Add create-layer sub command to create filesystem changeset

.gitignore

@@ -1,3 +1,4 @@
 /oci-create-runtime-bundle
 /oci-unpack
 /oci-image-validate
+/oci-create-layer

Makefile

@@ -7,7 +7,8 @@ EPOCH_TEST_COMMIT ?= v0.2.0
 TOOLS := \
 	oci-create-runtime-bundle \
 	oci-image-validate \
-	oci-unpack
+	oci-unpack \
+	oci-create-layer
 
 default: help
 

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)
+}

cmd/oci-create-layer/oci-create-layer.1.md

@@ -0,0 +1,29 @@
+% OCI(1) OCI-CREATE-LAYER User Manuals
+% OCI Community
+% October 2016
+# NAME
+oci-create-layer \- Create filesystem changeset
+
+# SYNOPSIS
+**oci-create-layer** [child] [parent] [flags]
+
+# DESCRIPTION
+`oci-create-layer` creates a filesystem changeset from two layers. It compares child with parent and generates a filsystem diff, pack the diff into a uncompressed tar archive. The output tar archive name is the child name with .tar suffix by default, use `--dest` to specify a custom one.
+
+# OPTIONS
+**--help**
+  Print usage statement
+
+**--dest**
+The dest specify a particular filename where the layer write to
+
+# EXAMPLES
+```
+$ oci-create-layer rootfs-1-s rootfs-1
+$ ls
+rootfs-1  rootfs-1-s  rootfs-1-s.tar
+
+```
+
+# HISTORY
+Oct 2016, Originally compiled by Lei Jitang (coolljt0725 at huawei dot com)

glide.yaml

@@ -12,3 +12,4 @@ import:
 - package: github.com/pkg/errors
   version: ~0.7.1
 - package: github.com/spf13/cobra
+- package: github.com/Sirupsen/logrus

image/layer.go

@@ -0,0 +1,58 @@
+// 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/opencontainers/image-tools/utils"
+)
+
+// CreateLayer cretes filesystem changset from child and parent
+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) (rc io.ReadCloser, err error) {
+	changes, err := utils.ChangesDirs(child, parent)
+	if err != nil {
+		return nil, err
+	}
+	archive, err := utils.ExportChanges(child, changes)
+	if err != nil {
+		return nil, err
+	}
+	return archive, nil
+}