les: print 'experimental feature' warning on startup

les/backend.go

@@ -38,6 +38,8 @@ import (
 	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/internal/ethapi"
 	"github.com/ethereum/go-ethereum/light"
+	"github.com/ethereum/go-ethereum/logger"
+	"github.com/ethereum/go-ethereum/logger/glog"
 	"github.com/ethereum/go-ethereum/node"
 	"github.com/ethereum/go-ethereum/p2p"
 	rpc "github.com/ethereum/go-ethereum/rpc"
@@ -195,6 +197,7 @@ func (s *LightEthereum) Protocols() []p2p.Protocol {
 // Start implements node.Service, starting all internal goroutines needed by the
 // Ethereum protocol implementation.
 func (s *LightEthereum) Start(srvr *p2p.Server) error {
+	glog.V(logger.Info).Infof("WARNING: light client mode is an experimental feature")
 	s.netRPCService = ethapi.NewPublicNetAPI(srvr, s.netVersionId)
 	s.protocolManager.Start(srvr)
 	return nil