add comments in the DI bundle loader

Author: vyzo

node/modules/builtin_actors.go

@@ -30,27 +30,36 @@ func LoadBuiltinActors(lc fx.Lifecycle, mctx helpers.MetricsCtx, r repo.LockedRe
 	}
 
 	for av, rel := range build.BuiltinActorReleases {
+		// first check to see if we know this release
 		key := dstore.NewKey(fmt.Sprintf("/builtin-actors/v%d/%s", av, rel))
 
 		data, err := ds.Get(ctx, key)
 		switch err {
 		case nil:
+			// ok, we do, this should be the manifest cid
 			mfCid, err := cid.Cast(data)
 			if err != nil {
 				return result, xerrors.Errorf("error parsing cid for %s: %w", key, err)
 			}
 
+			// check the blockstore for existence of the manifest
 			has, err := bs.Has(ctx, mfCid)
 			if err != nil {
 				return result, xerrors.Errorf("error checking blockstore for manifest cid %s: %w", mfCid, err)
 			}
 
 			if has {
+				// it's there, no need to reload the bundle to the blockstore; just add it to the manifest list.
 				actors.AddManifest(av, mfCid)
 				continue
 			}
 
+			// we have a release key but don't have the manifest in the blockstore; maybe the user
+			// nuked his blockstore to restart from a snapshot. So fallthrough to refetch (if necessary)
+			// and reload the bundle.
+
 		case dstore.ErrNotFound:
+			// we don't have a release key, we need to load the bundle
 
 		default:
 			return result, xerrors.Errorf("error loading %s from datastore: %w", key, err)
@@ -62,11 +71,13 @@ func LoadBuiltinActors(lc fx.Lifecycle, mctx helpers.MetricsCtx, r repo.LockedRe
 			return result, err
 		}
 
+		// add the release key with the manifest to avoid reloading it in next restart.
 		if err := ds.Put(ctx, key, mfCid.Bytes()); err != nil {
 			return result, xerrors.Errorf("error storing manifest CID for builtin-actors vrsion %d to the datastore: %w", av, err)
 		}
 	}
 
+	// we've loaded all the bundles, now load the manifests to get actor code CIDs.
 	cborStore := cbor.NewCborStore(bs)
 	if err := actors.LoadManifests(ctx, cborStore); err != nil {
 		return result, xerrors.Errorf("error loading actor manifests: %w", err)