On 25 July 2010 19:54, Angela Perez <perez.ange...@gmail.com> wrote:
> I haven't worked out how to get the snmp code to
> fetch only the specific row from the database table (i.e. SELECT *
> FROM DB_TABLE WHERE rowNum = snmpRequestedRowNum)
I presume the difficulty here is in determining the appropriate value
for "snmpRequestedRowNum" ?
I'll let Robert comment on how to do this within the MfD framework.
But in most of the other approaches, you'd do this using code such
as the following:
netsnmp_table_request_info *tinfo;
for ( request = requests; request; request = request->next) {
tinfo = netsnmp_extract_table_info(request);
snprintf( query, sizeof(query),
"SELECT * FROM DB_TABLE WHERE rowNum = %d",
*tinfo->indexes->val.integer)
// etc, etc, etc
}
The field 'indexes' is the head of a linked list of varbind structures,
one per index value. The name (object ID) field is unused, and the
value field holds the relevant index value.
For a simple single-indexed table, you would use code such as that
above. For a multiple-indexed table, you'd need to refer to
'tinfo->indexes->next_variable->val', and so on.
The other thing to note is that this needs to be done for each
varbind in the request. There's no guarantee that all the varbinds
in a single SNMP request will necessarily refer to the same row
of the table. Hence the netsnmp_extract_table_info() call is
placed within the loop, in the code fragment shown above.
I'll now let Robert explain how you'd do the same thing in MfD.
Dave
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