Add direct unpack support for overlay and aufs

Signed-off-by: Lantao Liu <lantaol@google.com>

diff/apply/apply_linux.go

@@ -0,0 +1,90 @@
+// +build linux
+
+/*
+   Copyright The containerd Authors.
+
+   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 apply
+
+import (
+	"context"
+	"io"
+	"strings"
+
+	"github.com/containerd/containerd/archive"
+	"github.com/containerd/containerd/mount"
+	"github.com/pkg/errors"
+)
+
+func apply(ctx context.Context, mounts []mount.Mount, r io.Reader) error {
+	switch {
+	case len(mounts) == 1 && mounts[0].Type == "overlay":
+		path, err := getOverlayPath(mounts[0].Options)
+		if err != nil {
+			return err
+		}
+		_, err = archive.Apply(ctx, path, r,
+			archive.WithConvertWhiteout(archive.OverlayConvertWhiteout))
+		return err
+	case len(mounts) == 1 && mounts[0].Type == "aufs":
+		path, err := getAufsPath(mounts[0].Options)
+		if err != nil {
+			return err
+		}
+		_, err = archive.Apply(ctx, path, r,
+			archive.WithConvertWhiteout(archive.AufsConvertWhiteout))
+		return err
+	default:
+		return mount.WithTempMount(ctx, mounts, func(root string) error {
+			_, err := archive.Apply(ctx, root, r)
+			return err
+		})
+	}
+}
+
+func getOverlayPath(options []string) (string, error) {
+	const upperdirPrefix = "upperdir="
+	for _, o := range options {
+		if strings.HasPrefix(o, upperdirPrefix) {
+			return strings.TrimPrefix(o, upperdirPrefix), nil
+		}
+	}
+	return "", errors.New("upperdir not found")
+}
+
+func getAufsPath(options []string) (string, error) {
+	const (
+		sep       = ":"
+		brPrefix1 = "br:"
+		brPrefix2 = "br="
+		rwSuffix  = "=rw"
+	)
+	for _, o := range options {
+		if strings.HasPrefix(o, brPrefix1) {
+			o = strings.TrimPrefix(o, brPrefix1)
+		} else if strings.HasPrefix(o, brPrefix2) {
+			o = strings.TrimPrefix(o, brPrefix2)
+		} else {
+			continue
+		}
+		for _, b := range strings.Split(o, sep) {
+			if strings.HasSuffix(b, rwSuffix) {
+				return strings.TrimSuffix(b, rwSuffix), nil
+			}
+		}
+		break
+	}
+	return "", errors.New("rw branch not found")
+}