BdsLibBootViaBootOption() - Boot up to load drivers

/*You can find the function in EDK1.6 BdsBoot.c*/

EFI_STATUS
BdsLibBootViaBootOption (
  IN  BDS_COMMON_OPTION             * Option,
  IN  EFI_DEVICE_PATH_PROTOCOL      * DevicePath,
  OUT UINTN                         *ExitDataSize,
  OUT CHAR16                        **ExitData OPTIONAL
  )
/*++

Routine Description:

  Process the boot option follow the EFI 1.1 specification and
  special treat the legacy boot option with BBS_DEVICE_PATH.

Arguments:

  Option       - The boot option need to be processed

  DevicePath   - The device path which describe where to load
                 the boot image or the legcy BBS device path
                 to boot the legacy OS

  ExitDataSize - Returned directly from gBS->StartImage ()

  ExitData     - Returned directly from gBS->StartImage ()

Returns:

  EFI_SUCCESS   - Status from gBS->StartImage ()

  EFI_NOT_FOUND - If the Device Path is not found in the system

--*/
{
  EFI_STATUS                Status;
  EFI_HANDLE                Handle;
  EFI_HANDLE                ImageHandle;
  EFI_DEVICE_PATH_PROTOCOL  *FilePath;
  EFI_LOADED_IMAGE_PROTOCOL *ImageInfo;
  EFI_EVENT                 ReadyToBootEvent;
  EFI_DEVICE_PATH_PROTOCOL  *WorkingDevicePath;
  EFI_ACPI_S3_SAVE_PROTOCOL *AcpiS3Save;
  EFI_LIST_ENTRY            TempBootLists;
  EFI_TCG_PLATFORM_PROTOCOL *TcgPlatformProtocol;
  //
  // Record the performance data for End of BDS
  //
  PERF_END (0, BDS_TOK, NULL, 0);

  *ExitDataSize = 0;
  *ExitData     = NULL;

  //
  // Notes: put EFI64 ROM Shadow Solution
  //
  EFI64_SHADOW_ALL_LEGACY_ROM ();

  //
  // Notes: this code can be remove after the s3 script table
  // hook on the event EFI_EVENT_SIGNAL_READY_TO_BOOT or
  // EFI_EVENT_SIGNAL_LEGACY_BOOT
  //
  Status = gBS->LocateProtocol (&gEfiAcpiS3SaveGuid, NULL, &AcpiS3Save);
  if (!EFI_ERROR (Status)) {
    AcpiS3Save->S3Save (AcpiS3Save, NULL);
  }
  //
  // If it's Device Path that starts with a hard drive path, append it with the front part to compose a
  // full device path
  //
  WorkingDevicePath = NULL;
  if ((DevicePathType (DevicePath) == MEDIA_DEVICE_PATH) &&
      (DevicePathSubType (DevicePath) == MEDIA_HARDDRIVE_DP)) {
    WorkingDevicePath = BdsExpandPartitionPartialDevicePathToFull (
                          (HARDDRIVE_DEVICE_PATH *)DevicePath
                          );
    if (WorkingDevicePath != NULL) {
      DevicePath = WorkingDevicePath;
    }
  }
  
  //
  // Set Boot Current
  //
  gRT->SetVariable (
        L"BootCurrent",
        &gEfiGlobalVariableGuid,
        EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS,
        sizeof (UINT16),
        &Option->BootCurrent
        );
        
  //
  // Signal the EFI_EVENT_SIGNAL_READY_TO_BOOT event
  //
  Status = EfiCreateEventReadyToBoot (
             EFI_TPL_CALLBACK,
             NULL,
             NULL,
             &ReadyToBootEvent
             );

  if (!EFI_ERROR (Status)) {
    gBS->SignalEvent (ReadyToBootEvent);
    gBS->CloseEvent (ReadyToBootEvent);
  }


  if ((DevicePathType (Option->DevicePath) == BBS_DEVICE_PATH) &&
      (DevicePathSubType (Option->DevicePath) == BBS_BBS_DP)
    ) {
    //
    // Check to see if we should legacy BOOT. If yes then do the legacy boot
    //
    return BdsLibDoLegacyBoot (Option);
  }
  
  //
  // If the boot option point to Internal FV shell, make sure it is valid
  //
  Status = BdsLibUpdateFvFileDevicePath (&DevicePath, &gEfiShellFileGuid);
  if (!EFI_ERROR(Status)) {
    if (Option->DevicePath != NULL) {
      EfiLibSafeFreePool(Option->DevicePath);
    }
    Option->DevicePath  = EfiLibAllocateZeroPool (EfiDevicePathSize (DevicePath));
    EfiCopyMem (Option->DevicePath, DevicePath, EfiDevicePathSize (DevicePath));
    //
    // Update the shell boot option
    //
    InitializeListHead (&TempBootLists);
    BdsLibRegisterNewOption (&TempBootLists, DevicePath, L"EFI Internal Shell", L"BootOrder"); 
    //
    // free the temporary device path created by BdsLibUpdateFvFileDevicePath()
    //
    gBS->FreePool (DevicePath); 
    DevicePath = Option->DevicePath;
  }
  //
  // Measure GPT Table
  //
  Status = gBS->LocateProtocol (
                  &gEfiTcgPlatformProtocolGuid,
                  NULL,
                  &TcgPlatformProtocol
                  );  
  if (!EFI_ERROR (Status)) {
    Status = TcgPlatformProtocol->MeasureGptTable (DevicePath);
  }
  
  //
  // Drop the TPL level from EFI_TPL_DRIVER to EFI_TPL_APPLICATION
  //
  gBS->RestoreTPL (EFI_TPL_APPLICATION);

  DEBUG ((EFI_D_INFO | EFI_D_LOAD, "Booting EFI way %S\n", Option->Description));

  Status = gBS->LoadImage (
                  TRUE,
                  mBdsImageHandle,
                  DevicePath,
                  NULL,
                  0,
                  &ImageHandle
                  );
                  
  //
  // If we didn't find an image directly, we need to try as if it is a removable device boot opotion 
  // and load the image according to the default boot behavior for removable device.
  //
  if (EFI_ERROR (Status)) {
    //
    // check if there is a bootable removable media could be found in this device path , 
    // and get the bootable media handle 
    //
    Handle = BdsLibGetBootableHandle(DevicePath);
    if (Handle == NULL) {
       goto Done;
    }
    //
    // Load the default boot file \EFI\BOOT\boot{machinename}.EFI from removable Media
    //  machinename is ia32, ia64, x64, ...
    //
    FilePath = EfiFileDevicePath (Handle, DEFAULT_REMOVABLE_FILE_NAME); 
    if (FilePath) {
      Status = gBS->LoadImage (
                      TRUE,
                      mBdsImageHandle,
                      FilePath,
                      NULL,
                      0,
                      &ImageHandle
                      );
      if (EFI_ERROR (Status)) {
        //
        // The DevicePath failed, and it's not a valid
        // removable media device.
        //
        goto Done;
      }
    }   
  }

  if (EFI_ERROR (Status)) {
    //
    // It there is any error from the Boot attempt exit now.
    //
    goto Done;
  }
  //
  // Provide the image with it's load options
  //
  Status = gBS->HandleProtocol (ImageHandle, &gEfiLoadedImageProtocolGuid, &ImageInfo);
  ASSERT_EFI_ERROR (Status);

  if (Option->LoadOptionsSize != 0) {
    ImageInfo->LoadOptionsSize  = Option->LoadOptionsSize;
    ImageInfo->LoadOptions      = Option->LoadOptions;
  }
  //
  // Before calling the image, enable the Watchdog Timer for
  // the 5 Minute period
  //
  gBS->SetWatchdogTimer (5 * 60, 0x0000, 0x00, NULL);

  //
  // Write boot to OS performance data for UEFI boot
  //
  WRITE_BOOT_TO_OS_PERFORMANCE_DATA;
  
  Status = gBS->StartImage (ImageHandle, ExitDataSize, ExitData);
  DEBUG ((EFI_D_INFO | EFI_D_LOAD, "Image Return Status = %r\n", Status));

  //
  // Clear the Watchdog Timer after the image returns
  //
  gBS->SetWatchdogTimer (0x0000, 0x0000, 0x0000, NULL);

Done:
  //
  // Clear Boot Current
  //
  gRT->SetVariable (
        L"BootCurrent",
        &gEfiGlobalVariableGuid,
        EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS,
        0,
        &Option->BootCurrent
        );

  //
  // Raise the TPL level back to EFI_TPL_DRIVER
  //
  gBS->RaiseTPL (EFI_TPL_DRIVER);

  return Status;
}