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function OpenVolume(ADrive: char): THandle;
var
  RootName, VolumeName: string;
  AccessFlags: DWORD;
begin
  RootName := ADrive + ':' + #134; // ADrive + ':\' kills the syntax highlighting
  case GetDriveType(PChar(RootName)) of
    DRIVE_REMOVABLE:
      AccessFlags := GENERIC_READ or GENERIC_WRITE;
    DRIVE_CDROM:
      AccessFlags := GENERIC_READ;
  else
    Result := INVALID_HANDLE_VALUE;
    exit;
  end;
  VolumeName := Format('\\.\%s:', [ADrive]);
  Result := CreateFile(PChar(VolumeName), AccessFlags,
    FILE_SHARE_READ or FILE_SHARE_WRITE, nil, OPEN_EXISTING, 0, 0);
  if Result = INVALID_HANDLE_VALUE then
    RaiseLastWin32Error;
end;

function LockVolume(AVolumeHandle: THandle): boolean;
const
  LOCK_TIMEOUT = 10 * 1000; // 10 Seconds
  LOCK_RETRIES = 20;
  LOCK_SLEEP = LOCK_TIMEOUT div LOCK_RETRIES;

// #define FSCTL_LOCK_VOLUME CTL_CODE(FILE_DEVICE_FILE_SYSTEM, 6, METHOD_BUFFERED, FILE_ANY_ACCESS)
  FSCTL_LOCK_VOLUME = (9 shl 16) or (0 shl 14) or (6 shl 2) or 0;
var
  Retries: integer;
  BytesReturned: Cardinal;
begin
  for Retries := 1 to LOCK_RETRIES do begin
    Result := DeviceIoControl(AVolumeHandle, FSCTL_LOCK_VOLUME, nil, 0,
      nil, 0, BytesReturned, nil);
    if Result then
      break;
    Sleep(LOCK_SLEEP);
  end;
end;

function DismountVolume(AVolumeHandle: THandle): boolean;
const
// #define FSCTL_DISMOUNT_VOLUME CTL_CODE(FILE_DEVICE_FILE_SYSTEM, 8, METHOD_BUFFERED, FILE_ANY_ACCESS)
  FSCTL_DISMOUNT_VOLUME = (9 shl 16) or (0 shl 14) or (8 shl 2) or 0;
var
  BytesReturned: Cardinal;
begin
  Result := DeviceIoControl(AVolumeHandle, FSCTL_DISMOUNT_VOLUME, nil, 0,
    nil, 0, BytesReturned, nil);
  if not Result then
    RaiseLastWin32Error;
end;

function PreventRemovalOfVolume(AVolumeHandle: THandle;
  APreventRemoval: boolean): boolean;
const
// #define IOCTL_STORAGE_MEDIA_REMOVAL CTL_CODE(IOCTL_STORAGE_BASE, 0x0201, METHOD_BUFFERED, FILE_READ_ACCESS)
  IOCTL_STORAGE_MEDIA_REMOVAL = ($2d shl 16) or (1 shl 14) or ($201 shl 2) or 0;
type
  TPreventMediaRemoval = record
    PreventMediaRemoval: BOOL;
  end;
var
  BytesReturned: Cardinal;
  PMRBuffer: TPreventMediaRemoval;
begin
  PMRBuffer.PreventMediaRemoval := APreventRemoval;
  Result := DeviceIoControl(AVolumeHandle, IOCTL_STORAGE_MEDIA_REMOVAL,
    @PMRBuffer, SizeOf(TPreventMediaRemoval), nil, 0, BytesReturned, nil);
  if not Result then
    RaiseLastWin32Error;
end;

function AutoEjectVolume(AVolumeHandle: THandle): boolean;
const
// #define IOCTL_STORAGE_EJECT_MEDIA CTL_CODE(IOCTL_STORAGE_BASE, 0x0202, METHOD_BUFFERED, FILE_READ_ACCESS)
  IOCTL_STORAGE_EJECT_MEDIA = ($2d shl 16) or (1 shl 14) or ($202 shl 2) or 0;
var
  BytesReturned: Cardinal;
begin
  Result := DeviceIoControl(AVolumeHandle, IOCTL_STORAGE_EJECT_MEDIA, nil, 0,
    nil, 0, BytesReturned, nil);
  if not Result then
    RaiseLastWin32Error;
end;

function EjectVolume(ADrive: char): boolean;
var
  VolumeHandle: THandle;
begin
  Result := FALSE;
  // Open the volume
  VolumeHandle := OpenVolume(ADrive);
  if VolumeHandle = INVALID_HANDLE_VALUE then
    exit;
  try
    // Lock and dismount the volume
    if LockVolume(VolumeHandle) and DismountVolume(VolumeHandle) then begin
      // Set prevent removal to false and eject the volume
      if PreventRemovalOfVolume(VolumeHandle, FALSE) then
        AutoEjectVolume(VolumeHandle);
    end;
  finally