Implement Windows snapshotter and differ

This implements the Windows snapshotter and diff Apply function.
This allows for Windows layers to be created, and layers to be pulled
from the hub.

Signed-off-by: Darren Stahl <darst@microsoft.com>

mount/mount_windows.go

@@ -1,6 +1,13 @@
 package mount
 
-import "github.com/pkg/errors"
+import (
+	"encoding/json"
+	"path/filepath"
+	"strings"
+
+	"github.com/Microsoft/hcsshim"
+	"github.com/pkg/errors"
+)
 
 var (
 	// ErrNotImplementOnWindows is returned when an action is not implemented for windows
@@ -9,15 +16,73 @@ var (
 
 // Mount to the provided target
 func (m *Mount) Mount(target string) error {
-	return ErrNotImplementOnWindows
+	home, layerID := filepath.Split(m.Source)
+
+	parentLayerPaths, err := m.GetParentPaths()
+	if err != nil {
+		return err
+	}
+
+	var di = hcsshim.DriverInfo{
+		HomeDir: home,
+	}
+
+	if err = hcsshim.ActivateLayer(di, layerID); err != nil {
+		return errors.Wrapf(err, "failed to activate layer %s", m.Source)
+	}
+	defer func() {
+		if err != nil {
+			hcsshim.DeactivateLayer(di, layerID)
+		}
+	}()
+
+	if err = hcsshim.PrepareLayer(di, layerID, parentLayerPaths); err != nil {
+		return errors.Wrapf(err, "failed to prepare layer %s", m.Source)
+	}
+	defer func() {
+		if err != nil {
+			hcsshim.UnprepareLayer(di, layerID)
+		}
+	}()
+	return nil
+}
+
+// ParentLayerPathsFlag is the options flag used to represent the JSON encoded
+// list of parent layers required to use the layer
+const ParentLayerPathsFlag = "parentLayerPaths="
+
+// GetParentPaths of the mount
+func (m *Mount) GetParentPaths() ([]string, error) {
+	var parentLayerPaths []string
+	for _, option := range m.Options {
+		if strings.HasPrefix(option, ParentLayerPathsFlag) {
+			err := json.Unmarshal([]byte(option[len(ParentLayerPathsFlag):]), &parentLayerPaths)
+			if err != nil {
+				return nil, errors.Wrap(err, "failed to unmarshal parent layer paths from mount")
+			}
+		}
+	}
+	return parentLayerPaths, nil
 }
 
 // Unmount the mount at the provided path
 func Unmount(mount string, flags int) error {
-	return ErrNotImplementOnWindows
+	home, layerID := filepath.Split(mount)
+	var di = hcsshim.DriverInfo{
+		HomeDir: home,
+	}
+
+	if err := hcsshim.UnprepareLayer(di, layerID); err != nil {
+		return errors.Wrapf(err, "failed to unprepare layer %s", mount)
+	}
+	if err := hcsshim.DeactivateLayer(di, layerID); err != nil {
+		return errors.Wrapf(err, "failed to deactivate layer %s", mount)
+	}
+
+	return nil
 }
 
-// UnmountAll mounts at the provided path
+// UnmountAll unmounts from the provided path
 func UnmountAll(mount string, flags int) error {
-	return ErrNotImplementOnWindows
+	return Unmount(mount, flags)
 }