plugin: refactor plugin system to support initialization reporting

Signed-off-by: Stephen J Day <stephen.day@docker.com>

differ/differ.go

@@ -13,6 +13,7 @@ import (
 	"github.com/containerd/containerd/images"
 	"github.com/containerd/containerd/metadata"
 	"github.com/containerd/containerd/mount"
+	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/plugin"
 	digest "github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
@@ -27,11 +28,13 @@ func init() {
 		Requires: []plugin.Type{
 			plugin.MetadataPlugin,
 		},
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
 			md, err := ic.Get(plugin.MetadataPlugin)
 			if err != nil {
 				return nil, err
 			}
+
+			ic.Meta.Platforms = append(ic.Meta.Platforms, platforms.DefaultSpec())
 			return NewWalkingDiff(md.(*metadata.DB).ContentStore())
 		},
 	})

linux/runtime.go

@@ -23,6 +23,7 @@ import (
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/metadata"
 	"github.com/containerd/containerd/namespaces"
+	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/reaper"
 	"github.com/containerd/containerd/runtime"
@@ -30,9 +31,9 @@ import (
 	runc "github.com/containerd/go-runc"
 	"github.com/containerd/typeurl"
 	google_protobuf "github.com/golang/protobuf/ptypes/empty"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
-
 	"golang.org/x/sys/unix"
 )
 
@@ -49,9 +50,9 @@ const (
 
 func init() {
 	plugin.Register(&plugin.Registration{
-		Type: plugin.RuntimePlugin,
-		ID:   "linux",
-		Init: New,
+		Type:   plugin.RuntimePlugin,
+		ID:     "linux",
+		InitFn: New,
 		Requires: []plugin.Type{
 			plugin.TaskMonitorPlugin,
 			plugin.MetadataPlugin,
@@ -92,6 +93,8 @@ type Config struct {
 
 // New returns a configured runtime
 func New(ic *plugin.InitContext) (interface{}, error) {
+	ic.Meta.Platforms = []ocispec.Platform{platforms.DefaultSpec()}
+
 	if err := os.MkdirAll(ic.Root, 0711); err != nil {
 		return nil, err
 	}
@@ -121,6 +124,7 @@ func New(ic *plugin.InitContext) (interface{}, error) {
 	if err != nil {
 		return nil, err
 	}
+
 	// TODO: need to add the tasks to the monitor
 	for _, t := range tasks {
 		if err := r.tasks.AddWithNamespace(t.namespace, t); err != nil {

metrics/cgroups/cgroups.go

@@ -9,6 +9,7 @@ import (
 	"github.com/containerd/containerd/linux"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/namespaces"
+	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/runtime"
 	metrics "github.com/docker/go-metrics"
@@ -24,7 +25,7 @@ func init() {
 	plugin.Register(&plugin.Registration{
 		Type:   plugin.TaskMonitorPlugin,
 		ID:     "cgroups",
-		Init:   New,
+		InitFn: New,
 		Config: &Config{},
 	})
 }
@@ -44,6 +45,7 @@ func New(ic *plugin.InitContext) (interface{}, error) {
 	if ns != nil {
 		metrics.Register(ns)
 	}
+	ic.Meta.Platforms = append(ic.Meta.Platforms, platforms.DefaultSpec())
 	return &cgroupsMonitor{
 		collector: collector,
 		oom:       oom,

plugin/context.go

@@ -2,48 +2,123 @@ package plugin
 
 import (
 	"context"
-	"fmt"
 	"path/filepath"
 
+	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/events"
 	"github.com/containerd/containerd/log"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/pkg/errors"
 )
 
-// NewContext returns a new plugin InitContext
-func NewContext(ctx context.Context, plugins map[Type]map[string]interface{}, root, state, id string) *InitContext {
-	return &InitContext{
-		plugins: plugins,
-		Root:    filepath.Join(root, id),
-		State:   filepath.Join(state, id),
-		Context: log.WithModule(ctx, id),
-	}
-}
-
 // InitContext is used for plugin inititalization
 type InitContext struct {
+	Context context.Context
 	Root    string
 	State   string
-	Address string
-	Context context.Context
 	Config  interface{}
+	Address string
 	Events  *events.Exchange
 
-	plugins map[Type]map[string]interface{}
+	Meta *Meta // plugins can fill in metadata at init.
+
+	plugins *PluginSet
+}
+
+// NewContext returns a new plugin InitContext
+func NewContext(ctx context.Context, r *Registration, plugins *PluginSet, root, state string) *InitContext {
+	return &InitContext{
+		Context: log.WithModule(ctx, r.URI()),
+		Root:    filepath.Join(root, r.URI()),
+		State:   filepath.Join(state, r.URI()),
+		Meta: &Meta{
+			Exports: map[string]string{},
+		},
+		plugins: plugins,
+	}
 }
 
 // Get returns the first plugin by its type
 func (i *InitContext) Get(t Type) (interface{}, error) {
-	for _, v := range i.plugins[t] {
-		return v, nil
-	}
-	return nil, fmt.Errorf("no plugins registered for %s", t)
+	return i.plugins.Get(t)
 }
 
-// GetAll returns all plugins with the specific type
-func (i *InitContext) GetAll(t Type) (map[string]interface{}, error) {
-	p, ok := i.plugins[t]
-	if !ok {
-		return nil, fmt.Errorf("no plugins registered for %s", t)
+// Meta contains information gathered from the registration and initialization
+// process.
+type Meta struct {
+	Platforms    []ocispec.Platform // platforms supported by plugin
+	Exports      map[string]string  // values exported by plugin
+	Capabilities []string           // feature switches for plugin
+}
+
+// Plugin represents an initialized plugin, used with an init context.
+type Plugin struct {
+	Registration *Registration // registration, as initialized
+	Config       interface{}   // config, as initialized
+	Meta         *Meta
+
+	instance interface{}
+	err      error // will be set if there was an error initializing the plugin
+}
+
+func (p *Plugin) Err() error {
+	return p.err
+}
+
+func (p *Plugin) Instance() (interface{}, error) {
+	return p.instance, p.err
+}
+
+// PluginSet defines a plugin collection, used with InitContext.
+//
+// This maintains ordering and unique indexing over the set.
+//
+// After iteratively instantiating plugins, this set should represent, the
+// ordered, initialization set of plugins for a containerd instance.
+type PluginSet struct {
+	ordered     []*Plugin // order of initialization
+	byTypeAndID map[Type]map[string]*Plugin
+}
+
+func NewPluginSet() *PluginSet {
+	return &PluginSet{
+		byTypeAndID: make(map[Type]map[string]*Plugin),
 	}
+}
+
+func (ps *PluginSet) Add(p *Plugin) error {
+	if byID, typeok := ps.byTypeAndID[p.Registration.Type]; !typeok {
+		ps.byTypeAndID[p.Registration.Type] = map[string]*Plugin{
+			p.Registration.ID: p,
+		}
+	} else if _, idok := byID[p.Registration.ID]; !idok {
+		byID[p.Registration.ID] = p
+	} else {
+		return errors.Wrapf(errdefs.ErrAlreadyExists, "plugin %v already initialized", p.Registration.URI())
+	}
+
+	ps.ordered = append(ps.ordered, p)
+	return nil
+}
+
+// Get returns the first plugin by its type
+func (ps *PluginSet) Get(t Type) (interface{}, error) {
+	for _, v := range ps.byTypeAndID[t] {
+		return v.Instance()
+	}
+	return nil, errors.Wrapf(errdefs.ErrNotFound, "no plugins registered for %s", t)
+}
+
+func (i *InitContext) GetAll() []*Plugin {
+	return i.plugins.ordered
+}
+
+// GetByType returns all plugins with the specific type.
+func (i *InitContext) GetByType(t Type) (map[string]*Plugin, error) {
+	p, ok := i.plugins.byTypeAndID[t]
+	if !ok {
+		return nil, errors.Wrapf(errdefs.ErrNotFound, "no plugins registered for %s", t)
+	}
+
 	return p, nil
 }

plugin/plugin.go

@@ -31,6 +31,8 @@ func IsSkipPlugin(err error) bool {
 // Type is the type of the plugin
 type Type string
 
+func (t Type) String() string { return string(t) }
+
 const (
 	// RuntimePlugin implements a runtime
 	RuntimePlugin Type = "io.containerd.runtime.v1"
@@ -54,9 +56,22 @@ type Registration struct {
 	ID       string
 	Config   interface{}
 	Requires []Type
-	Init     func(*InitContext) (interface{}, error)
 
-	added bool
+	// InitFn is called when initializing a plugin. The registration and
+	// context are passed in. The init function may modify the registration to
+	// add exports, capabilites and platform support declarations.
+	InitFn func(*InitContext) (interface{}, error)
+}
+
+func (r *Registration) Init(ic *InitContext) *Plugin {
+	p, err := r.InitFn(ic)
+	return &Plugin{
+		Registration: r,
+		Config:       ic.Config,
+		Meta:         ic.Meta,
+		instance:     p,
+		err:          err,
+	}
 }
 
 // URI returns the full plugin URI

server/server.go

@@ -1,7 +1,6 @@
 package server
 
 import (
-	"errors"
 	"expvar"
 	"net"
 	"net/http"
@@ -29,6 +28,7 @@ import (
 	"github.com/containerd/containerd/snapshot"
 	metrics "github.com/docker/go-metrics"
 	grpc_prometheus "github.com/grpc-ecosystem/go-grpc-prometheus"
+	"github.com/pkg/errors"
 	"golang.org/x/net/context"
 
 	"google.golang.org/grpc"
@@ -66,7 +66,7 @@ func New(ctx context.Context, config *Config) (*Server, error) {
 			rpc:    rpc,
 			events: events.NewExchange(),
 		}
-		initialized = make(map[plugin.Type]map[string]interface{})
+		initialized = plugin.NewPluginSet()
 	)
 	for _, p := range plugins {
 		id := p.URI()
@@ -74,10 +74,10 @@ func New(ctx context.Context, config *Config) (*Server, error) {
 
 		initContext := plugin.NewContext(
 			ctx,
+			p,
 			initialized,
 			config.Root,
 			config.State,
-			id,
 		)
 		initContext.Events = s.events
 		initContext.Address = config.GRPC.Address
@@ -90,7 +90,12 @@ func New(ctx context.Context, config *Config) (*Server, error) {
 			}
 			initContext.Config = pluginConfig
 		}
-		instance, err := p.Init(initContext)
+		result := p.Init(initContext)
+		if err := initialized.Add(result); err != nil {
+			return nil, errors.Wrapf(err, "could not add plugin result to plugin set")
+		}
+
+		instance, err := result.Instance()
 		if err != nil {
 			if plugin.IsSkipPlugin(err) {
 				log.G(ctx).WithField("type", p.Type).Infof("skip loading plugin %q...", id)
@@ -99,14 +104,6 @@ func New(ctx context.Context, config *Config) (*Server, error) {
 			}
 			continue
 		}
-
-		if types, ok := initialized[p.Type]; ok {
-			types[p.ID] = instance
-		} else {
-			initialized[p.Type] = map[string]interface{}{
-				p.ID: instance,
-			}
-		}
 		// check for grpc services that should be registered with the server
 		if service, ok := instance.(plugin.Service); ok {
 			services = append(services, service)
@@ -171,7 +168,8 @@ func loadPlugins(config *Config) ([]*plugin.Registration, error) {
 	plugin.Register(&plugin.Registration{
 		Type: plugin.ContentPlugin,
 		ID:   "content",
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			ic.Meta.Exports["root"] = ic.Root
 			return local.NewStore(ic.Root)
 		},
 	})
@@ -182,7 +180,7 @@ func loadPlugins(config *Config) ([]*plugin.Registration, error) {
 			plugin.ContentPlugin,
 			plugin.SnapshotPlugin,
 		},
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
 			if err := os.MkdirAll(ic.Root, 0711); err != nil {
 				return nil, err
 			}
@@ -191,17 +189,26 @@ func loadPlugins(config *Config) ([]*plugin.Registration, error) {
 				return nil, err
 			}
 
-			rawSnapshotters, err := ic.GetAll(plugin.SnapshotPlugin)
+			snapshottersRaw, err := ic.GetByType(plugin.SnapshotPlugin)
 			if err != nil {
 				return nil, err
 			}
 
 			snapshotters := make(map[string]snapshot.Snapshotter)
-			for name, sn := range rawSnapshotters {
+			for name, sn := range snapshottersRaw {
+				sn, err := sn.Instance()
+				if err != nil {
+					log.G(ic.Context).WithError(err).
+						Warnf("could not use snapshotter %v in metadata plugin", name)
+					continue
+				}
 				snapshotters[name] = sn.(snapshot.Snapshotter)
 			}
 
-			db, err := bolt.Open(filepath.Join(ic.Root, "meta.db"), 0644, nil)
+			path := filepath.Join(ic.Root, "meta.db")
+			ic.Meta.Exports["path"] = path
+
+			db, err := bolt.Open(path, 0644, nil)
 			if err != nil {
 				return nil, err
 			}

services/containers/service.go

@@ -23,7 +23,7 @@ func init() {
 		Requires: []plugin.Type{
 			plugin.MetadataPlugin,
 		},
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
 			m, err := ic.Get(plugin.MetadataPlugin)
 			if err != nil {
 				return nil, err

services/content/service.go

@@ -41,19 +41,22 @@ func init() {
 		Requires: []plugin.Type{
 			plugin.MetadataPlugin,
 		},
-		Init: NewService,
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			m, err := ic.Get(plugin.MetadataPlugin)
+			if err != nil {
+				return nil, err
+			}
+
+			s, err := NewService(m.(*metadata.DB).ContentStore(), ic.Events)
+			return s, err
+		},
 	})
 }
 
-func NewService(ic *plugin.InitContext) (interface{}, error) {
-	m, err := ic.Get(plugin.MetadataPlugin)
-	if err != nil {
-		return nil, err
-	}
-
+func NewService(cs content.Store, publisher events.Publisher) (*Service, error) {
 	return &Service{
-		store:     m.(*metadata.DB).ContentStore(),
-		publisher: ic.Events,
+		store:     cs,
+		publisher: publisher,
 	}, nil
 }
 

services/diff/service.go

@@ -32,8 +32,8 @@ func init() {
 		Config: &config{
 			Order: []string{"walking"},
 		},
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
-			differs, err := ic.GetAll(plugin.DiffPlugin)
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			differs, err := ic.GetByType(plugin.DiffPlugin)
 			if err != nil {
 				return nil, err
 			}
@@ -41,10 +41,15 @@ func init() {
 			orderedNames := ic.Config.(*config).Order
 			ordered := make([]plugin.Differ, len(orderedNames))
 			for i, n := range orderedNames {
-				differ, ok := differs[n]
+				differp, ok := differs[n]
 				if !ok {
 					return nil, errors.Errorf("needed differ not loaded: %s", n)
 				}
+				differ, err := differp.Instance()
+				if err != nil {
+					return nil, errors.Wrapf(err, "could not load required differ due plugin init error: %s", n)
+				}
+
 				ordered[i] = differ.(plugin.Differ)
 			}
 

services/events/service.go

@@ -15,7 +15,7 @@ func init() {
 	plugin.Register(&plugin.Registration{
 		Type: plugin.GRPCPlugin,
 		ID:   "events",
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
 			return NewService(ic.Events), nil
 		},
 	})

services/healthcheck/service.go

@@ -16,11 +16,13 @@ func init() {
 	plugin.Register(&plugin.Registration{
 		Type: plugin.GRPCPlugin,
 		ID:   "healthcheck",
-		Init: NewService,
+		InitFn: func(*plugin.InitContext) (interface{}, error) {
+			return NewService()
+		},
 	})
 }
 
-func NewService(ic *plugin.InitContext) (interface{}, error) {
+func NewService() (*Service, error) {
 	return &Service{
 		health.NewServer(),
 	}, nil

services/images/service.go

@@ -23,7 +23,7 @@ func init() {
 		Requires: []plugin.Type{
 			plugin.MetadataPlugin,
 		},
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
 			m, err := ic.Get(plugin.MetadataPlugin)
 			if err != nil {
 				return nil, err

services/namespaces/service.go

@@ -24,7 +24,7 @@ func init() {
 		Requires: []plugin.Type{
 			plugin.MetadataPlugin,
 		},
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
 			m, err := ic.Get(plugin.MetadataPlugin)
 			if err != nil {
 				return nil, err

services/snapshot/service.go

@@ -25,7 +25,7 @@ func init() {
 		Requires: []plugin.Type{
 			plugin.MetadataPlugin,
 		},
-		Init: newService,
+		InitFn: newService,
 	})
 }
 

services/tasks/service.go

@@ -2,6 +2,7 @@ package tasks
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -46,15 +47,16 @@ func init() {
 			plugin.RuntimePlugin,
 			plugin.MetadataPlugin,
 		},
-		Init: New,
+		InitFn: New,
 	})
 }
 
 func New(ic *plugin.InitContext) (interface{}, error) {
-	rt, err := ic.GetAll(plugin.RuntimePlugin)
+	rt, err := ic.GetByType(plugin.RuntimePlugin)
 	if err != nil {
 		return nil, err
 	}
+
 	m, err := ic.Get(plugin.MetadataPlugin)
 	if err != nil {
 		return nil, err
@@ -62,9 +64,18 @@ func New(ic *plugin.InitContext) (interface{}, error) {
 	cs := m.(*metadata.DB).ContentStore()
 	runtimes := make(map[string]runtime.Runtime)
 	for _, rr := range rt {
-		r := rr.(runtime.Runtime)
+		ri, err := rr.Instance()
+		if err != nil {
+			log.G(ic.Context).WithError(err).Warn("could not load runtime instance due to initialization error")
+			continue
+		}
+		r := ri.(runtime.Runtime)
 		runtimes[r.ID()] = r
 	}
+
+	if len(runtimes) == 0 {
+		return nil, errors.New("no runtimes available to create task service")
+	}
 	return &Service{
 		runtimes:  runtimes,
 		db:        m.(*metadata.DB),

services/version/service.go

@@ -13,9 +13,9 @@ var _ api.VersionServer = &Service{}
 
 func init() {
 	plugin.Register(&plugin.Registration{
-		Type: plugin.GRPCPlugin,
-		ID:   "version",
-		Init: New,
+		Type:   plugin.GRPCPlugin,
+		ID:     "version",
+		InitFn: New,
 	})
 }
 

snapshot/btrfs/btrfs.go

@@ -12,9 +12,11 @@ import (
 	"github.com/containerd/btrfs"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/mount"
+	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/snapshot"
 	"github.com/containerd/containerd/snapshot/storage"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 )
@@ -23,7 +25,9 @@ func init() {
 	plugin.Register(&plugin.Registration{
 		ID:   "btrfs",
 		Type: plugin.SnapshotPlugin,
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			ic.Meta.Platforms = []ocispec.Platform{platforms.DefaultSpec()}
+			ic.Meta.Exports = map[string]string{"root": ic.Root}
 			return NewSnapshotter(ic.Root)
 		},
 	})

snapshot/naive/naive.go

@@ -9,6 +9,7 @@ import (
 	"github.com/containerd/containerd/fs"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/mount"
+	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/snapshot"
 	"github.com/containerd/containerd/snapshot/storage"
@@ -19,7 +20,8 @@ func init() {
 	plugin.Register(&plugin.Registration{
 		Type: plugin.SnapshotPlugin,
 		ID:   "naive",
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			ic.Meta.Platforms = append(ic.Meta.Platforms, platforms.DefaultSpec())
 			return NewSnapshotter(ic.Root)
 		},
 	})

snapshot/overlay/overlay.go

@@ -14,6 +14,7 @@ import (
 	"github.com/containerd/containerd/fs"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/mount"
+	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/snapshot"
 	"github.com/containerd/containerd/snapshot/storage"
@@ -24,7 +25,9 @@ func init() {
 	plugin.Register(&plugin.Registration{
 		Type: plugin.SnapshotPlugin,
 		ID:   "overlayfs",
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			ic.Meta.Platforms = append(ic.Meta.Platforms, platforms.DefaultSpec())
+			ic.Meta.Exports["root"] = ic.Root
 			return NewSnapshotter(ic.Root)
 		},
 	})

snapshot/windows/windows.go

@@ -19,7 +19,7 @@ func init() {
 	plugin.Register(&plugin.Registration{
 		Type: plugin.SnapshotPlugin,
 		ID:   "windows",
-		Init: func(ic *plugin.InitContext) (interface{}, error) {
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
 			return NewSnapshotter(ic.Root)
 		},
 	})

windows/runtime.go

@@ -41,9 +41,9 @@ var _ = (runtime.Runtime)(&windowsRuntime{})
 
 func init() {
 	plugin.Register(&plugin.Registration{
-		ID:   runtimeName,
-		Type: plugin.RuntimePlugin,
-		Init: New,
+		ID:     runtimeName,
+		Type:   plugin.RuntimePlugin,
+		InitFn: New,
 		Requires: []plugin.Type{
 			plugin.MetadataPlugin,
 		},