Programmatically mount a Microsoft Virtual Hard Drive (VHD)

Question

I am trying to mount a Virtual Hard Drive (.VHD) using the Windows 7 API function, but I can't find the relevant function, does one exist?

I am programming in C++ using Visual Studio 2010, for information.

Thanks in advance ;)

Answer 1

This is an old question but it still has no answer so I'll provide one in case someone stumble upon it like I did.

Attaching the VHD

For the complete Reference on MSDN [VHD Reference]: http://msdn.microsoft.com/en-us/library/windows/desktop/dd323700(v=vs.85).aspx

OPEN_VIRTUAL_DISK_PARAMETERS openParameters;
openParameters.Version = OPEN_VIRTUAL_DISK_VERSION_1;
openParameters.Version1.RWDepth = OPEN_VIRTUAL_DISK_RW_DEPTH_DEFAULT;

VIRTUAL_STORAGE_TYPE storageType;
storageType.DeviceID = VIRTUAL_STORAGE_TYPE_DEVICE_VHD;
storageType.VendorId = VIRTUAL_STORAGE_TYPE_VENDOR_MICROSOFT;

ATTACH_VIRTUAL_DISK_PARAMETERS attachParameters;
attachParameters.Version = ATTACH_VIRTUAL_DISK_VERSION_1;

HANDLE vhdHandle;

if (OpenVirtualDisk(&openStorageType, "{VHD PATH GOES HERE}", 
        VIRTUAL_DISK_ACCESS_ALL, OPEN_VIRTUAL_DISK_FLAG_NONE, 
        &openParameters, &vhdHandle) != ERROR_SUCCESS) {
    // If return value of OpenVirtualDisk isn't ERROR_SUCCESS, there was a problem opening the VHD
}

// Warning: AttachVirtualDisk requires elevation
if (AttachVirtualDisk(vhdHandle, 0, ATTACH_VIRTUAL_DISK_FLAG_PERMANENT_LIFETIME,
        0, &attachParameters, 0) != ERROR_SUCCESS) {
    // If return value of AttachVirtualDisk isn't ERROR_SUCCESS, there was a problem attach the disk
}

VHD successfully attached, now it'll show up like any other physical disks and a drive letter will automatically be assigned to the volume(s) contained in the VHD. If you'd like to choose what drive letter is used to mount it, keep reading.

Assigning a drive letter

First, add the ATTACH_VIRTUAL_DISK_FLAG_NO_DRIVE_LETTER flag to your AttachVirtualDisk call so it won't do this automatic letter assigning. Next, you'll have to find the volume path of the VHD volumes [it has this format: \\?\Volume{GUID}]:

wchar_t physicalDrive[MAX_PATH];
ULONG bufferSize = sizeof(physicalDrive);
GetVirtualDiskPhysicalPath(vhdHandle, &bufferSize, physicalDrive);

Now you'll have the physical path of your attached VHD in physical drive in the following format: \\.\PhysicalDrive# where # is the drive number you'll need to find your VHD volumes with FindFirstVolume/FindNextVolume. Extract the number and convert it to an integer and you'll be ready for the next piece of code:

char volumeName[MAX_PATH];
DWORD bytesReturned;
VOLUME_DISK_EXTENTS diskExtents;    
HANDLE hFVol = FindFirstVolume(volumeName, sizeof(volumeName)); 
bool hadTrailingBackslash = false;

do {
    // I had a problem where CreateFile complained about the trailing \ and
    // SetVolumeMountPoint desperately wanted the backslash there. I ended up 
    // doing this to get it working but I'm not a fan and I'd greatly 
    // appreciate it if someone has any further info on this matter
    int backslashPos = strlen(volumeName) - 1;
    if (hadTrailingBackslash = volumeName[backslashPos] == '\\') {
        volumeName[backslashPos] = 0;
    }

    HANDLE hVol = CreateFile(volumeName, 0, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL);
    if (hVol == INVALID_HANDLE_VALUE) {
        return;
    }

    DeviceIoControl(hVol, IOCTL_VOLUME_GET_VOLUME_DISK_EXTENTS, NULL,
        0, &diskExtents, sizeof(diskExtents), &bytesReturned, NULL);

    // If the volume were to span across multiple physical disks, you'd find 
    // more than one Extents here but we don't have to worry about that with VHD
    // Note that 'driveNumber' would be the integer you extracted out of 
    // 'physicalDrive' in the previous snippet
    if (diskExtents.Extents[0].DiskNumber == driveNumber) {
        if (hadTrailingBackslash) {
            volumeName[backslashPos] = '\\';
        }

        // Found volume that's on the VHD, let's mount it with a letter of our choosing.
        // Warning: SetVolumeMountPoint requires elevation
        SetVolumeMountPoint("H:\\", volumeName);
    } 
} while (FindNextVolume(hFVol, volumeName, sizeof(volumeName)));
FindVolumeClose(hFVol);

Don't forget these includes and link to this library:

#define WINVER _WIN32_WINNT_WIN7
#include <windows.h>
#include <winioctl.h>
#include <virtdisk.h>

#pragma comment(lib, "virtdisk.lib")

Disclaimer: This is something I was doing in a C# codebase, I translated the code to C/C++ because of the question but haven't tried to actually compile it. If you find errors in the code, please edit it or let me know so I can do it.

Edits: Typos, includes and lib, forgot FindVolumeClose, elevation warnings