Mysql源码学习——用户认证原理与实现(4)

             ("New connection received on %s", vio_description(net->vio)));

#ifdef SIGNAL_WITH_VIO_CLOSE

  thd->set_active_vio(net->vio);

#endif

  if (!thd->main_security_ctx.host)         // If TCP/IP connection

  {

    char ip[30];

    if (vio_peer_addr(net->vio, ip, &thd->peer_port))

    {

      my_error(ER_BAD_HOST_ERROR, MYF(0), thd->main_security_ctx.host_or_ip);

      return 1;

    }

    if (!(thd->main_security_ctx.ip= my_strdup(ip,MYF(MY_WME))))

      return 1; /* The error is set by my_strdup(). */

    thd->main_security_ctx.host_or_ip= thd->main_security_ctx.ip;

    vio_in_addr(net->vio,&thd->remote.sin_addr);

    if (!(specialflag & SPECIAL_NO_RESOLVE))

    {

      vio_in_addr(net->vio,&thd->remote.sin_addr);

      thd->main_security_ctx.host=

        ip_to_hostname(&thd->remote.sin_addr, &connect_errors);

      /* Cut very long hostnames to avoid possible overflows */

      if (thd->main_security_ctx.host)

      {

        if (thd->main_security_ctx.host != my_localhost)

          thd->main_security_ctx.host[min(strlen(thd->main_security_ctx.host),

                                          HOSTNAME_LENGTH)]= 0;

        thd->main_security_ctx.host_or_ip= thd->main_security_ctx.host;

      }

      if (connect_errors > max_connect_errors)

      {

        my_error(ER_HOST_IS_BLOCKED, MYF(0), thd->main_security_ctx.host_or_ip);

        return 1;

      }

    }

    ...

if (acl_check_host(thd->main_security_ctx.host, thd->main_security_ctx.ip))//此处验证主机名或IP是否存在

    {

      my_error(ER_HOST_NOT_PRIVILEGED, MYF(0),