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Working with Enumeration Objects

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[Beginning with Windows 8 and Windows Server 2012, the Virtual Disk Service COM interface is superseded by the Windows Storage Management API.]

The code example that follows demonstrates how a caller works with enumeration objects using the IEnumVdsObject interface. Note that the information that is returned by an enumeration object is static. You must query the object again to see new configuration changes.

The GetControllerById function takes an IVdsSubSystem interface, specified by the pSubsystem parameter, and queries for the controllers in the subsystem, then iterates through the returned enumeration searching for a controller with a GUID that matches the GUID that is specified by the pControllerId parameter. If a matching controller is found, it is returned by the ppController parameter along with an S_OK HRESULT.

//
// Simple macro to release non-null interfaces.
//
#include <windows.h>
#include "vds.h"
#include <stdio.h>

#define _SafeRelease(x) {if (NULL != x) { x->Release(); x = NULL; } }

HRESULT GetControllerById(
         IN IVdsSubSystem       *pSubsystem,
         IN CONST VDS_OBJECT_ID *pControllerId,
         OUT IVdsController     **ppController)
{
    VDS_CONTROLLER_PROP vdsControllerProperties;
    IEnumVdsObject      *pEnumController = NULL;
    IVdsController      *pController     = NULL;
    IUnknown            *pUnknown        = NULL;
    HRESULT             hResult          = S_OK;
    ULONG               ulFetched        = 0;
    BOOL                bDone            = FALSE;

    ZeroMemory(&vdsControllerProperties, sizeof(VDS_CONTROLLER_PROP));

    // Query for the enumeration of controllers belonging
    // to the given subsystem.
    hResult = pSubsystem->QueryControllers(&pEnumController);

    if (SUCCEEDED(hResult) && (!pEnumController)) 
    {
        hResult = E_UNEXPECTED; // Errant provider, 
        // returned S_OK 
        // with a NULL pointer.
    }

    if (SUCCEEDED(hResult)) 
    {
        // Enumerate through all the controllers this subsystem 
        // contains to find the controller of interest.
        while (!bDone) 
        {
            ulFetched = 0;
            hResult = pEnumController->Next(1, &pUnknown, &ulFetched);

            if (hResult == S_FALSE) 
            {
                hResult = E_INVALIDARG;
                break;
            }

            if (SUCCEEDED(hResult) && (!pUnknown)) 
            {
                hResult = E_UNEXPECTED; // Errant provider, 
                // returned S_OK with
                // a NULL pointer 
            }

            // Use an IVdsController interface to get the controller 
            // properties and check for the desired GUID.
            if (SUCCEEDED(hResult)) 
            {
                hResult = pUnknown->QueryInterface(IID_IVdsController,  
                    (void **) &pController);
            }

            if (SUCCEEDED(hResult) && (!pController)) 
            {
                hResult = E_UNEXPECTED; // Errant provider, 
                // returned S_OK 
                // with a NULL pointer
            }

            if (SUCCEEDED(hResult)) 
            {
                hResult = pController->  
                GetProperties( &vdsControllerProperties);
            }

            if (SUCCEEDED(hResult) 
                && IsEqualGUID(*pControllerId, vdsControllerProperties.id)) 
            {
                bDone = TRUE;
            } 
            else 
            {
                _SafeRelease(pController);
            }

            _SafeRelease(pUnknown);

            //Free the strings in the properties structure.
            if (NULL != vdsControllerProperties.pwszIdentification) 
            {
                CoTaskMemFree(vdsControllerProperties.pwszIdentification);
            }

            ZeroMemory(&vdsControllerProperties, sizeof(VDS_CONTROLLER_PROP));
        }
    }

    if (SUCCEEDED(hResult)) 
    {
        *ppController = pController;
    }

    _SafeRelease(pEnumController);
    return hResult;
}

Using VDS

Helper Objects

IEnumVdsObject

IVdsSubSystem