UCHAR
HalpNextDriveLetter(
  IN  PUNICODE_STRING DeviceName,
  IN  PSTRING         NtDeviceName,
  OUT PUCHAR          NtSystemPath,
  IN  BOOLEAN         UseHardLinksIfNecessary
  );

Routine Description:

    This routine gives the device the next available drive letter.

Arguments:

    DeviceName      - Supplies the device name.

    NtDeviceName    - Supplies the NT device name.

    NtSystemPath    - Supplies the NT system path.

Return Value:

    The drive letter assigned or 0.