*ebuf = '\0';

  pd = pcap_open_live(device, snaplen, !pflag, 1000, ebuf);   if (pd == NULL)    error("%s", ebuf);   else if (*ebuf)    warning("%s", ebuf);   #endif /* HAVE_PCAP_CREATE */   //如果没有定义HAVE_PCAP_CREATE,   //则通过pcap_open_live 获得用于捕获网络数据包的数据包捕获描述字   、、~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/*    * Let user own process after socket has been opened.    */   #ifndef WIN32    if (setgid(getgid()) != 0 || setuid(getuid()) != 0)     fprintf(stderr, "Warning: setgid/setuid failed !\n");   #endif /* WIN32 */   //设置用户ID和组ID

 

//~~~~~~~~~~~~~~~~~~~~~~~~~~~

#if !defined(HAVE_PCAP_CREATE) && defined(WIN32)

     if(Bflag != 0)    if(pcap_setbuff(pd, Bflag)==-1)    {     error("%s", pcap_geterr(pd));    }   #endif /* !defined(HAVE_PCAP_CREATE) && defined(WIN32) */   //设置内核缓冲区   //自定义检查点: 1 2 3

、、~~~~~~~~~~~~~~~~~~~~~~~~~~

i = pcap_snapshot(pd);  

  if (snaplen < i)   {    warning("snaplen raised from %d to %d", snaplen, i);    snaplen = i;   }   //返回快照长度,并与snaplen比较

、、~~~~~~~~~~

 if (pcap_lookupnet(device, &localnet, &netmask, ebuf) < 0)

    {      localnet = 0;      netmask = 0;      warning("%s", ebuf);     }    //获取网卡的配置信息

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`

 if (infile)

  cmdbuf = read_infile(infile);  else   cmdbuf = copy_argv(&argv[optind]);  //这里假设我们没有读取文件  //设置cmdbuf指向缓冲区

//自定义检查点: 1 2 3

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 if (pcap_compile(pd, &fcode, cmdbuf, Oflag, netmask) < 0)

  error("%s", pcap_geterr(pd));  //设置过滤条件

/

 

init_addrtoname(localnet, netmask);

    init_checksum();  //做一些初始化操作  

 

 #ifndef WIN32   (void)setsignal(SIGPIPE, cleanup);  (void)setsignal(SIGTERM, cleanup);  (void)setsignal(SIGINT, cleanup);  #endif /* WIN32 */  //设置一些信号处理函数句柄

 #if defined(HAVE_FORK) || defined(HAVE_VFORK)

 (void)setsignal(SIGCHLD, child_cleanup);  #endif  /* Cooperate with nohup(1) */  //设置一些信号处理函数句柄