DrmForwardContentToDeviceObject function (drmk.h)

Article
10/21/2021

The DrmForwardContentToDeviceObject function accepts a device object representing a device to which the caller intends to forward protected content. The function authenticates the device and sends it the content ID and DRM rights that the system has assigned to the protected content.

Syntax

NTSTATUS DrmForwardContentToDeviceObject(
  [in]           ULONG        ContentId,
  [in, optional] PVOID        Reserved,
  [in]           PCDRMFORWARD DrmForward
);

Parameters

[in] ContentId

Specifies the DRM content ID. This parameter identifies a protected KS audio stream.

[in, optional] Reserved

Reserved for future use. Set to NULL.

[in] DrmForward

Pointer to a DRMFORWARD structure specifying a device object and file object that identify the target device and a KS audio pin on that device, respectively. The structure also contains the context value that the KSPROPERTY_DRMAUDIOSTREAM_CONTENTIDset-property request passes to the device.

Return value

DrmForwardContentToDeviceObject returns STATUS_SUCCESS if the call was successful. Otherwise, it returns an appropriate error code.

Remarks

Before allowing protected content to flow through a data path, the system verifies that the data path is secure. To do so, the system authenticates each module in the data path beginning at the upstream end of the data path and moving downstream. As each module is authenticated, that module gives the system information about the next module in the data path so that it can also be authenticated. To be successfully authenticated, a module's binary file must be signed as DRM-compliant.

Two adjacent modules in the data path can communicate with each other in one of several ways. If the upstream module calls the downstream module through IoCallDriver, the downstream module is part of a WDM driver. In this case, the upstream module calls the DrmForwardContentToDeviceObject function to provide the system with the device object representing the downstream module. (If the two modules communicate through the downstream module's COM interface or content handlers, the upstream module calls DrmForwardContentToInterface or DrmAddContentHandlers instead.)

The caller fills in the DeviceObject, FileObject, and Context members of the DRMFORWARD structure that parameter DrmForward points to. DrmForwardContentToDeviceObject uses these values as follows:

DeviceObject specifies the device object that represents the driver (the downstream module). DrmForwardContentToDeviceObject uses the device object to authenticate the driver. If successful, the function sets the KSPROPERTY_DRMAUDIOSTREAM_CONTENTID property on the device by sending a set-property request to a KS pin on the device.
FileObject specifies the KS pin to which DrmForwardContentToDeviceObject sends the property request.
Context specifies a context value that the caller passes to the driver through the property request. DrmForwardContentToDeviceObject copies the context value into the request's property descriptor. The context value is typically a pointer to a buffer containing data in some custom format that both the caller and driver understand. By convention, if the downstream module is a KS filter, the Context member points to a file object that specifies the KS pin to which the DrmForwardContentToDeviceObject function sends the property request. In other words, the Context member points to the same file object as the FileObject member. USB audio drivers must set the Context parameter to a USBD_PIPE_HANDLE value.

The property request also contains the DRM content ID from parameter ContentId and the DRM content rights belonging to that content ID. DrmForwardContentToDeviceObject copies these values into the request's property value. DrmForwardContentToDeviceObject makes no further use of the device object after returning.

DrmForwardContentToDeviceObject performs the same function as PcForwardContentToDeviceObject and IDrmPort2::ForwardContentToDeviceObject. For more information, see DRM Functions and Interfaces.

The KSPROPERTY_DRMAUDIOSTREAM_CONTENTID property assigns the DRM content ID and DRM content rights to a KS audio pin.

Usage Summary Table

Get	Set	Target	Property descriptor type	Property value type
No	Yes	Pin	KSP_DRMAUDIOSTREAM_CONTENTID	KSDRMAUDIOSTREAM_CONTENTID

The property value (operation data) is a KSDRMAUDIOSTREAM_CONTENTID structure that specifies the stream's DRM content ID and DRM content rights.

Return Value

A KSPROPERTY_DRMAUDIOSTREAM_CONTENTID property request returns a status code that indicates whether the KS filter can enforce the specified DRM content rights, as shown in the following table.

Status Code	Meaning
STATUS_SUCCESS	The KS audio filter enforces the specified DRM content rights.
STATUS_NOT_IMPLEMENTED	The KS filter cannot enforce the specified DRM content rights.

The DrmForwardContentToDeviceObject function uses this property to set the DRM content ID and content rights on the audio stream entering the KS pin that is the target of the property request.

A KS audio filter handles this property request synchronously. If the request returns STATUS_SUCCESS, all the downstream KS audio nodes (see Audio Topology Nodes) of the target KS audio pin were also successfully configured with the specified DRM content ID and DRM content rights. (Note that a downstream node is a direct or indirect sink for the audio content flowing through an audio pin.)

The DRM system can set this property at any time during the lifetime of the file object that represents a KS audio pin. If the request does not succeed, the previously set DRM content ID and DRM content rights remain in effect on the KS audio stream.

The handler for the KSPROPERTY_DRMAUDIOSTREAM_CONTENTID property must verify that the property-request IRP originates in kernel mode (that is, confirm that the IRP's RequestorMode field equals KernelMode). If the IRP originates in user mode, the handler must fail the IRP and return status code INVALID_DEVICE_REQUEST.

DrmForwardContentToDeviceObject is an entry point in the DRMK system driver, Drmk.sys. DRMK sends an IOCTL_KS_PROPERTY request for the KSPROPERTY_DRMAUDIOSTREAM_CONTENTID property at IRQL PASSIVE_LEVEL.

Requirements

Requirement	Value
Target Platform	Universal
Header	drmk.h (include Drmk.h)
Library	Drmk.lib
IRQL	PASSIVE_LEVEL

Share via