Agent Architecture - Revision history

Rmallins: /* The What: A Handler Definition */ remove "Popeye" style typo"

2015-11-24T16:03:28Z

‎The What: A Handler Definition: remove "Popeye" style typo"

Anirudhrudr: /* Handler Chains */

2015-03-30T10:29:43Z

‎Handler Chains

Wes: Reverted edits by Domtheo (talk) to last revision by Baerm

2013-09-06T14:03:36Z

Reverted edits by Domtheo (talk) to last revision by Baerm

Domtheo at 09:39, 6 September 2013

2013-09-06T09:39:08Z

Baerm: /* Multi-tasking */

2011-08-10T23:13:49Z

‎Multi-tasking

Baerm: /* Agent Data */

2011-08-10T23:08:07Z

‎Agent Data

@@ Line 96: / Line 96: @@
 ==== The ''What'': A Handler Definition ====
-Now that we know ''where'' something needs to be registered, we needs to indicate ''what'' will actually handle the request.  Information about the handler is stored in a struct, netsnmp_mib_handler, which indicates the ''handler''.  It can store extra handler information and holds the handler access_method.  The access_method is  a pointer to the procedure that will actually fulfill and processes the SNMP requests for the registered OID location.  For simple MIB handling, the access_method procedure is what the MIB coder will have to fill-in or write in order to handle the MIB requests.  This is often done on a access_method per MIB table basis.  The struct netsnmp_mib_handler definition follows:
+Now that we know ''where'' something needs to be registered, we need to indicate ''what'' will actually handle the request.  Information about the handler is stored in a struct, netsnmp_mib_handler, which indicates the ''handler''.  It can store extra handler information and holds the handler access_method.  The access_method is  a pointer to the procedure that will actually fulfill and processes the SNMP requests for the registered OID location.  For simple MIB handling, the access_method procedure is what the MIB coder will have to fill-in or write in order to handle the MIB requests.  This is often done on a access_method per MIB table basis.  The struct netsnmp_mib_handler definition follows:
    typedef struct netsnmp_mib_handler_s {

@@ Line 145: / Line 145: @@
 == Handler Chains ==
-Actually, most handler implementations aren't "singular".  That is, they break the processing up into several steps and the resulting code is actually chained together in a serious of function calls, ending in the lowest-level handler's code.  For example, there are ''helpers'' which are handlers that are designed to "sit in the middle" of a request and do some processing before the request gets to the lower level.  This is useful if some of the code is so common that it's silly to implement the same code in a zillion low level handlers.  For example, the most common problems are separating indexes and the column from a table's OID, caching data from slow operations, and sorting data into a standard SNMP order.  So in the end, simple MIB objects (e.g. scalars) will likely have few steps in the handler chain, but complex MIB objects (e.g. tables) may have many handlers in the middle to "help out along the way".
+Actually, most handler implementations aren't "singular".  That is, they break the processing up into several steps and the resulting code is actually chained together in a series of function calls, ending in the lowest-level handler's code.  For example, there are ''helpers'' which are handlers that are designed to "sit in the middle" of a request and do some processing before the request gets to the lower level.  This is useful if some of the code is so common that it's silly to implement the same code in a zillion low level handlers.  For example, the most common problems are separating indexes and the column from a table's OID, caching data from slow operations, and sorting data into a standard SNMP order.  So in the end, simple MIB objects (e.g. scalars) will likely have few steps in the handler chain, but complex MIB objects (e.g. tables) may have many handlers in the middle to "help out along the way".
 Most of these "middle-class" handlers will have their own registration functions that properly take the lower level's registration object and add themselves to the chain, and then call something higher up to complete the registration.  We refer to this process as "injection".  I.e., a registration function typically "injects" its own handler into the chain.

@@ Line 26: / Line 26: @@
 # sends a [[coldStart]] trap
 # invokes ''receive()'' to perform the main packet handling
 === MIB Module Registration ===

@@ Line 26: / Line 26: @@
 # sends a [[coldStart]] trap
 # invokes ''receive()'' to perform the main packet handling
 === MIB Module Registration ===

@@ Line 343: / Line 343: @@
 == Multi-tasking ==
-Some requests can be processed in parallel.  Although the Net-SNMP agent is not thread-safe, it is capable of performing some tasks in parallel.  In particular, if a mib module implementation indicates to the main agent that it's "not yet done; please ask again later", the agent will continue to receive packets and process them if it is safe to do so.  Typically, the mib modules that support this ''delegated'' support are waiting for data to be returned from another network, file handle or other socket.
+Some requests can be processed in parallel.  Although the Net-SNMP
-It is not safe to process every type of request in paralell though.  In particular:
+It is not safe to process every type of request in parallel though.
 * PDUs safely parallel processed:
@@ Line 354: / Line 362: @@
 ** SET
-For SNMP SETs, the agent finishes all outstanding requests and then acts on the SET that has arrived before continuing on to any other requests in the queue.
+For SNMP SETs, the agent finishes all outstanding requests and then acts on the SETs that have arrived before continuing on to any other requests in the queue.
 == Shutting Down ==

@@ Line 333: / Line 333: @@
 Besides storing information, per request, you can also store
-information for a complete set of requests.  IE, if you need to store
+information for a complete set of requests.  I.e., if you need to store
 a single piece of information regardless of whether it's for a single
-request or a huge number (think a 1000 OID GET), you can use the
+request or a huge number (think a 1,000 OID GET), you can use the
 ''_agent_'' version of the APIs instead: