From 86dd2473c1351df87520111b1b1ba9953f9e5f09 Mon Sep 17 00:00:00 2001
From: Solomon Hykes <solomon@dotcloud.com>
Date: Fri, 1 Nov 2013 05:06:49 +0000
Subject: [PATCH] Work In Progress: devmapper backend plugin

---
 devmapper/plugin.go | 72 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 devmapper/plugin.go

diff --git a/devmapper/plugin.go b/devmapper/plugin.go
new file mode 100644
index 0000000000..e0534b4dca
--- /dev/null
+++ b/devmapper/plugin.go
@@ -0,0 +1,72 @@
+package devmapper
+
+import (
+	"github.com/dotcloud/docker/archive"
+)
+
+type Image interface {
+	ID() string
+	Parent() (Image, error)
+	Path() string
+}
+
+type DMBackend struct {
+	*DeviceSet
+}
+
+func (b *DMBackend) Init(home string) error {
+	b.DeviceSet = NewDeviceSet(home)
+	if err := b.DeviceSet.ensureInit(); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (b *DMBackend) Shutdown() error {
+	return b.DeviceSet.Shutdown()
+}
+
+func (b *DMBackend) Create(img image, layer archive.Archive) error {
+	// Determine the source of the snapshot (parent id or init device)
+	var parentID string
+	if parent, err := img.Parent(); err != nil {
+		return err
+	} else if parent != nil {
+		parentID = parent.ID()
+	}
+	// Create the device for this image by snapshotting source
+	if err := b.DeviceSet.AddDevice(img.ID(), parentID); err != nil {
+		return err
+	}
+	// Mount the device in rootfs
+	mp := b.mountpoint(id)
+	if err := os.MkdirAll(mp); err != nil {
+		return err
+	}
+	if err := b.DeviceSet.MountDevice(id, mp, false); err != nil {
+		return err
+	}
+	// Apply the layer as a diff 
+	if layer != nil {
+		if err := archive.ApplyLayer(mp, layer); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+
+func (b *DMBackend) mountpoint(id string) string {
+	if b.home == "" {
+		return ""
+	}
+	return path.Join(b.home, "mnt", id)
+}
+
+func (b *DMBackend) Changes(img *Image, dest string) ([]Change, error) {
+	return nil, fmt.Errorf("Not implemented")
+}
+
+func (b *DMBackend) Layer(img *Image, dest string) (Archive, error) {
+	return nil, fmt.Errorf("Not implemented")
+}