KS Properties

A Property represents a capability or control-state setting that belongs to a kernel streaming object, such as a filter or pin. Clients of a kernel streaming minidriver can send get and set property requests (KSPROPERTY_TYPE_GET and KSPROPERTY_TYPE_SET) to the filters and pins that the minidriver has instantiated. A group of related properties is referred to as a property set.

To get or set individual properties, user-mode clients call the Win32 function DeviceIoControl with the dwIoControlCode parameter set to IOCTL_KS_PROPERTY. DeviceIoControl is described in the Microsoft Windows SDK documentation. Kernel-mode clients should call KsSynchronousDeviceControl.

The input buffer is either a KSPROPERTY structure or a wrapper containing a KSPROPERTY structure and other information relevant to the request. In response to this call, the operating system dispatches an IRP to the class driver.

When the class driver receives the resulting IRP, it calls KsPropertyHandler. The class driver includes as a call parameter the address of the KSPROPERTY structure that identifies the specifics of the property request. The property request is either handled automatically at the class driver level or by a minidriver-provided handler. See Kernel Streaming Property Sets for reference information including which property sets are handled by the class driver and which require minidriver-provided handlers. A minidriver can override or augment the class driver handler by providing callbacks for a property that is by default handled by the class driver.

If the minidriver has provided handlers for this property, KsPropertyHandler in turn hands off the request to the appropriate minidriver-supplied callback.

A minidriver provides pointers to its property support callbacks in a structure of type KSPROPERTY_ITEM. A minidriver groups an array of related KSPROPERTY_ITEM structures in a KSPROPERTY_SET structure. Different class driver models have slightly different methods for the minidriver to make property set data available to the class driver. You can find class driver-specific information by following the links in Kernel Streaming.

The minidriver also provides a pointer to a KSPROPERTY_VALUES structure in a KSPROPERTY_ITEM structure. The KSPROPERTY_VALUES structure in turn contains an array of KSPROPERTY_MEMBERSLIST structures. This is where the minidriver specifies the size and type of acceptable values for the property. Each KSPROPERTY_MEMBERSLIST structure contains a header member: see KSPROPERTY_MEMBERSHEADER For information about how to specify legal ranges or values for a property that your minidriver supports. You can also find an implementation of this mechanism in the Testcap sample in the Microsoft Windows Driver Kit (WDK).

To report the size and type of acceptable values for a property, the class driver returns a KSPROPERTY_DESCRIPTION structure in response to a KSPROPERTY_TYPE_BASICSUPPORT request from the client.

The class driver may append a list of KSPROPERTY_MEMBERSHEADER structures to the KSPROPERTY_DESCRIPTION structure.



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