net-snmp  5.4.1
Data Structures | Modules | Defines | Typedefs | Functions
Net-SNMP Agent handler and extensibility API
The Net-SNMP agent

The basic theory goes something like this: In the past, with the original mib module api (which derived from the original CMU SNMP code) the underlying mib modules were passed very little information (only the truly most basic information about a request). More...

Data Structures

struct  netsnmp_mib_handler_s
 the mib handler structure to be registered More...
struct  netsnmp_handler_registration_s
 Root registration info. More...
struct  netsnmp_handler_args_s
struct  netsnmp_delegated_cache_s

Modules

 utility_handlers
 

Simplify request processing A group of handlers intended to simplify certain aspects of processing a request for a MIB object.


 leaf_handlers
 

Process individual leaf objects A group of handlers to implement individual leaf objects and instances (both scalar objects, and individual objects and instances within a table).


 baby_steps
 

Calls your handler in baby_steps for set processing.


 old_api
 

Calls mib module code written in the old style of code.


 stash_cache
 

Automatically caches data for certain handlers.


 table
 

Helps you implement a table.


Defines

#define MIB_HANDLER_AUTO_NEXT   0x00000001
#define MIB_HANDLER_AUTO_NEXT_OVERRIDE_ONCE   0x00000002
#define MIB_HANDLER_INSTANCE   0x00000004
#define MIB_HANDLER_CUSTOM4   0x10000000
#define MIB_HANDLER_CUSTOM3   0x20000000
#define MIB_HANDLER_CUSTOM2   0x40000000
#define MIB_HANDLER_CUSTOM1   0x80000000
#define HANDLER_CAN_GETANDGETNEXT   0x01 /* must be able to do both */
#define HANDLER_CAN_SET   0x02 /* implies create, too */
#define HANDLER_CAN_GETBULK   0x04
#define HANDLER_CAN_NOT_CREATE   0x08 /* auto set if ! CAN_SET */
#define HANDLER_CAN_BABY_STEP   0x10
#define HANDLER_CAN_STASH   0x20
#define HANDLER_CAN_RONLY   (HANDLER_CAN_GETANDGETNEXT)
#define HANDLER_CAN_RWRITE   (HANDLER_CAN_GETANDGETNEXT | HANDLER_CAN_SET)
#define HANDLER_CAN_SET_ONLY   (HANDLER_CAN_SET | HANDLER_CAN_NOT_CREATE)
#define HANDLER_CAN_DEFAULT   (HANDLER_CAN_RONLY | HANDLER_CAN_NOT_CREATE)
#define REQUEST_IS_DELEGATED   1
#define REQUEST_IS_NOT_DELEGATED   0

Typedefs

typedef struct
netsnmp_mib_handler_s 
netsnmp_mib_handler
 Typedefs the netsnmp_mib_handler_s struct into netsnmp_mib_handler.
typedef struct
netsnmp_handler_registration_s 
netsnmp_handler_registration
 Typedefs the netsnmp_handler_registration_s struct into netsnmp_handler_registration.
typedef int( Netsnmp_Node_Handler )(netsnmp_mib_handler *handler, netsnmp_handler_registration *reginfo, netsnmp_agent_request_info *reqinfo, netsnmp_request_info *requests)
typedef struct
netsnmp_handler_args_s 
netsnmp_handler_args
typedef struct
netsnmp_delegated_cache_s 
netsnmp_delegated_cache

Functions

netsnmp_mib_handlernetsnmp_create_handler (const char *name, Netsnmp_Node_Handler *handler_access_method)
 creates a netsnmp_mib_handler structure given a name and a access method.
netsnmp_handler_registrationnetsnmp_handler_registration_create (const char *name, netsnmp_mib_handler *handler, oid *reg_oid, size_t reg_oid_len, int modes)
 creates a handler registration structure given a name, a access_method function, a registration location oid and the modes the handler supports.
netsnmp_handler_registrationnetsnmp_create_handler_registration (const char *name, Netsnmp_Node_Handler *handler_access_method, oid *reg_oid, size_t reg_oid_len, int modes)
int netsnmp_register_handler (netsnmp_handler_registration *reginfo)
 register a handler, as defined by the netsnmp_handler_registration pointer.
int netsnmp_unregister_handler (netsnmp_handler_registration *reginfo)
 unregister a handler, as defined by the netsnmp_handler_registration pointer.
int netsnmp_register_handler_nocallback (netsnmp_handler_registration *reginfo)
 register a handler, as defined by the netsnmp_handler_registration pointer.
int netsnmp_inject_handler_before (netsnmp_handler_registration *reginfo, netsnmp_mib_handler *handler, const char *before_what)
 inject a new handler into the calling chain of the handlers definedy by the netsnmp_handler_registration pointer.
int netsnmp_inject_handler (netsnmp_handler_registration *reginfo, netsnmp_mib_handler *handler)
 inject a new handler into the calling chain of the handlers definedy by the netsnmp_handler_registration pointer.
NETSNMP_INLINE int netsnmp_call_handler (netsnmp_mib_handler *next_handler, netsnmp_handler_registration *reginfo, netsnmp_agent_request_info *reqinfo, netsnmp_request_info *requests)
 calls a handler with with appropriate NULL checking of arguments, etc.
int netsnmp_call_handlers (netsnmp_handler_registration *reginfo, netsnmp_agent_request_info *reqinfo, netsnmp_request_info *requests)
NETSNMP_INLINE int netsnmp_call_next_handler (netsnmp_mib_handler *current, netsnmp_handler_registration *reginfo, netsnmp_agent_request_info *reqinfo, netsnmp_request_info *requests)
 calls the next handler in the chain after the current one with with appropriate NULL checking, etc.
NETSNMP_INLINE int netsnmp_call_next_handler_one_request (netsnmp_mib_handler *current, netsnmp_handler_registration *reginfo, netsnmp_agent_request_info *reqinfo, netsnmp_request_info *requests)
 calls the next handler in the chain after the current one with with appropriate NULL checking, etc.
void netsnmp_handler_free (netsnmp_mib_handler *handler)
 free's the resourceses associated with a given handler
netsnmp_mib_handlernetsnmp_handler_dup (netsnmp_mib_handler *handler)
 dulpicates a handler and all subsequent handlers see also _clone_handler
void netsnmp_handler_registration_free (netsnmp_handler_registration *reginfo)
 free the resources associated with a handler registration object
netsnmp_handler_registrationnetsnmp_handler_registration_dup (netsnmp_handler_registration *reginfo)
 duplicates the handler registration object
NETSNMP_INLINE
netsnmp_delegated_cache
netsnmp_create_delegated_cache (netsnmp_mib_handler *handler, netsnmp_handler_registration *reginfo, netsnmp_agent_request_info *reqinfo, netsnmp_request_info *requests, void *localinfo)
 creates a cache of information which can be saved for future reference.
NETSNMP_INLINE
netsnmp_delegated_cache
netsnmp_handler_check_cache (netsnmp_delegated_cache *dcache)
 check's a given cache and returns it if it is still valid (ie, the agent still considers it to be an outstanding request.
NETSNMP_INLINE void netsnmp_free_delegated_cache (netsnmp_delegated_cache *dcache)
 frees a cache once you're finished using it
void netsnmp_handler_mark_requests_as_delegated (netsnmp_request_info *requests, int isdelegated)
 marks a list of requests as delegated (or not if isdelegaded = 0)
NETSNMP_INLINE void netsnmp_request_add_list_data (netsnmp_request_info *request, netsnmp_data_list *node)
 add data to a request that can be extracted later by submodules
NETSNMP_INLINE int netsnmp_request_remove_list_data (netsnmp_request_info *request, const char *name)
 remove data from a request
NETSNMP_INLINE void * netsnmp_request_get_list_data (netsnmp_request_info *request, const char *name)
 extract data from a request that was added previously by a parent module
NETSNMP_INLINE void netsnmp_free_request_data_set (netsnmp_request_info *request)
 Free the extra data stored in a request.
NETSNMP_INLINE void netsnmp_free_request_data_sets (netsnmp_request_info *request)
 Free the extra data stored in a bunch of requests (all data in the chain)
netsnmp_mib_handlernetsnmp_find_handler_by_name (netsnmp_handler_registration *reginfo, const char *name)
 Returns a handler from a chain based on the name.
void * netsnmp_find_handler_data_by_name (netsnmp_handler_registration *reginfo, const char *name)
 Returns a handler's void * pointer from a chain based on the name.
void handler_free_callback (void *free)
void netsnmp_register_handler_by_name (const char *name, netsnmp_mib_handler *handler)
 registers a given handler by name so that it can be found easily later.
void netsnmp_clear_handler_list (void)
 clears the entire handler-registration list
void netsnmp_inject_handler_into_subtree (netsnmp_subtree *tp, const char *name, netsnmp_mib_handler *handler, const char *before_what)
void parse_injectHandler_conf (const char *token, char *cptr)
void netsnmp_init_handler_conf (void)
void * netsnmp_handler_get_parent_data (netsnmp_request_info *, const char *)

Detailed Description

The basic theory goes something like this: In the past, with the original mib module api (which derived from the original CMU SNMP code) the underlying mib modules were passed very little information (only the truly most basic information about a request).

This worked well at the time but in todays world of subagents, device instrumentation, low resource consumption, etc, it just isn't flexible enough. "handlers" are here to fix all that.

With the rewrite of the agent internals for the net-snmp 5.0 release, we introduce a modular calling scheme that allows agent modules to be written in a very flexible manner, and more importantly allows reuse of code in a decent way (and without the memory and speed overheads of OO languages like C++).

Functionally, the notion of what a handler does is the same as the older api: A handler is created and then registered with the main agent at a given OID in the OID tree and gets called any time a request is made that it should respond to. You probably should use one of the convenience helpers instead of doing anything else yourself though:

Most importantly, though, is that the handlers are built on the notion of modularity and reuse. Specifically, rather than do all the really hard work (like parsing table indexes out of an incoming oid request) in each module, the API is designed to make it easy to write "helper" handlers that merely process some aspect of the request before passing it along to the final handler that returns the real answer. Most people will want to make use of the instance, table, table_iterator, table_data, or table_dataset helpers to make their life easier. These "helpers" interpert important aspects of the request and pass them on to you.

For instance, the table helper is designed to hand you a list of extracted index values from an incoming request. THe table_iterator helper is built on top of the table helper, and is designed to help you iterate through data stored elsewhere (like in a kernel) that is not in OID lexographical order (ie, don't write your own index/oid sorting routine, use this helper instead). The beauty of the table_iterator helper, as well as the instance helper is that they take care of the complex GETNEXT processing entirely for you and hand you everything you need to merely return the data as if it was a GET request. Much less code and hair pulling. I've pulled all my hair out to help you so that only one of us has to be bald.


Typedef Documentation

Typedefs the netsnmp_handler_registration_s struct into netsnmp_handler_registration.

Typedefs the netsnmp_mib_handler_s struct into netsnmp_mib_handler.


Function Documentation

calls a handler with with appropriate NULL checking of arguments, etc.

Definition at line 394 of file agent_handler.c.

calls the next handler in the chain after the current one with with appropriate NULL checking, etc.

Definition at line 524 of file agent_handler.c.

calls the next handler in the chain after the current one with with appropriate NULL checking, etc.

Definition at line 546 of file agent_handler.c.

void netsnmp_clear_handler_list ( void  )

clears the entire handler-registration list

Definition at line 905 of file agent_handler.c.

NETSNMP_INLINE netsnmp_delegated_cache * netsnmp_create_delegated_cache ( netsnmp_mib_handler handler,
netsnmp_handler_registration reginfo,
netsnmp_agent_request_info reqinfo,
netsnmp_request_info requests,
void *  localinfo 
)

creates a cache of information which can be saved for future reference.

Use netsnmp_handler_check_cache() later to make sure it's still valid before referencing it in the future.

Examples:
delayed_instance.c.

Definition at line 696 of file agent_handler.c.

netsnmp_mib_handler * netsnmp_create_handler ( const char *  name,
Netsnmp_Node_Handler *  handler_access_method 
)

creates a netsnmp_mib_handler structure given a name and a access method.

The returned handler should then be registered.

Parameters:
nameis the handler name and is copied then assigned to netsnmp_mib_handler->handler_name
handler_access_methodis a function pointer used as the access method for this handler registration instance for whatever required needs.
Returns:
a pointer to a populated netsnmp_mib_handler struct to be registered
See also:
netsnmp_create_handler_registration()
netsnmp_register_handler()

Definition at line 105 of file agent_handler.c.

Returns a handler from a chain based on the name.

Definition at line 838 of file agent_handler.c.

void * netsnmp_find_handler_data_by_name ( netsnmp_handler_registration reginfo,
const char *  name 
)

Returns a handler's void * pointer from a chain based on the name.

This probably shouldn't be used by the general public as the void * data may change as a handler evolves. Handlers should really advertise some function for you to use instead.

Definition at line 855 of file agent_handler.c.

NETSNMP_INLINE void netsnmp_free_delegated_cache ( netsnmp_delegated_cache dcache)

frees a cache once you're finished using it

Examples:
delayed_instance.c.

Definition at line 734 of file agent_handler.c.

NETSNMP_INLINE void netsnmp_free_request_data_set ( netsnmp_request_info request)

Free the extra data stored in a request.

Definition at line 820 of file agent_handler.c.

NETSNMP_INLINE void netsnmp_free_request_data_sets ( netsnmp_request_info request)

Free the extra data stored in a bunch of requests (all data in the chain)

Definition at line 828 of file agent_handler.c.

check's a given cache and returns it if it is still valid (ie, the agent still considers it to be an outstanding request.

Returns NULL if it's no longer valid.

Examples:
delayed_instance.c.

Definition at line 720 of file agent_handler.c.

dulpicates a handler and all subsequent handlers see also _clone_handler

Definition at line 591 of file agent_handler.c.

free's the resourceses associated with a given handler

make sure we aren't pointing to ourselves.

XXX : segv here at shutdown if SHUTDOWN_AGENT_CLEANLY defined. About 30 functions down the stack, starting in clear_context() -> clear_subtree()

Definition at line 569 of file agent_handler.c.

void netsnmp_handler_mark_requests_as_delegated ( netsnmp_request_info requests,
int  isdelegated 
)

marks a list of requests as delegated (or not if isdelegaded = 0)

Definition at line 748 of file agent_handler.c.

netsnmp_handler_registration * netsnmp_handler_registration_create ( const char *  name,
netsnmp_mib_handler handler,
oid *  reg_oid,
size_t  reg_oid_len,
int  modes 
)

creates a handler registration structure given a name, a access_method function, a registration location oid and the modes the handler supports.

If modes == 0, then modes will automatically be set to the default value of only HANDLER_CAN_DEFAULT, which is by default read-only GET and GETNEXT requests. A hander which supports sets but not row creation should set us a mode of HANDLER_CAN_SET_ONLY.

Note:
This ends up calling netsnmp_create_handler(name, handler_access_method)
Parameters:
nameis the handler name and is copied then assigned to netsnmp_handler_registration->handlerName.
handleris a function pointer used as the access method for this handler registration instance for whatever required needs.
reg_oidis the registration location oid.
reg_oid_lenis the length of reg_oid, can use the macro, OID_LENGTH
modesis used to configure read/write access. If modes == 0, then modes will automatically be set to the default value of only HANDLER_CAN_DEFAULT, which is by default read-only GET and GETNEXT requests. The other two mode options are read only, HANDLER_CAN_RONLY, and read/write, HANDLER_CAN_RWRITE.
  • HANDLER_CAN_GETANDGETNEXT
  • HANDLER_CAN_SET
  • HANDLER_CAN_GETBULK
  • HANDLER_CAN_RONLY (HANDLER_CAN_GETANDGETNEXT)
  • HANDLER_CAN_RWRITE (HANDLER_CAN_GETANDGETNEXT | HANDLER_CAN_SET)
  • HANDLER_CAN_DEFAULT HANDLER_CAN_RONLY
Returns:
Returns a pointer to a netsnmp_handler_registration struct. NULL is returned only when memory could not be allocated for the netsnmp_handler_registration struct.
See also:
netsnmp_create_handler()
netsnmp_register_handler()

Definition at line 163 of file agent_handler.c.

duplicates the handler registration object

Definition at line 634 of file agent_handler.c.

free the resources associated with a handler registration object

Definition at line 620 of file agent_handler.c.

inject a new handler into the calling chain of the handlers definedy by the netsnmp_handler_registration pointer.

The new handler is injected at the top of the list and hence will be the new handler to be called first.

Definition at line 386 of file agent_handler.c.

int netsnmp_inject_handler_before ( netsnmp_handler_registration reginfo,
netsnmp_mib_handler handler,
const char *  before_what 
)

inject a new handler into the calling chain of the handlers definedy by the netsnmp_handler_registration pointer.

The new handler is injected after the before_what handler, or if NULL at the top of the list and hence will be the new handler to be called first.

Definition at line 329 of file agent_handler.c.

register a handler, as defined by the netsnmp_handler_registration pointer.

Definition at line 202 of file agent_handler.c.

void netsnmp_register_handler_by_name ( const char *  name,
netsnmp_mib_handler handler 
)

registers a given handler by name so that it can be found easily later.

Definition at line 893 of file agent_handler.c.

register a handler, as defined by the netsnmp_handler_registration pointer.

Definition at line 277 of file agent_handler.c.

NETSNMP_INLINE void netsnmp_request_add_list_data ( netsnmp_request_info request,
netsnmp_data_list node 
)

add data to a request that can be extracted later by submodules

Parameters:
requestthe netsnmp request info structure
nodethis is the data to be added to the linked list request->parent_data
Returns:
void
Examples:
delayed_instance.c.

Definition at line 768 of file agent_handler.c.

NETSNMP_INLINE void * netsnmp_request_get_list_data ( netsnmp_request_info request,
const char *  name 
)

extract data from a request that was added previously by a parent module

Parameters:
requestthe netsnmp request info function
nameused to compare against the request->parent_data->name value, if a match is found request->parent_data->data is returned
Returns:
a void pointer(request->parent_data->data), otherwise NULL is returned if request is NULL or request->parent_data is NULL or request->parent_data object is not found.
Examples:
delayed_instance.c.

Definition at line 810 of file agent_handler.c.

NETSNMP_INLINE int netsnmp_request_remove_list_data ( netsnmp_request_info request,
const char *  name 
)

remove data from a request

Parameters:
requestthe netsnmp request info structure
namethis is the name of the previously added data
Returns:
0 on successful find-and-delete, 1 otherwise.

Definition at line 789 of file agent_handler.c.

unregister a handler, as defined by the netsnmp_handler_registration pointer.

Definition at line 267 of file agent_handler.c.