FSCTL_GET_OBJECT_ID

Using the FSCTL_GET_OBJECT_ID control code gets the object identifier for an existing, open object in a Windows 2000 NTFS file system.

To perform this operation, call the DeviceIoControl function with the following parameters.

BOOL DeviceIoControl(
  (HANDLE) hDevice,           // handle to device
  FSCTL_GET_OBJECT_ID,        // dwIoControlCode operation
  NULL,                       // lpInBuffer; must be NULL
  0,                          // nInBufferSize; must be zero
  (LPVOID) lpOutBuffer,       // output buffer
  (DWORD) nOutBufferSize,     // size of output buffer
  (LPDWORD) lpBytesReturned,  // number of bytes returned
  (LPOVERLAPPED) lpOverlapped // OVERLAPPED structure
);

Parameters

hDevice

[in] Handle to the directory, file, or alternate stream from which the object identifier is to be retrieved. To obtain a device handle, call the CreateFile function.

dwIoControlCode

[in] Control code for the operation. This value identifies the specific operation to be performed and the type of device on which to perform it. Use FSCTL_GET_OBJECT_ID for this operation.

lpInBuffer

[in] Pointer to the input buffer. Not used; must be NULL.

nInBufferSize

[in] Size, in bytes, of the input buffer. Not used; must be zero.

lpOutBuffer

[out] Pointer to the output buffer, a FILE_OBJECTID_BUFFER structure. The object identifier associated with the input hDevice is returned in this buffer.

nOutBufferSize

[in] Size, in bytes, of the output buffer, FILE_OBJECTID_BUFFER.

lpBytesReturned

[out] Pointer to a variable that receives the actual count of bytes returned by the function in the output buffer.

If the output buffer is too small to return any data, then the call fails, GetLastError returns the error code ERROR_INSUFFICIENT_BUFFER, and the returned byte count is zero.

If the output buffer is too small to hold all of the data but can hold some entries, then the operating system returns as much as fits, the call fails, GetLastError returns the error code ERROR_MORE_DATA, and lpBytesReturned indicates the amount of data returned. Your application should call DeviceIoControl again with the same operation, specifying a new starting point.

If lpOverlapped is NULL (nonoverlapped I/O), lpBytesReturned cannot be NULL.

If lpOverlapped is not NULL (overlapped I/O), lpBytesReturned can be NULL. If this is an overlapped operation, you can retrieve the number of bytes returned by calling the GetOverlappedResult function. If hDevice is associated with an I/O completion port, you can get the number of bytes returned by calling the GetQueuedCompletionStatus function.

lpOverlapped

[in] Pointer to an OVERLAPPED structure.

If hDevice was opened with the FILE_FLAG_OVERLAPPED flag, lpOverlapped must point to a valid OVERLAPPED structure. In this case, DeviceIoControl is performed as an overlapped (asynchronous) operation. If the device was opened with the FILE_FLAG_OVERLAPPED flag and lpOverlapped is NULL, the function fails in unpredictable ways.

If hDevice was opened without specifying the FILE_FLAG_OVERLAPPED flag, lpOverlapped is ignored and DeviceIoControl does not return until the operation has been completed, or until an error occurs.

Return Values

If the operation succeeds, DeviceIoControl returns a nonzero value.

If the operation fails, DeviceIoControl returns zero. To get extended error information, call GetLastError.

Remarks

Object identifiers are Windows 2000 internal objects used by the operating system to track other objects such as files and directories. They are invisible to most applications and should never be modified by applications. Modifying an object identifier can result in the loss of data from portions of a file, up to and including entire volumes of data. Also, there is no guarantee that code to manipulate object identifiers will be forward compatible with future versions of Windows. Therefore, use standard Win32 functions to manipulate object identifiers and other operating system objects.

If there is no object identifier associated with the specified handle, none is created and an error is returned. To create an object identifier where there was none previously, and return it, use the FSCTL_CREATE_OR_GET_OBJECT_ID operation.

Requirements

  Windows NT/2000: Requires Windows 2000.
  Windows 95/98: Unsupported.
  Header: Declared in Winioctl.h.

See Also

Device Input and Output Overview, Device Input and Output Control Codes, DeviceIoControl, CreateFile, FILE_OBJECTID_BUFFER, FSCTL_CREATE_OR_GET_OBJECT_ID, FSCTL_DELETE_OBJECT_ID, FSCTL_SET_OBJECT_ID, FSCTL_SET_OBJECT_ID_EXTENDED