(WMI) ExecMethod out parameter - ResultingSnapshot is NULL irrespective of the result of the call, Why?

Question

I am using WMI to create an RCT Checkpoint. Below is the code snippet. The problem is when I call the method Create Snapshot using ExecMethodthe ch

Answer 1

You provide a ppCallResult parameter. From the documentation:

ppCallResult [out] If NULL, this is not used. If ppCallResult is specified, it must be set to point to NULL on entry. In this case, the call returns immediately with WBEM_S_NO_ERROR. The ppCallResult parameter receives a pointer to a new IWbemCallResult object, which must be polled to obtain the result of the method execution using the GetCallStatus method. The out parameters for the call are available by calling IWbemCallResult::GetResultObject.

Therefore you need to use GetCallStatus on pCallResult until the method has finished and then GetResultObject to get the out parameters:

LONG status;
while ((hr = pCallResult->GetCallStatus(1000, &status)) == WBEM_S_TIMEDOUT);
/* check hr and status here */
hr = pCallResult->GetResultObject(0, &pResObj);

or use WBEM_INFINITE:

LONG status;
hr = pCallResult->GetCallStatus(WBEM_INFINITE, &status);
/* check hr and status here */
hr = pCallResult->GetResultObject(0, &pResObj);

Alternatively provide NULL instead of pCallResult and it will be a synchronous call where pOutParameters will be set:

hr = m_pWbemServices->ExecMethod(path, L"CreateSnapshot", 0, NULL, pInParams, &pOutParameters, NULL);

Answer 2

Was SnapshotType=32768 giving error to you? Because snapshot is not created when I use this Snapshot Type.

The following log is getting created:

Checkpoint creation failed for 'Ubuntu1' because an invalid checkpoint type has been specified. (Virtual machine ID 5C773BB5-B630-48B4-AB9E-71C548F3FAE4)

Edit: I am not sure if it will help but this solved my problem: https://docs.microsoft.com/en-us/answers/questions/160321/wmi-createsnapshot-not-working-with-snapshottype-3.html

Answer 3

HRESULT GetRelated(PWSTR sAssociatePath, PWSTR sResultClass, IWbemClassObject** ppResultObject)
{
CStringW query;
query.Format(L"associators of {%s} where ResultClass = %s", sAssociatePath, sResultClass);

CComPtr<IEnumWbemClassObject> pEnumOb;

HRESULT hr = m_pWbemServices->ExecQuery(
    BSTR(L"WQL"),
    CComBSTR(query),
    WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY,
    NULL,
    &pEnumOb));
ULONG uReturn = 0;
CComPtr<IWbemClassObject> pObject;
hr = pEnumOb->Next(WBEM_INFINITE, 1, &pObject, &uReturn);
return hr;
}
// Call the GetRelated function above with the __PATH parameter of JOB
CComPtr<IWbemClassObject> pOutParam = NULL;
CHK_HRES(this->ExecMethod(pHyperVObject, L"ConvertToReferencePoint", pInParams, &pOutParam, NULL));
CComVariant jobPath;
CHK_HRES(pOutParam->Get(L"Job", 0, &jobPath, NULL, NULL));
CComPtr<IWbemClassObject> pResult;
GetRelated(jobPath.bstrVal, L"Msvm_VirtualSystemReferencePoint", &pResult);