plugins.go

/*
Copyright 2014 Google Inc. All rights reserved.

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 volume

import (
	"fmt"
	"strings"
	"sync"

	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/client"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/types"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/util"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/util/errors"
	"github.com/golang/glog"
)

// VolumePlugin is an interface to volume plugins that can be used on a
// kubernetes node (e.g. by kubelet) to instantiate and manage volumes.
type VolumePlugin interface {
	// Init initializes the plugin.  This will be called exactly once
	// before any New* calls are made - implementations of plugins may
	// depend on this.
	Init(host VolumeHost)

	// Name returns the plugin's name.  Plugins should use namespaced names
	// such as "example.com/volume".  The "kubernetes.io" namespace is
	// reserved for plugins which are bundled with kubernetes.
	Name() string

	// CanSupport tests whether the plugin supports a given volume
	// specification from the API.  The spec pointer should be considered
	// const.
	CanSupport(spec *api.Volume) bool

	// NewBuilder creates a new volume.Builder from an API specification.
	// Ownership of the spec pointer in *not* transferred.
	// - spec: The api.Volume spec
	// - podRef: a reference to the enclosing pod
	NewBuilder(spec *api.Volume, podRef *api.ObjectReference) (Builder, error)

	// NewCleaner creates a new volume.Cleaner from recoverable state.
	// - name: The volume name, as per the api.Volume spec.
	// - podUID: The UID of the enclosing pod
	NewCleaner(name string, podUID types.UID) (Cleaner, error)
}

// PersistentVolumePlugin is an extended interface of VolumePlugin and is used
// by volumes that want to provide long term persistence of data
type PersistentVolumePlugin interface {
	VolumePlugin
	// GetAccessModes describes the ways a given volume can be accessed/mounted.
	GetAccessModes() []api.AccessModeType
}

// VolumeHost is an interface that plugins can use to access the kubelet.
type VolumeHost interface {
	// GetPluginDir returns the absolute path to a directory under which
	// a given plugin may store data.  This directory might not actually
	// exist on disk yet.  For plugin data that is per-pod, see
	// GetPodPluginDir().
	GetPluginDir(pluginName string) string

	// GetPodVolumeDir returns the absolute path a directory which
	// represents the named volume under the named plugin for the given
	// pod.  If the specified pod does not exist, the result of this call
	// might not exist.
	GetPodVolumeDir(podUID types.UID, pluginName string, volumeName string) string

	// GetPodPluginDir returns the absolute path to a directory under which
	// a given plugin may store data for a given pod.  If the specified pod
	// does not exist, the result of this call might not exist.  This
	// directory might not actually exist on disk yet.
	GetPodPluginDir(podUID types.UID, pluginName string) string

	// GetKubeClient returns a client interface
	GetKubeClient() client.Interface

	// NewWrapperBuilder finds an appropriate plugin with which to handle
	// the provided spec.  This is used to implement volume plugins which
	// "wrap" other plugins.  For example, the "secret" volume is
	// implemented in terms of the "emptyDir" volume.
	NewWrapperBuilder(spec *api.Volume, podRef *api.ObjectReference) (Builder, error)

	// NewWrapperCleaner finds an appropriate plugin with which to handle
	// the provided spec.  See comments on NewWrapperBuilder for more
	// context.
	NewWrapperCleaner(spec *api.Volume, podUID types.UID) (Cleaner, error)
}

// VolumePluginMgr tracks registered plugins.
type VolumePluginMgr struct {
	mutex   sync.Mutex
	plugins map[string]VolumePlugin
}

// InitPlugins initializes each plugin.  All plugins must have unique names.
// This must be called exactly once before any New* methods are called on any
// plugins.
func (pm *VolumePluginMgr) InitPlugins(plugins []VolumePlugin, host VolumeHost) error {
	pm.mutex.Lock()
	defer pm.mutex.Unlock()

	if pm.plugins == nil {
		pm.plugins = map[string]VolumePlugin{}
	}

	allErrs := []error{}
	for _, plugin := range plugins {
		name := plugin.Name()
		if !util.IsQualifiedName(name) {
			allErrs = append(allErrs, fmt.Errorf("volume plugin has invalid name: %#v", plugin))
			continue
		}

		if _, found := pm.plugins[name]; found {
			allErrs = append(allErrs, fmt.Errorf("volume plugin %q was registered more than once", name))
			continue
		}
		plugin.Init(host)
		pm.plugins[name] = plugin
		glog.V(1).Infof("Loaded volume plugin %q", name)
	}
	return errors.NewAggregate(allErrs)
}

// FindPluginBySpec looks for a plugin that can support a given volume
// specification.  If no plugins can support or more than one plugin can
// support it, return error.
func (pm *VolumePluginMgr) FindPluginBySpec(spec *api.Volume) (VolumePlugin, error) {
	pm.mutex.Lock()
	defer pm.mutex.Unlock()

	matches := []string{}
	for k, v := range pm.plugins {
		if v.CanSupport(spec) {
			matches = append(matches, k)
		}
	}
	if len(matches) == 0 {
		return nil, fmt.Errorf("no volume plugin matched")
	}
	if len(matches) > 1 {
		return nil, fmt.Errorf("multiple volume plugins matched: %s", strings.Join(matches, ","))
	}
	return pm.plugins[matches[0]], nil
}

// FindPluginByName fetches a plugin by name or by legacy name.  If no plugin
// is found, returns error.
func (pm *VolumePluginMgr) FindPluginByName(name string) (VolumePlugin, error) {
	pm.mutex.Lock()
	defer pm.mutex.Unlock()

	// Once we can get rid of legacy names we can reduce this to a map lookup.
	matches := []string{}
	for k, v := range pm.plugins {
		if v.Name() == name {
			matches = append(matches, k)
		}
	}
	if len(matches) == 0 {
		return nil, fmt.Errorf("no volume plugin matched")
	}
	if len(matches) > 1 {
		return nil, fmt.Errorf("multiple volume plugins matched: %s", strings.Join(matches, ","))
	}
	return pm.plugins[matches[0]], nil
}

// FindPluginByName fetches a plugin by name or by legacy name.  If no plugin
// is found, returns error.
func (pm *VolumePluginMgr) FindPersistentPluginByName(name string) (PersistentVolumePlugin, error) {
	volumePlugin, err := pm.FindPluginByName(name)
	if err != nil {
		return nil, err
	}
	if persistentVolumePlugin, ok := volumePlugin.(PersistentVolumePlugin); ok {
		return persistentVolumePlugin, nil
	}
	return nil, fmt.Errorf("no persistent volume plugin matched")
}