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+><TITLE
+>Starting the SNMP Agent</TITLE
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+TITLE="Configuring eCos"
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+>eCos Reference Manual</TH
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+>Prev</A
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+><TD
+WIDTH="80%"
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+>Chapter 47. SNMP for <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>eCos</I
+></SPAN
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+><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
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+CLASS="NAVFOOTER"
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