table_iterator(3) net-snmp table_iterator(3)
NAME
table_iterator - The table iterator helper is designed to simplify the task of writing a table
handler for the net-snmp agent when the data being accessed is not in an oid sorted form and must be
accessed externally.
Data Structures
struct ti_cache_info_s
struct netsnmp_iterator_info_s
Holds iterator information containing functions which should be called by the iterator_handler to
loop over your data set and sort it in a SNMP specific manner.
struct netsnmp_iterator_info_s
Holds iterator information containing functions which should be called by the iterator_handler to
loop over your data set and sort it in a SNMP specific manner.
Defines
#define TI_REQUEST_CACHE 'ti_cache'
#define TABLE_ITERATOR_NOTAGAIN 255
#define TABLE_ITERATOR_NAME 'table_iterator'
Typedefs
typedef ti_cache_info_s ti_cache_info
typedef netsnmp_variable_list *( Netsnmp_First_Data_Point )(void **loop_context, void **data_context,
netsnmp_variable_list *, struct netsnmp_iterator_info_s *)
typedef netsnmp_variable_list *( Netsnmp_Next_Data_Point )(void **loop_context, void **data_context,
netsnmp_variable_list *, struct netsnmp_iterator_info_s *)
typedef void *( Netsnmp_Make_Data_Context )(void *loop_context, struct netsnmp_iterator_info_s *)
typedef void( Netsnmp_Free_Loop_Context )(void *, struct netsnmp_iterator_info_s *)
typedef void( Netsnmp_Free_Data_Context )(void *, struct netsnmp_iterator_info_s *)
typedef netsnmp_iterator_info_s netsnmp_iterator_info
Typedefs the netsnmp_iterator_info_s struct into netsnmp_iterator_info.
Functions
netsnmp_iterator_info * netsnmp_iterator_create_table (Netsnmp_First_Data_Point *firstDP,
Netsnmp_Next_Data_Point *nextDP, Netsnmp_First_Data_Point *getidx, netsnmp_variable_list
*indexes)
void netsnmp_iterator_delete_table (netsnmp_iterator_info *iinfo)
netsnmp_mib_handler * netsnmp_get_table_iterator_handler (netsnmp_iterator_info *iinfo)
returns a netsnmp_mib_handler object for the table_iterator helper
int netsnmp_register_table_iterator (netsnmp_handler_registration *reginfo, netsnmp_iterator_info
*iinfo)
Creates and registers a table iterator helper handler calling netsnmp_create_handler with a
handler name set to TABLE_ITERATOR_NAME and access method, netsnmp_table_iterator_helper_handler.
NETSNMP_INLINE void * netsnmp_extract_iterator_context (netsnmp_request_info *request)
extracts the table_iterator specific data from a request.
NETSNMP_INLINE void netsnmp_insert_iterator_context (netsnmp_request_info *request, void *data)
inserts table_iterator specific data for a newly created row into a request
int netsnmp_table_iterator_helper_handler (netsnmp_mib_handler *handler, netsnmp_handler_registration
*reginfo, netsnmp_agent_request_info *reqinfo, netsnmp_request_info *requests)
void * netsnmp_iterator_row_first (netsnmp_iterator_info *iinfo)
void * netsnmp_iterator_row_get (netsnmp_iterator_info *iinfo, void *row)
void * netsnmp_iterator_row_next (netsnmp_iterator_info *iinfo, void *row)
void * netsnmp_iterator_row_get_byidx (netsnmp_iterator_info *iinfo, netsnmp_variable_list *indexes)
void * netsnmp_iterator_row_next_byidx (netsnmp_iterator_info *iinfo, netsnmp_variable_list *indexes)
void * netsnmp_iterator_row_get_byoid (netsnmp_iterator_info *iinfo, oid *instance, size_t len)
void * netsnmp_iterator_row_next_byoid (netsnmp_iterator_info *iinfo, oid *instance, size_t len)
int netsnmp_iterator_row_count (netsnmp_iterator_info *iinfo)
Variables
Netsnmp_Node_Handler netsnmp_table_iterator_helper_handler
Detailed Description
The table iterator helper is designed to simplify the task of writing a table handler for the net-snmp netsnmp
snmp agent when the data being accessed is not in an oid sorted form and must be accessed externally.
Functionally, it is a specialized version of the more generic table helper but easies the burden of
GETNEXT processing by manually looping through all the data indexes retrieved through function calls
which should be supplied by the module that wishes help. The module the table_iterator helps should,
afterwards, never be called for the case of 'MODE_GETNEXT' and only for the GET and SET related modes
instead.
The fundamental notion between the table iterator is that it allows your code to iterate over each
'row' within your data storage mechanism, without requiring that it be sorted in a SNMP-index-compliant SNMP-indexcompliant
compliant manner. Through the get_first_data_point and get_next_data_point hooks, the table_iterator
helper will repeatedly call your hooks to find the 'proper' row of data that needs processing. The
following concepts are important:
A loop context is a pointer which indicates where in the current processing of a set of rows you
currently are. Allows the get_*_data_point routines to move from one row to the next, once the
iterator handler has identified the appropriate row for this request, the job of the loop context
is done. The most simple example would be a pointer to an integer which simply counts rows from 1
to X. More commonly, it might be a pointer to a linked list node, or someother internal or external
reference to a data set (file seek value, array pointer, ...). If allocated during iteration,
either the free_loop_context_at_end (preferably) or the free_loop_context pointers should be set.
A data context is something that your handler code can use in order to retrieve the rest of the
data for the needed row. This data can be accessed in your handler via
netsnmp_extract_iterator_context api with the netsnmp_request_info structure that's passed in. The
important difference between a loop context and a data context is that multiple data contexts can
be kept by the table_iterator helper, where as only one loop context will ever be held by the
table_iterator helper. If allocated during iteration the free_data_context pointer should be set to
an appropriate function.
The table iterator operates in a series of steps that call your code hooks from your
netsnmp_iterator_info registration pointer.
the get_first_data_point hook is called at the beginning of processing. It should set the variable
list to a list of indexes for the given table. It should also set the loop_context and maybe a
data_context which you will get a pointer back to when it needs to call your code to retrieve
actual data later. The list of indexes should be returned after being update.
the get_next_data_point hook is then called repeatedly and is passed the loop context and the data
context for it to update. The indexes, loop context and data context should all be updated if more
data is available, otherwise they should be left alone and a NULL should be returned. Ideally, it
should update the loop context without the need to reallocate it. If reallocation is necessary for
every iterative step, then the free_loop_context function pointer should be set. If not, then the
free_loop_context_at_end pointer should be set, which is more efficient since a malloc/free will
only be performed once for every iteration.
Typedef Documentation
struct netsnmp_iterator_info_s netsnmp_iterator_info
Typedefs the netsnmp_iterator_info_s struct into netsnmp_iterator_info.
Function Documentation
void * netsnmp_extract_iterator_context (netsnmp_request_info * request)
extracts the table_iterator specific data from a request.
This function extracts the table iterator specific data from a netsnmp_request_info object. Calls
netsnmp_request_get_list_data with request->parent_data set with data from a request that was added
previously by a module and TABLE_ITERATOR_NAME handler name.
Parameters:
request the netsnmp request info structure
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.the net
Definition at line 234 of file table_iterator.c.
References netsnmp_request_get_list_data(), and TABLE_ITERATOR_NAME.
netsnmp_mib_handler * netsnmp_get_table_iterator_handler (netsnmp_iterator_info * iinfo)
returns a netsnmp_mib_handler object for the table_iterator helper
Definition at line 169 of file table_iterator.c.
References netsnmp_mib_handler_s::myvoid, netsnmp_create_handler(),
netsnmp_table_iterator_helper_handler, NULL, and TABLE_ITERATOR_NAME.
Referenced by netsnmp_register_table_iterator().
void netsnmp_insert_iterator_context (netsnmp_request_info * request, void * data)
inserts table_iterator specific data for a newly created row into a request
Definition at line 242 of file table_iterator.c.
References build_oid_noalloc(), netsnmp_table_request_info_s::indexes, netsnmp_create_data_list(),
netsnmp_extract_table_info(), netsnmp_request_add_list_data(), netsnmp_request_info_s::next, NULL,
netsnmp_request_info_s::prev, snmp_oid_compare(), and TABLE_ITERATOR_NAME.
int netsnmp_register_table_iterator (netsnmp_handler_registration * reginfo, netsnmp_iterator_info *
iinfo)
Creates and registers a table iterator helper handler calling netsnmp_create_handler with a handler
name set to TABLE_ITERATOR_NAME and access method, netsnmp_table_iterator_helper_handler.
If NOT_SERIALIZED is not defined the function injects the serialize handler into the calling chain
prior to calling netsnmp_register_table.
Parameters:
reginfo is a pointer to a netsnmp_handler_registration struct
iinfo is a pointer to a netsnmp_iterator_info struct
Returns:
MIB_REGISTERED_OK is returned if the registration was a success. Failures are
MIB_REGISTRATION_FAILED, MIB_DUPLICATE_REGISTRATION. If iinfo is NULL, SNMPERR_GENERR is
returned.
Definition at line 205 of file table_iterator.c.
References HANDLER_CAN_STASH, netsnmp_table_registration_info_s::indexes,
netsnmp_iterator_info_s::indexes, netsnmp_handler_registration_s::modes,
netsnmp_get_table_iterator_handler(), netsnmp_inject_handler(), netsnmp_register_table(),
snmp_clone_varbind(), and netsnmp_iterator_info_s::table_reginfo.
Version 5.4.1 27 Jul 2007 table_iterator(3)
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