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 port to configure
 110   @param[in]  Context                The context to the function
 111
 112   @retval EFI_SUCCESS            The UDP IO port is successfully configured.
 113   @retval Others                 Failed to configure the UDP child.
 114
 115 **/
 116 EFI_STATUS
 117 DhcpConfigUdpIo (
 118   IN UDP_IO_PORT            *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->Udp->Configure (UdpIo->Udp, &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     UdpIoFreePort (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 = UdpIoCreatePort (Controller, ImageHandle, DhcpConfigUdpIo, NULL);
 241
 242   if (DhcpSb->UdpIo == NULL) {
 243     Status = EFI_OUT_OF_RESOURCES;
 244     goto ON_ERROR;
 245   }
 246
 247   DhcpSb->HwLen  = (UINT8) DhcpSb->UdpIo->SnpMode.HwAddressSize;
 248   DhcpSb->HwType = DhcpSb->UdpIo->SnpMode.IfType;
 249   CopyMem (&DhcpSb->Mac, &DhcpSb->UdpIo->SnpMode.CurrentAddress, sizeof (DhcpSb->Mac));
 250
 251   *Service       = DhcpSb;
 252   return EFI_SUCCESS;
 253
 254 ON_ERROR:
 255   Dhcp4CloseService (DhcpSb);
 256   FreePool (DhcpSb);
 257
 258   return Status;
 259 }
 260
 261
 262 /**
 263   Start this driver on ControllerHandle. This service is called by the
 264   EFI boot service ConnectController(). In order to make
 265   drivers as small as possible, there are a few calling restrictions for
 266   this service. ConnectController() must follow these
 267   calling restrictions. If any other agent wishes to call Start() it
 268   must also follow these calling restrictions.
 269
 270   @param[in]  This                 Protocol instance pointer.
 271   @param[in]  ControllerHandle     Handle of device to bind driver to
 272   @param[in]  RemainingDevicePath  Optional parameter use to pick a specific child
 273                                    device to start.
 274
 275   @retval EFI_SUCCESS          This driver is added to ControllerHandle
 276   @retval EFI_ALREADY_STARTED  This driver is already running on ControllerHandle
 277   @retval other                This driver does not support this device
 278
 279 **/
 280 EFI_STATUS
 281 EFIAPI
 282 Dhcp4DriverBindingStart (
 283   IN EFI_DRIVER_BINDING_PROTOCOL  *This,
 284   IN EFI_HANDLE                   ControllerHandle,
 285   IN EFI_DEVICE_PATH_PROTOCOL     *RemainingDevicePath OPTIONAL
 286   )
 287 {
 288   DHCP_SERVICE              *DhcpSb;
 289   EFI_STATUS                Status;
 290
 291   //
 292   // First: test for the DHCP4 Protocol
 293   //
 294   Status = gBS->OpenProtocol (
 295                   ControllerHandle,
 296                   &gEfiDhcp4ServiceBindingProtocolGuid,
 297                   NULL,
 298                   This->DriverBindingHandle,
 299                   ControllerHandle,
 300                   EFI_OPEN_PROTOCOL_TEST_PROTOCOL
 301                   );
 302
 303   if (Status == EFI_SUCCESS) {
 304     return EFI_ALREADY_STARTED;
 305   }
 306
 307   Status = Dhcp4CreateService (ControllerHandle, This->DriverBindingHandle, &DhcpSb);
 308
 309   if (EFI_ERROR (Status)) {
 310     return Status;
 311   }
 312
 313   //
 314   // Start the receiving
 315   //
 316   Status = UdpIoRecvDatagram (DhcpSb->UdpIo, DhcpInput, DhcpSb, 0);
 317
 318   if (EFI_ERROR (Status)) {
 319     goto ON_ERROR;
 320   }
 321   Status = gBS->SetTimer (DhcpSb->Timer, TimerPeriodic, TICKS_PER_SECOND);
 322
 323   if (EFI_ERROR (Status)) {
 324     goto ON_ERROR;
 325   }
 326
 327   //
 328   // Install the Dhcp4ServiceBinding Protocol onto ControlerHandle
 329   //
 330   Status = gBS->InstallMultipleProtocolInterfaces (
 331                   &ControllerHandle,
 332                   &gEfiDhcp4ServiceBindingProtocolGuid,
 333                   &DhcpSb->ServiceBinding,
 334                   NULL
 335                   );
 336
 337   if (EFI_ERROR (Status)) {
 338     goto ON_ERROR;
 339   }
 340
 341   return Status;
 342
 343 ON_ERROR:
 344   Dhcp4CloseService (DhcpSb);
 345   FreePool (DhcpSb);
 346   return Status;
 347 }
 348
 349
 350 /**
 351   Stop this driver on ControllerHandle. This service is called by the
 352   EFI boot service DisconnectController(). In order to
 353   make drivers as small as possible, there are a few calling
 354   restrictions for this service. DisconnectController()
 355   must follow these calling restrictions. If any other agent wishes
 356   to call Stop() it must also follow these calling restrictions.
 357
 358   @param[in]  This              Protocol instance pointer.
 359   @param[in]  ControllerHandle  Handle of device to stop driver on
 360   @param[in]  NumberOfChildren  Number of Handles in ChildHandleBuffer. If number of
 361                                 children is zero stop the entire bus driver.
 362   @param[in]  ChildHandleBuffer List of Child Handles to Stop.
 363
 364   @retval EFI_SUCCESS       This driver is removed ControllerHandle
 365   @retval other             This driver was not removed from this device
 366
 367 **/
 368 EFI_STATUS
 369 EFIAPI
 370 Dhcp4DriverBindingStop (
 371   IN  EFI_DRIVER_BINDING_PROTOCOL  *This,
 372   IN  EFI_HANDLE                   ControllerHandle,
 373   IN  UINTN                        NumberOfChildren,
 374   IN  EFI_HANDLE                   *ChildHandleBuffer
 375   )
 376 {
 377   EFI_SERVICE_BINDING_PROTOCOL  *ServiceBinding;
 378   DHCP_SERVICE                  *DhcpSb;
 379   DHCP_PROTOCOL                 *Instance;
 380   EFI_HANDLE                    NicHandle;
 381   EFI_STATUS                    Status;
 382   EFI_TPL                       OldTpl;
 383
 384   //
 385   // DHCP driver opens UDP child, So, the ControllerHandle is the
 386   // UDP child handle. locate the Nic handle first.
 387   //
 388   NicHandle = NetLibGetNicHandle (ControllerHandle, &gEfiUdp4ProtocolGuid);
 389
 390   if (NicHandle == NULL) {
 391     return EFI_DEVICE_ERROR;
 392   }
 393
 394    Status = gBS->OpenProtocol (
 395                   NicHandle,
 396                   &gEfiDhcp4ServiceBindingProtocolGuid,
 397                   (VOID **) &ServiceBinding,
 398                   This->DriverBindingHandle,
 399                   NicHandle,
 400                   EFI_OPEN_PROTOCOL_GET_PROTOCOL
 401                   );
 402
 403   if (EFI_ERROR (Status)) {
 404     return EFI_DEVICE_ERROR;
 405   }
 406
 407   DhcpSb = DHCP_SERVICE_FROM_THIS (ServiceBinding);
 408
 409   if (DhcpSb->InDestory) {
 410     return EFI_SUCCESS;
 411   }
 412
 413   OldTpl = gBS->RaiseTPL (TPL_CALLBACK);
 414
 415   if (NumberOfChildren == 0) {
 416
 417     DhcpSb->InDestory    = TRUE;
 418     DhcpSb->ServiceState = DHCP_DESTORY;
 419
 420     gBS->UninstallProtocolInterface (
 421            NicHandle,
 422            &gEfiDhcp4ServiceBindingProtocolGuid,
 423            ServiceBinding
 424            );
 425
 426     Dhcp4CloseService (DhcpSb);
 427
 428     FreePool (DhcpSb);
 429   } else {
 430     //
 431     // Don't use NET_LIST_FOR_EACH_SAFE here, Dhcp4ServiceBindingDestoryChild
 432     // may cause other child to be deleted.
 433     //
 434     while (!IsListEmpty (&DhcpSb->Children)) {
 435       Instance = NET_LIST_HEAD (&DhcpSb->Children, DHCP_PROTOCOL, Link);
 436       ServiceBinding->DestroyChild (ServiceBinding, Instance->Handle);
 437     }
 438
 439     if (DhcpSb->NumChildren != 0) {
 440       Status = EFI_DEVICE_ERROR;
 441     }
 442   }
 443
 444   gBS->RestoreTPL (OldTpl);
 445
 446   return Status;
 447 }
 448
 449
 450 /**
 451   Initialize a new DHCP instance.
 452
 453   @param  DhcpSb                 The dhcp service instance
 454   @param  Instance               The dhcp instance to initialize
 455
 456 **/
 457 VOID
 458 DhcpInitProtocol (
 459   IN     DHCP_SERVICE           *DhcpSb,
 460   IN OUT DHCP_PROTOCOL          *Instance
 461   )
 462 {
 463   Instance->Signature         = DHCP_PROTOCOL_SIGNATURE;
 464   CopyMem (&Instance->Dhcp4Protocol, &mDhcp4ProtocolTemplate, sizeof (Instance->Dhcp4Protocol));
 465   InitializeListHead (&Instance->Link);
 466   Instance->Handle            = NULL;
 467   Instance->Service           = DhcpSb;
 468   Instance->InDestory         = FALSE;
 469   Instance->CompletionEvent   = NULL;
 470   Instance->RenewRebindEvent  = NULL;
 471   Instance->Token             = NULL;
 472   Instance->UdpIo             = NULL;
 473   NetbufQueInit (&Instance->ResponseQueue);
 474 }
 475
 476
 477 /**
 478   Creates a child handle and installs a protocol.
 479
 480   The CreateChild() function installs a protocol on ChildHandle.
 481   If ChildHandle is a pointer to NULL, then a new handle is created and returned in ChildHandle.
 482   If ChildHandle is not a pointer to NULL, then the protocol installs on the existing ChildHandle.
 483
 484   @param  This        Pointer to the EFI_SERVICE_BINDING_PROTOCOL instance.
 485   @param  ChildHandle Pointer to the handle of the child to create. If it is NULL,
 486                       then a new handle is created. If it is a pointer to an existing UEFI handle,
 487                       then the protocol is added to the existing UEFI handle.
 488
 489   @retval EFI_SUCCES            The protocol was added to ChildHandle.
 490   @retval EFI_INVALID_PARAMETER ChildHandle is NULL.
 491   @retval EFI_OUT_OF_RESOURCES  There are not enough resources availabe to create
 492                                 the child
 493   @retval other                 The child handle was not created
 494
 495 **/
 496 EFI_STATUS
 497 EFIAPI
 498 Dhcp4ServiceBindingCreateChild (
 499   IN EFI_SERVICE_BINDING_PROTOCOL  *This,
 500   IN EFI_HANDLE                    *ChildHandle
 501   )
 502 {
 503   DHCP_SERVICE              *DhcpSb;
 504   DHCP_PROTOCOL             *Instance;
 505   EFI_STATUS                Status;
 506   EFI_TPL                   OldTpl;
 507   VOID                      *Udp4;
 508
 509   if ((This == NULL) || (ChildHandle == NULL)) {
 510     return EFI_INVALID_PARAMETER;
 511   }
 512
 513   Instance = AllocatePool (sizeof (*Instance));
 514
 515   if (Instance == NULL) {
 516     return EFI_OUT_OF_RESOURCES;
 517   }
 518
 519   DhcpSb = DHCP_SERVICE_FROM_THIS (This);
 520   DhcpInitProtocol (DhcpSb, Instance);
 521
 522   //
 523   // Install DHCP4 onto ChildHandle
 524   //
 525   Status = gBS->InstallMultipleProtocolInterfaces (
 526                   ChildHandle,
 527                   &gEfiDhcp4ProtocolGuid,
 528                   &Instance->Dhcp4Protocol,
 529                   NULL
 530                   );
 531
 532   if (EFI_ERROR (Status)) {
 533     FreePool (Instance);
 534     return Status;
 535   }
 536
 537   Instance->Handle  = *ChildHandle;
 538
 539   //
 540   // Open the Udp4 protocol BY_CHILD.
 541   //
 542   Status = gBS->OpenProtocol (
 543                   DhcpSb->UdpIo->UdpHandle,
 544                   &gEfiUdp4ProtocolGuid,
 545                   (VOID **) &Udp4,
 546                   gDhcp4DriverBinding.DriverBindingHandle,
 547                   Instance->Handle,
 548                   EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER
 549                   );
 550   if (EFI_ERROR (Status)) {
 551     gBS->UninstallMultipleProtocolInterfaces (
 552            Instance->Handle,
 553            &gEfiDhcp4ProtocolGuid,
 554            &Instance->Dhcp4Protocol,
 555            NULL
 556            );
 557
 558     FreePool (Instance);
 559     return Status;
 560   }
 561
 562   OldTpl = gBS->RaiseTPL (TPL_CALLBACK);
 563
 564   InsertTailList (&DhcpSb->Children, &Instance->Link);
 565   DhcpSb->NumChildren++;
 566
 567   gBS->RestoreTPL (OldTpl);
 568
 569   return EFI_SUCCESS;
 570 }
 571
 572
 573 /**
 574   Destroys a child handle with a protocol installed on it.
 575
 576   The DestroyChild() function does the opposite of CreateChild(). It removes a protocol
 577   that was installed by CreateChild() from ChildHandle. If the removed protocol is the
 578   last protocol on ChildHandle, then ChildHandle is destroyed.
 579
 580   @param  This        Pointer to the EFI_SERVICE_BINDING_PROTOCOL instance.
 581   @param  ChildHandle Handle of the child to destroy
 582
 583   @retval EFI_SUCCES            The protocol was removed from ChildHandle.
 584   @retval EFI_UNSUPPORTED       ChildHandle does not support the protocol that is being removed.
 585   @retval EFI_INVALID_PARAMETER Child handle is not a valid UEFI Handle.
 586   @retval EFI_ACCESS_DENIED     The protocol could not be removed from the ChildHandle
 587                                 because its services are being used.
 588   @retval other                 The child handle was not destroyed
 589
 590 **/
 591 EFI_STATUS
 592 EFIAPI
 593 Dhcp4ServiceBindingDestroyChild (
 594   IN EFI_SERVICE_BINDING_PROTOCOL  *This,
 595   IN EFI_HANDLE                    ChildHandle
 596   )
 597 {
 598   DHCP_SERVICE              *DhcpSb;
 599   DHCP_PROTOCOL             *Instance;
 600   EFI_DHCP4_PROTOCOL        *Dhcp;
 601   EFI_TPL                   OldTpl;
 602   EFI_STATUS                Status;
 603
 604   if ((This == NULL) || (ChildHandle == NULL)) {
 605     return EFI_INVALID_PARAMETER;
 606   }
 607
 608   //
 609   // Retrieve the private context data structures
 610   //
 611   Status = gBS->OpenProtocol (
 612                   ChildHandle,
 613                   &gEfiDhcp4ProtocolGuid,
 614                   (VOID **) &Dhcp,
 615                   gDhcp4DriverBinding.DriverBindingHandle,
 616                   ChildHandle,
 617                   EFI_OPEN_PROTOCOL_GET_PROTOCOL
 618                   );
 619
 620   if (EFI_ERROR (Status)) {
 621     return EFI_UNSUPPORTED;
 622   }
 623
 624   Instance  = DHCP_INSTANCE_FROM_THIS (Dhcp);
 625   DhcpSb    = DHCP_SERVICE_FROM_THIS (This);
 626
 627   if (Instance->Service != DhcpSb) {
 628     return EFI_INVALID_PARAMETER;
 629   }
 630
 631   //
 632   // A child can be destroyed more than once. For example,
 633   // Dhcp4DriverBindingStop will destroy all of its children.
 634   // when caller driver is being stopped, it will destory the
 635   // dhcp child it opens.
 636   //
 637   if (Instance->InDestory) {
 638     return EFI_SUCCESS;
 639   }
 640
 641   OldTpl = gBS->RaiseTPL (TPL_CALLBACK);
 642   Instance->InDestory = TRUE;
 643
 644   //
 645   // Close the Udp4 protocol.
 646   //
 647   gBS->CloseProtocol (
 648          DhcpSb->UdpIo->UdpHandle,
 649          &gEfiUdp4ProtocolGuid,
 650          gDhcp4DriverBinding.DriverBindingHandle,
 651          ChildHandle
 652          );
 653
 654   //
 655   // Uninstall the DHCP4 protocol first to enable a top down destruction.
 656   //
 657   Status = gBS->UninstallProtocolInterface (
 658                   ChildHandle,
 659                   &gEfiDhcp4ProtocolGuid,
 660                   Dhcp
 661                   );
 662
 663   if (EFI_ERROR (Status)) {
 664     Instance->InDestory = FALSE;
 665
 666     gBS->RestoreTPL (OldTpl);
 667     return Status;
 668   }
 669
 670   if (DhcpSb->ActiveChild == Instance) {
 671     DhcpYieldControl (DhcpSb);
 672   }
 673
 674   RemoveEntryList (&Instance->Link);
 675   DhcpSb->NumChildren--;
 676
 677   gBS->RestoreTPL (OldTpl);
 678
 679   FreePool (Instance);
 680   return EFI_SUCCESS;
 681 }