Separate overlay implementation from plugin

Put the overlay plugin in a separate package to allow the overlay package to be
used without needing to import and initialize the plugin.

Signed-off-by: Derek McGowan <derek@mcg.dev>

cmd/containerd/builtins_linux.go

@@ -23,5 +23,5 @@ import (
 	_ "github.com/containerd/containerd/runtime/v2"
 	_ "github.com/containerd/containerd/runtime/v2/runc/options"
 	_ "github.com/containerd/containerd/snapshots/native"
-	_ "github.com/containerd/containerd/snapshots/overlay"
+	_ "github.com/containerd/containerd/snapshots/overlay/plugin"
 )

snapshots/overlay/overlay.go

@@ -29,38 +29,12 @@ import (
 
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/mount"
-	"github.com/containerd/containerd/platforms"
-	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/snapshots"
 	"github.com/containerd/containerd/snapshots/storage"
 	"github.com/containerd/continuity/fs"
 	"github.com/pkg/errors"
 )
 
-func init() {
-	plugin.Register(&plugin.Registration{
-		Type:   plugin.SnapshotPlugin,
-		ID:     "overlayfs",
-		Config: &Config{},
-		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
-			ic.Meta.Platforms = append(ic.Meta.Platforms, platforms.DefaultSpec())
-
-			config, ok := ic.Config.(*Config)
-			if !ok {
-				return nil, errors.New("invalid overlay configuration")
-			}
-
-			root := ic.Root
-			if config.RootPath != "" {
-				root = config.RootPath
-			}
-
-			ic.Meta.Exports["root"] = root
-			return NewSnapshotter(root, AsynchronousRemove)
-		},
-	})
-}
-
 // SnapshotterConfig is used to configure the overlay snapshotter instance
 type SnapshotterConfig struct {
 	asyncRemove bool

snapshots/overlay/plugin/plugin.go

@@ -18,8 +18,40 @@
 
 package overlay
 
+import (
+	"errors"
+
+	"github.com/containerd/containerd/platforms"
+	"github.com/containerd/containerd/plugin"
+	"github.com/containerd/containerd/snapshots/overlay"
+)
+
 // Config represents configuration for the overlay plugin.
 type Config struct {
 	// Root directory for the plugin
 	RootPath string `toml:"root_path"`
 }
+
+func init() {
+	plugin.Register(&plugin.Registration{
+		Type:   plugin.SnapshotPlugin,
+		ID:     "overlayfs",
+		Config: &Config{},
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			ic.Meta.Platforms = append(ic.Meta.Platforms, platforms.DefaultSpec())
+
+			config, ok := ic.Config.(*Config)
+			if !ok {
+				return nil, errors.New("invalid overlay configuration")
+			}
+
+			root := ic.Root
+			if config.RootPath != "" {
+				root = config.RootPath
+			}
+
+			ic.Meta.Exports["root"] = root
+			return overlay.NewSnapshotter(root, overlay.AsynchronousRemove)
+		},
+	})
+}