Start mysqld for mysql_upgrade with --skip-grant-tables and --skip-networking.

When mysqld is started on a database from an older version (the only use case
when mysql_upgrade will do anything and is really necessary) it may fail to
start due to mysql.* tables having old structure. --skip-grant-tables will
ensure that mysqld doesn't try to read mysql.* tables before mysql_upgrade fixed
their structure. Since anyone can connect to mysqld without password when it's
started with --skip-grant-tables, we should also pass --skip-networking to it.

To make passing those flags to mysqld possible I'm extending notion of
mysqld_start hook to accept list of any arguments that should be passed to
mysqld.

go/cmd/mysqlctl/mysqlctl.go

@@ -13,6 +13,7 @@ import (
 
 	log "github.com/golang/glog"
 	"github.com/youtube/vitess/go/exit"
+	"github.com/youtube/vitess/go/flagutil"
 	"github.com/youtube/vitess/go/netutil"
 	"github.com/youtube/vitess/go/vt/dbconfigs"
 	"github.com/youtube/vitess/go/vt/logutil"
@@ -93,6 +94,8 @@ func shutdownCmd(subFlags *flag.FlagSet, args []string) error {
 
 func startCmd(subFlags *flag.FlagSet, args []string) error {
 	waitTime := subFlags.Duration("wait_time", 5*time.Minute, "how long to wait for startup")
+	var mysqldArgs flagutil.StringListValue
+	subFlags.Var(&mysqldArgs, "mysqld_args", "List of comma-separated flags to pass additionally to mysqld")
 	subFlags.Parse(args)
 
 	// There ought to be an existing my.cnf, so use it to find mysqld.
@@ -104,7 +107,7 @@ func startCmd(subFlags *flag.FlagSet, args []string) error {
 
 	ctx, cancel := context.WithTimeout(context.Background(), *waitTime)
 	defer cancel()
-	if err := mysqld.Start(ctx); err != nil {
+	if err := mysqld.Start(ctx, mysqldArgs...); err != nil {
 		return fmt.Errorf("failed start mysql: %v", err)
 	}
 	return nil

go/vt/mysqlctl/backup.go

@@ -654,8 +654,14 @@ func Restore(ctx context.Context, mysqld MysqlDaemon, dir string, restoreConcurr
 	}
 
 	// mysqld needs to be running in order for mysql_upgrade to work.
+	// If we've just restored from a backup from previous MySQL version then mysqld
+	// may fail to start due to a different structure of mysql.* tables. The flag
+	// --skip-grant-tables ensures that these tables are not read until mysql_upgrade
+	// is executed. And since with --skip-grant-tables anyone can connect to MySQL
+	// without password, we are passing --skip-networking to greatly reduce the set
+	// of those who can connect.
 	logger.Infof("Restore: starting mysqld for mysql_upgrade")
-	err = mysqld.Start(ctx)
+	err = mysqld.Start(ctx, "--skip-grant-tables", "--skip-networking")
 	if err != nil {
 		return replication.Position{}, err
 	}

go/vt/mysqlctl/grpcmysqlctlclient/client.go

@@ -41,8 +41,10 @@ func factory(network, addr string, dialTimeout time.Duration) (mysqlctlclient.My
 }
 
 // Start is part of the MysqlctlClient interface.
-func (c *client) Start(ctx context.Context) error {
-	_, err := c.c.Start(ctx, &mysqlctlpb.StartRequest{})
+func (c *client) Start(ctx context.Context, mysqldArgs ...string) error {
+	_, err := c.c.Start(ctx, &mysqlctlpb.StartRequest{
+		MysqldArgs: mysqldArgs,
+	})
 	return err
 }
 

go/vt/mysqlctl/grpcmysqlctlserver/server.go

@@ -24,7 +24,7 @@ type server struct {
 
 // Start implements the server side of the MysqlctlClient interface.
 func (s *server) Start(ctx context.Context, request *mysqlctlpb.StartRequest) (*mysqlctlpb.StartResponse, error) {
-	return &mysqlctlpb.StartResponse{}, s.mysqld.Start(ctx)
+	return &mysqlctlpb.StartResponse{}, s.mysqld.Start(ctx, request.MysqldArgs...)
 }
 
 // Shutdown implements the server side of the MysqlctlClient interface.

go/vt/mysqlctl/mysql_daemon.go

@@ -29,7 +29,7 @@ type MysqlDaemon interface {
 	TabletDir() string
 
 	// methods related to mysql running or not
-	Start(ctx context.Context) error
+	Start(ctx context.Context, mysqldArgs ...string) error
 	Shutdown(ctx context.Context, waitForMysqld bool) error
 	RunMysqlUpgrade() error
 	ReinitConfig(ctx context.Context) error
@@ -229,7 +229,7 @@ func (fmd *FakeMysqlDaemon) TabletDir() string {
 }
 
 // Start is part of the MysqlDaemon interface
-func (fmd *FakeMysqlDaemon) Start(ctx context.Context) error {
+func (fmd *FakeMysqlDaemon) Start(ctx context.Context, mysqldArgs ...string) error {
 	if fmd.Running {
 		return fmt.Errorf("fake mysql daemon already running")
 	}

go/vt/mysqlctl/mysqlctlclient/interface.go

@@ -21,7 +21,7 @@ var connectionTimeout = flag.Duration("mysqlctl_client_connection_timeout", 30*t
 // MysqlctlClient defines the interface used to send remote mysqlctl commands
 type MysqlctlClient interface {
 	// Start calls Mysqld.Start remotely.
-	Start(ctx context.Context) error
+	Start(ctx context.Context, mysqldArgs ...string) error
 
 	// Shutdown calls Mysqld.Shutdown remotely.
 	Shutdown(ctx context.Context, waitForMysqld bool) error

go/vt/mysqlctl/mysqld.go

@@ -169,7 +169,7 @@ func (mysqld *Mysqld) RunMysqlUpgrade() error {
 // Start will start the mysql daemon, either by running the 'mysqld_start'
 // hook, or by running mysqld_safe in the background.
 // If a mysqlctld address is provided in a flag, Start will run remotely.
-func (mysqld *Mysqld) Start(ctx context.Context) error {
+func (mysqld *Mysqld) Start(ctx context.Context, mysqldArgs ...string) error {
 	// Execute as remote action on mysqlctld if requested.
 	if *socketFile != "" {
 		log.Infof("executing Mysqld.Start() remotely via mysqlctld server: %v", *socketFile)
@@ -178,14 +178,14 @@ func (mysqld *Mysqld) Start(ctx context.Context) error {
 			return fmt.Errorf("can't dial mysqlctld: %v", err)
 		}
 		defer client.Close()
-		return client.Start(ctx)
+		return client.Start(ctx, mysqldArgs...)
 	}
 
 	var name string
 	ts := fmt.Sprintf("Mysqld.Start(%v)", time.Now().Unix())
 
 	// try the mysqld start hook, if any
-	switch hr := hook.NewSimpleHook("mysqld_start").Execute(); hr.ExitStatus {
+	switch hr := hook.NewHook("mysqld_start", mysqldArgs).Execute(); hr.ExitStatus {
 	case hook.HOOK_SUCCESS:
 		// hook exists and worked, we can keep going
 		name = "mysqld_start hook"
@@ -202,6 +202,7 @@ func (mysqld *Mysqld) Start(ctx context.Context) error {
 		}
 		arg := []string{
 			"--defaults-file=" + mysqld.config.path}
+		arg = append(arg, mysqldArgs...)
 		env := []string{os.ExpandEnv("LD_LIBRARY_PATH=$VT_MYSQL_ROOT/lib/mysql")}
 
 		cmd := exec.Command(name, arg...)

proto/mysqlctl.proto

@@ -5,7 +5,9 @@ syntax = "proto3";
 
 package mysqlctl;
 
-message StartRequest{}
+message StartRequest{
+  repeated string mysqld_args = 1;
+}
 
 message StartResponse{}