc ocispec.Descriptor) (ocispec.Descriptor, digest.Digest, error) {
+func writeContentsForImage(ctx context.Context, snName string, baseImg containerd.Image, newConfig ocispec.Image, diffLayerDesc ocispec.Descriptor, opts *Opts) (ocispec.Descriptor, digest.Digest, error) {
 	newConfigJSON, err := json.Marshal(newConfig)
 	if err != nil {
 		return ocispec.Descriptor{}, emptyDigest, err
 	}
 
+	// Select media types based on format choice
+	var configMediaType, manifestMediaType string
+	switch opts.Format {
+	case types.ImageFormatOCI:
+		configMediaType = ocispec.MediaTypeImageConfig
+		manifestMediaType = ocispec.MediaTypeImageManifest
+	case types.ImageFormatDocker:
+		configMediaType = images.MediaTypeDockerSchema2Config
+		manifestMediaType = images.MediaTypeDockerSchema2Manifest
+	default:
+		// Default to Docker Schema2 for compatibility
+		configMediaType = images.MediaTypeDockerSchema2Config
+		manifestMediaType = images.MediaTypeDockerSchema2Manifest
+	}
+
 	configDesc := ocispec.Descriptor{
-		MediaType: images.MediaTypeDockerSchema2Config,
+		MediaType: configMediaType,
 		Digest:    digest.FromBytes(newConfigJSON),
 		Size:      int64(len(newConfigJSON)),
 	}
@@ -310,7 +326,7 @@ func writeContentsForImage(ctx context.Context, snName string, baseImg container
 		MediaType string `json:"mediaType,omitempty"`
 		ocispec.Manifest
 	}{
-		MediaType: images.MediaTypeDockerSchema2Manifest,
+		MediaType: manifestMediaType,
 		Manifest: ocispec.Manifest{
 			Versioned: specs.Versioned{
 				SchemaVersion: 2,
@@ -326,7 +342,7 @@ func writeContentsForImage(ctx context.Context, snName string, baseImg container
 	}
 
 	newMfstDesc := ocispec.Descriptor{
-		MediaType: images.MediaTypeDockerSchema2Manifest,
+		MediaType: manifestMediaType,
 		Digest:    digest.FromBytes(newMfstJSON),
 		Size:      int64(len(newMfstJSON)),
 	}
@@ -357,14 +373,45 @@ func writeContentsForImage(ctx context.Context, snName string, baseImg container
 }
 
 // createDiff creates a layer diff into containerd's content store.
-func createDiff(ctx context.Context, name string, sn snapshots.Snapshotter, cs content.Store, comparer diff.Comparer, compression types.CompressionType) (ocispec.Descriptor, digest.Digest, error) {
-	opts := make([]diff.Opt, 0)
-	mediaType := images.MediaTypeDockerSchema2LayerGzip
-	if compression == types.Zstd {
-		opts = append(opts, diff.WithMediaType(ocispec.MediaTypeImageLayerZstd))
-		mediaType = images.MediaTypeDockerSchema2LayerZstd
-	}
-	newDesc, err := rootfs.CreateDiff(ctx, name, sn, comparer, opts...)
+func createDiff(ctx context.Context, name string, sn snapshots.Snapshotter, cs content.Store, comparer diff.Comparer, compression types.CompressionType, opts *Opts) (ocispec.Descriptor, digest.Digest, error) {
+	diffOpts := make([]diff.Opt, 0)
+	var mediaType string
+
+	// Select media type based on format and compression
+	switch opts.Format {
+	case types.ImageFormatOCI:
+		// Use OCI media types
+		switch compression {
+		case types.Zstd:
+			diffOpts = append(diffOpts, diff.WithMediaType(ocispec.MediaTypeImageLayerZstd))
+			mediaType = ocispec.MediaTypeImageLayerZstd
+		default:
+			diffOpts = append(diffOpts, diff.WithMediaType(ocispec.MediaTypeImageLayerGzip))
+			mediaType = ocispec.MediaTypeImageLayerGzip
+		}
+	case types.ImageFormatDocker:
+		// Use Docker Schema2 media types for compatibility
+		switch compression {
+		case types.Zstd:
+			diffOpts = append(diffOpts, diff.WithMediaType(ocispec.MediaTypeImageLayerZstd))
+			mediaType = images.MediaTypeDockerSchema2LayerZstd
+		default:
+			diffOpts = append(diffOpts, diff.WithMediaType(ocispec.MediaTypeImageLayerGzip))
+			mediaType = images.MediaTypeDockerSchema2LayerGzip
+		}
+	default:
+		// Default to Docker Schema2 media types for compatibility
+		switch compression {
+		case types.Zstd:
+			diffOpts = append(diffOpts, diff.WithMediaType(ocispec.MediaTypeImageLayerZstd))
+			mediaType = images.MediaTypeDockerSchema2LayerZstd
+		default:
+			diffOpts = append(diffOpts, diff.WithMediaType(ocispec.MediaTypeImageLayerGzip))
+			mediaType = images.MediaTypeDockerSchema2LayerGzip
+		}
+	}
+
+	newDesc, err := rootfs.CreateDiff(ctx, name, sn, comparer, diffOpts...)
 	if err != nil {
 		return ocispec.Descriptor{}, digest.Digest(""), err
 	}