dynamic: record deprecation for dynamic plugins

Signed-off-by: Samuel Karp <samuelkarp@google.com>

plugin/dynamic/dynamic.go

@@ -23,7 +23,7 @@ import "fmt"
 // Load is currently only implemented on non-static, non-gccgo builds for amd64
 // and arm64, and plugins must be built with the exact same version of Go as
 // containerd itself.
-func Load(path string) (err error) {
+func Load(path string) (loaded int, err error) {
 	defer func() {
 		if v := recover(); v != nil {
 			rerr, ok := v.(error)

plugin/dynamic/dynamic_supported.go

@@ -25,12 +25,13 @@ import (
 	"runtime"
 )
 
-// loadPlugins loads all plugins for the OS and Arch
-// that containerd is built for inside the provided path
-func loadPlugins(path string) error {
+// loadPlugins loads all plugins for the OS and Arch that containerd is built
+// for inside the provided path and returns the count of successfully-loaded
+// plugins
+func loadPlugins(path string) (int, error) {
 	abs, err := filepath.Abs(path)
 	if err != nil {
-		return err
+		return 0, err
 	}
 	pattern := filepath.Join(abs, fmt.Sprintf(
 		"*-%s-%s.%s",
@@ -40,14 +41,16 @@ func loadPlugins(path string) error {
 	))
 	libs, err := filepath.Glob(pattern)
 	if err != nil {
-		return err
+		return 0, err
 	}
+	loaded := 0
 	for _, lib := range libs {
 		if _, err := plugin.Open(lib); err != nil {
-			return err
+			return loaded, err
 		}
+		loaded++
 	}
-	return nil
+	return loaded, nil
 }
 
 // getLibExt returns a platform specific lib extension for

plugin/dynamic/dynamic_unsupported.go

@@ -23,6 +23,6 @@ package dynamic
 // - with gccgo: gccgo has no plugin support golang/go#36403
 // - on static builds; https://github.com/containerd/containerd/commit/0d682e24a1ba8e93e5e54a73d64f7d256f87492f
 // - on architectures other than amd64 and arm64 (other architectures need to be tested)
-func loadPlugins(path string) error {
-	return nil
+func loadPlugins(path string) (int, error) {
+	return 0, nil
 }

services/server/server.go

@@ -55,6 +55,7 @@ import (
 	"github.com/containerd/containerd/defaults"
 	"github.com/containerd/containerd/diff"
 	diffproxy "github.com/containerd/containerd/diff/proxy"
+	"github.com/containerd/containerd/pkg/deprecation"
 	"github.com/containerd/containerd/pkg/dialer"
 	"github.com/containerd/containerd/pkg/timeout"
 	"github.com/containerd/containerd/platforms"
@@ -356,7 +357,9 @@ func recordConfigDeprecations(ctx context.Context, config *srvconfig.Config, set
 		return
 	}
 
-	_ = warn // TODO(samuelkarp): placeholder for future use
+	if config.PluginDir != "" { //nolint:staticcheck
+		warn.Emit(ctx, deprecation.GoPluginLibrary)
+	}
 }
 
 // Server is the containerd main daemon
@@ -463,9 +466,11 @@ func LoadPlugins(ctx context.Context, config *srvconfig.Config) ([]plugin.Regist
 	if path == "" {
 		path = filepath.Join(config.Root, "plugins")
 	}
-	log.G(ctx).Warning("`go_plugin` is deprecated, please use `external plugins` instead")
-	if err := dynamic.Load(path); err != nil {
+	if count, err := dynamic.Load(path); err != nil {
 		return nil, err
+	} else if count > 0 || config.PluginDir != "" { //nolint:staticcheck
+		config.PluginDir = path //nolint:staticcheck
+		log.G(ctx).Warningf("loaded %d dynamic plugins. `go_plugin` is deprecated, please use `external plugins` instead", count)
 	}
 	// load additional plugins that don't automatically register themselves
 	registry.Register(&plugin.Registration{

services/warning/service.go

@@ -52,16 +52,6 @@ type Warning struct {
 
 var _ Service = (*service)(nil)
 
-func init() {
-	registry.Register(&plugin.Registration{
-		Type: plugins.InternalPlugin,
-		ID:   "warning",
-		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
-			return &service{warnings: make(map[deprecation.Warning]time.Time)}, nil
-		},
-	})
-}
-
 type service struct {
 	warnings map[deprecation.Warning]time.Time
 	m        sync.RWMutex