Microsoft Virtual Audio Device Driver Sample (MSVAD) only creates 44 bytes files

Question

I'm currently digging into the MSVAD simple driver. Unfortunately, it doesn't work the way I'd like it to work. When a new program starts, it creates as STREAM_NN.WAV under C:\

Unfortunately, this file is only 44 bytes in size (containing only the header). I attached the debugger view and got this output:

MSVAD: [CMiniportWaveCyclic::NewStream]
MSVAD: [CMiniportWaveCyclicMSVAD::ValidateFormat]
MSVAD: [CMiniportWaveCyclic::NewStream]
MSVAD: [CMiniportWaveCyclicMSVAD::ValidateFormat]
MSVAD: CMiniportWaveCyclicMSVAD::ValidatePcm
MSVAD: [CSaveData::InitializeWorkItems]
MSVAD: [CMiniportWaveCyclicStreamMSVAD::Init]
MSVAD: SaveData 845A754C
MSVAD: [CSaveData::SetDataFormat]
MSVAD: [CSaveData::Initialize]
MSVAD: [CMiniportWaveCyclicStreamMSVAD::AllocateBuffer]
MSVAD: [CMiniportWaveCyclicStreamMSVAD::SetFormat]
MSVAD: [CSaveData::SetDataFormat]
MSVAD: New Format: 44100
MSVAD: [CMiniportWaveCyclicStreamMSVAD::SetNotificationFreq]
MSVAD: [CMiniportWaveCyclicStreamMSVAD::SetState]
MSVAD: [CMiniportWaveCyclicStreamMSVAD::SetState]
MSVAD: KSSTATE_PAUSE
MSVAD: [CMiniportWaveCyclicStreamMSVAD::SetState]
MSVAD: KSSTATE_RUN
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=480]
MSVAD: [CSaveData::WriteData ulByteCount=1284]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=628]
MSVAD: [CSaveData::WriteData ulByteCount=1136]
//Truncated for convenience
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=776]
MSVAD: [CSaveData::WriteData ulByteCount=988]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CSaveData::WriteData ulByteCount=1764]
MSVAD: [CMiniportWaveCyclicStreamMSVAD::SetState]
MSVAD: KSSTATE_PAUSE
MSVAD: [CMiniportWaveCyclicStreamMSVAD::SetState]
MSVAD: KSSTATE_STOP
MSVAD: [CSaveData::WaitAllWorkItems]
MSVAD: [CSaveData::SaveFrame]
MSVAD: [CMiniportWaveCyclicStreamMSVAD::SetState]
MSVAD: [CMiniportWaveCyclicStream::~CMiniportWaveCyclicStream]
MSVAD: [CMiniportWaveCyclicStreamMS::~CMiniportWaveCyclicStreamMS]
MSVAD: [CMiniportWaveCyclicStreamMSVAD::FreeBuffer]
MSVAD: [CSaveData::~CSaveData]

That looks pretty straight forward to me, e.g. all necessary functions got called. I'm wondering if there is a known bug in this example, or any caveats I have to take into account?

The OS is Windows 7 32bit in a virtual machine, normal audio playback works like a charm. The Simple driver is set as default playback device.

Answer 1

The problem is that since the DDK 8 in the method CSaveData::InitializeWorkItems (savedata.cpp) were added following lines:

if (m_pWorkItems)
{
    return ntStatus;
}

But CSaveData::~CSaveData is freeing only "work items", not the m_pWorkItems array. This leads to the use of the freed "work items" in future.

To solve this problem you need to replace the code in savedata.cpp, CSaveData::InitializeWorkItems:

if (m_pWorkItems)
{
    return ntStatus;
}

m_pWorkItems = (PSAVEWORKER_PARAM)
    ExAllocatePoolWithTag
    (
        NonPagedPool,
        sizeof(SAVEWORKER_PARAM) * MAX_WORKER_ITEM_COUNT,
        MSVAD_POOLTAG
    );

By this code:

if (!m_pWorkItems)
{
    m_pWorkItems = (PSAVEWORKER_PARAM)
        ExAllocatePoolWithTag
        (
            NonPagedPool,
            sizeof(SAVEWORKER_PARAM) * MAX_WORKER_ITEM_COUNT,
            MSVAD_POOLTAG
        );
}