add support for running pre-migrations and caching their results

This can significantly speedup state migrations.

node/builder.go

@@ -269,7 +269,7 @@ func Online() Option {
 			Override(new(vm.SyscallBuilder), vm.Syscalls),
 			Override(new(*store.ChainStore), modules.ChainStore),
 			Override(new(stmgr.UpgradeSchedule), stmgr.DefaultUpgradeSchedule()),
-			Override(new(*stmgr.StateManager), stmgr.NewStateManagerWithUpgradeSchedule),
+			Override(new(*stmgr.StateManager), modules.StateManager),
 			Override(new(*wallet.LocalWallet), wallet.NewWallet),
 			Override(new(wallet.Default), From(new(*wallet.LocalWallet))),
 			Override(new(api.WalletAPI), From(new(wallet.MultiWallet))),

node/modules/stmgr.go

@@ -0,0 +1,20 @@
+package modules
+
+import (
+	"go.uber.org/fx"
+
+	"github.com/filecoin-project/lotus/chain/stmgr"
+	"github.com/filecoin-project/lotus/chain/store"
+)
+
+func StateManager(lc fx.Lifecycle, cs *store.ChainStore, us stmgr.UpgradeSchedule) (*stmgr.StateManager, error) {
+	sm, err := stmgr.NewStateManagerWithUpgradeSchedule(cs, us)
+	if err != nil {
+		return nil, err
+	}
+	lc.Append(fx.Hook{
+		OnStart: sm.Start,
+		OnStop:  sm.Stop,
+	})
+	return sm, nil
+}