macos - How to map memory in DriverKit using IOMemoryDescriptor::CreateMapping?

Question

I am trying to learn more about DriverKit and memory management, and I read this question:

How to allocate memory in a DriverKit system extension and map it to another process?

And I would like to understand how to use IOMemoryDescriptor::CreateMapping.

I wrote a little app to test this where I do (very simplified code):

uint8_t * buffer = new uint8_t[256];
for (int i = 0 ; i < 256 ; i++)
   buffer[i] = 0xC6;

clientData in, out;
in.nbytes = 256;
in.pbuffer = buffer;
size_t sout = sizeof(out);

IOConnectCallStructMethod(connection, selector,&in,sizeof(in),&out,&sout);

// out.pbuffer now has new values in it

In my Kext user client class, I was doing (I am simplifying):

IOReturn UserClient::MyExtFunction(clientData * in, clientData * out, IOByteCount inSize, IOByteCount * outSize)
{
   MyFunction(in->nBytes, in->pbuffer);//this will change the content of pbuffer

   *out = *in; 
}


IOReturn UserClient::MyFunction(SInt32 nBytesToRead,void* pUserBuffer,SInt32* nBytesRead)
{
    PrepareBuffer(nBytesToRead,&pBuffer);
    ...
    (call function that will fill pBuffer)
}


IOReturn UserClient::PrepareBuffer(UInt32 nBytes,void** pBuffer);
{
   IOMemoryDescriptor * desc = IOMemoryDescriptor::withAddressRange((mach_vm_address_t)*pBuffer,nBytes,direction, owner task);

   desc->prepare();
   IOMemoryMap * map = desc->map();
   *pBuffer = (void*)map->getVirtualAddress();

   return kIOReturnSuccess;
}

This is what I don't know how to reproduce in a DExt and where I think I really don't understand the basic of CreateMapping.

Or is what I used to do not possible?

In my driver, this is where I don't know how to use CreateMapping and IOMemoryMap so this buffer can be mapped to a memory location and updated with different values.

I can create an IOBufferMemoryDescriptor but how do I tie it to the buffer from my application? I also don't understand the various options for CreateMapping.

Please note that in another test app I have successfully used IOConnectMapMemory64()/CopyClientMemoryForType() but I would like to learn specifically about CreateMapping().

(I hope it is alright I edited this question a lot... still new to StackOverflow)