etcdmain: add command line flag to etcdmain

etcdmain/config.go

@@ -158,6 +158,7 @@ func newConfig() *config {
 
 	fs.BoolVar(&cfg.StrictReconfigCheck, "strict-reconfig-check", cfg.StrictReconfigCheck, "Reject reconfiguration requests that would cause quorum loss.")
 	fs.BoolVar(&cfg.EnableV2, "enable-v2", true, "Accept etcd V2 client requests.")
+	fs.StringVar(&cfg.ExperimentalEnableV2V3, "experimental-enable-v2v3", cfg.ExperimentalEnableV2V3, "v3 prefix for serving emulated v2 state.")
 
 	// proxy
 	fs.Var(cfg.proxy, "proxy", fmt.Sprintf("Valid values include %s", strings.Join(cfg.proxy.Values, ", ")))

etcdmain/help.go

@@ -183,5 +183,7 @@ auth flags:
 experimental flags:
 	--experimental-corrupt-check-time '0s'
 	        duration of time between cluster corruption check passes.
+	--experimental-enable-v2v3 ''
+		serve v2 requests through the v3 backend under a given prefix.
 `
 )