About Network Kernel Extensions
Important: The information provided in this document is relevant for Mac OS 10.1 through 10.3. Specific mention is made for items which apply to newer releases of the OS.
An important change has long been noted in the <sys/mbuf.h> header file since the release of Mac OS X 10.2. Note that the header file is bracketed by the __APPLE_API_UNSTABLE define. The mbuf structure is a key to the processing of packets in an NKE. As part of the formalizing the NKE APIs, it is expected that the mbuf structure will be changed. Details will be provided in the future. Changes to the existing NKE API are not expected be applied to System Updates to Mac OS X 10.3.x, however, bug fixes or features for future systems may require some interim changes.
For all shipping releases of Mac OS X prior to 10.4, the Network Kernel Extensions (NKE) APIs have not been officially supported. The legacy NKE architecture was implemented as an interim solution. The legacy API was never designed to be officially supported. Other aspects of the OS X networking implementation have received a higher priority, and so the interim solution has remained in effect to OS X 10.3.x.
The NKE mechanism for Mac OS X version 10.4 and later is described in the document Network Kernel Extensions Programming Guide.
Network kernel extensions (NKEs) provide a way to extend and modify the networking infrastructure of Mac OS X while the kernel is running and therefore without requiring the kernel to be recompiled, relinked, or rebooted.
NKEs allow you to
create protocol stacks that can be loaded and unloaded dynamically and configured automatically.
create modules that can be loaded and unloaded dynamically at specific positions in the network hierarchy. These modules can monitor network traffic, modify network traffic, and receive notification of asynchronous events at the data link and network layers from the driver layer, such as power management events and interface status changes.
An NKE is a specific case of a Mac OS X kernel extension. It is a separately compiled module (produced, for example, by XCode using the Kernel Extension project type).
An installed and enabled NKE is invoked automatically, depending on its position in the sequence of protocol components, to process an incoming or an outgoing packet. Loading (installing) a kernel extension is handled by the kextload(8) command line utility, which adds the NKE to the running Mac OS X kernel as part of the kernel's address space. Eventually, the system will provide automatic mechanisms for loading extensions. Currently, automatic loading is only possible for IOKit extensions and other extensions that IOKit extensions depend on.
As a kernel extension, an NKE provides initialization and termination routines that the Kernel Extension Manager invokes when it loads or unloads an NKE. The initialization routine handles any operations needed to complete the incorporation of the NKE into the kernel, such as updating protosw and domain structures. Similarly, the termination routine must remove references to the NKE from these structures in order to unload itself successfully. NKEs must provide a mechanism, such as a reference count, to ensure that the NKE can terminate without leaving dangling pointers.
Contents:
NKE Implementation
PF_NKE Domain
Implementing a Preference File for NKE
About Protocol Family NKEs
About Protocol Handler NKEs
About Socket NKEs
About Data Link NKEs
For more information
Last updated: 2006-10-03
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