NetSNMP开源代码学习——mib扩展

扩展MIB库
关于MIB库的扩展网络文章非常多，这里我主要参考了http://blog.csdn.net/qq_27204267/article/details/51595708，这篇文章介绍的比较简单，流程清晰，内容全面，没有太多的理论讲解。
闲言少叙，参考前人经验直接在我的环境里来个“傻瓜”操作并记录步骤，防止忘记。哎，年纪大了健忘啊^^^^^^同时为了后续的移植操作和深入分析做基础。
1. 编译MIB库文件

一. 编译MIB库文件

-- Test-MIB.my
    Test-MIB DEFINITIONS ::= BEGIN
 
        IMPORTS
            OBJECT-GROUP, MODULE-COMPLIANCE, NOTIFICATION-GROUP    
                FROM SNMPv2-CONF    
            enterprises, Integer32, Unsigned32, OBJECT-TYPE, MODULE-IDENTITY, 
            NOTIFICATION-TYPE    
                FROM SNMPv2-SMI    
            DisplayString    
                FROM SNMPv2-TC;
    
-- October 09, 2002 at 14:50 GMT
        -- 1.3.6.1.4.1.16535
        Test MODULE-IDENTITY 
            LAST-UPDATED "200210091450Z"        -- October 09, 2002 at 14:50 GMT
            ORGANIZATION 
                ""  
            CONTACT-INFO 
                ""  
            DESCRIPTION 
                "Video's Server MIB."
            ::= { enterprises 16535 }
    
--  Node definitions
-- This part will include all details about the Test.
        -- 1.3.6.1.4.1.16535.1
        Time OBJECT IDENTIFIER ::= { Test 1 } 

    
        -- 1.3.6.1.4.1.16535.1.1
        GetTime OBJECT-TYPE
            SYNTAX DisplayString (SIZE (0..100))
            MAX-ACCESS read-only
            STATUS current
            DESCRIPTION
                "Example : 2013/4/11"
            ::= { Time 1 }
    END

-- Test-MIB.my

二. 生成源代码并修改实现的函数

/*
 * Note: this file originally auto-generated by mib2c using
 *        $
 */

#include <net-snmp/net-snmp-config.h>
#include <net-snmp/net-snmp-includes.h>
#include <net-snmp/agent/net-snmp-agent-includes.h>
#include "Test.h"
#include <time.h>

/** Initializes the Test module */
void
init_Test(void)
{
    const oid       GetTime_oid[] = { 1, 3, 6, 1, 4, 1, 16535, 1, 1 };

    DEBUGMSGTL(("Test", "Initializing\n"));

    netsnmp_register_scalar(netsnmp_create_handler_registration
                            ("GetTime", handle_GetTime, GetTime_oid,
                             OID_LENGTH(GetTime_oid), HANDLER_CAN_RONLY));
}

int
handle_GetTime(netsnmp_mib_handler *handler,
               netsnmp_handler_registration *reginfo,
               netsnmp_agent_request_info *reqinfo,
               netsnmp_request_info *requests)
{
    /*  
     * We are never called for a GETNEXT if it's registered as a
     * "instance", as it's "magically" handled for us.  
     */
     /*
     * a instance handler also only hands us one request at a time, so
     * we don't need to loop over a list of requests; we'll only get one. 
     */

    time_t t;
    switch (reqinfo->mode) {
    case MODE_GET:
        time(&t);
        char szTime[100];
        snprintf(szTime,100,"%s",ctime(&t));
        snmp_set_var_typed_value(requests->requestvb, ASN_OCTET_STR,
                                 /*
                                  * XXX: a pointer to the scalar's data 
                                  */ szTime,
                                 /*
                                  * XXX: the length of the data in bytes 
                                  */ strlen(szTime));
        break;


    default:
        /*
         * we should never get here, so this is a really bad error 
         */
        snmp_log(LOG_ERR, "unknown mode (%d) in handle_GetTime\n",
                 reqinfo->mode);
        return SNMP_ERR_GENERR;
    }

    return SNMP_ERR_NOERROR;
}

三. 静态库编译安装

./configure --prefix=/usr/local/net-snmp --with-default-snmp-version=2c --with-sys-contact="xxx@163.com" --with-sys-location="China" --with-logfile="/var/log/snmpd.log" --with-persistent-directory=/var/net-snmp/ --enable-applications --enable-ipv6 --with-out-transports="TCP TCPv6 Unix" --with-transports="Callback UDP UDPIPv6"  --disable-nls --enable-shared --enable-static --disable-embedded-perl --with-mib-modules=Test

将.c 和.h文件移动到源码目录下，我的是/opt/net-snmp-5.7.3/agent/mibgroup。
运行configure命令，并且添加--with-mib-modules=Test，进行MIB库文件的配置。
运行make && make install编译安装
测试：
执行命令：snmpget -v2c -c public localhost Test-MIB:GetTime.0测试

四. 生成共享库编译
具体编译命令为：  

gcc -I `net-snmp-config --cflags` -fPIC -shared -g -O0 -o Test.so Test.c  `net-snmp-config --libs`

修改snmpd.conf，添加一行：
dlmod Test /usr/local/net-snmp/share/snmp/mibs/Test.so
测试：
重新configure（不要--with-mib-modules=Test），make,make install,安装snmpd程序
执行命令：snmpget -v2c -c public localhost Test-MIB:GetTime.0测试