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<!-- Copyright (C) 2003 Red Hat, Inc. --> <!-- This material may be distributed only subject to the terms --> <!-- and conditions set forth in the Open Publication License, v1.0 --> <!-- or later (the latest version is presently available at --> <!-- http://www.opencontent.org/openpub/). --> <!-- Distribution of the work or derivative of the work in any --> <!-- standard (paper) book form is prohibited unless prior --> <!-- permission is obtained from the copyright holder. --> <HTML ><HEAD ><TITLE >DHCP</TITLE ><meta name="MSSmartTagsPreventParsing" content="TRUE"> <META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ "><LINK REL="HOME" TITLE="eCos Reference Manual" HREF="ecos-ref.html"><LINK REL="UP" TITLE="Support Features" HREF="net-common-support.html"><LINK REL="PREVIOUS" TITLE="Support Features" HREF="net-common-support.html"><LINK REL="NEXT" TITLE="TCP/IP Library Reference" HREF="tcpip-library-reference.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >eCos Reference Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="net-common-support.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 37. Support Features</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="tcpip-library-reference.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="NET-COMMON-DHCP">DHCP</H1 ><P >This API publishes a routine to maintain DHCP state, and a semaphore that is signalled when a lease requires attention: this is your clue to call the aforementioned routine.</P ><P >The intent with this API is that a simple DHCP client thread, which maintains the state of the interfaces, can go as follows: (after <TT CLASS="FUNCTION" >init_all_network_interfaces()</TT > is called from elsewhere)</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >while ( 1 ) { while ( 1 ) { cyg_semaphore_wait( &dhcp_needs_attention ); if ( ! dhcp_bind() ) // a lease expired break; // If we need to re-bind } dhcp_halt(); // tear everything down init_all_network_interfaces(); // re-initialize }</PRE ></TD ></TR ></TABLE ><P >and if the application does not want to suffer the overhead of a separate thread and its stack for this, this functionality can be placed in the app’s server loop in an obvious fashion. That is the goal of breaking out these internal elements. For example, some server might be arranged to poll DHCP from time to time like this:</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >while ( 1 ) { init_all_network_interfaces(); open-my-listen-sockets(); while ( 1 ) { serve-one-request(); // sleeps if no connections, but not forever; // so this loop is polled a few times a minute... if ( cyg_semaphore_trywait( &dhcp_needs_attention )) { if ( ! dhcp_bind() ) { close-my-listen-sockets(); dhcp_halt(); break; } } } }</PRE ></TD ></TR ></TABLE ><P >If the configuration option CYGOPT_NET_DHCP_DHCP_THREAD is defined, then eCos provides a thread as described initially. Independent of this option, initialization of the interfaces still occurs in <TT CLASS="FUNCTION" >init_all_network_interfaces()</TT > and your startup code can call that. It will start the DHCP management thread if configured. If a lease fails to be renewed, the management thread will shut down all interfaces and attempt to initialize all the interfaces again from scratch. This may cause chaos in the app, which is why managing the DHCP state in an application aware thread is actually better, just far less convenient for testing.</P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="net-common-support.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ecos-ref.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="tcpip-library-reference.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Support Features</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="net-common-support.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >TCP/IP Library Reference</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
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