Registering a Winsock Kernel Application

WSK Client Object Registration

A Winsock Kernel (WSK) application must register as a WSK client by calling the WskRegister function. WskRegister requires the WSK application to initialize and pass a pointer to its WSK client's Network Programming Interface (NPI)(a WSK_CLIENT_NPI structure) and a WSK registration object (a WSK_REGISTRATION structure) that will be initialized by WskRegister upon successful return.

The following code example shows how a WSK application can register as a WSK client.

// Include the WSK header file
#include "wsk.h"

// WSK Client Dispatch table that denotes the WSK version
// that the WSK application wants to use and optionally a pointer
// to the WskClientEvent callback function
const WSK_CLIENT_DISPATCH WskAppDispatch = {
  MAKE_WSK_VERSION(1,0), // Use WSK version 1.0
  0,    // Reserved
  NULL  // WskClientEvent callback not required for WSK version 1.0

// WSK Registration object

// DriverEntry function
    PDRIVER_OBJECT DriverObject,
    PUNICODE_STRING RegistryPath
  NTSTATUS Status;
  WSK_CLIENT_NPI wskClientNpi;


  // Register the WSK application
  wskClientNpi.ClientContext = NULL;
  wskClientNpi.Dispatch = &WskAppDispatch;
  Status = WskRegister(&wskClientNpi, &WskRegistration);

  if(!NT_SUCCESS(Status)) {
      return Status;


A WSK application is not required to call WskRegister from within its DriverEntry function. For example, if a WSK application is a subcomponent of a complex driver, the registration of the application might occur only when the WSK application subcomponent is activated.

A WSK application must keep the WSK_CLIENT_DISPATCH structure passed to WskRegister valid and resident in memory until WskDeregister is called and the registration is no longer valid. The WSK_REGISTRATION structure must also be kept valid and resident in memory until the WSK application stops making calls to the other WSK registration functions. The previous code example keeps these two structures in the global data section of the driver, thereby keeping the structure data resident in memory until the driver is unloaded.

WSK Provider NPI Capture

After a WSK application has registered as a WSK client with WskRegister, it must use the WskCaptureProviderNPI function to capture the WSK provider NPI from the WSK subsystem in order to start using the WSK interface.

Because the WSK subsystem might not yet be ready when a WSK application attempts to capture the WSK provider NPI, the WskCaptureProviderNPI function allows the WSK application to poll or wait for the WSK subsystem to become ready as follows:

  • If the WaitTimeout parameter is WSK_NO_WAIT, the function will always return immediately without waiting.

  • If WaitTimeout is WSK_INFINITE_WAIT, the function will wait until the WSK subsystem becomes ready.

  • If WaitTimeout is any other value, the function will return either when the WSK subsystem becomes ready or when the wait time, in milliseconds, reaches the value of WaitTimeout, whichever occurs first.

Important  To avoid adversely affecting the start of other drivers and services, a WSK application that calls WskCaptureProviderNPI from its DriverEntry function should not set the WaitTimeout parameter to WSK_INFINITE_WAIT or an excessive wait time. Also, if a WSK application starts very early in the system startup phase, it should wait for the WSK subsystem to become ready in a different worker thread than the one in which DriverEntry runs.

If the call to WskCaptureProviderNPI fails with STATUS_NOINTERFACE, the WSK application can use the WskQueryProviderCharacteristics function to discover the range of WSK NPI versions supported by the WSK subsystem. The WSK application can call WskDeregister to unregister its current registration instance, and then register again by using a different WSK_CLIENT_DISPATCH instance that uses a supported WSK NPI version.

When WskCaptureProviderNPI returns successfully, its WskProviderNpi parameter points to a WSK provider NPI ( WSK_PROVIDER_NPI) ready for use by the WSK application. The WSK_PROVIDER_NPI structure contains pointers to the WSK client object ( WSK_CLIENT) and the WSK_PROVIDER_DISPATCH dispatch table of WSK functions that the WSK application can use to create WSK sockets and perform other operations on the WSK client object. After the WSK application is finished using the WSK_PROVIDER_DISPATCH functions, it must release the WSK provider NPI by calling WskReleaseProviderNPI.

The following code example shows how a WSK application can capture the WSK provider NPI, use it to create a socket, and then release it.

// WSK application routine that waits for WSK subsystem
// to become ready and captures the WSK Provider NPI
  NTSTATUS Status;
  WSK_PROVIDER_NPI wskProviderNpi;
  // Capture the WSK Provider NPI. If WSK subsystem is not ready yet,
  // wait until it becomes ready.
  Status = WskCaptureProviderNPI(
    &WskRegistration, // must have been initialized with WskRegister

    // The WSK Provider NPI could not be captured.
    if( Status == STATUS_NOINTERFACE ) {
      // WSK application's requested version is not supported
    else if( status == STATUS_DEVICE_NOT_READY ) {
      // WskDeregister was invoked in another thread thereby causing
      // WskCaptureProviderNPI to be canceled.
    else {
      // Some other unexpected failure has occurred

    return Status;

  // The WSK Provider NPI has been captured.
  // Create and set up a listening socket that accepts
   // incoming connections.
  Status = CreateListeningSocket(&wskProviderNpi, ...);

  // The WSK Provider NPI will not be used any more.
  // So, release it here immediately.

  // Return result of socket creation routine
  return Status;


A WSK application can call WskCaptureProviderNPI more than once. For each call to WskCaptureProviderNPI that returns successfully, there must be a corresponding call to WskReleaseProviderNPI. A WSK application must not make any further calls to the functions in WSK_PROVIDER_DISPATCH after calling WskReleaseProviderNPI.