How to access display memory in kernel mode ?

OSR_Community_User

I am trying to read display contents from a kernel mode application. Is
there any way to do this ? Most likely the source of call will be either
display driver or a miniport driver..

Don_Burn_1

> I am trying to read display contents from a kernel mode application. Is
> there any way to do this ? Most likely the source of call will be either
> display driver or a miniport driver..

Seriously, think about the fact that if your driver is general purpose,
Windows does not require a display. Also with a terminal services model
which "display" do you want to model. In general have any dependency in
your driver on displaying on a desktop is a bad idea.

Don Burn (MVP for DDK)
Windows Filesystem and Driver Consulting

OSR_Community_User

VideoPortMapMemory is mapping the video memory address to virtual address.

But the caller is NOT Display driver... , You must access Video miniport dirver.

How ? I don't know.... In general... video card provider prohibit... -.-;

But, U can access video memory, by .... Memory mapping... If U know address space of

Video Ram.

Then How can I access video memory information or something....?

The formal way... is through.. EngIoControl(?) in display driver.... But, as I mentioned...

U can get the information from registry....

HKLM\SYSTEM\CurrentControlSet\Enum\PCI\VEN_????&DEV_????....\Control\AllocConfig

Next, U can map the address to your user level application address, as follows

PHYSICAL_ADDRESS PhysicalAddress;
PhysicalAddress.u.HighPart = 0;
PhysicalAddress.u.LowPart = 0x????????; // IoAddress of video card.

if (!pBI->pBuf||pBI->nSize==0) return NULL;

//Virtual address which driver can access
pBI->pBuf = MmMapIoSpace( PhysicalAddress, pBI->nSize, FALSE );
if (pBI->pBuf == NULL)
{
return NULL;
}

pBI->pmdl = IoAllocateMdl( pBI->pBuf, pBI->nSize, 0, 0, 0 );
if (!pBI->pmdl)
{
MmUnmapIoSpace( pBI->pBuf, pBI->nSize);
return NULL;
}

MmBuildMdlForNonPagedPool( pBI->pmdl );
pBI->pUserVa = MmMapLockedPages( pBI->pmdl, UserMode );

if (!pBI->pUserVa)
{
IoFreeMdl(pBI->pmdl);
MmUnmapIoSpace( pBI->pBuf, pBI->nSize);
return NULL;
}

OSR_Community_User

You see the thing is I am not sure I need a driver. My goal is to have
access to display data across Windows logics (locked workstation, fast
user switching etc).

If you ever tried to get display using GDI, GDI+, DirectX, or any other
high level APIs, there is a problem which is like, display data handles,
variables, or objects you use to access the data, become invalid when you
hit 'Lock Workstation' or switch user... For me this is an indication,
that i need to go deeper, to get under this logics, because my remote
desktop application is not a user mode service but a terminal emulator.
This means that a remote client can logon to a locked workstation and log
in remotely... While Terminal Services EMULATES user login screens, I want
to send those screens to client as-is and provide remote keyboard and
mouse services.

This is the only reason for my question Hope I made this clear, i dont
know how to explain it better !

Maxim_S._Shatskih

> in remotely... While Terminal Services EMULATES user login screens, I want
> to send those screens to client as-is and provide remote keyboard and
> mouse services.

Add a mirror driver, and mirror the display drawing to some in-memory surface.

Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
[email protected]
http://www.storagecraft.com