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><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"
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>#ifdef CYGPKG_SNMPAGENT
{
extern void cyg_net_snmp_init(void);
cyg_net_snmp_init();
}
#endif</PRE
></TD
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><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
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><PRE
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>externC void (*<SPAN
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><I
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>snmpd_reinit_function</I
></SPAN
>)( void );</PRE
></TD
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>
with a suitable function pointer.</P
><P
>The entry point to the SNMP agent is
<TABLE
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><PRE
CLASS="PROGRAMLISTING"
>externC void <TT
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>snmpd</TT
>( void (*<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>initfunc</I
></SPAN
>)( void ) );</PRE
></TD
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>
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:
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><PRE
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>void <TT
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>SnmpdShutDown</TT
>(int <SPAN
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><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
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