porting.doxygen

via usb driver that support vt6656 chipsets

/**
\page porting Porting to different target boards and operating systems

%wpa_supplicant was designed to be easily portable to different
hardware (board, CPU) and software (OS, drivers) targets. It is
already used with number of operating systems and numerous wireless
card models and drivers. The main %wpa_supplicant repository includes
support for Linux, FreeBSD, and Windows. In addition, at least VxWorks
and PalmOS are supported in separate repositories. On the hardware
side, %wpa_supplicant is used on various systems: desktops, laptops,
PDAs, and embedded devices with CPUs including x86, PowerPC,
arm/xscale, and MIPS. Both big and little endian configurations are
supported.


\section driver_iface_porting Driver interface

Unless the target OS and driver is already supported, most porting
projects have to implement a driver wrapper. This may be done by
adding a new driver interface module or modifying an existing module
(driver_*.c) if the new target is similar to one of them. \ref
driver_wrapper "Driver wrapper implementation" describes the details
of the driver interface and discusses the tasks involved in porting
this part of %wpa_supplicant.


\section l2_packet_porting l2_packet (link layer access)

%wpa_supplicant needs to have access to sending and receiving layer 2
(link layer) packets with two Ethertypes: EAP-over-LAN (EAPOL) 0x888e
and RSN pre-authentication 0x88c7. l2_packet.h defines the interfaces
used for this in the core %wpa_supplicant implementation.

If the target operating system supports a generic mechanism for link
layer access, that is likely the best mechanism for providing the
needed functionality for %wpa_supplicant. Linux packet socket is an
example of such a generic mechanism. If this is not available, a
separate interface may need to be implemented to the network stack or
driver. This is usually an intermediate or protocol driver that is
operating between the device driver and the OS network stack. If such
a mechanism is not feasible, the interface can also be implemented
directly in the device driver.

The main %wpa_supplicant repository includes l2_packet implementations
for Linux using packet sockets (l2_packet_linux.c), more portable
version using libpcap/libdnet libraries (l2_packet_pcap.c; this
supports WinPcap, too), and FreeBSD specific version of libpcap
interface (l2_packet_freebsd.c).

If the target operating system is supported by libpcap (receiving) and
libdnet (sending), l2_packet_pcap.c can likely be used with minimal or
no changes. If this is not a case or a proprietary interface for link
layer is required, a new l2_packet module may need to be
added. Alternatively, struct wpa_driver_ops::send_eapol() handler can
be used to override the l2_packet library if the link layer access is
integrated with the driver interface implementation.


\section eloop_porting Event loop

%wpa_supplicant uses a single process/thread model and an event loop
to provide callbacks on events (registered timeout, received packet,
signal). eloop.h defines the event loop interface. eloop.c is an
implementation of such an event loop using select() and sockets. This
is suitable for most UNIX/POSIX systems. When porting to other
operating systems, it may be necessary to replace that implementation
with OS specific mechanisms that provide similar functionality.


\section ctrl_iface_porting Control interface

%wpa_supplicant uses a \ref ctrl_iface_page "control interface"
to allow external processed
to get status information and to control the operations. Currently,
this is implemented with socket based communication; both UNIX domain
sockets and UDP sockets are supported. If the target OS does not
support sockets, this interface will likely need to be modified to use
another mechanism like message queues. The control interface is
optional component, so it is also possible to run %wpa_supplicant
without porting this part.

The %wpa_supplicant side of the control interface is implemented in
ctrl_iface.c. Matching client side is implemented as a control
interface library in wpa_ctrl.c.


\section entry_point Program entry point

%wpa_supplicant defines a set of functions that can be used to
initialize main supplicant processing. Each operating system has a
mechanism for starting new processing or threads. This is usually a
function with a specific set of arguments and calling convention. This
function is responsible on initializing %wpa_supplicant.

main.c includes an entry point for UNIX-like operating system, i.e.,
main() function that uses command line arguments for setting
parameters for %wpa_supplicant. When porting to other operating
systems, similar OS-specific entry point implementation is needed. It
can be implemented in a new file that is then linked with
%wpa_supplicant instead of main.o. main.c is also a good example on
how the initialization process should be done.

The supplicant initialization functions are defined in
wpa_supplicant_i.h. In most cases, the entry point function should
start by fetching configuration parameters. After this, a global
%wpa_supplicant context is initialized with a call to
wpa_supplicant_init(). After this, existing network interfaces can be
added with wpa_supplicant_add_iface(). wpa_supplicant_run() is then
used to start the main event loop. Once this returns at program
termination time, wpa_supplicant_deinit() is used to release global
context data.

wpa_supplicant_add_iface() and wpa_supplicant_remove_iface() can be
used dynamically to add and remove interfaces based on when
%wpa_supplicant processing is needed for them. This can be done, e.g.,
when hotplug network adapters are being inserted and ejected. It is
also possible to do this when a network interface is being
enabled/disabled if it is desirable that %wpa_supplicant processing
for the interface is fully enabled/disabled at the same time.

*/