Change to Readdirnames for some cases

There was a couple uses of Readdir/ReadDir here where the only thing the return
value was used for was the Name of the entry. This is exactly what Readdirnames
returns, so we can avoid the overhead of making/returning a bunch of interfaces
and calling lstat everytime in the case of Readdir(-1).

https://cs.opensource.google/go/go/+/refs/tags/go1.20.4:src/os/dir_unix.go;l=114-137

Signed-off-by: Danny Canter <danny@dcantah.dev>

runtime/v2/shim_load.go

@@ -83,12 +83,21 @@ func (m *ShimManager) loadShims(ctx context.Context) error {
 			return err
 		}
 		// fast path
-		bf, err := os.ReadDir(bundle.Path)
+		f, err := os.Open(bundle.Path)
 		if err != nil {
 			bundle.Delete()
 			log.G(ctx).WithError(err).Errorf("fast path read bundle path for %s", bundle.Path)
 			continue
 		}
+
+		bf, err := f.Readdirnames(-1)
+		if err != nil {
+			f.Close()
+			bundle.Delete()
+			log.G(ctx).WithError(err).Errorf("fast path read bundle path for %s", bundle.Path)
+			continue
+		}
+		f.Close()
 		if len(bf) == 0 {
 			bundle.Delete()
 			continue
@@ -177,16 +186,24 @@ func (m *ShimManager) cleanupWorkDirs(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
-	dirs, err := os.ReadDir(filepath.Join(m.root, ns))
+
+	f, err := os.Open(filepath.Join(m.root, ns))
 	if err != nil {
 		return err
 	}
-	for _, d := range dirs {
+	defer f.Close()
+
+	dirs, err := f.Readdirnames(-1)
+	if err != nil {
+		return err
+	}
+
+	for _, dir := range dirs {
 		// if the task was not loaded, cleanup and empty working directory
 		// this can happen on a reboot where /run for the bundle state is cleaned up
 		// but that persistent working dir is left
-		if _, err := m.shims.Get(ctx, d.Name()); err != nil {
-			path := filepath.Join(m.root, ns, d.Name())
+		if _, err := m.shims.Get(ctx, dir); err != nil {
+			path := filepath.Join(m.root, ns, dir)
 			if err := os.RemoveAll(path); err != nil {
 				log.G(ctx).WithError(err).Errorf("cleanup working dir %s", path)
 			}