1 files changed, 92 insertions, 0 deletions
diff --git a/runtime/graphdriver/driver.go b/runtime/graphdriver/driver.go
new file mode 100644
index 0000000000..bd4c2faaca
--- /dev/null
+++ b/runtime/graphdriver/driver.go
@@ -0,0 +1,92 @@
+package graphdriver
+
+import (
+	"fmt"
+	"github.com/dotcloud/docker/archive"
+	"github.com/dotcloud/docker/utils"
+	"os"
+	"path"
+)
+
+type InitFunc func(root string) (Driver, error)
+
+type Driver interface {
+	String() string
+
+	Create(id, parent string, mountLabel string) error
+	Remove(id string) error
+
+	Get(id string) (dir string, err error)
+	Put(id string)
+	Exists(id string) bool
+
+	Status() [][2]string
+
+	Cleanup() error
+}
+
+type Differ interface {
+	Diff(id string) (archive.Archive, error)
+	Changes(id string) ([]archive.Change, error)
+	ApplyDiff(id string, diff archive.ArchiveReader) error
+	DiffSize(id string) (bytes int64, err error)
+}
+
+var (
+	DefaultDriver string
+	// All registred drivers
+	drivers map[string]InitFunc
+	// Slice of drivers that should be used in an order
+	priority = []string{
+		"aufs",
+		"btrfs",
+		"devicemapper",
+		"vfs",
+	}
+)
+
+func init() {
+	drivers = make(map[string]InitFunc)
+}
+
+func Register(name string, initFunc InitFunc) error {
+	if _, exists := drivers[name]; exists {
+		return fmt.Errorf("Name already registered %s", name)
+	}
+	drivers[name] = initFunc
+
+	return nil
+}
+
+func GetDriver(name, home string) (Driver, error) {
+	if initFunc, exists := drivers[name]; exists {
+		return initFunc(path.Join(home, name))
+	}
+	return nil, fmt.Errorf("No such driver: %s", name)
+}
+
+func New(root string) (driver Driver, err error) {
+	for _, name := range []string{os.Getenv("DOCKER_DRIVER"), DefaultDriver} {
+		if name != "" {
+			return GetDriver(name, root)
+		}
+	}
+
+	// Check for priority drivers first
+	for _, name := range priority {
+		if driver, err = GetDriver(name, root); err != nil {
+			utils.Debugf("Error loading driver %s: %s", name, err)
+			continue
+		}
+		return driver, nil
+	}
+
+	// Check all registered drivers if no priority driver is found
+	for _, initFunc := range drivers {
+		if driver, err = initFunc(root); err != nil {
+			continue
+		}
+		return driver, nil
+	}
+	return nil, err
+}