};

对输出队列的操作函数，simple and beauty

/*

* Output queues (ifp->if_snd) and internetwork datagram level (pup level 1)

* input routines have queues of messages stored on ifqueue structures

* (defined above). Entries are added to and deleted from these structures

* by these macros, which should be called with ipl raised to splimp().

*/

#define IF_QFULL(ifq) ((ifq)->ifq_len >= (ifq)->ifq_maxlen)

#define IF_DROP(ifq) ((ifq)->ifq_drops++)

#define IF_ENQUEUE(ifq, m) { \

(m)->m_nextpkt = 0; \

if ((ifq)->ifq_tail == 0) \

(ifq)->ifq_head = m; \

else \

(ifq)->ifq_tail->m_nextpkt = m; \

(ifq)->ifq_tail = m; \

(ifq)->ifq_len++; \

}

#define IF_PREPEND(ifq, m) { \

(m)->m_nextpkt = (ifq)->ifq_head; \

if ((ifq)->ifq_tail == 0) \

(ifq)->ifq_tail = (m); \

(ifq)->ifq_head = (m); \

(ifq)->ifq_len++; \

}

#define IF_DEQUEUE(ifq, m) { \

(m) = (ifq)->ifq_head; \

if (m) { \

if (((ifq)->ifq_head = (m)->m_nextpkt) == 0) \

(ifq)->ifq_tail = 0; \

(m)->m_nextpkt = 0; \

(ifq)->ifq_len--; \

} \

}

/*

* The ifaddr structure contains information about one address

* of an interface. They are maintained by the different address families,

* are allocated and attached when an address is set, and are linked

* together so all addresses for an interface can be located.

*/

struct ifaddr {

struct sockaddr *ifa_addr; /* address of interface */

struct sockaddr *ifa_dstaddr; /* other end of p-to-p link */

#define ifa_broadaddr ifa_dstaddr /* broadcast address interface */

struct sockaddr *ifa_netmask; /* used to determine subnet */

struct ifnet *ifa_ifp; /* back-pointer to interface */

struct ifaddr *ifa_next; /* next address for interface */

void (*ifa_rtrequest)(); /* check or clean routes (+ or -)'d */

u_short ifa_flags; /* mostly rt_flags for cloning */

short ifa_refcnt; /* extra to malloc for link info */

int ifa_metric; /* cost of going out this interface */

#ifdef notdef

struct rtentry *ifa_rt; /* XXXX for ROUTETOIF */

#endif

};

以loop设备为例，其初始化函数为loopattach,相当于linux下的probe函数。

81 loopattach(n)

82 int n;

83 {

有专用的ifnet,其他的设备需要申请，并初始化

84 register struct ifnet *ifp = &loif;

85

86 #ifdef lint

87 n = n; /* Highlander: there can only be one... */

88 #endif

89 ifp->if_name = "lo";

90 ifp->if_mtu = LOMTU;

91 ifp->if_flags = IFF_LOOPBACK | IFF_MULTICAST;

92 ifp->if_ioctl = loioctl;

93 ifp->if_output = looutput;

94 ifp->if_type = IFT_LOOP;

95 ifp->if_hdrlen = 0;

96 ifp->if_addrlen = 0;

注册给内核，相当于register_netdevice

97 if_attach(ifp);

98 #if NBPFILTER > 0

分组过滤相关，按下不表

99 bpfattach(&ifp->if_bpf, ifp, DLT_NULL, sizeof(u_int));

100 #endif

101 }

if_attach主要就是把ifp放到一个链表里，初始化后 找到组织了

void

if_attach(ifp)

struct ifnet *ifp;

{

unsigned socksize, ifasize;

int namelen, unitlen, masklen, ether_output();

char workbuf[12], *unitname;

全局的一个结构

register struct ifnet **p = &ifnet;

register struct sockaddr_dl *sdl;

register struct ifaddr *ifa;

static int if_indexlim = 8;

extern void link_rtrequest();

这个循环很有意思，看了半天才明白

p指向的是ifnet结构中的一个成员，这个成员是ifnet*，＊P指向下一个结构。所以＊P＝＝NULL，说明P所指的成员所在的结构是最后一个ifnet,所以可以直接对＊P，既ifnet->if_next赋值。

while (*p)

p = &((*p)->if_next);

*p = ifp;

增加全区的if_index,如果有接口删除了，占用的if_index也不能用了

ifp->if_index = ++if_index;

动态的扩充ifnet_addr的大小，方法不错

if (ifnet_addrs == 0 || if_index >= if_indexlim) {

unsigned n = (if_indexlim <<= 1) * sizeof(ifa);