change_master->global_init_info->Master_info::mi_init_info->Rpl_info_handler::init_info->Rpl_info_file::do_init_info???->mi->rli->rli_init_info()->初始化./relay-bin.000001,4如果relay-log.info不存在的話，否則讀取

//初始化master_info結構??
int?Master_info::mi_init_info()??
{??if?(inited)??DBUG_RETURN(0);//如果已經創建master_info文件，直接退出??handler->init_info();//創建/打開master_info文件??if?(check_return?==?REPOSITORY_DOES_NOT_EXIST){//如果master_info文件是剛創建的，設置需讀取的log位置是4??init_master_log_pos();??|--master_log_name[0]=?0;??|--master_log_pos=?BIN_LOG_HEADER_SIZE;??|--ssl_verify_server_cert=?0;??|--?heartbeat_period=?min<float>(SLAVE_MAX_HEARTBEAT_PERIOD,(slave_net_timeout/2.0));??}else{??read_info(handler);//讀取文件??}??inited=?1;??flush_info(TRUE);??|--handler->set_sync_period(sync_masterinfo_period);//默認10000??|--flush_io_cache(&info_file);??|--my_sync(info_fd,?MYF(MY_WME));??DBUG_RETURN(0);

int?Rpl_info_file::do_init_info()??
{??if?(ret_check?==?REPOSITORY_DOES_NOT_EXIST){??info_fd?=?my_open(info_fname,?O_CREAT|O_RDWR|O_BINARY,?MYF(MY_WME));??init_io_cache(&info_file,?info_fd,?IO_SIZE*2,?READ_CACHE,?0L,0,MYF(MY_WME));??}else?if?(ret_check?==?REPOSITORY_EXISTS){??info_fd?=?my_open(info_fname,?O_RDWR|O_BINARY,?MYF(MY_WME));??init_io_cache(&info_file,?info_fd,?IO_SIZE*2,?READ_CACHE,?0L,0,?MYF(MY_WME))??}??
}

如果master.info不存在，就創建并初始化對應的IO_CACHE
如果存在，就打開，并初始化對應的IO_CACHE