arp.c

cf8020+cp2200(网络)的驱动实现

//-----------------------------------------------------------------------------
// Copyright (c) 2002 Jim Brady
// Do not use commercially without author's permission
// Last revised August 2002
// Net ARP.C
//
// This module handles ARP messages and ARP resolution and manages
// the ARP cache. Refer to RFC 826 and RFC 1122
//-----------------------------------------------------------------------------
//#include "stdio.h"

#include "stdlib.h"
#include "net.h"
#include "eth.h"
#include "serial.h"
#include "ip.h"
#include "arp.h"
#include "utils.h"


extern WAIT  wait;
extern UCHAR  my_hwaddr[];
extern UCHAR  broadcast_hwaddr[]; 
extern ulong  my_ipaddr;
extern ulong  my_subnet;
extern ulong  gateway_ipaddr;
extern UCHAR  debug;
ARP_CACHE  arp_cache[CACHESIZE];
UCHAR waiting_for_arp;


void init_arp(void)
{
  	memset(arp_cache, 0, sizeof(arp_cache)); 
	memset(&wait, 0, sizeof(wait));
	waiting_for_arp = FALSE;
}




//------------------------------------------------------------------------
//	This is called every 60 seconds to age the ARP cache
// If an entry times out then it is deleted from the cache
// See "TCP/IP Illustrated, Volume 1" Sect 4.3
//------------------------------------------------------------------------

//每隔60 s刷新一次ARP表. 超过60s未用的记录删掉.
void age_arp_cache(void)
{
 	UCHAR i;
    	
   for (i=0; i < CACHESIZE; i++)
   {  //如果ARP cahce表的某一记录的ipaddr和timer不为0,此记录的timer减一．如果减一等于0,　此记录丢弃. 
      if ((arp_cache[i].ipaddr != 0) && (arp_cache[i].timer))
      {
         arp_cache[i].timer--;
		if (arp_cache[i].timer == 0)
         {
				// Timed out so clear out cache entry
				// Do not need to zero hwaddr
				arp_cache[i].ipaddr = 0;
//				if (debug) serial_send("ARP: Aged out a cache entry\r");
			}
		}
   }
}




//------------------------------------------------------------------------
// This allocates memory for the entire outgoing message,
// including eth and ip headers, then builds an outgoing
// ARP response message
// See "TCP/IP Illustrated, Volume 1" Sect 4.4
//------------------------------------------------------------------------
//arp_send(arp->source_hwaddr, arp->source_ipaddr, ARP_RESPONSE);
// UCHAR * hwaddr,  本端硬件地址；
// ulong ipaddr,    对端IP地址；
// UCHAR msg_type,  本端ARP类型为: ARP请求还是ARP应答

void arp_send(UCHAR * hwaddr, ulong ipaddr, UCHAR msg_type)
{
	UCHAR  * outbuf;
	ARP_HEADER  * arp;
         
   
   // Allocate memory for entire outgoing message including
   // eth header. Always 42 bytes
  // outbuf = (UCHAR  *)malloc(42);
	outbuf = TX_BUFF;
   if (outbuf == NULL)
   {
//      if (debug) serial_send("ARP: Oops, out of memory\r");
      return;
   }      
     
   // Allow 14 bytes for the ethernet header
   arp = (ARP_HEADER  *)(outbuf + 14); //定位ARP头
 	
   arp->hardware_type = DIX_ETHERNET;   //硬件地址类型: DIX_DIX_ETHERNET
   
   arp->protocol_type = IP_PACKET;      //上层协议类型: IP_PACKET
   
   arp->hwaddr_len = 6;                 //硬件地址长度: 6
   arp->ipaddr_len = 4;                 //上层协议长度: 6
   arp->message_type = (uint)msg_type;  //ARP类型: 请求还是应答
   
   // My hardware address and IP addresses 
   memcpy((char *)arp->source_hwaddr, my_hwaddr, 6);
   arp->source_ipaddr = my_ipaddr;

   // Destination hwaddr and dest IP addr
   if (msg_type == ARP_REQUEST)       //如果是ARP请求,向所有主机(EtherADDR = 0)查询指定IP地址的对应硬件地址(取0)；
	  memset((char *)arp->dest_hwaddr, 0, 6);
   else                               
	  memcpy((char *)arp->dest_hwaddr, hwaddr, 6);
   
   arp->dest_ipaddr = ipaddr;  
   
#ifdef __LITTLEENDIAN__
   arp->hardware_type  = ntohs(arp->hardware_type);
   arp->protocol_type =  ntohs(arp->protocol_type);
   arp->message_type = ntohs(arp->message_type);
   arp->source_ipaddr = ntohl(arp->source_ipaddr);
   arp->dest_ipaddr = ntohl(arp->dest_ipaddr);
#endif  

   // If request then the message is a brodcast, if a response then
   // send to specified hwaddr
   // ARP payload size is always 28 bytes
	if (msg_type == ARP_REQUEST)   //如果是ARP请求,向所有主机(EtherADDR = 0)查询指定IP地址的对应硬件地址(取0)
		eth_send(outbuf, broadcast_hwaddr, ARP_PACKET, 28);
   else 
	    eth_send(outbuf, hwaddr, ARP_PACKET, 28);
#ifdef __LITTLEENDIAN__ 
   free(outbuf);
#endif

}



//------------------------------------------------------------------------
// This re-sends an ARP request if there was no response to
// the first one.	 It is called every 0.5 seconds.  If there
// is no response after 2 re-tries, the datagram that IP was 
// trying to send is deleted
//-----------------------------------------------------------------------
void arp_retransmit()
{
	static UCHAR  retries = 0; 
	
	if ((waiting_for_arp) && (wait.timer))
	{
		wait.timer--;
		if (wait.timer == 0)
		{
			retries++;
			if (retries <= 2)
			{
//				//if (debug) serial_send("ARP: Re-sending ARP broadcast\r");
	 			arp_send(NULL, wait.ipaddr, ARP_REQUEST);
				wait.timer = ARP_TIMEOUT;
			}
			else
			{	
//				//if (debug) serial_send("ARP: Gave up waiting for response\r");
	 			wait.timer = 0;
				waiting_for_arp = 0;
				free(wait.buf);
			}
		}
	}
}




//------------------------------------------------------------------------
// Find the ethernet hardware address for the given ip address
// If destination IP is on my subnet then we want the eth
// address	of destination, otherwise we want eth addr of gateway. 
// Look in ARP cache first.  If not found there, send ARP request.
// Return pointer to the hardware address or NULL if not found
// See "TCP/IP Illustrated, Volume 1" Sect 4.5
//------------------------------------------------------------------------
unsigned char * arp_resolve(ulong dest_ipaddr)
{
   UCHAR i;
      
   // If destination IP is not on my subnet then we really want eth addr
	// of gateway, not destination IP如果目的ip地址跟本机ip地址不是一个子网，就用网关地址
	if ((dest_ipaddr ^ my_ipaddr) & my_subnet)
	{
		if (gateway_ipaddr == 0)
		{
//			//if (debug) serial_send("ARP: Error, gateway addr not set\r");
			return (NULL);	
	 	}
	 	else dest_ipaddr = gateway_ipaddr;
	}
	
	   
   // See if IP addr of interest is in ARP cache
   for (i=0; i < CACHESIZE; i++)
   {
      if (arp_cache[i].ipaddr == dest_ipaddr)  //在cache里找到与dest_ipaddr一致的选项，取选项中对应的硬件地址返回;
         return (&arp_cache[i].hwaddr[0]);
   }

	//if (debug) serial_send("ARP: IP addr not found in cache\r");
	//if (debug) serial_send("ARP: Sending an ARP broadcast\r");
	// Not in cache so broadcast ARP request
  	arp_send(NULL, dest_ipaddr, ARP_REQUEST);
     	   
   // Set a flag to indicate that an IP datagram is waiting
   // to be sent
   waiting_for_arp = TRUE;
				      
   // Null means that we have sent an ARP request
   return (NULL); 
}





//------------------------------------------------------------------------
// This handles incoming ARP messages
// See "TCP/IP Illustrated, Volume 1" Sect 4.4
// Todo:  Resolve problem of trying to add to a full cache
//------------------------------------------------------------------------
void arp_rcve(UCHAR  * inbuf)
{
   UCHAR  i, cached, oldest;
   uint  minimum;
   ARP_HEADER  * arp;
      
   arp = (ARP_HEADER  *)(inbuf + 14);
   cached = FALSE;
#ifdef __LITTLEENDIAN__

   arp->message_type = ntohs(arp->message_type);
   arp->hardware_type = ntohs(arp->hardware_type);
   arp->protocol_type = ntohs(arp->protocol_type);
   arp->source_ipaddr = ntohl(arp->source_ipaddr);
   arp->dest_ipaddr = ntohl(arp->dest_ipaddr);

#endif
   // Print message
   if (debug)
   {
    //   if (arp->message_type == ARP_REQUEST)
     //     serial_send("ARP: Request rcvd\n");
     //  else serial_send("ARP: Response rcvd\n");
   }
         
   // Validate incoming frame
   //非法ARP帧丢弃
   if ((arp->hardware_type != DIX_ETHERNET) ||
       (arp->protocol_type != IP_PACKET)) 
	   return;

   // Search ARP cache for senders IP address
   // If found, update entry and restart timer

   //如果收到ARP报文的源协议IP地址在ARP CACHE表中,根据此报文的源硬件地址刷新cache表相同IP地址选项的硬件地址
   for (i=0; i < CACHESIZE; i++)
   {
      if (arp_cache[i].ipaddr == arp->source_ipaddr)
      {
         memcpy((char*)&arp_cache[i].hwaddr[0], (char*)&arp->source_hwaddr[0], 6);
         arp_cache[i].timer = CACHETIME;		
         cached = TRUE;
//         if (debug) serial_send("ARP: Cache entry updated\r\n");
                  
         break;  
      }
   }

//   	printf("%02x-%02x-%02x-%02x-%02x-%02x==souceip=%x---destip=%X\n", arp->source_hwaddr[0], arp->source_hwaddr[1], arp->source_hwaddr[2], arp->source_hwaddr[3], arp->source_hwaddr[4], arp->source_hwaddr[5], arp->source_ipaddr, arp->dest_ipaddr);
   //如果ARP包不是送往本机(目的地址非本机),丢弃
   if (arp->dest_ipaddr != my_ipaddr)
   {
	   return;
   }
   
   // At this point we know the the frame is addressed to me
   // If not already in cache then add entry and start timer

   //如果cache表没有收到ARP报文的选项
   if (cached == FALSE)
   {
      // Find first blank space and add entry
		// Blank entries are indicated by ip addr = 0
      for (i=0; i < CACHESIZE; i++)
      {
         //找到cache表第一个空选项, 把收到ARP报文相应源协议IP地址和硬件地址插入;
         if (arp_cache[i].ipaddr == 0) 
         {
            arp_cache[i].ipaddr = arp->source_ipaddr;
            memcpy((char*)&arp_cache[i].hwaddr[0], (char*)&arp->source_hwaddr[0], 6);   
            arp_cache[i].timer = CACHETIME;
         	//if (debug) serial_send("ARP: New cache entry added\r");
         	break;
         }
      }

		// If no blank entries in arp cache	then sort cache
		// to find oldest entry and replace it
	    //如果cache表没有多余选项，拿最老的选项替换
		if (i == CACHESIZE)
		{
			// Oldest entry is the one with lowest timer value			
			minimum = 0xFFFF;
			for (i=0; i < CACHESIZE; i++)
      	{
				if (arp_cache[i].timer < minimum) 
				{
					minimum = arp_cache[i].timer;
					oldest = i;
				}
			}
      	
		 // "oldest" is now index of oldest entry, so replace it
		 arp_cache[oldest].ipaddr = arp->source_ipaddr;
         memcpy((char*)&arp_cache[oldest].hwaddr[0], (char*)&arp->source_hwaddr[0], 6);   
         arp_cache[oldest].timer = CACHETIME;
//         if (debug) serial_send("ARP: Cache full, so replaced oldest\r\n");
   	}
	}

   
   // If we are waiting for an arp response and the arp response
  	// that just came in is addressed to me and is from the host
  	// we are waiting for, then send	the message-in-waiting
   if (arp->message_type == ARP_RESPONSE)
   {
	   if ((waiting_for_arp) && (wait.ipaddr == arp->source_ipaddr))
	   {
		   waiting_for_arp = FALSE;
		   //收到的ARP应答包含协议地址与等待中的IP地址一致,向此等待地址和等待端口发送以前的消息；
		   ip_send(wait.buf, wait.ipaddr, wait.proto_id, wait.len);
	   }
   }
   else if (arp->message_type == ARP_REQUEST) //对于ARP请求
   {
	   // Send ARP response 
	   //if (debug) serial_send("ARP: Sending response\r");
	   //返回包括本端协议(IP)地址和硬件(MAC)地址的应答
	   arp_send((UCHAR *)arp->source_hwaddr, arp->source_ipaddr, ARP_RESPONSE);
   }
}