MdeModulePkg/Universal/Network/Dhcp4Dxe/Dhcp4Driver.c

   1 /** @file
   2
   3 Copyright (c) 2006 - 2009, Intel Corporation.<BR>
   4 All rights reserved. This program and the accompanying materials
   5 are licensed and made available under the terms and conditions of the BSD License
   6 which accompanies this distribution.  The full text of the license may be found at
   7 http://opensource.org/licenses/bsd-license.php
   8
   9 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  10 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  11
  12 **/
  13
  14 #include "Dhcp4Impl.h"
  15 #include "Dhcp4Driver.h"
  16
  17 EFI_DRIVER_BINDING_PROTOCOL gDhcp4DriverBinding = {
  18   Dhcp4DriverBindingSupported,
  19   Dhcp4DriverBindingStart,
  20   Dhcp4DriverBindingStop,
  21   0xa,
  22   NULL,
  23   NULL
  24 };
  25
  26 EFI_SERVICE_BINDING_PROTOCOL mDhcp4ServiceBindingTemplate = {
  27   Dhcp4ServiceBindingCreateChild,
  28   Dhcp4ServiceBindingDestroyChild
  29 };
  30
  31 /**
  32   This is the declaration of an EFI image entry point. This entry point is
  33   the same for UEFI Applications, UEFI OS Loaders, and UEFI Drivers including
  34   both device drivers and bus drivers.
  35
  36   Entry point of the DHCP driver to install various protocols.
  37
  38   @param[in]  ImageHandle           The firmware allocated handle for the UEFI image.
  39   @param[in]  SystemTable           A pointer to the EFI System Table.
  40
  41   @retval EFI_SUCCESS           The operation completed successfully.
  42   @retval EFI_OUT_OF_RESOURCES  The request could not be completed due to a lack of resources.
  43
  44 **/
  45 EFI_STATUS
  46 EFIAPI
  47 Dhcp4DriverEntryPoint (
  48   IN EFI_HANDLE             ImageHandle,
  49   IN EFI_SYSTEM_TABLE       *SystemTable
  50   )
  51 {
  52   return EfiLibInstallDriverBindingComponentName2 (
  53            ImageHandle,
  54            SystemTable,
  55            &gDhcp4DriverBinding,
  56            ImageHandle,
  57            &gDhcp4ComponentName,
  58            &gDhcp4ComponentName2
  59            );
  60 }
  61
  62
  63 /**
  64   Test to see if this driver supports ControllerHandle. This service
  65   is called by the EFI boot service ConnectController(). In
  66   order to make drivers as small as possible, there are a few calling
  67   restrictions for this service. ConnectController() must
  68   follow these calling restrictions. If any other agent wishes to call
  69   Supported() it must also follow these calling restrictions.
  70
  71   @param[in]  This                Protocol instance pointer.
  72   @param[in]  ControllerHandle    Handle of device to test
  73   @param[in]  RemainingDevicePath Optional parameter use to pick a specific child
  74                                   device to start.
  75
  76   @retval EFI_SUCCESS         This driver supports this device
  77   @retval EFI_ALREADY_STARTED This driver is already running on this device
  78   @retval other               This driver does not support this device
  79
  80 **/
  81 EFI_STATUS
  82 EFIAPI
  83 Dhcp4DriverBindingSupported (
  84   IN EFI_DRIVER_BINDING_PROTOCOL  *This,
  85   IN EFI_HANDLE                   ControllerHandle,
  86   IN EFI_DEVICE_PATH_PROTOCOL     *RemainingDevicePath OPTIONAL
  87   )
  88 {
  89   EFI_STATUS  Status;
  90
  91   Status = gBS->OpenProtocol (
  92                   ControllerHandle,
  93                   &gEfiUdp4ServiceBindingProtocolGuid,
  94                   NULL,
  95                   This->DriverBindingHandle,
  96                   ControllerHandle,
  97                   EFI_OPEN_PROTOCOL_TEST_PROTOCOL
  98                   );
  99
 100   return Status;
 101 }
 102
 103
 104
 105 /**
 106   Configure the default UDP child to receive all the DHCP traffics
 107   on this network interface.
 108
 109   @param[in]  UdpIo                  The UDP IO to configure
 110   @param[in]  Context                The context to the function
 111
 112   @retval EFI_SUCCESS            The UDP IO is successfully configured.
 113   @retval Others                 Failed to configure the UDP child.
 114
 115 **/
 116 EFI_STATUS
 117 DhcpConfigUdpIo (
 118   IN UDP_IO                 *UdpIo,
 119   IN VOID                   *Context
 120   )
 121 {
 122   EFI_UDP4_CONFIG_DATA      UdpConfigData;
 123
 124   UdpConfigData.AcceptBroadcast           = TRUE;
 125   UdpConfigData.AcceptPromiscuous         = FALSE;
 126   UdpConfigData.AcceptAnyPort             = FALSE;
 127   UdpConfigData.AllowDuplicatePort        = TRUE;
 128   UdpConfigData.TypeOfService             = 0;
 129   UdpConfigData.TimeToLive                = 64;
 130   UdpConfigData.DoNotFragment             = FALSE;
 131   UdpConfigData.ReceiveTimeout            = 0;
 132   UdpConfigData.TransmitTimeout           = 0;
 133
 134   UdpConfigData.UseDefaultAddress         = FALSE;
 135   UdpConfigData.StationPort               = DHCP_CLIENT_PORT;
 136   UdpConfigData.RemotePort                = DHCP_SERVER_PORT;
 137
 138   ZeroMem (&UdpConfigData.StationAddress, sizeof (EFI_IPv4_ADDRESS));
 139   ZeroMem (&UdpConfigData.SubnetMask, sizeof (EFI_IPv4_ADDRESS));
 140   ZeroMem (&UdpConfigData.RemoteAddress, sizeof (EFI_IPv4_ADDRESS));
 141
 142   return UdpIo->Protocol.Udp4->Configure (UdpIo->Protocol.Udp4, &UdpConfigData);;
 143 }
 144
 145
 146
 147 /**
 148   Destory the DHCP service. The Dhcp4 service may be partly initialized,
 149   or partly destroyed. If a resource is destroyed, it is marked as so in
 150   case the destroy failed and being called again later.
 151
 152   @param[in]  DhcpSb                 The DHCP service instance to destory.
 153
 154   @retval EFI_SUCCESS            Always return success.
 155
 156 **/
 157 EFI_STATUS
 158 Dhcp4CloseService (
 159   IN DHCP_SERVICE           *DhcpSb
 160   )
 161 {
 162   DhcpCleanLease (DhcpSb);
 163
 164   if (DhcpSb->UdpIo != NULL) {
 165     UdpIoFreeIo (DhcpSb->UdpIo);
 166     DhcpSb->UdpIo = NULL;
 167   }
 168
 169   if (DhcpSb->Timer != NULL) {
 170     gBS->SetTimer (DhcpSb->Timer, TimerCancel, 0);
 171     gBS->CloseEvent (DhcpSb->Timer);
 172
 173     DhcpSb->Timer = NULL;
 174   }
 175
 176   return EFI_SUCCESS;
 177 }
 178
 179
 180
 181 /**
 182   Create a new DHCP service binding instance for the controller.
 183
 184   @param[in]  Controller             The controller to install DHCP service binding
 185                                      protocol onto
 186   @param[in]  ImageHandle            The driver's image handle
 187   @param[out] Service                The variable to receive the created DHCP service
 188                                      instance.
 189
 190   @retval EFI_OUT_OF_RESOURCES   Failed to allocate resource .
 191   @retval EFI_SUCCESS            The DHCP service instance is created.
 192   @retval other                  Other error occurs.
 193
 194 **/
 195 EFI_STATUS
 196 Dhcp4CreateService (
 197   IN  EFI_HANDLE            Controller,
 198   IN  EFI_HANDLE            ImageHandle,
 199   OUT DHCP_SERVICE          **Service
 200   )
 201 {
 202   DHCP_SERVICE              *DhcpSb;
 203   EFI_STATUS                Status;
 204
 205   *Service  = NULL;
 206   DhcpSb    = AllocateZeroPool (sizeof (DHCP_SERVICE));
 207
 208   if (DhcpSb == NULL) {
 209     return EFI_OUT_OF_RESOURCES;
 210   }
 211
 212   DhcpSb->Signature       = DHCP_SERVICE_SIGNATURE;
 213   DhcpSb->ServiceState    = DHCP_UNCONFIGED;
 214   DhcpSb->InDestory       = FALSE;
 215   DhcpSb->Controller      = Controller;
 216   DhcpSb->Image           = ImageHandle;
 217   InitializeListHead (&DhcpSb->Children);
 218   DhcpSb->DhcpState       = Dhcp4Stopped;
 219   DhcpSb->Xid             = NET_RANDOM (NetRandomInitSeed ());
 220   CopyMem (
 221     &DhcpSb->ServiceBinding,
 222     &mDhcp4ServiceBindingTemplate,
 223     sizeof (EFI_SERVICE_BINDING_PROTOCOL)
 224     );
 225   //
 226   // Create various resources, UdpIo, Timer, and get Mac address
 227   //
 228   Status = gBS->CreateEvent (
 229                   EVT_NOTIFY_SIGNAL | EVT_TIMER,
 230                   TPL_CALLBACK,
 231                   DhcpOnTimerTick,
 232                   DhcpSb,
 233                   &DhcpSb->Timer
 234                   );
 235
 236   if (EFI_ERROR (Status)) {
 237     goto ON_ERROR;
 238   }
 239
 240   DhcpSb->UdpIo = UdpIoCreateIo (
 241                     Controller,
 242                     ImageHandle,
 243                     DhcpConfigUdpIo,
 244                     UDP_IO_UDP4_VERSION,
 245                     NULL
 246                     );
 247
 248   if (DhcpSb->UdpIo == NULL) {
 249     Status = EFI_OUT_OF_RESOURCES;
 250     goto ON_ERROR;
 251   }
 252
 253   DhcpSb->HwLen  = (UINT8) DhcpSb->UdpIo->SnpMode.HwAddressSize;
 254   DhcpSb->HwType = DhcpSb->UdpIo->SnpMode.IfType;
 255   CopyMem (&DhcpSb->Mac, &DhcpSb->UdpIo->SnpMode.CurrentAddress, sizeof (DhcpSb->Mac));
 256
 257   *Service       = DhcpSb;
 258   return EFI_SUCCESS;
 259
 260 ON_ERROR:
 261   Dhcp4CloseService (DhcpSb);
 262   FreePool (DhcpSb);
 263
 264   return Status;
 265 }
 266
 267
 268 /**
 269   Start this driver on ControllerHandle. This service is called by the
 270   EFI boot service ConnectController(). In order to make
 271   drivers as small as possible, there are a few calling restrictions for
 272   this service. ConnectController() must follow these
 273   calling restrictions. If any other agent wishes to call Start() it
 274   must also follow these calling restrictions.
 275
 276   @param[in]  This                 Protocol instance pointer.
 277   @param[in]  ControllerHandle     Handle of device to bind driver to
 278   @param[in]  RemainingDevicePath  Optional parameter use to pick a specific child
 279                                    device to start.
 280
 281   @retval EFI_SUCCESS          This driver is added to ControllerHandle
 282   @retval EFI_ALREADY_STARTED  This driver is already running on ControllerHandle
 283   @retval other                This driver does not support this device
 284
 285 **/
 286 EFI_STATUS
 287 EFIAPI
 288 Dhcp4DriverBindingStart (
 289   IN EFI_DRIVER_BINDING_PROTOCOL  *This,
 290   IN EFI_HANDLE                   ControllerHandle,
 291   IN EFI_DEVICE_PATH_PROTOCOL     *RemainingDevicePath OPTIONAL
 292   )
 293 {
 294   DHCP_SERVICE              *DhcpSb;
 295   EFI_STATUS                Status;
 296
 297   //
 298   // First: test for the DHCP4 Protocol
 299   //
 300   Status = gBS->OpenProtocol (
 301                   ControllerHandle,
 302                   &gEfiDhcp4ServiceBindingProtocolGuid,
 303                   NULL,
 304                   This->DriverBindingHandle,
 305                   ControllerHandle,
 306                   EFI_OPEN_PROTOCOL_TEST_PROTOCOL
 307                   );
 308
 309   if (Status == EFI_SUCCESS) {
 310     return EFI_ALREADY_STARTED;
 311   }
 312
 313   Status = Dhcp4CreateService (ControllerHandle, This->DriverBindingHandle, &DhcpSb);
 314
 315   if (EFI_ERROR (Status)) {
 316     return Status;
 317   }
 318
 319   //
 320   // Start the receiving
 321   //
 322   Status = UdpIoRecvDatagram (DhcpSb->UdpIo, DhcpInput, DhcpSb, 0);
 323
 324   if (EFI_ERROR (Status)) {
 325     goto ON_ERROR;
 326   }
 327   Status = gBS->SetTimer (DhcpSb->Timer, TimerPeriodic, TICKS_PER_SECOND);
 328
 329   if (EFI_ERROR (Status)) {
 330     goto ON_ERROR;
 331   }
 332
 333   //
 334   // Install the Dhcp4ServiceBinding Protocol onto ControlerHandle
 335   //
 336   Status = gBS->InstallMultipleProtocolInterfaces (
 337                   &ControllerHandle,
 338                   &gEfiDhcp4ServiceBindingProtocolGuid,
 339                   &DhcpSb->ServiceBinding,
 340                   NULL
 341                   );
 342
 343   if (EFI_ERROR (Status)) {
 344     goto ON_ERROR;
 345   }
 346
 347   return Status;
 348
 349 ON_ERROR:
 350   Dhcp4CloseService (DhcpSb);
 351   FreePool (DhcpSb);
 352   return Status;
 353 }
 354
 355
 356 /**
 357   Stop this driver on ControllerHandle. This service is called by the
 358   EFI boot service DisconnectController(). In order to
 359   make drivers as small as possible, there are a few calling
 360   restrictions for this service. DisconnectController()
 361   must follow these calling restrictions. If any other agent wishes
 362   to call Stop() it must also follow these calling restrictions.
 363
 364   @param[in]  This              Protocol instance pointer.
 365   @param[in]  ControllerHandle  Handle of device to stop driver on
 366   @param[in]  NumberOfChildren  Number of Handles in ChildHandleBuffer. If number of
 367                                 children is zero stop the entire bus driver.
 368   @param[in]  ChildHandleBuffer List of Child Handles to Stop.
 369
 370   @retval EFI_SUCCESS       This driver is removed ControllerHandle
 371   @retval other             This driver was not removed from this device
 372
 373 **/
 374 EFI_STATUS
 375 EFIAPI
 376 Dhcp4DriverBindingStop (
 377   IN  EFI_DRIVER_BINDING_PROTOCOL  *This,
 378   IN  EFI_HANDLE                   ControllerHandle,
 379   IN  UINTN                        NumberOfChildren,
 380   IN  EFI_HANDLE                   *ChildHandleBuffer
 381   )
 382 {
 383   EFI_SERVICE_BINDING_PROTOCOL  *ServiceBinding;
 384   DHCP_SERVICE                  *DhcpSb;
 385   DHCP_PROTOCOL                 *Instance;
 386   EFI_HANDLE                    NicHandle;
 387   EFI_STATUS                    Status;
 388   EFI_TPL                       OldTpl;
 389
 390   //
 391   // DHCP driver opens UDP child, So, the ControllerHandle is the
 392   // UDP child handle. locate the Nic handle first.
 393   //
 394   NicHandle = NetLibGetNicHandle (ControllerHandle, &gEfiUdp4ProtocolGuid);
 395
 396   if (NicHandle == NULL) {
 397     return EFI_DEVICE_ERROR;
 398   }
 399
 400    Status = gBS->OpenProtocol (
 401                   NicHandle,
 402                   &gEfiDhcp4ServiceBindingProtocolGuid,
 403                   (VOID **) &ServiceBinding,
 404                   This->DriverBindingHandle,
 405                   NicHandle,
 406                   EFI_OPEN_PROTOCOL_GET_PROTOCOL
 407                   );
 408
 409   if (EFI_ERROR (Status)) {
 410     return EFI_DEVICE_ERROR;
 411   }
 412
 413   DhcpSb = DHCP_SERVICE_FROM_THIS (ServiceBinding);
 414
 415   if (DhcpSb->InDestory) {
 416     return EFI_SUCCESS;
 417   }
 418
 419   OldTpl = gBS->RaiseTPL (TPL_CALLBACK);
 420
 421   if (NumberOfChildren == 0) {
 422
 423     DhcpSb->InDestory    = TRUE;
 424     DhcpSb->ServiceState = DHCP_DESTORY;
 425
 426     gBS->UninstallProtocolInterface (
 427            NicHandle,
 428            &gEfiDhcp4ServiceBindingProtocolGuid,
 429            ServiceBinding
 430            );
 431
 432     Dhcp4CloseService (DhcpSb);
 433
 434     FreePool (DhcpSb);
 435   } else {
 436     //
 437     // Don't use NET_LIST_FOR_EACH_SAFE here, Dhcp4ServiceBindingDestoryChild
 438     // may cause other child to be deleted.
 439     //
 440     while (!IsListEmpty (&DhcpSb->Children)) {
 441       Instance = NET_LIST_HEAD (&DhcpSb->Children, DHCP_PROTOCOL, Link);
 442       ServiceBinding->DestroyChild (ServiceBinding, Instance->Handle);
 443     }
 444
 445     if (DhcpSb->NumChildren != 0) {
 446       Status = EFI_DEVICE_ERROR;
 447     }
 448   }
 449
 450   gBS->RestoreTPL (OldTpl);
 451
 452   return Status;
 453 }
 454
 455
 456 /**
 457   Initialize a new DHCP instance.
 458
 459   @param  DhcpSb                 The dhcp service instance
 460   @param  Instance               The dhcp instance to initialize
 461
 462 **/
 463 VOID
 464 DhcpInitProtocol (
 465   IN     DHCP_SERVICE           *DhcpSb,
 466   IN OUT DHCP_PROTOCOL          *Instance
 467   )
 468 {
 469   Instance->Signature         = DHCP_PROTOCOL_SIGNATURE;
 470   CopyMem (&Instance->Dhcp4Protocol, &mDhcp4ProtocolTemplate, sizeof (Instance->Dhcp4Protocol));
 471   InitializeListHead (&Instance->Link);
 472   Instance->Handle            = NULL;
 473   Instance->Service           = DhcpSb;
 474   Instance->InDestory         = FALSE;
 475   Instance->CompletionEvent   = NULL;
 476   Instance->RenewRebindEvent  = NULL;
 477   Instance->Token             = NULL;
 478   Instance->UdpIo             = NULL;
 479   NetbufQueInit (&Instance->ResponseQueue);
 480 }
 481
 482
 483 /**
 484   Creates a child handle and installs a protocol.
 485
 486   The CreateChild() function installs a protocol on ChildHandle.
 487   If ChildHandle is a pointer to NULL, then a new handle is created and returned in ChildHandle.
 488   If ChildHandle is not a pointer to NULL, then the protocol installs on the existing ChildHandle.
 489
 490   @param  This        Pointer to the EFI_SERVICE_BINDING_PROTOCOL instance.
 491   @param  ChildHandle Pointer to the handle of the child to create. If it is NULL,
 492                       then a new handle is created. If it is a pointer to an existing UEFI handle,
 493                       then the protocol is added to the existing UEFI handle.
 494
 495   @retval EFI_SUCCES            The protocol was added to ChildHandle.
 496   @retval EFI_INVALID_PARAMETER ChildHandle is NULL.
 497   @retval EFI_OUT_OF_RESOURCES  There are not enough resources availabe to create
 498                                 the child
 499   @retval other                 The child handle was not created
 500
 501 **/
 502 EFI_STATUS
 503 EFIAPI
 504 Dhcp4ServiceBindingCreateChild (
 505   IN EFI_SERVICE_BINDING_PROTOCOL  *This,
 506   IN EFI_HANDLE                    *ChildHandle
 507   )
 508 {
 509   DHCP_SERVICE              *DhcpSb;
 510   DHCP_PROTOCOL             *Instance;
 511   EFI_STATUS                Status;
 512   EFI_TPL                   OldTpl;
 513   VOID                      *Udp4;
 514
 515   if ((This == NULL) || (ChildHandle == NULL)) {
 516     return EFI_INVALID_PARAMETER;
 517   }
 518
 519   Instance = AllocatePool (sizeof (*Instance));
 520
 521   if (Instance == NULL) {
 522     return EFI_OUT_OF_RESOURCES;
 523   }
 524
 525   DhcpSb = DHCP_SERVICE_FROM_THIS (This);
 526   DhcpInitProtocol (DhcpSb, Instance);
 527
 528   //
 529   // Install DHCP4 onto ChildHandle
 530   //
 531   Status = gBS->InstallMultipleProtocolInterfaces (
 532                   ChildHandle,
 533                   &gEfiDhcp4ProtocolGuid,
 534                   &Instance->Dhcp4Protocol,
 535                   NULL
 536                   );
 537
 538   if (EFI_ERROR (Status)) {
 539     FreePool (Instance);
 540     return Status;
 541   }
 542
 543   Instance->Handle  = *ChildHandle;
 544
 545   //
 546   // Open the Udp4 protocol BY_CHILD.
 547   //
 548   Status = gBS->OpenProtocol (
 549                   DhcpSb->UdpIo->UdpHandle,
 550                   &gEfiUdp4ProtocolGuid,
 551                   (VOID **) &Udp4,
 552                   gDhcp4DriverBinding.DriverBindingHandle,
 553                   Instance->Handle,
 554                   EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER
 555                   );
 556   if (EFI_ERROR (Status)) {
 557     gBS->UninstallMultipleProtocolInterfaces (
 558            Instance->Handle,
 559            &gEfiDhcp4ProtocolGuid,
 560            &Instance->Dhcp4Protocol,
 561            NULL
 562            );
 563
 564     FreePool (Instance);
 565     return Status;
 566   }
 567
 568   OldTpl = gBS->RaiseTPL (TPL_CALLBACK);
 569
 570   InsertTailList (&DhcpSb->Children, &Instance->Link);
 571   DhcpSb->NumChildren++;
 572
 573   gBS->RestoreTPL (OldTpl);
 574
 575   return EFI_SUCCESS;
 576 }
 577
 578
 579 /**
 580   Destroys a child handle with a protocol installed on it.
 581
 582   The DestroyChild() function does the opposite of CreateChild(). It removes a protocol
 583   that was installed by CreateChild() from ChildHandle. If the removed protocol is the
 584   last protocol on ChildHandle, then ChildHandle is destroyed.
 585
 586   @param  This        Pointer to the EFI_SERVICE_BINDING_PROTOCOL instance.
 587   @param  ChildHandle Handle of the child to destroy
 588
 589   @retval EFI_SUCCES            The protocol was removed from ChildHandle.
 590   @retval EFI_UNSUPPORTED       ChildHandle does not support the protocol that is being removed.
 591   @retval EFI_INVALID_PARAMETER Child handle is not a valid UEFI Handle.
 592   @retval EFI_ACCESS_DENIED     The protocol could not be removed from the ChildHandle
 593                                 because its services are being used.
 594   @retval other                 The child handle was not destroyed
 595
 596 **/
 597 EFI_STATUS
 598 EFIAPI
 599 Dhcp4ServiceBindingDestroyChild (
 600   IN EFI_SERVICE_BINDING_PROTOCOL  *This,
 601   IN EFI_HANDLE                    ChildHandle
 602   )
 603 {
 604   DHCP_SERVICE              *DhcpSb;
 605   DHCP_PROTOCOL             *Instance;
 606   EFI_DHCP4_PROTOCOL        *Dhcp;
 607   EFI_TPL                   OldTpl;
 608   EFI_STATUS                Status;
 609
 610   if ((This == NULL) || (ChildHandle == NULL)) {
 611     return EFI_INVALID_PARAMETER;
 612   }
 613
 614   //
 615   // Retrieve the private context data structures
 616   //
 617   Status = gBS->OpenProtocol (
 618                   ChildHandle,
 619                   &gEfiDhcp4ProtocolGuid,
 620                   (VOID **) &Dhcp,
 621                   gDhcp4DriverBinding.DriverBindingHandle,
 622                   ChildHandle,
 623                   EFI_OPEN_PROTOCOL_GET_PROTOCOL
 624                   );
 625
 626   if (EFI_ERROR (Status)) {
 627     return EFI_UNSUPPORTED;
 628   }
 629
 630   Instance  = DHCP_INSTANCE_FROM_THIS (Dhcp);
 631   DhcpSb    = DHCP_SERVICE_FROM_THIS (This);
 632
 633   if (Instance->Service != DhcpSb) {
 634     return EFI_INVALID_PARAMETER;
 635   }
 636
 637   //
 638   // A child can be destroyed more than once. For example,
 639   // Dhcp4DriverBindingStop will destroy all of its children.
 640   // when caller driver is being stopped, it will destory the
 641   // dhcp child it opens.
 642   //
 643   if (Instance->InDestory) {
 644     return EFI_SUCCESS;
 645   }
 646
 647   OldTpl = gBS->RaiseTPL (TPL_CALLBACK);
 648   Instance->InDestory = TRUE;
 649
 650   //
 651   // Close the Udp4 protocol.
 652   //
 653   gBS->CloseProtocol (
 654          DhcpSb->UdpIo->UdpHandle,
 655          &gEfiUdp4ProtocolGuid,
 656          gDhcp4DriverBinding.DriverBindingHandle,
 657          ChildHandle
 658          );
 659
 660   //
 661   // Uninstall the DHCP4 protocol first to enable a top down destruction.
 662   //
 663   Status = gBS->UninstallProtocolInterface (
 664                   ChildHandle,
 665                   &gEfiDhcp4ProtocolGuid,
 666                   Dhcp
 667                   );
 668
 669   if (EFI_ERROR (Status)) {
 670     Instance->InDestory = FALSE;
 671
 672     gBS->RestoreTPL (OldTpl);
 673     return Status;
 674   }
 675
 676   if (DhcpSb->ActiveChild == Instance) {
 677     DhcpYieldControl (DhcpSb);
 678   }
 679
 680   RemoveEntryList (&Instance->Link);
 681   DhcpSb->NumChildren--;
 682
 683   gBS->RestoreTPL (OldTpl);
 684
 685   FreePool (Instance);
 686   return EFI_SUCCESS;
 687 }