Retrieving virtual disk file name from disk number

Question

When I list virtual disks within diskpart:

DISKPART> list vdisk

  VDisk ###  Disk ###  State                 Type       File
  ---------  --------  -----         


        

Answer 1

P/Invoking the GetStorageDependencyInformation will provide a strictly VHD API solution. While this function does not take a drive number as an input parameter, a wrapper method will. The wrapper method converts a drive number to a string of the form "\\\\.\\PhysicalDriveN" which is passed to CreateFile and the resultant handle is passed to GetStorageDependencyInformation. A similar wrapper method will take an input of a single char drive letter.
The following code was translated to C# from an unmanaged example:

using DWORD = System.UInt32;
using ULONG = System.UInt32;

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using Microsoft.Win32.SafeHandles;
using System.IO;

namespace VhdTest
{
    class Program
    {
        static void Main(string[] args)
        {
            String[] arr;
            arr = VirtualDisk.GetDependentVolumePaths('e');
            arr = VirtualDisk.GetDependentVolumePaths(1);

        }
    }


    class VirtualDisk
    {
        #region [ Native ]

        #region [ Constants ]
        const DWORD ERROR_INSUFFICIENT_BUFFER = 122;
        const DWORD ERROR_SUCCESS = 0;

        const DWORD GENERIC_READ = 0x80000000;

        const DWORD FILE_SHARE_READ = 1;
        const DWORD FILE_SHARE_WRITE = 2;
        const DWORD OPEN_EXISTING = 3;

        const DWORD FILE_ATTRIBUTE_NORMAL = 0x00000080;
        const DWORD FILE_FLAG_BACKUP_SEMANTICS = 0x02000000;
        #endregion 

        #region [ Enums ]
        [Flags]
        enum DEPENDENT_DISK_FLAG
        {
            DEPENDENT_DISK_FLAG_NONE = 0x00000000,

            //
            // Multiple files backing the virtual storage device
            //
            DEPENDENT_DISK_FLAG_MULT_BACKING_FILES = 0x00000001,
            DEPENDENT_DISK_FLAG_FULLY_ALLOCATED = 0x00000002,
            DEPENDENT_DISK_FLAG_READ_ONLY = 0x00000004,

            //
            //Backing file of the virtual storage device is not local to the machine
            //
            DEPENDENT_DISK_FLAG_REMOTE = 0x00000008,

            //
            // Volume is the system volume
            //
            DEPENDENT_DISK_FLAG_SYSTEM_VOLUME = 0x00000010,

            //
            // Volume backing the virtual storage device file is the system volume
            //
            DEPENDENT_DISK_FLAG_SYSTEM_VOLUME_PARENT = 0x00000020,
            DEPENDENT_DISK_FLAG_REMOVABLE = 0x00000040,

            //
            // Drive letters are not assigned to the volumes
            // on the virtual disk automatically.
            //
            DEPENDENT_DISK_FLAG_NO_DRIVE_LETTER = 0x00000080,
            DEPENDENT_DISK_FLAG_PARENT = 0x00000100,

            //
            // Virtual disk is not attached on the local host
            // (instead attached on a guest VM for instance)
            //
            DEPENDENT_DISK_FLAG_NO_HOST_DISK = 0x00000200,

            //
            // Indicates the lifetime of the disk is not tied
            // to any system handles
            //
            DEPENDENT_DISK_FLAG_PERMANENT_LIFETIME = 0x00000400
        }

        [Flags]
        enum GET_STORAGE_DEPENDENCY_FLAG
        {
            GET_STORAGE_DEPENDENCY_FLAG_NONE = 0x00000000,

            // Return information for volumes or disks hosting the volume specified
            // If not set, returns info about volumes or disks being hosted by
            // the volume or disk specified
            GET_STORAGE_DEPENDENCY_FLAG_HOST_VOLUMES = 0x00000001,
            GET_STORAGE_DEPENDENCY_FLAG_PARENTS = GET_STORAGE_DEPENDENCY_FLAG_HOST_VOLUMES,
            //  The handle provided is to a disk, not volume or file
            GET_STORAGE_DEPENDENCY_FLAG_DISK_HANDLE = 0x00000002,

        }

        enum STORAGE_DEPENDENCY_INFO_VERSION
        {
            STORAGE_DEPENDENCY_INFO_VERSION_UNSPECIFIED = 0,
            STORAGE_DEPENDENCY_INFO_VERSION_1 = 1,
            STORAGE_DEPENDENCY_INFO_VERSION_2 = 2,
        }
        #endregion

        #region [ Structures ]
        [StructLayout(LayoutKind.Sequential)]
        struct STORAGE_DEPENDENCY_INFO_TYPE_1
        {
            DEPENDENT_DISK_FLAG DependencyTypeFlags;
            ULONG ProviderSpecificFlags;
            VIRTUAL_STORAGE_TYPE VirtualStorageType;
        }

        [StructLayout(LayoutKind.Sequential)]
        struct STORAGE_DEPENDENCY_INFO_TYPE_2
        {
            public DEPENDENT_DISK_FLAG DependencyTypeFlags;
            public ULONG ProviderSpecificFlags;
            public VIRTUAL_STORAGE_TYPE VirtualStorageType;
            public ULONG AncestorLevel;
            public IntPtr DependencyDeviceName;
            public IntPtr HostVolumeName;
            public IntPtr DependentVolumeName;
            public IntPtr DependentVolumeRelativePath;
        }

        [StructLayout(LayoutKind.Explicit)]
        struct STORAGE_DEPENDENCY_INFO_Union
        {
            [FieldOffset(0)]
            STORAGE_DEPENDENCY_INFO_TYPE_1 Version1Entries;
            [FieldOffset(0)]
            STORAGE_DEPENDENCY_INFO_TYPE_2 Version2Entries;
        }

        [StructLayout(LayoutKind.Sequential)]
        struct STORAGE_DEPENDENCY_INFO
        {
            public STORAGE_DEPENDENCY_INFO_VERSION Version;
            public ULONG NumberEntries;
            public STORAGE_DEPENDENCY_INFO_Union Union;
        }

        [StructLayout(LayoutKind.Sequential)]
        struct VIRTUAL_STORAGE_TYPE
        {
            public ULONG DeviceId;
            public Guid VendorId;
        }
        #endregion

        #region [ PInvokes ]
        [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        public static extern SafeFileHandle CreateFile(string lpFileName,
            DWORD dwDesiredAccess,
            DWORD dwShareMode,
            IntPtr lpSecurityAttributes,
            DWORD dwCreationDisposition,
            DWORD dwFlagsAndAttributes,
            IntPtr hTemplateFile);


        [DllImport("virtdisk.dll", SetLastError = true, CharSet = CharSet.Unicode)]
        static extern DWORD GetStorageDependencyInformation(SafeHandle ObjectHandle,
            GET_STORAGE_DEPENDENCY_FLAG Flags,
            ULONG StorageDependencyInfoSize,
            IntPtr StorageDependencyInfo,
            ref ULONG SizeUsed);
        #endregion

        #endregion

        #region [ Managed Methods ]
        public static String[] GetDependentVolumePaths(char driveLetter)
        {
            driveLetter = Char.ToUpper(driveLetter);
            if (driveLetter < 'A' || driveLetter > 'Z')
            {
                String paramName = "driveLetter";
                String message = "Drive letter must fall in range [a-zA-Z]";
                throw new ArgumentOutOfRangeException(paramName, message);
            }
            String fileName = String.Format(@"\\.\{0}:\", driveLetter);
            return getDependentVolumePaths(fileName);
        }

        public static String[] GetDependentVolumePaths(UInt32 driveNumber)
        {
            // TODO:  Per SO, isn't max drive 15? 
            // http://stackoverflow.com/questions/327718/how-to-list-physical-disks
            if (driveNumber > 9)
            {
                String paramName = "driveNumber";
                String message = "Drive number must be <= 9";
                throw new ArgumentOutOfRangeException(paramName, message);
            }
            String fileName = String.Format(@"\\.\PhysicalDrive{0}", driveNumber);
            return getDependentVolumePaths(fileName);
        }

        static unsafe String[] getDependentVolumePaths(String fileName)
        {
            DWORD dwDesiredAccess = GENERIC_READ;
            DWORD dwShareMode = FILE_SHARE_READ | FILE_SHARE_WRITE;
            DWORD dwCreationDisposition = OPEN_EXISTING;
            DWORD dwFlagsAndAttributes = FILE_ATTRIBUTE_NORMAL | FILE_FLAG_BACKUP_SEMANTICS;

            SafeHandle driveHandle = null;
            STORAGE_DEPENDENCY_INFO info = new STORAGE_DEPENDENCY_INFO();
            info.Version = STORAGE_DEPENDENCY_INFO_VERSION.STORAGE_DEPENDENCY_INFO_VERSION_2;
            IntPtr ptr;

            try
            {
                driveHandle = CreateFile(fileName,
                    dwDesiredAccess, //GENERIC_READ,
                    dwShareMode,
                    IntPtr.Zero,
                    dwCreationDisposition,
                    dwFlagsAndAttributes,
                    IntPtr.Zero);
                if (driveHandle.IsInvalid)
                {
                    return null;
                }

                GET_STORAGE_DEPENDENCY_FLAG flags = GET_STORAGE_DEPENDENCY_FLAG.GET_STORAGE_DEPENDENCY_FLAG_NONE;
                flags |= GET_STORAGE_DEPENDENCY_FLAG.GET_STORAGE_DEPENDENCY_FLAG_PARENTS;
                if (fileName.ToUpper().Contains("PHYSICAL"))
                    flags |= GET_STORAGE_DEPENDENCY_FLAG.GET_STORAGE_DEPENDENCY_FLAG_DISK_HANDLE;

                DWORD infoSize = (DWORD)Marshal.SizeOf(info);

                byte[] infoByteArray;
                DWORD cbSize = 0;
                DWORD opStatus;

                #region [ Pull STORAGE_DEPENDENCY_INFO into byte array  ]
                infoByteArray = new byte[infoSize];
                fixed (byte* p1 = infoByteArray)
                {
                    ptr = (IntPtr)p1;
                    Marshal.StructureToPtr(info, ptr, true);
                    opStatus = GetStorageDependencyInformation(driveHandle, flags, infoSize, ptr, ref cbSize);

                    if (opStatus == ERROR_INSUFFICIENT_BUFFER)
                    {
                        infoSize = cbSize;
                        cbSize = 0;

                        infoByteArray = new byte[infoSize];
                        fixed (byte* p2 = infoByteArray)
                        {
                            ptr = (IntPtr)p2;
                            Marshal.StructureToPtr(info, ptr, true);
                            opStatus = GetStorageDependencyInformation(driveHandle, flags, infoSize, ptr, ref cbSize);
                        }
                    }

                }

                #endregion
                if (opStatus != ERROR_SUCCESS)
                {
                    //
                    // This is most likely due to the disk not being a mounted VHD.
                    //
                    return null;
                }
            }
            finally
            {
                if (driveHandle != null && !driveHandle.IsInvalid && !driveHandle.IsClosed)
                {
                    driveHandle.Close();
                }
            }

            List pathList = new List();
            info = (STORAGE_DEPENDENCY_INFO)Marshal.PtrToStructure(ptr, typeof(STORAGE_DEPENDENCY_INFO));
            //STORAGE_DEPENDENCY_INFO_TYPE_2 sdi2 = new STORAGE_DEPENDENCY_INFO_TYPE_2();
            STORAGE_DEPENDENCY_INFO_TYPE_2* p = (STORAGE_DEPENDENCY_INFO_TYPE_2*)&info.Union;
            for (DWORD i = 0; i < info.NumberEntries; i++, p++)
            {
                ptr = (IntPtr)p;
                STORAGE_DEPENDENCY_INFO_TYPE_2 sdi2 = (STORAGE_DEPENDENCY_INFO_TYPE_2)Marshal.PtrToStructure(ptr, typeof(STORAGE_DEPENDENCY_INFO_TYPE_2));
                String str1 = Marshal.PtrToStringUni(sdi2.DependencyDeviceName);
                String str2 = Marshal.PtrToStringUni(sdi2.HostVolumeName);
                String str3 = Marshal.PtrToStringUni(sdi2.DependentVolumeName);
                String relativePath = Marshal.PtrToStringUni(sdi2.DependentVolumeRelativePath);
                String fullPath = Path.GetFullPath(relativePath);
                pathList.Add(fullPath);
            }
            return pathList.ToArray();
        }
        #endregion
    }

}