add initial version of our new documentation - not too pretty yet, but will be improved

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@5060 3c298f89-4303-0410-b956-a3cf2f4a3e73

docs/network-scripts.tex

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+\subsubsection{Using the network scripts}
+
+To be able to access the network functions, you need to include
+the necessary shell scripts by running:
+
+\begin{Verbatim}
+. /etc/functions.sh      # common functions
+include /lib/network     # include /lib/network/*.sh
+scan_interfaces          # read and parse the network config
+\end{Verbatim}
+
+Some protocols, such as PPP might change the configured interface names
+at run time (e.g. \texttt{eth0} => \texttt{ppp0} for PPPoE). That's why you have to run
+\texttt{scan\_interfaces} instead of reading the values from the config directly.
+After running \texttt{scan\_interfaces}, the \texttt{'ifname'} option will always contain
+the effective interface name (which is used for IP traffic) and if the
+physical device name differs from it, it will be stored in the \texttt{'device'}
+option.
+That means that running \texttt{config\_get lan ifname}
+after \texttt{scan\_interfaces} might not return the same result as running it before.
+
+After running \texttt{scan\_interfaces}, the following functions are available:
+
+\begin{itemize}
+	\item{\texttt{find\_config \textit{interface}}} \\
+		looks for a network configuration that includes
+  		the specified network interface.
+
+	\item{\texttt{setup\_interface \textit{interface [config] [protocol]}}} \\
+	  will set up the specified interface, optionally overriding the network configuration
+	  name or the protocol that it uses.
+\end{itemize}
+
+\subsubsection{Writing protocol handlers}
+
+You can add custom protocol handlers by adding shell scripts to
+\texttt{/lib/network}. They provide the following two shell functions:
+
+\begin{Verbatim}
+scan_<protocolname>() {
+	local config="$1"
+	# change the interface names if necessary
+}
+
+setup_interface_<protocolname>() {
+	local interface="\$1"
+	local config="\$2"
+	# set up the interface
+}
+\end{Verbatim}
+
+\texttt{scan\_\textit{protocolname}} is optional and only necessary if your protocol
+uses a custom device, e.g. a tunnel or a PPP device.
+