Linux?????????????????????UDPЭ??

???????????? ???????[ 2012/12/27 10:30:20 ] ????????

/*
* All we need to do is get the socket?? and then do a checksum.
*/

int udp_rcv(struct sk_buff *skb?? struct device *dev?? struct options *opt??
unsigned long daddr?? unsigned short len??
unsigned long saddr?? int redo?? struct inet_protocol *protocol)
{
   struct sock *sk;
   struct udphdr *uh;
unsigned short ulen;
int addr_type = IS_MYADDR;

if(!dev || dev->pa_addr!=daddr)//??????????????????????????????
addr_type=ip_chk_addr(daddr);//?ú?????????devinet.c?У???????ip????????????????????

/*
* Get the header.
*/
   uh = (struct udphdr *) skb->h.uh;//???UDP?????????

   ip_statistics.IpInDelivers++;

/*
* Validate the packet and the UDP length.
*/

ulen = ntohs(uh->len);
//????len???ip???????(IP?????????????????)= UDP??????+UDP??????????????+????????
//ulen???????UDP??????????????????????????????????len>=ulen
if (ulen > len || len < sizeof(*uh) || ulen < sizeof(*uh))
{
printk("UDP: short packet: %d/%d "?? ulen?? len);
udp_statistics.UdpInErrors++;
kfree_skb(skb?? FREE_WRITE);
return(0);
}

if (uh->check && udp_check(uh?? len?? saddr?? daddr)) //????UDP?????У??
{
/* <mea@utu.fi> wants to know?? who sent it?? to
     go and stomp on the garbage sender... */
printk("UDP: bad checksum. From %08lX:%d to %08lX:%d ulen %d "??
         ntohl(saddr)??ntohs(uh->source)??
         ntohl(daddr)??ntohs(uh->dest)??
         ulen);
udp_statistics.UdpInErrors++;
kfree_skb(skb?? FREE_WRITE);
return(0);
}

len=ulen;//??len????????UDP?????????

#ifdef CONFIG_IP_MULTICAST//?????????д???
if (addr_type!=IS_MYADDR)
{
/*
   * Multicasts and broadcasts go to each listener.
   */
struct sock *sknext=NULL;//next???

/*get_sock_mcast ????????????????????
*???溯??????????α??:sock???????????????????????????????
*/

sk=get_sock_mcast(udp_prot.sock_array[ntohs(uh->dest)&(SOCK_ARRAY_SIZE-1)]?? uh->dest??
    saddr?? uh->source?? daddr);
if(sk)
{
   do
   {
    struct sk_buff *skb1;

    sknext=get_sock_mcast(sk->next?? uh->dest?? saddr?? uh->source?? daddr);//????????????????????
    if(sknext)
     skb1=skb_clone(skb??GFP_ATOMIC);
    else
     skb1=skb;
    if(skb1)
     udp_deliver(sk?? uh?? skb1?? dev??saddr??daddr??len);//???????????????????÷??????????
    sk=sknext;
   }
   while(sknext!=NULL);
}
else
   kfree_skb(skb?? FREE_READ);
return 0;
}
#endif
   sk = get_sock(&udp_prot?? uh->dest?? saddr?? uh->source?? daddr);
if (sk == NULL) //????????????????????????г??????
   {
    udp_statistics.UdpNoPorts++;
if (addr_type == IS_MYADDR)
{
   icmp_send(skb?? ICMP_DEST_UNREACH?? ICMP_PORT_UNREACH?? 0?? dev);//???ICMP????????????????????
}
/*
   * Hmm. We got an UDP broadcast to a port to which we
   * don't wanna listen. Ignore it.
   */
skb->sk = NULL;
kfree_skb(skb?? FREE_WRITE);
return(0);
   }