NDISwrapper

NDISwrapper is a free software driver wrapper that enables the use of Windows XP network device drivers (for devices such as PCI cards, USB modems, and routers) on Linux operating systems. NDISwrapper works by implementing the Windows kernel and NDIS APIs and dynamically linking Windows network drivers to this implementation. As a result, it only works on systems based on the instruction set architectures supported by Windows, namely IA-32 and x86-64.
Native drivers for some network adapters are not available on Linux as some manufacturers maintain proprietary interfaces and do not write cross-platform drivers. NDISwrapper allows the use of Windows drivers, which are available for virtually all modern PC network adapters.
Use.
There are three steps: Creating a Linux driver, installing it, and using it. NDISwrapper is composed of two main parts, a command-line tool used at installation time and a Windows subsystem used when an application calls the Wi-Fi subsystem.
As the outcome of an NDISwrapper installation should be some sort of Linux driver to be able to work with Linux applications, the first action the user does is to "compile" a couple or more of Windows files, and the NDISwrapper's version of Windows DDK into a Linux Kernel Module. This is done with a tool named "ndiswrapper". The resultant linux driver is then installed (often manually) in the OS. A Linux application can then send request to this Linux driver that automatically does the needed adaptations to call its—now—internal Windows driver and DDK.
To achieve this "compilation" NDISwrapper requires at least the ".inf" and the ".sys" files invariably supplied as parts of the Windows driver. For example, if the driver is called "mydriver", with the files mydriver.inf and mydriver.sys and vendorid:productid 0000:0000, then NDISwrapper installs the driver to /etc/ndiswrapper/mydriver/. This directory contains three files:
Graphical frontends.
There are graphical frontends to NDISwrapper, such as Ndisgtk and NdisConfig, which allow NDISwrapper to be installed using a graphical user interface rather than console commands.
Architecture.
NDISwrapper enables a Unix-like system to use Windows drivers of type NDIS and WIFI.
It was useful at a time where there were no Linux Wi-Fi drivers for common Wi-Fi cards.
It is composed of:
How it works.
Ndiswrapper uses Windows INF files.
When a Linux application calls a device which is registered on Linux as an NDISwrapper device, the NDISwrapper determines which Windows driver is targeted. It then converts the Linux query into Windows parlance, it calls the Windows driver, waits for the result and translates it into Linux parlance then sends the result back to the Linux application.
It's possible from a Linux driver (NDISwrapper is a Linux driver) to call a Windows driver because they both execute in the same address space (the same as the Linux kernel).
If the Windows driver is composed of layered drivers (for example one for Ethernet above one for USB) it's the upper layer driver which is called, and this upper layer will create new calls (IRP in Windows parlance) by calling the "mini ntoskrnl". So the "mini ntoskrnl" must know there are other drivers, it must have registered them in its internal database a priori by reading the Windows ".inf" files.