NAME
snmpstrucfiller - snmpkit functions for taking making snmp requests
based upon a structure.
SYNOPSIS
#include <snmpkit.h>
SNMPSTRUCTFILLER *new_snmpstructfiller(SNMPSESSION *session);
void delete_snmpstructfiller(SNMPSTRUCTFILLER *doomed);
void snmpstructfiller_append(SNMPSTRUCTFILLER *sf, const char *oidstr,Tags tag, unsigned int offset);
void snmpstructfiller_remove(SNMPSTRUCTFILLER *sf,const char *oidstr);
void *snmpstructfiller_get(SNMPSTRUCTFILLER *sf,void *tobefilled);
void *snmpstructfiller_get_next(SNMPSTRUCTFILLER *sf, void *tobefilled);
DESCRIPTION
A snmpstructfiller is an opaque data structure used fill C structures
with data from the snmp requests.
The SNMP protocol is designed in a way where there is significant
overhead in process of encoding and exchanging a packet. Therefore it
is very inefficient and time consuming to exchange many variables in
individual request packets. The way around this is to bulk up a bunch
of snmp requests into one packet. Since you are most frequently
fetching information which is related the snmp structure filler is
designed to associate the snmp objects and data types with the offsets
into the structure. That way when you do a get or a get_next you will
get back a completely filled in structure.
The new_snmpstructfiller() function creates new structfiller. You will
need one of these for every different set of objects that you want to
fetch. It starts out not having any requests associated with it. To add
requests to this structure use the snmpstructfiller_append() function.
To actually do the request, use the snmpstructfiller_get() or the
snmpstructfiller_get_next() functions.
The delete_snmpstructfiller() function is the opposite of the new
function. It frees all the resources used by the structfiller
structure.
The snmpstructfiller_append() function appends a new snmp object to the
structure filler. It requires the oidstring. This snmp library doesn’t
bother attempting to read MIBS. You must specify the snmp object in
dotted decimal notation. For example, system.sysDesc is
"1.3.6.1.2.1.1.1.0". This means that you must look up the objects ID’s
before hand. This sounds like a lot of work but I have found that when
writing an application it is really not that much of a problem. The tag
is the type of data that the object is supposed to have as defined in
the MIB and cooresponds directly to the space used in the structure you
are filling. The tag can be one of the following:
INT_TAG long
STRING_TAG char*
IPADDR_TAG unsigned long
You get the IPADDR back in binary format. You must translate it
byte for byte to get an IPADDR in the format that is usually
expected.
COUNTER_TAG long
This could concievably be an unsigned long but enough
implementations of MIBS are fouled up in such that even though
the mib specifies a counter, the device returns an integer. That
it is best to store this number in an integer rather than an
unsigned..
TIME_TICK_TAG long
The final parameter is offset into the structure. For example if you
have a structure and a variable like:
struct info {
char *descr; char *contact;
} foo;
Then the offset of descr would be (char*)&(foo.descr)-(char*)&foo and
the offset of contact would be (char*)&(foo.contact)-(char*)&foo I know
that this is a very bad way of doing things and I intend to change it
in the future. Probably what I will do is change this to a function
pointer which when called takes the pointer to the structure that it is
supposed to insert the data in as well as the value of the data and it
will insert it into the data into the structure.
AUTHOR
Ben Woodard <ben@users.sourceforge.net>
BUGS
The library can possibly throw different kinds of C++ execptions that
won’t be caught by the glue code and therefore it can cause your
program to crash inexplicably.
There is no support for SNMP sets.
There is no support for getting back an OID.
There is no support for
SEE ALSO
libsnmpkit(3), snmpsession(3), snmpsock(3), snmptable(3),
snmpstructfiller(3)