C# Signature:

[DllImport("kernel32.dll", SetLastError=true)]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool GetVolumePathNamesForVolumeNameW(string lpszVolumeName,
        char [] lpszVolumePathNames, uint cchBuferLength,
        ref UInt32 lpcchReturnLength);

C# Signature 2:

[DllImport("kernel32.dll", SetLastError=true)]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool GetVolumePathNamesForVolumeNameW(
        [MarshalAs(UnmanagedType.LPWStr)]
        string lpszVolumeName,
        [MarshalAs(UnmanagedType.LPWStr)]
        string lpszVolumePathNames,
        uint cchBuferLength,
        ref UInt32 lpcchReturnLength);

VB Signature:

Declare Function GetVolumePathNamesForVolumeName Lib "kernel32.dll" (TODO) As TODO

VB Signature #2:

Imports System.Runtime.InteropServices

Partial Public Class Win32Methods

'''Return Type: BOOL->int
'''param0: LPCTSTR->LPCWSTR->WCHAR*
'''param1: LPTSTR->LPWSTR->WCHAR*
'''param2: DWORD->unsigned int
'''param3: PDWORD->DWORD*
  <DllImportAttribute("kernel32.dll", _
    SetLastError:=True, _
    EntryPoint:="GetVolumePathNamesForVolumeNameW")> _
  Public Shared Function GetVolumePathNamesForVolumeNameW(
                               <[In]()> <MarshalAs(UnmanagedType.LPTStr)>
                                ByVal sVolumeName As String, _
                                <MarshalAs(UnmanagedType.LPWStr)> _
                                ByVal lpBuffer As IntPtr, _
                                ByVal uintBufferLen As UInteger, _
                                <Out()> ByRef uintReturnLen As UInteger) _
                             As <MarshalAs(UnmanagedType.Bool)> Boolean
  End Function

End Class

User-Defined Types:

None.

Alternative Managed API:

Do you know one? Please contribute it!

Notes:

The VB Code was generated by the tool at http://clrinterop.codeplex.com/releases/view/14120. I believe this to be the same tool referenced at http://blogs.msdn.com/b/vbteam/archive/2008/03/14/making-pinvoke-easy.aspx. The StringBuilder limitation appears to apply to this code as well, and it will only return the first path/mountpoint found, but the method does work inside that limitation. I will post updated code as soon as I code and test.

Updated: VB code now uses IntPtr instead of StringBuilder - see sample below

Using StringBuilder for the buffer does not work since this function returns the names as a bunch of strings separated by the null character ('\0'). So StringBuilder would only report the first item. Therefore we store it in a char array, which can later be converted to a bunch of strings.

Tips & Tricks:

Please add some!

Sample Code:

        UInt32 dwRequired = 0;

        char[] buffer = new char[260];

        if (!GetVolumePathNamesForVolumeName(volumeName, buffer, (uint)buffer.Length, ref dwRequired))
        {
        // Not enough room in buffer perhaps? Try a bigger one
        buffer = new char[dwRequired];
        if (!GetVolumePathNamesForVolumeName(volumeName, buffer, (uint)buffer.Length, ref dwRequired))
            throw new Win32Exception();
        }

Sample Code 2:

    public List<string> GetMountPointsForVolume(string volumeDeviceName)
    {
        List<string> result = new List<string>();

        // GetVolumePathNamesForVolumeName is only available on Windows XP/2003 and above
        int osVersionMajor = Environment.OSVersion.Version.Major;
        int osVersionMinor = Environment.OSVersion.Version.Minor;
        if (osVersionMajor < 5 || (osVersionMajor == 5 && osVersionMinor < 1))
        {
        return result;
        }

        try
        {
        uint lpcchReturnLength = 0;
        string buffer = "";

        GetVolumePathNamesForVolumeNameW(volumeDeviceName, buffer, (uint)buffer.Length, ref lpcchReturnLength);
        if (lpcchReturnLength == 0)
        {
            return result;
        }

        buffer = new string(new char[lpcchReturnLength]);

        if (!GetVolumePathNamesForVolumeNameW(volumeDeviceName, buffer, lpcchReturnLength, ref lpcchReturnLength))
        {
            throw new Win32Exception(Marshal.GetLastWin32Error());
        }

        string[] mounts = buffer.Split('\0');
        foreach (string mount in mounts)
        {
            if (mount.Length > 0)
            {
            result.Add(mount);
            }
        }
        }
        catch (Exception ex)
        {
        Console.WriteLine(ex.ToString());
        }

        return result;
    }

Sample VB.Net Code (.Net Framework 3.5sp1)

  Private Sub ListMountPoints(Optional strVolumeName As String = "")
    ' if no Volume GUID passed to sub, use this one (corresponds to my USB stick)
    If strVolumeName = "" Then
        strVolumeName = "\\?\Volume{9a615499-414c-11e0-bd72-78e7d1722cbc}\"
    End If
    ' make this a static in order to stop race condition/thread lock - suspect garbage collector
    Static lpBuffer As IntPtr = Marshal.AllocHGlobal(1)
    Dim uintBufferLen As UInteger = 0, uintBuffReqLen As UInteger = 0
    Const ERROR_MORE_DATA = 234, ERROR_FILE_NOT_FOUND = 2
    Dim retval As Boolean = False

    Try
        ' call function to get Required Buffer Length first
        retval = Win32Methods.GetMountPointsIntPtr(strVolumeName, lpBuffer, uintBufferLen, uintBuffReqLen)
        If Not retval Then
        Dim errVal As Integer = Marshal.GetLastWin32Error()
        If errVal = ERROR_MORE_DATA Then
            'MsgBox("The last Win32 error was: ERROR_MORE_DATA")
        ElseIf errVal = ERROR_FILE_NOT_FOUND Then
            MsgBox("File not found, did you remember to plug in the USB drive?")
            Exit Sub
        Else
            MsgBox("Error! The last Win32 error was: " + CStr(errVal))
        End If
        End If
        ' now set the buffer length
        uintBufferLen = uintBuffReqLen
        'zero out the length indicator
        uintBuffReqLen = 0

    Catch ex As Exception
        Dim errVal As Integer = Runtime.InteropServices.Marshal.GetLastWin32Error()
        MsgBox(ex.Message + ". The last Win32 error was: " + CStr(errVal))
    End Try

    ' now call the function again with the right buffer length
    lpBuffer = Runtime.InteropServices.Marshal.ReAllocHGlobal(lpBuffer, CType(uintBuffReqLen, IntPtr))
    ' uintBufferLen = uintBuffReqLen
    uintBuffReqLen = 0
    Try
        If CBool(Not (Win32Methods.GetMountPointsIntPtr(strVolumeName, lpBuffer, uintBufferLen, uintBuffReqLen))) Then
        Dim errVal As Integer = Runtime.InteropServices.Marshal.GetLastWin32Error()
        MsgBox("The last Win32 error was: " + CStr(errVal))
        End If
    Catch ex As Exception
        Dim errVal As Integer = Runtime.InteropServices.Marshal.GetLastWin32Error()
        MsgBox(ex.Message + ". The last Win32 error was: " + CStr(errVal))
    End Try

    Dim strOutput As String = Runtime.InteropServices.Marshal.PtrToStringUni(lpBuffer, CInt(uintBuffReqLen))
    Dim tmp As Integer = InStr(strOutput, vbNullChar)
    strOutput = Strings.Replace(strOutput, vbNullChar, vbCrLf, , , vbBinaryCompare)
    ' Free the buffer.
    Runtime.InteropServices.Marshal.FreeHGlobal(lpBuffer)
    lpBuffer = IntPtr.Zero
    MsgBox(strVolumeName + vbCrLf + " has the following mountpoints: " + vbCrLf + strOutput.ToString)

  End Sub