How to call DeviceIoControl to retrieve the amount of memory it needs?

Question

I\'m trying to call DeviceIoControl(IOCTL_VOLUME_GET_VOLUME_DISK_EXTENTS) API, as shown here, but I need it to first \"tell me\" how much memory it needs (unlike th

Answer 1

Following @IInspectable's advice, here's what I came up with for a more general case:

BYTE* DeviceIoControl_Dynamic(HANDLE hDevice, DWORD dwIoControlCode, DWORD dwszCbInitialSuggested, LPVOID lpInBuffer, DWORD nInBufferSize, DWORD* pncbOutDataSz)
{
    //Calls DeviceIoControl() API by pre-allocating buffer internally
    //'dwIoControlCode' = control code, see DeviceIoControl() API
    //'dwszCbInitialSuggested' = suggested initial size of the buffer in BYTEs, must be set depending on the description of 'dwIoControlCode'
    //'lpInBuffer' = input buffer, see DeviceIoControl() API
    //'nInBufferSize' = size of 'lpInBuffer', see DeviceIoControl() API
    //'pncbOutDataSz' = if not NULL, receives the size of returned data in BYTEs
    //RETURN:
    //      = Data obtained from DeviceIoControl() API -- must be removed with delete[]!
    //      = NULL if error -- check GetLastError() for info
    BYTE* pData = NULL;
    int nOSError = NO_ERROR;

    DWORD ncbSzData = 0;

    if((int)dwszCbInitialSuggested > 0)
    {
        //Initially go with suggested memory size
        DWORD dwcbMemSz = dwszCbInitialSuggested;

        //Try no more than 10 times
        for(int t = 0; t < 10; t++)
        {
            //Reserve mem
            ASSERT(!pData);
            pData = new (std::nothrow) BYTE[dwcbMemSz];
            if(!pData)
            {
                //Memory fault
                nOSError = ERROR_NOT_ENOUGH_MEMORY;
                break;
            }

            //And try calling with that size
            DWORD bytesReturned = 0;
            if(::DeviceIoControl(hDevice, dwIoControlCode, lpInBuffer, nInBufferSize, 
                pData, dwcbMemSz, &bytesReturned, NULL))
            {
                //Got it
                ncbSzData = bytesReturned;
                nOSError = NO_ERROR;

                break;
            }

            //Check last error
            nOSError = ::GetLastError();

            //Knowing how badly Windows drivers are written, don't rely on the last error code!

            //Alloc more memory (we'll just "wing it" on the amount)
            dwcbMemSz += 1024;

            //Free old mem
            delete[] pData;
            pData = NULL;
        }
    }
    else
    {
        //Bad initial size
        nOSError = ERROR_INVALID_MINALLOCSIZE;
    }

    if(pncbOutDataSz)
        *pncbOutDataSz = ncbSzData;

    ::SetLastError(nOSError);
    return pData;
}

and then to call it, say for IOCTL_VOLUME_GET_VOLUME_DISK_EXTENTS:

DWORD bytesReturned;
VOLUME_DISK_EXTENTS* p_vde = (VOLUME_DISK_EXTENTS*)DeviceIoControl_Dynamic(hDsk, 
    IOCTL_VOLUME_GET_VOLUME_DISK_EXTENTS, sizeof(VOLUME_DISK_EXTENTS), NULL, NULL, &bytesReturned);

which can be later used as such:

//Ensure that driver returned the correct data
if(p_vde &&
    offsetof(VOLUME_DISK_EXTENTS, Extents[p_vde->NumberOfDiskExtents]) <= bytesReturned)
{
    //All good
    for(int x = 0; x < p_vde->NumberOfDiskExtents; x++)
    {
        DWORD diskNumber = p_vde->Extents[x].DiskNumber;
        //...
    }
}

//Remember to free mem when not needed!
if(p_vde)
{
    delete[] (BYTE*)p_vde;
    p_vde = NULL;
}