snmp_client, snmp_send_cb_f, snmp_timeout_cb_f, snmp_timeout_start_f,
snmp_timeout_stop_f, snmp_open, snmp_close, snmp_pdu_create,
snmp_add_binding, snmp_pdu_check, snmp_pdu_send, snmp_oid_append,
snmp_receive, snmp_table_cb_f, snmp_table_fetch, snmp_table_fetch_async,
snmp_dialog -- SNMP client library
Begemot SNMP library (libbsnmp, -lbsnmp)
#include <asn1.h>
#include <snmp.h>
#include <snmpclient.h>
typedef void
(*snmp_send_cb_f)(struct snmp_pdu *req, struct snmp_pdu *resp,
void *uarg);
typedef void
(*snmp_timeout_cb_f)(void *uarg);
typedef void *
(*snmp_timeout_start_f)(struct timeval *timeout,
snmp_timeout_cb_f callback, void *uarg);
typedef void
(*snmp_timeout_stop_f)(void *timeout_id);
extern struct snmp_client snmp_client;
void
snmp_client_init(struct snmp_client *client);
int
snmp_client_set_host(struct snmp_client *client, const char *host);
int
snmp_client_set_port(struct snmp_client *client, const char *port);
int
snmp_open(const char *host, const char *port, const char *read_community,
const char *write_community);
void
snmp_close(void);
void
snmp_pdu_create(struct snmp_pdu *pdu, u_int op);
int
snmp_add_binding(struct snmp_pdu *pdu, ...);
int
snmp_pdu_check(const struct snmp_pdu *req, const struct snmp_pdu *resp);
int32_t
snmp_pdu_send(struct snmp_pdu *pdu, snmp_send_cb_f func, void *uarg);
int
snmp_oid_append(struct asn_oid *oid, const char *fmt, ...);
int
snmp_receive(int blocking);
typedef void
(*snmp_table_cb_f)(void *list, void *arg, int res);
int
snmp_table_fetch(const struct snmp_table *descr, void *list);
int
snmp_table_fetch_async(const struct snmp_table *descr, void *list,
snmp_table_cb_f callback, void *uarg);
int
snmp_dialog(struct snmp_pdu *req, struct snmp_pdu *resp);
The SNMP library contains routines to easily build SNMP client applications
that use SNMP versions 1 or 2. Most of the routines use a struct
snmp_client:
struct snmp_client {
enum snmp_version version;
int local; /* use local socket */
/* these two are read-only for the application */
char *cport; /* port number as string */
char *chost; /* host name or IP address as string */
char read_community[SNMP_COMMUNITY_MAXLEN + 1];
char write_community[SNMP_COMMUNITY_MAXLEN + 1];
struct timeval timeout;
u_int retries;
int dump_pdus;
size_t txbuflen;
size_t rxbuflen;
int fd;
int32_t next_reqid;
int32_t max_reqid;
int32_t min_reqid;
char error[SNMP_STRERROR_LEN];
snmp_timeout_start_f timeout_start;
snmp_timeout_stop_f timeout_stop;
/* private */
char local_path[sizeof(SNMP_LOCAL_PATH)];
};
The fields of this structure are described below.
version This is the version of SNMP to use. See bsnmplib(3) for
applicable values. The default version is SNMP_V2c.
local If this is set to true, the library opens a UNIX domain
socket rather than an UDP socket. It uses the chost field
as the path to the server's socket.
cport The SNMP agent's UDP port number. This may be a symbolic
port number (from /etc/services or a numeric port number.
If this field is NULL (the default) the standard SNMP port
is used. This field should not be changed directly but
rather by calling snmp_client_set_port().
chost The SNMP agent's host name, IP address or UNIX domain
socket path name. If this is NULL (the default) localhost
is assumed. This field should not be changed directly but
rather through calling snmp_client_set_host().
read_community
This is the community name to be used for all requests
except SET requests. The default is `public'.
write_community
The community name to be used for SET requests. The
default is `private'.
timeout The maximum time to wait for responses to requests. If the
time elapses, the request is resent up to retries times.
The default is 3 seconds.
retries Number of times a request PDU is to be resent. If set to
0, the request is sent only once. The default is 3
retransmissions.
dump_pdus If set to a non-zero value all received and sent PDUs are
dumped via snmp_pdu_dump(3). The default is not to dump
PDUs.
txbuflen The encoding buffer size to be allocated for transmitted
PDUs. The default is 10000 octets.
rxbuflen The decoding buffer size to be allocated for received
PDUs. This is the size of the maximum PDU that can be
received. The default is 10000 octets.
fd After calling snmp_open() this is the file socket file
descriptor used for sending and receiving PDUs.
next_reqid The request id of the next PDU to send. Used internal by
the library.
max_reqid The maximum request id to use for outging PDUs. The
default is INT32_MAX.
min_reqid The minimum request id to use for outgoing PDUs. Request
ids are allocated linerily starting at min_reqid up to
max_reqid.
error If an error happens, this field is set to a printable
string describing the error.
timeout_start This field must point to a function setting up a one shot
timeout. After the timeout has elapsed, the given callback
function must be called with the user argument. The
timeout_start() function must return a void * identifying
the timeout.
timeout_stop This field must be set to a function that stops a running
timeout. The function will be called with the return value
of the corresponding timeout_start() function.
local_path If in local socket mode, the name of the clients socket.
Not needed by the application.
In the current implementation there is a global variable
extern struct snmp_client snmp_client;
that is used by all the library functions. The first call into the
library must be a call to snmp_client_init() to initialize this global
variable to the default values. After this call and before calling
snmp_open() the fields of the variable may be modified by the user. The
modification of the chost and cport fields should be done only via the
functions snmp_client_set_host() and snmp_client_set_port().
The function snmp_open() creates a UDP or UNIX domain socket and connects
it to the agent's IP address and port. If any of the arguments of the
call is not NULL the corresponding field in the global snmp_client is set
from the argument. Otherwise the values that are already in that variable
are used. The function snmp_close() closes the socket, stops all timeouts
and frees all dynamically allocated resources.
The next three functions are used to create request PDUs. The function
snmp_pdu_create() initializes a PDU of type op. It does not allocate
space for the PDU itself. This is the responsibility of the caller.
snmp_add_binding() adds bindings to the PDU and returns the (zero based)
index of the first new binding. The arguments are pairs of pointer to the
OIDs and syntax constants, terminated by a NULL. The call
snmp_add_binding(&pdu,
&oid1, SNMP_SYNTAX_INTEGER,
&oid2, SNMP_SYNTAX_OCTETSTRING,
NULL);
adds two new bindings to the PDU and returns the index of the first one.
It is the responsibility of the caller to set the value part of the binding
if neccesary. The functions returns -1 if the maximum number of bindings
is exhausted. The function snmp_oid_append() can be used to construct
variable OIDs for requests. It takes a pointer to an struct
asn_oid that is to be constructed, a format string, and a number of arguments
the type of which depends on the format string. The format string
is interpreted character by character in the following way:
i This format expects an argument of type asn_subid_t and appends this
as a single integer to the OID.
a This format expects an argument of type struct in_addr and appends
to four parts of the IP address to the OID.
s This format expects an argument of type const char * and appends the
length of the string (as computed by strlen(3)) and each of the
characters in the string to the OID.
(N) This format expects no argument. N must be a decimal number and is
stored into an internal variable size.
b This format expects an argument of type const char * and appends
size characters from the string to the OID. The string may contain
NUL characters.
c This format expects two arguments: one of type size_t and one of
type const u_char *. The first argument gives the number of bytes
to append to the OID from the string pointed to by the second argument.
The function snmp_pdu_check() may be used to check a response PDU. A number
of checks are performed (error code, equal number of bindings, syntaxes
and values for SET PDUs). The function returns +1 if everything is
ok, 0 if a NOSUCHNAME or similar error was detected, -1 if the response
PDU had fatal errors and -2 if resp is NULL (a timeout occured).
The function snmp_pdu_send() encodes and sends the given PDU. It records
the PDU together with the callback and user pointers in an internal list
and arranges for retransmission if no response is received. When a
response is received or the retransmission count is exceeded the callback
func is called with the orignal request PDU, the response PDU and the
user argument uarg. If the retransmit count is exceeded, func is called
with the original request PDU, the reponse pointer set to NULL and the
user argument uarg. The caller should not free the request PDU until the
callback function is called. The callback function must free the request
PDU and the response PDU (if not NULL ).
The function snmp_receive() tries to receive a PDU. If the argument is
zero, the function polls to see whether a packet is available, if the
argument is non-zero, the function blocks until the next packet is
received. The packet is delivered via the usual callback mechanism (nonresponse
packets are silently dropped). The function returns 0, if a
packet was received and successfully dispatched, -1 if an error occured
or no packet was available (in polling mode).
The next two functions are used to retrieve tables from SNMP agents. The
use the following input structure, that describes the table:
struct snmp_table {
struct asn_oid table;
struct asn_oid last_change;
u_int max_iter;
size_t entry_size;
u_int index_size;
u_int64_t req_mask;
struct snmp_table_entry {
asn_subid_t subid;
enum snmp_syntax syntax;
off_t offset;
} entries[];
};
The fields of this structure have the following meaning:
table This is the base OID of the table.
last_change Some tables have a scalar variable of type TIMETICKS
attached to them, that holds the time when the table was
last changed. This OID should be the OID of this variable
(without the .0 index). When the table is retrieved with
multiple GET requests, and the variable changes between two
request, the table fetch is restarted.
max_iter Maximum number of tries to fetch the table.
entry_size The table fetching routines return a list of structure one
for each table row. This variable is the size of one structure
and used to malloc(3) the structure.
index_size This is the number of index columns in the table.
req_mask This is a bit mask with a 1 for each table column that is
required. Bit 0 corresponds to the first element (index 0)
in the array entries, bit 1 to the second (index 1) and so
on. SNMP tables may be sparse. For sparse columns the bit
should not be set. If the bit for a given column is set and
the column value cannot be retrieved for a given row, the
table fetch is restarted assuming that the table is currently
beeing modified by the agent. The bits for the index
columns are ignored.
entries This is a variable sized array of column descriptors. This
array is terminated by an element with syntax
SNMP_SYNTAX_NULL. The first index_size elements describe
all the index columns of the table, the rest are normal columns.
If for a the column at `entries[N]' the expression
`req_mask & (1 << N)' yields true, the column is considered
a required column. The fields of this the array elements
have the following meaning:
subid This is the OID subid of the column. This is ignored
for index entries. Index entries are decoded according
to the syntax field.
syntax This is the syntax of the column or index. A syntax
of SNMP_SYNTAX_NULL terminates the array.
offset This is the starting offset of the value of the column
in the return structures. This field can be set
with the ISO-C offsetof() macro.
Both table fetching functions return TAILQ (see queue(3)) of structures--one
for each table row. These structures must start with a
TAILQ_ENTRY() and a u_int64_t and are allocated via malloc(3). The list
argument of the table functions must point to a TAILQ_HEAD(). The
u_int64_t fields, usually called found is used to indicate which of the
columns have been found for the given row. It is encoded like the
req_mask field.
The function snmp_table_fetch() synchronuosly fetches the given table. If
everything is ok 0 is returned. Otherwise the function returns -1 and
sets an appropriate error string. The function snmp_table_fetch_async()
fetches the tables asynchronuosly. If either the entire table is fetch,
or an error occures the callback function callback is called with the
callers arguments list and uarg and a parameter that is either 0 if the
table was fetched, or -1 if there was an error. The function itself
returns -1 if it could not initialize fetching of the table.
The following table description is used to fetch the ATM interface table:
/*
* ATM interface table
*/
struct atmif {
TAILQ_ENTRY(atmif) link;
u_int64_t found;
int32_t index;
u_char *ifname;
size_t ifnamelen;
u_int32_t node_id;
u_int32_t pcr;
int32_t media;
u_int32_t vpi_bits;
u_int32_t vci_bits;
u_int32_t max_vpcs;
u_int32_t max_vccs;
u_char *esi;
size_t esilen;
int32_t carrier;
};
TAILQ_HEAD(atmif_list, atmif);
/* list of all ATM interfaces */
struct atmif_list atmif_list;
static const struct snmp_table atmif_table = {
OIDX_begemotAtmIfTable,
OIDX_begemotAtmIfTableLastChange, 2,
sizeof(struct atmif),
1, 0x7ffULL,
{
{ 0, SNMP_SYNTAX_INTEGER,
offsetof(struct atmif, index) },
{ 1, SNMP_SYNTAX_OCTETSTRING,
offsetof(struct atmif, ifname) },
{ 2, SNMP_SYNTAX_GAUGE,
offsetof(struct atmif, node_id) },
{ 3, SNMP_SYNTAX_GAUGE,
offsetof(struct atmif, pcr) },
{ 4, SNMP_SYNTAX_INTEGER,
offsetof(struct atmif, media) },
{ 5, SNMP_SYNTAX_GAUGE,
offsetof(struct atmif, vpi_bits) },
{ 6, SNMP_SYNTAX_GAUGE,
offsetof(struct atmif, vci_bits) },
{ 7, SNMP_SYNTAX_GAUGE,
offsetof(struct atmif, max_vpcs) },
{ 8, SNMP_SYNTAX_GAUGE,
offsetof(struct atmif, max_vccs) },
{ 9, SNMP_SYNTAX_OCTETSTRING,
offsetof(struct atmif, esi) },
{ 10, SNMP_SYNTAX_INTEGER,
offsetof(struct atmif, carrier) },
{ 0, SNMP_SYNTAX_NULL, 0 }
}
};
...
if (snmp_table_fetch(&atmif_table, &atmif_list) != 0)
errx(1, "AtmIf table: %s", snmp_client.error);
...
The function snmp_dialog() is used to execute a synchonuous dialog with
the agent. The request PDU req is sent and the function blocks until the
response PDU is received. Note, that asynchonuous receives are handled
(i.e. callback functions of other send calls or table fetches may be
called while in the function). The response PDU is returned in resp. If
no reponse could be received after all timeouts and retries, the function
returns -1. If a response was received 0 is returned.
If an error occures in any of the function an error indication as
described above is returned. Additionally the function sets a printable
error string in the error filed of snmp_client.
snmpd(1), gensnmptree(1), bsnmplib(3) bsnmpagent(3)
This implementation conforms to the applicable IETF RFCs and ITU-T recommendations.
Hartmut Brandt <[email protected]>
Kendy Kutzner <[email protected]>
FreeBSD 5.2.1 August 15, 2002 FreeBSD 5.2.1 [ Back ] |
