@@ -24,7 +24,15 @@ import (

 const defaultPluginRuntimeDestination = "/run/docker/plugins"

-var manager *Manager

+var (

+	manager *Manager

+

+	/* allowV1PluginsFallback determines daemon's support for V1 plugins.

+	 * When the time comes to remove support for V1 plugins, flipping

+	 * this bool is all that will be needed.

+	 */

+	allowV1PluginsFallback = true

+)

 // ErrNotFound indicates that a plugin was not found locally.

 type ErrNotFound string

@@ -103,7 +111,6 @@ type Manager struct {

 	handlers          map[string]func(string, *plugins.Client)

 	containerdClient  libcontainerd.Client

 	registryService   registry.Service

-	handleLegacy      bool

 	liveRestore       bool

 	shutdown          bool

 	pluginEventLogger eventLogger

@@ -129,7 +136,6 @@ func Init(root string, remote libcontainerd.Remote, rs registry.Service, liveRes

 		nameToID:          make(map[string]string),

 		handlers:          make(map[string]func(string, *plugins.Client)),

 		registryService:   rs,

-		handleLegacy:      true,

 		liveRestore:       liveRestore,

 		pluginEventLogger: evL,

 	}

@@ -151,7 +157,7 @@ func Init(root string, remote libcontainerd.Remote, rs registry.Service, liveRes

 func Handle(capability string, callback func(string, *plugins.Client)) {

 	pluginType := fmt.Sprintf("docker.%s/1", strings.ToLower(capability))

 	manager.handlers[pluginType] = callback

-	if manager.handleLegacy {

+	if allowV1PluginsFallback {

 		plugins.Handle(capability, callback)

 	}

 }

@@ -175,12 +181,15 @@ func (pm *Manager) get(name string) (*plugin, error) {

 // FindWithCapability returns a list of plugins matching the given capability.

 func FindWithCapability(capability string) ([]Plugin, error) {

-	handleLegacy := true

 	result := make([]Plugin, 0, 1)

+

+	/* Daemon start always calls plugin.Init thereby initializing a manager.

+	 * So manager on experimental builds can never be nil, even while

+	 * handling legacy plugins. However, there are legacy plugin unit

+	 * tests where volume subsystem directly talks with the plugin,

+	 * bypassing the daemon. For such tests, this check is necessary.*/

 	if manager != nil {

-		handleLegacy = manager.handleLegacy

 		manager.RLock()

-		defer manager.RUnlock()

 		for _, p := range manager.plugins {

 			for _, typ := range p.PluginObj.Manifest.Interface.Types {

 				if strings.EqualFold(typ.Capability, capability) && typ.Prefix == "docker" {

@@ -189,16 +198,17 @@ func FindWithCapability(capability string) ([]Plugin, error) {

 				}

 			}

 		}

+		manager.RUnlock()

 	}

-	if handleLegacy {

+

+	// Lookup with legacy model.

+	if allowV1PluginsFallback {

 		pl, err := plugins.GetAll(capability)

 		if err != nil {

 			return nil, fmt.Errorf("legacy plugin: %v", err)

 		}

 		for _, p := range pl {

-			if _, ok := manager.nameToID[p.Name()]; !ok {

-				result = append(result, p)

-			}

+			result = append(result, p)

 		}

 	}

 	return result, nil

@@ -210,7 +220,8 @@ func LookupWithCapability(name, capability string) (Plugin, error) {

 		p   *plugin

 		err error

 	)

-	handleLegacy := true

+

+	// Lookup using new model.

 	if manager != nil {

 		fullName := name

 		if named, err := reference.ParseNamed(fullName); err == nil { // FIXME: validate

@@ -224,31 +235,30 @@ func LookupWithCapability(name, capability string) (Plugin, error) {

 			fullName = ref.String()

 		}

 		p, err = manager.get(fullName)

-		if err != nil {

-			if _, ok := err.(ErrNotFound); !ok {

-				return nil, err

+		if err == nil {

+			capability = strings.ToLower(capability)

+			for _, typ := range p.PluginObj.Manifest.Interface.Types {

+				if typ.Capability == capability && typ.Prefix == "docker" {

+					return p, nil

+				}

 			}

-			handleLegacy = manager.handleLegacy

-		} else {

-			handleLegacy = false

+			return nil, ErrInadequateCapability{name, capability}

+		}

+		if _, ok := err.(ErrNotFound); !ok {

+			return nil, err

 		}

 	}

-	if handleLegacy {

+

+	// Lookup using legacy model

+	if allowV1PluginsFallback {

 		p, err := plugins.Get(name, capability)

 		if err != nil {

 			return nil, fmt.Errorf("legacy plugin: %v", err)

 		}

 		return p, nil

-	} else if err != nil {

-		return nil, err

 	}

-	for _, typ := range p.PluginObj.Manifest.Interface.Types {

-		if strings.EqualFold(typ.Capability, capability) && typ.Prefix == "docker" {

-			return p, nil

-		}

-	}

-	return nil, ErrInadequateCapability{name, capability}

+	return nil, err

 }

 // StateChanged updates plugin internals using libcontainerd events.