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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 >Starting the SNMP Agent</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="SNMP for eCos" HREF="net-snmp-ecos-port.html"><LINK REL="PREVIOUS" TITLE="Changes to eCos sources" HREF="net-snmp-ecos-changes.html"><LINK REL="NEXT" TITLE="Configuring eCos" HREF="net-snmp-configuring-ecos.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-snmp-ecos-changes.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 47. SNMP for <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >eCos</I ></SPAN ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="net-snmp-configuring-ecos.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="NET-SNMP-STARTING-THE-SNMP-AGENT">Starting the SNMP Agent</H1 ><P >A routine to instantiate and start the SNMP agent thread in the default configuration is provided in <TT CLASS="FILENAME" >PACKAGES/net/snmp/agent/VERSION/src/snmptask.c</TT ></P ><P >It starts the snmpd thread at priority <TT CLASS="LITERAL" >CYGPKG_NET_THREAD_PRIORITY+1</TT > by default, ie. one step less important than the TCP/IP stack service thread. It also statically creates and uses a very large stack of around 100 KiloBytes. To use that convenience function, this code fragment may be copied (in plain C).</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >#ifdef CYGPKG_SNMPAGENT { extern void cyg_net_snmp_init(void); cyg_net_snmp_init(); } #endif</PRE ></TD ></TR ></TABLE ><P >In case you need to perform initialization, for example setting up SNMPv3 security features, when the snmp agent starts and every time it restarts, you can register a callback function by simply writing the global variable: <TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >externC void (*<SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >snmpd_reinit_function</I ></SPAN >)( void );</PRE ></TD ></TR ></TABLE > with a suitable function pointer.</P ><P >The entry point to the SNMP agent is <TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >externC void <TT CLASS="FUNCTION" >snmpd</TT >( void (*<SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >initfunc</I ></SPAN >)( void ) );</PRE ></TD ></TR ></TABLE > so you can of course easily start it in a thread of your choice at another priority instead if required, after performing whatever other initialization your SNMP MIBs need. A larger than default stacksize is required. The <TT CLASS="LITERAL" >initfunc</TT > parameter is the callback function mentioned above — a NULL parameter there is safe and obviously means no callback is registered.</P ><P >Note that if you call <TT CLASS="LITERAL" >snmpd();</TT > yourself and do <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >not</I ></SPAN > call <TT CLASS="LITERAL" >cyg_net_snmp_init();</TT > then that routine, global variable, and the default large stack will not be used. This is the recommended way control such features from your application; create and start the thread yourself at the appropriate moment.</P ><P >Other APIs from the <TT CLASS="LITERAL" >snmpd</TT > module are available, specifically: <TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >void <TT CLASS="FUNCTION" >SnmpdShutDown</TT >(int <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >a</I ></SPAN >);</PRE ></TD ></TR ></TABLE > which causes the <TT CLASS="LITERAL" >snmpd</TT > to restart itself — including the callback to your init function — as soon as possible.</P ><P >The parameter <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >a</I ></SPAN > is ignored. It is there because in <TT CLASS="LITERAL" >snmpd</TT >'s “natural environment” this routine is a <TT CLASS="LITERAL" >UNIX</TT > signal handler.</P ><P >The helper functions in the network stack for managing <TT CLASS="LITERAL" >DHCP</TT > leases will call <TT CLASS="FUNCTION" >SnmpdShutDown()</TT > when necessary, for example if network interfaces go down and/or come up again.</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-snmp-ecos-changes.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="net-snmp-configuring-ecos.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Changes to eCos sources</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="net-snmp-ecos-port.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Configuring eCos</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
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