FSCTL_SET_SPARSE

[This is preliminary documentation and subject to change.]

The FSCTL_SET_SPARSE operation marks the indicated file as sparse. In a sparse file, large ranges of zeroes may not require disk allocation. Space for nonzero data will be allocated as needed as the file is written. To perform this operation, call the DeviceIoControl function with the following parameters.

BOOL DeviceIoControl(
  (HANDLE) hDevice,        // handle to a file
  FSCTL_SET_SPARSE,        // dwIoControlCode, control code of
                           // operation to perform
  NULL,                    // lpInBuffer is not used; must be NULL
  0,                       // nInBufferSize is not used; must be zero
  NULL,                    // lpOutBuffer is not used; must be NULL
  0,                       // nOutBufferSize is not used; must be zero
  (LPDWORD) lpBytesReturned,   // pointer to variable to receive
                           // output byte count
  (LPOVERLAPPED) lpOverlapped  // pointer to OVERLAPPED structure
                           // for asynchronous operation
);

Parameters

hDevice

Handle to the file to be made sparse. Call the CreateFile function to obtain a file handle. The file must be on an NTFS 5.0 file system or later. This operation cannot be called with a directory or volume handle.

dwIoControlCode

Control code for the operation. This value identifies the specific operation to be performed and the type of device on which the operation is to be performed. Use FSCTL_SET_SPARSE for this operation.

lpInBuffer

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

nInBufferSize

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

lpOutBuffer

Pointer to the output buffer. Not used; must be NULL

nOutBufferSize

Size, in bytes, of the output buffer. Not used; must be zero.

lpBytesReturned

Pointer to a DWORD variable.

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

If lpOverlapped is not NULL (overlapped I/O), lpBytesReturned can be NULL.

lpOverlapped

Pointer to an OVERLAPPED structure.

If hDevice was opened with the FILE_FLAG_OVERLAPPED flag, this parameter 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, this parameter is ignored and the DeviceIoControl function 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

See the Remarks section of the DeviceIoControl topic for the implications of overlapped I/O on this operation.

The FSCTL_SET_SPARSE operation sets the FILE_ATTRIBUTE_SPARSE_FILE attribute of the specified file. The only way to clear this attribute is to overwrite the file, for example, by calling the CreateFile function with the CREATE_ALWAYS flag..

QuickInfo

  Windows NT: Requires version 5.0 or later.
  Windows: Unsupported.
  Windows CE: Unsupported.
  Header: Declared in winioctl.h.

See Also

Device Input and Output Overview, Device Input and Output Operations, DeviceIoControl, FSCTL_QUERY_ALLOCATED_RANGES, FSCTL_SET_ZERO_DATA