How do you get the physical drive number of a removable device from the drive letter in Windows 7?

I'm trying to look up the physical drive number (as in, I need the N in \\.\PhysicalDriveN to open the block device for reading) from the drive letter of a CDROM drive on Windows 7. This page indicates that IOCTL_STORAGE_GET_DEVICE_NUMBER should work, but it returns 0 for the drive number for both C: and D: (where D: is the removable drive), so that can't be right. IOCTL_VOLUME_GET_VOLUME_DISK_EXTENTS is also suggested, but that fails with an ERROR_INVALID_FUNCTION on D:.

I can't help but feel that I've missed a crucial concept somewhere.

Here's my code:

#include "stdafx.h"
#include "Windows.h"


void printLastError(){
  DWORD lastError;
  DWORD bytesReturned;
  WCHAR outbuf[2048];

  lastError = GetLastError();

  bytesReturned = FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM,
    NULL, lastError, LANG_USER_DEFAULT, outbuf, 2048, NULL);

  if (bytesReturned > 0){
    wprintf(outbuf);
  } else {
    printf("Error %d while formatting error %d\n", GetLastError(),     lastError);
  }
}

void readDeviceNumberByExtents(HANDLE hFile){
  BOOL ioctlSuccess;
  DWORD bytesReturned;

  VOLUME_DISK_EXTENTS vde;

  ioctlSuccess = DeviceIoControl(hFile,
    IOCTL_VOLUME_GET_VOLUME_DISK_EXTENTS,
    NULL, 0, &vde, sizeof(vde), &bytesReturned, NULL);

    if (ioctlSuccess != 0){
      printf("%d\n", vde.Extents->DiskNumber );
    } else {
      printLastError();
  }
}

void readDeviceNumberByStorage(HANDLE hFile){
  BOOL ioctlSuccess;
  DWORD bytesReturned;

  STORAGE_DEVICE_NUMBER sdn;

  ioctlSuccess = DeviceIoControl(hFile,
    IOCTL_STORAGE_GET_DEVICE_NUMBER,
    NULL, 0, &sdn, sizeof(sdn), &bytesReturned, NULL);

  if (ioctlSuccess != 0){
    printf("%d\n", sdn.DeviceNumber );
  } else {
    printLastError();
  }
}

void runTest(WCHAR* driveName){
  HANDLE driveHandle;
  DWORD diskNumber;

  driveHandle = CreateFile(driveName,
    0,
    FILE_SHARE_READ | FILE_SHARE_WRITE,
    NULL,
    OPEN_EXISTING,
    FILE_ATTRIBUTE_NORMAL,
    NULL);

  if (driveHandle != INVALID_HANDLE_VA开发者_运维知识库LUE){
    wprintf(L"Opened %s\n", driveName);

    printf("Device number by extents: ");
    readDeviceNumberByExtents(driveHandle);
    printf("Device number by storage: ");
    readDeviceNumberByStorage(driveHandle);

    CloseHandle(driveHandle);
  } else {
    printf("Failure!\n");   
  }
}

int _tmain(int argc, _TCHAR* argv[])
{
  runTest(L"\\\\.\\C:");
  printf("\n");
  runTest(L"\\\\.\\D:");

  getc(stdin);
  return 0;
}

...and the output when I run it, either as Administrator or not:

Opened \\.\C:
Device number by extents: 0
Device number by storage: 0

Opened \\.\D:
Device number by extents: Incorrect function.
Device number by storage: 0

The "\\.\PhysicalDriveN" only works for (things that act like) hard drives, not removable disks. If something acts like a removable disk (or floppy, CD-ROM, etc.), "\\.\X:" opens the raw drive (other drives don't support partitions, so the distinction between "\\.\x:" and "\\.\PhysicalDiskN" doesn't exist for them). You normally want to use GetDriveType to figure out what kind of disk you have, and only if that says it's a DRIVE_FIXED do you attempt to find the drive number and use "\\.\PhysicalDriveN" with it.

It's C#.Net code, but this is what i've written to do the job:

using System.Management; //Add in a reference to this as well in the project settings
public static string GetPhysicalDevicePath(char DriveLetter)
{
    ManagementClass devs = new ManagementClass( @"Win32_Diskdrive");
    {
        ManagementObjectCollection moc = devs.GetInstances();
        foreach(ManagementObject mo in moc)
        {
            foreach (ManagementObject b in mo.GetRelated("Win32_DiskPartition"))
            {
                foreach (ManagementBaseObject c in b.GetRelated("Win32_LogicalDisk"))
                {
                    string DevName = string.Format("{0}", c["Name"]);
                    if (DevName[0] == DriveLetter)
                        return string.Format("{0}", mo["DeviceId"]); 
                }
            }
        }
    }
    return "";
}