Wes: Created page with "{{MFDTutorial}} == MIBs For Dummies : ifXTable data GET == Once the correct table context has been found, the individual node get routines will be called. These are generated..."

2011-07-13T22:03:28Z

Created page with "{{MFDTutorial}} == MIBs For Dummies : ifXTable data GET == Once the correct table context has been found, the individual node get routines will be called. These are generated..."

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{{MFDTutorial}}

== MIBs For Dummies : ifXTable data GET ==

Once the correct table context has been found, the individual node
get routines will be called. These are generated in the file
''ifXTable_data_get.c''. The code generated for each node
defaults to returning ''MFD_SKIP'', which will cause Net-SNMP to
skip the column for the given table context. If you compile and run the
code before implementing any code in the get routines, and try to walk
the ifXTable, each node's get routine will be called once for each
interface. Since every function will return ''MFD_SKIP'', snmpwalk
will eventually return END OF MIB.

=== Implementing the get routines ===

We are using the same data structures that the ''ifTable''
implementation uses for the Linux kernel. I won't cover every
node, as they are all very similar.

==== ifName_get ====

The ''ifName'' node is a string. First we check that the string
is large enough to hold the name in our ''data context'',
allocating memory if it is not. Then the name is copied and the length
variable is set.
<table><tr> <td width=20></td> <td>'''Generated code'''</td> <td width=20></td> <td>'''Modified code'''</td> </tr><tr> <td></td> <td bgcolor=CCCCCC>
int
ifName_get(ifXTable_ctx * ctx, char **ifName_ptr_ptr,
size_t * ifName_len_ptr)
{
/** syntax-DisplayString-get.m2i not found, using generic */
/** we should have a non-NULL pointer and enough storage */
netsnmp_assert((NULL != ifName_ptr_ptr) && (NULL != *ifName_ptr_ptr));
netsnmp_assert(NULL != ifName_len_ptr);

netsnmp_assert(NULL != ctx);

/*
* TODO:
* set (* ifName_ptr_ptr) and (* ifName_len_ptr) from ctx->data.
*/
return MFD_SKIP; /* TODO: remove this once you've set data */

return SNMP_ERR_NOERROR;
}
</td><td></td><td bgcolor=CCCCCC>
int
ifName_get(ifXTable_ctx * ctx, char **ifName_ptr_ptr,
size_t * ifName_len_ptr)
{
/** syntax-DisplayString-get.m2i not found, using generic */
/** we should have a non-NULL pointer and enough storage */
netsnmp_assert((NULL != ifName_ptr_ptr) && (NULL != *ifName_ptr_ptr));
netsnmp_assert(NULL != ifName_len_ptr);

netsnmp_assert(NULL != ctx);

/*
* TODO:
* set (* ifName_ptr_ptr) and (* ifName_len_ptr) from ctx->data.
*/<font color=blue>
if (*ifName_len_ptr < strnlen(ctx->data.Name,sizeof(ctx->data.Name))) {
*ifName_ptr_ptr = malloc(strnlen(ctx->data.Name,sizeof(ctx->data.Name)));
}
*ifName_len_ptr = strnlen(ctx->data.Name,sizeof(ctx->data.Name));
memcpy(*ifName_ptr_ptr, ctx->data.Name, *ifName_len_ptr);
</font>
return SNMP_ERR_NOERROR;
}
</td> </tr> </table>

==== ifInMulticastPkts_get ====

The ''ifInMulticastPkts'' node is a integer. However, we don't
always have the data for this node. At compile time we test a macro that
will be set during configure to determine if the data is available.
variable is set.
<table><tr> <td width=20></td> <td>'''Generated code'''</td> <td width=20></td> <td>'''Modified code'''</td> </tr><tr> <td></td> <td bgcolor=CCCCCC>
int
ifInMulticastPkts_get(ifXTable_ctx * ctx, u_long * ifInMulticastPkts_ptr)
{
/** syntax-COUNTER-get.m2i not found, using generic */
/** we should have a non-NULL pointer */
netsnmp_assert(NULL != ifInMulticastPkts_ptr);

netsnmp_assert(NULL != ctx);

/*
* TODO:
* set (* ifInMulticastPkts_ptr) from ctx->data.
*/
return MFD_SKIP; /* TODO: remove this once you've set data */

/*
* TODO:
* value mapping
*
* If the values for your data type don't exactly match the
* possible values defined by the mib, you should map them here.
*/

return SNMP_ERR_NOERROR;
}
</td>
<td></td><td bgcolor=CCCCCC>
int
ifInMulticastPkts_get(ifXTable_ctx * ctx, u_long * ifInMulticastPkts_ptr)
{
/** syntax-COUNTER-get.m2i not found, using generic */
/** we should have a non-NULL pointer */
netsnmp_assert(NULL != ifInMulticastPkts_ptr);

netsnmp_assert(NULL != ctx);

/*
* TODO:
* set (* ifInMulticastPkts_ptr) from ctx->data.
*/<font color=blue>
#if STRUCT_IFNET_HAS_IF_IMCASTS
temp_ifInMulticastPkts = (u_long) ctx->data.ifnet.if_imcasts;
#else</font>
return MFD_SKIP; /* TODO: remove this once you've set data */<font color=blue>
#endif
</font>
/*
* TODO:
* value mapping
*
* If the values for your data type don't exactly match the
* possible values defined by the mib, you should map them here.
*/

return SNMP_ERR_NOERROR;
}
</td>
</tr>
</table>

==== ifHCInOctets_get ====

The ''ifHCInOctets'' node is a 64 bit counter. Net-SNMP uses a
structure containing the high and low 32 bits for 64 bit counters. We
use if_ibytes if it is available, or if_ipackets otherwise. This logic
is straight from the current ''ifTable'' implementation.
<table><tr> <td width=20></td> <td>'''Generated code'''</td> <td width=20></td> <td>'''Modified code'''</td> </tr><tr> <td></td> <td bgcolor=CCCCCC>
int
ifHCInOctets_get(ifXTable_ctx * ctx, U64 * ifHCInOctets_ptr)
{
/** we should have a non-NULL pointer */
netsnmp_assert(NULL != ifHCInOctets_ptr);

/*
* TODO:
* get (* ifHCInOctets_ptr).low and (* ifHCInOctets_ptr).high from ctx->data.
*/

return SNMP_ERR_NOERROR;
}
</td>
<td></td><td bgcolor=CCCCCC>
int
ifHCInOctets_get(ifXTable_ctx * ctx, U64 * ifHCInOctets_ptr)
{
/** we should have a non-NULL pointer */
netsnmp_assert(NULL != ifHCInOctets_ptr);

/*
* TODO:
* get (* ifHCInOctets_ptr).low and (* ifHCInOctets_ptr).high from ctx->data.
*/<font color=blue>
(*ifHCInOctets_ptr).high = 0;
#ifdef STRUCT_IFNET_HAS_IF_IBYTES
(*ifHCInOctets_ptr).low = (u_long) ctx->data.ifnet.if_ibytes;
#else
(*ifHCInOctets_ptr).low = (u_long) ctx->data.ifnet.if_ipackets * 308; /* XXX */
#endif
</font>

return SNMP_ERR_NOERROR;
}
</td> </tr> </table>

MFD:ifXTable:Get Data - Revision history

Wes: Created page with "{{MFDTutorial}} == MIBs For Dummies : ifXTable data GET == Once the correct table context has been found, the individual node get routines will be called. These are generated..."