if_ethersubr.c

Details description of Free BSD network source code.Those documents have explained each line of code

		(*ng_ether_input_p)(ifp, &m, eh);
		if (m == NULL)
			return;
	}

/* -------------------------------------------到此为止,这意味着可以加入自己的代码----------------------------------- */
	ether_demux(ifp, eh, m);
}

/*
 * 真正处理以太网封包.
 */
void
ether_demux(ifp, eh, m)  /*该三参数和ether_input()函数的参数一样*/
	struct ifnet *ifp;
	struct ether_header *eh;
	struct mbuf *m;
{
	struct ifqueue *inq;  /*
			 * 结构定义了一个网络接口队列.
 
			struct	ifqueue {
				struct	mbuf *ifq_head;         /*封包的队列头指针
				struct	mbuf *ifq_tail;         /*尾指针
				int	ifq_len;                    /*队列长度
				int	ifq_maxlen;                 /*队列的最大长度
				int	ifq_drops;                  /*丢弃的数量
			};
            */
	u_short ether_type;
	int s;


	if ((ifp->if_flags & IFF_PROMISC) != 0       /*不在混杂模式,目的主机硬件地址的第一字节的最后一位是0即非多播地址*/
	    && (eh->ether_dhost[0] & 1) == 0         /*不是本机地址.注意:在XIE_FIREWALL中不能使用之,应调用一函数*/
	    && bcmp(eh->ether_dhost,                 /*该函数功能是先将其转化为IP头部,取目的IP地址(是本地网吗?是),再查*/
	      IFP2AC(ifp)->ac_enaddr, ETHER_ADDR_LEN) != 0) {/*对应的硬件地址,该硬件地址如为空则发出ARP请求*/
		m_freem(m);                                       /*本地网络如下图:*/
		return;
	}
                                      
	
	*/
	/* 如果接口没启动则放弃包 */
	if ((ifp->if_flags & IFF_UP) == 0) {
		m_freem(m);
		return;
	}
	ifp->if_ibytes += m->m_pkthdr.len + sizeof (*eh); /*接口的接收到的字节数,eh为以太网包头*/
	if (eh->ether_dhost[0] & 1) {/*以太网的包头的目的地址(硬件)的第一字节不为全0则为广播或多播包*/
		if (bcmp((caddr_t)etherbroadcastaddr, (caddr_t)eh->ether_dhost,/*是广播还是多播*/
			 sizeof(etherbroadcastaddr)) == 0)
			m->m_flags |= M_BCAST;
		else
			m->m_flags |= M_MCAST;
	}
	if (m->m_flags & (M_BCAST|M_MCAST))
		ifp->if_imcasts++;

	ether_type = ntohs(eh->ether_type);/*网络到主机字节方式*/



	switch (ether_type) {
#ifdef INET
	case ETHERTYPE_IP:/*是IP协议吗?*/
		if (ipflow_fastforward(m))
			return;
		schednetisr(NETISR_IP);/*调用软中断*/
		inq = &ipintrq;/*IP对列*/
		break;

	case ETHERTYPE_ARP:/*是ARP协议吗?*/
		if (ifp->if_flags & IFF_NOARP) {
			/* 如果接口不支持ARP方式,释放包 */
			m_freem(m);
			return;
		}
		schednetisr(NETISR_ARP);
		inq = &arpintrq;
		break;
#endif

	default:
	}

	s = splimp();/*关网络中断*/
	if (IF_QFULL(inq)) {
      /*#原型是define	IF_QFULL(ifq)		((ifq)->ifq_len >= (ifq)->ifq_maxlen)  队列满*/

		IF_DROP(inq);
		/*原型是#define	IF_DROP(ifq)		((ifq)->ifq_drops++)     丢弃数加1*/

		m_freem(m);
	} else
		IF_ENQUEUE(inq, m);
	/*以下是原型
	#define	IF_ENQUEUE(ifq, m) { \
	(m)->m_nextpkt = 0; \
	if ((ifq)->ifq_tail == 0) \  如果队列尾巴为没有,则该队列没初始化
		(ifq)->ifq_head = m; \   初始化队列头为M
	else \                       有尾巴,即该队列已经有mbuf
		(ifq)->ifq_tail->m_nextpkt = m; \  当前的尾巴mbuf的下一mbuf指向m 
	(ifq)->ifq_tail = m; \        队列的尾巴指向m
	(ifq)->ifq_len++; \           队列长度加1
}
	*/
	splx(s); /*开网络中断*/
}

/*
 * 当接口链入到接口列表时执行的普通动作
 */
void/*在我的网络设备驱动程序中有描写, 主要是由网卡驱动调用*/
ether_ifattach(ifp, bpf)
	register struct ifnet *ifp;
	int bpf;
{
	register struct ifaddr *ifa;
	register struct sockaddr_dl *sdl;

	if_attach(ifp);/*调用if.c中的过程*/
	ifp->if_type = IFT_ETHER;
	ifp->if_addrlen = 6;
	ifp->if_hdrlen = 14;
	ifp->if_mtu = ETHERMTU;/*1500*/
	ifp->if_resolvemulti = ether_resolvemulti;/*解释多播的过程指针*/
	if (ifp->if_baudrate == 0)           /*初始化波特率*/
	    ifp->if_baudrate = 10000000;
	ifa = ifnet_addrs[ifp->if_index - 1];
	KASSERT(ifa != NULL, ("%s: no lladdr!\n", __FUNCTION__));
	sdl = (struct sockaddr_dl *)ifa->ifa_addr;
	sdl->sdl_type = IFT_ETHER;
	sdl->sdl_alen = ifp->if_addrlen;
	bcopy((IFP2AC(ifp))->ac_enaddr, LLADDR(sdl), ifp->if_addrlen);
	if (bpf)/*BPF支持*/
		bpfattach(ifp, DLT_EN10MB, sizeof(struct ether_header));
	if (ng_ether_attach_p != NULL)/*PPPoE支持即ADSL*/
		(*ng_ether_attach_p)(ifp);
}

void
ether_ifdetach(ifp, bpf)
	struct ifnet *ifp;
	int bpf;
{
	if (ng_ether_detach_p != NULL)
		(*ng_ether_detach_p)(ifp);
	if (bpf)
		bpfdetach(ifp);
	if_detach(ifp);
}

SYSCTL_DECL(_net_link);/*申明从哪个根接上*/
SYSCTL_NODE(_net_link, IFT_ETHER, ether, CTLFLAG_RW, 0, "Ethernet");/*做一个节点*/

int /*inctl控制代码和多播代码我就不写了,太平常了*/
ether_ioctl(ifp, command, data)
	struct ifnet *ifp;
	int command;
	caddr_t data;
{
	struct ifaddr *ifa = (struct ifaddr *) data;
	struct ifreq *ifr = (struct ifreq *) data;
	int error = 0;

	switch (command) {
	case SIOCSIFADDR:
		ifp->if_flags |= IFF_UP;

		switch (ifa->ifa_addr->sa_family) {
#ifdef INET
		case AF_INET:
			ifp->if_init(ifp->if_softc);	/* before arpwhohas */
			arp_ifinit(IFP2AC(ifp), ifa);
			break;
#endif

		default:
			ifp->if_init(ifp->if_softc);
			break;
		}
		break;

	case SIOCGIFADDR:
		{
			struct sockaddr *sa;

			sa = (struct sockaddr *) & ifr->ifr_data;
			bcopy(IFP2AC(ifp)->ac_enaddr,
			      (caddr_t) sa->sa_data, ETHER_ADDR_LEN);
		}
		break;

	case SIOCSIFMTU:
		/*
		 * Set the interface MTU.
		 */
		if (ifr->ifr_mtu > ETHERMTU) {
			error = EINVAL;
		} else {
			ifp->if_mtu = ifr->ifr_mtu;
		}
		break;
	}
	return (error);
}

int
ether_resolvemulti(ifp, llsa, sa)
	struct ifnet *ifp;
	struct sockaddr **llsa;
	struct sockaddr *sa;
{
	struct sockaddr_dl *sdl;
	struct sockaddr_in *sin;

	u_char *e_addr;

	switch(sa->sa_family) {
	case AF_LINK:
		/*
		 * No mapping needed. Just check that it's a valid MC address.
		 */
		sdl = (struct sockaddr_dl *)sa;
		e_addr = LLADDR(sdl);
		if ((e_addr[0] & 1) != 1)
			return EADDRNOTAVAIL;
		*llsa = 0;
		return 0;

#ifdef INET
	case AF_INET:
		sin = (struct sockaddr_in *)sa;
		if (!IN_MULTICAST(ntohl(sin->sin_addr.s_addr)))
			return EADDRNOTAVAIL;
		MALLOC(sdl, struct sockaddr_dl *, sizeof *sdl, M_IFMADDR,
		       M_WAITOK|M_ZERO);
		sdl->sdl_len = sizeof *sdl;
		sdl->sdl_family = AF_LINK;
		sdl->sdl_index = ifp->if_index;
		sdl->sdl_type = IFT_ETHER;
		sdl->sdl_alen = ETHER_ADDR_LEN;
		e_addr = LLADDR(sdl);
		ETHER_MAP_IP_MULTICAST(&sin->sin_addr, e_addr);
		*llsa = (struct sockaddr *)sdl;
		return 0;
#endif

	default:
		/*
		 * Well, the text isn't quite right, but it's the name
		 * that counts...
		 */
		return EAFNOSUPPORT;
	}
}