Add direct unpack support for overlay and aufs

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

diff/apply/apply_linux_test.go

@@ -0,0 +1,79 @@
+// +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 (
+	"testing"
+)
+
+func TestGetOverlayPath(t *testing.T) {
+	good := []string{"upperdir=/test/upper", "lowerdir=/test/lower", "workdir=/test/work"}
+	path, err := getOverlayPath(good)
+	if err != nil {
+		t.Fatalf("Get overlay path failed: %v", err)
+	}
+	if path != "/test/upper" {
+		t.Fatalf("Unexpected upperdir: %q", path)
+	}
+
+	bad := []string{"lowerdir=/test/lower"}
+	_, err = getOverlayPath(bad)
+	if err == nil {
+		t.Fatalf("An error is expected")
+	}
+}
+
+func TestGetAufsPath(t *testing.T) {
+	rwDir := "/test/rw"
+	for _, test := range []struct {
+		options   []string
+		expectErr bool
+	}{
+		{
+			options:   []string{"random:option", "br:" + rwDir + "=rw:/test/ro=ro+wh"},
+			expectErr: false,
+		},
+		{
+			options:   []string{"random:option", "br=" + rwDir + "=rw:/test/ro=ro+wh"},
+			expectErr: false,
+		},
+		{
+			options:   []string{"random:option"},
+			expectErr: true,
+		},
+		{
+			options:   []string{"br:/test/ro=ro+wh"},
+			expectErr: true,
+		},
+	} {
+		path, err := getAufsPath(test.options)
+		if test.expectErr {
+			if err == nil {
+				t.Fatalf("An error is expected")
+			}
+			continue
+		}
+		if err != nil {
+			t.Fatalf("Get aufs path failed: %v", err)
+		}
+		if path != rwDir {
+			t.Fatalf("Unexpected rw dir: %q", path)
+		}
+	}
+}