NTSTATUS
HalpQueryDriveLayout(
  IN  PUNICODE_STRING             DeviceName,
  OUT PDRIVE_LAYOUT_INFORMATION*  DriveLayout
  );

Routine Description:

    This routine gives the device the next available drive letter.

Arguments:

    DeviceName  - Supplies the device name.

    DriveLetter - Returns the drive letter assigned or 0.

Return Value:

    NTSTATUS