Add oci-create-layer command to create filesystem changesets

Signed-off-by: Lei Jitang <leijitang@huawei.com>

Makefile

@@ -22,6 +22,7 @@ tools:
 	go build ./cmd/oci-create-runtime-bundle
 	go build ./cmd/oci-unpack
 	go build ./cmd/oci-image-validate
+	go build ./cmd/oci-create-layer
 
 lint:
 	@echo "checking lint"

cmd/oci-create-layer/main.go

@@ -0,0 +1,80 @@
+// Copyright 2016 The Linux Foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"log"
+	"os"
+
+	"github.com/opencontainers/image-tools/image"
+	"github.com/spf13/cobra"
+)
+
+type layerCmd struct {
+	stdout *log.Logger
+	stderr *log.Logger
+	dest   string
+}
+
+func main() {
+	stdout := log.New(os.Stdout, "", 0)
+	stderr := log.New(os.Stderr, "", 0)
+
+	cmd := newLayerCmd(stdout, stderr)
+	if err := cmd.Execute(); err != nil {
+		stderr.Println(err)
+		os.Exit(1)
+	}
+}
+
+func newLayerCmd(stdout, stderr *log.Logger) *cobra.Command {
+	v := &layerCmd{
+		stdout: stdout,
+		stderr: stderr,
+	}
+
+	cmd := &cobra.Command{
+		Use:   "oci-create-layer [child] [parent]",
+		Short: "Create an OCI layer",
+		Long:  `Create an OCI layer based on the changeset between filesystems.`,
+		Run:   v.Run,
+	}
+	cmd.Flags().StringVar(
+		&v.dest, "dest", "",
+		`The dest specify a particular filename where the layer write to`,
+	)
+	return cmd
+}
+
+func (v *layerCmd) Run(cmd *cobra.Command, args []string) {
+	if len(args) != 1 && len(args) != 2 {
+		v.stderr.Print("One or two filesystems are required")
+		if err := cmd.Usage(); err != nil {
+			v.stderr.Println(err)
+		}
+		os.Exit(1)
+	}
+	var err error
+	if len(args) == 1 {
+		err = image.CreateLayer(args[0], "", v.dest)
+	} else {
+		err = image.CreateLayer(args[0], args[1], v.dest)
+	}
+	if err != nil {
+		v.stderr.Printf("create layer failed: %v", err)
+		os.Exit(1)
+	}
+	os.Exit(0)
+}

glide.yaml

@@ -12,3 +12,5 @@ import:
 - package: github.com/pkg/errors
   version: ~0.7.1
 - package: github.com/spf13/cobra
+- package: github.com/containers/storage
+

image/layer.go

@@ -0,0 +1,65 @@
+// Copyright 2016 The Linux Foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package image
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+
+	"github.com/containers/storage/pkg/archive"
+)
+
+func CreateLayer(child, parent, dest string) error {
+	arch, err := Diff(child, parent)
+	if err != nil {
+		return err
+	}
+	defer arch.Close()
+	filename := fmt.Sprintf("%s.tar", filepath.Clean(child))
+	if dest != "" {
+		filename = filepath.Clean(dest)
+	}
+	f, err := os.Create(filename)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	_, err = io.Copy(f, arch)
+	return err
+}
+
+// Diff produces an archive of the changes between the specified
+// layer and its parent layer which may be "".
+func Diff(child, parent string) (arch archive.Archive, err error) {
+	if parent == "" {
+		archive, err := archive.Tar(child, archive.Uncompressed)
+		if err != nil {
+			return nil, err
+		}
+		return archive, nil
+	}
+
+	changes, err := archive.ChangesDirs(child, parent)
+	if err != nil {
+		return nil, err
+	}
+	archive, err := archive.ExportChanges(child, changes, nil, nil)
+	if err != nil {
+		return nil, err
+	}
+	return archive, nil
+}