linux下用netdevice来描述一个接口，而BSD则用ifnet,包括接口的属性，硬件信息，统计信息，函数指针，输出队列
/*
* Structure describing information about an interface
* which may be of interest to management entities.
*/
struct ifnet {
char *if_name; /* name, e.g. ``en'' or ``lo'' */
struct ifnet *if_next; /* all struct ifnets are chained */
struct ifaddr *if_addrlist; /* linked list of addresses per if */
int if_pcount; /* number of promiscuous listeners */
caddr_t if_bpf; /* packet filter structure */
唯一的表示这个接口
u_short if_index; /* numeric abbreviation for this if */
区分相同驱动的接口
short if_unit; /* sub-unit for lower level driver */
short if_timer; /* time 'til if_watchdog called */
#define IFF_UP 0x1 /* interface is up */
#define IFF_BROADCAST 0x2 /* broadcast address valid */
#define IFF_DEBUG 0x4 /* turn on debugging */
#define IFF_LOOPBACK 0x8 /* is a loopback net */
#define IFF_POINTOPOINT 0x10 /* interface is point-to-point link */
#define IFF_NOTRAILERS 0x20 /* avoid use of trailers */
#define IFF_RUNNING 0x40 /* resources allocated */
#define IFF_NOARP 0x80 /* no address resolution protocol */
#define IFF_PROMISC 0x100 /* receive all packets */
#define IFF_ALLMULTI 0x200 /* receive all multicast packets */
#define IFF_OACTIVE 0x400 /* transmission in progress */
#define IFF_SIMPLEX 0x800 /* can't hear own transmissions */
#define IFF_LINK0 0x1000 /* per link layer defined bit */
#define IFF_LINK1 0x2000 /* per link layer defined bit */
#define IFF_LINK2 0x4000 /* per link layer defined bit */
#define IFF_MULTICAST 0x8000 /* supports multicast */
short if_flags; /* up/down, broadcast, etc. */
struct if_data {
/* generic interface information */
u_char ifi_type; /* ethernet, tokenring, etc */
u_char ifi_addrlen; /* media address length */
u_char ifi_hdrlen; /* media header length */
u_long ifi_mtu; /* maximum transmission unit */
u_long ifi_metric; /* routing metric (external only) */
u_long ifi_baudrate; /* linespeed */
/* volatile statistics */
u_long ifi_ipackets; /* packets received on interface */
u_long ifi_ierrors; /* input errors on interface */
u_long ifi_opackets; /* packets sent on interface */
u_long ifi_oerrors; /* output errors on interface */
u_long ifi_collisions; /* collisions on csma interfaces */
u_long ifi_ibytes; /* total number of octets received */
u_long ifi_obytes; /* total number of octets sent */
u_long ifi_imcasts; /* packets received via multicast */
u_long ifi_omcasts; /* packets sent via multicast */
u_long ifi_iqdrops; /* dropped on input, this interface */
u_long ifi_noproto; /* destined for unsupported protocol */
struct timeval ifi_lastchange;/* last updated */
} if_data;
/* procedure handles */
驱动函数的挂载点
int (*if_init) /* init routine */
__P((int));
int (*if_output) /* output routine (enqueue) */
__P((struct ifnet *, struct mbuf *, struct sockaddr *,
struct rtentry *));
int (*if_start) /* initiate output routine */
__P((struct ifnet *));
int (*if_done) /* output complete routine */
__P((struct ifnet *)); /* (XXX not used; fake prototype) */
int (*if_ioctl) /* ioctl routine */
__P((struct ifnet *, int, caddr_t));
int (*if_reset)
__P((int)); /* new autoconfig will permit removal */
int (*if_watchdog) /* timer routine */
__P((int));
输出队列结构，很简洁
struct ifqueue {
struct mbuf *ifq_head;
struct mbuf *ifq_tail;
int ifq_len;
int ifq_maxlen;
int ifq_drops;
} if_snd; /* output queue */
};
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);
struct ifaddr **q = (struct ifaddr **)
malloc(n, M_IFADDR, M_WAITOK);
if (ifnet_addrs) {
bcopy((caddr_t)ifnet_addrs, (caddr_t)q, n/2);
free((caddr_t)ifnet_addrs, M_IFADDR);
}
ifnet_addrs = q;
}
/*
* create a Link Level name for this device
*/
这个函数也很有意思，很有意思
把ifp->if_unit转换成字符串，相当于itoa()....
unitname = sprint_d((u_int)ifp->if_unit, workbuf, sizeof(workbuf));
namelen = strlen(ifp->if_name);
unitlen = strlen(unitname);
#define _offsetof(t, m) ((int)((caddr_t)&((t *)0)->m))
masklen = _offsetof(struct sockaddr_dl, sdl_data[0]) +
unitlen + namelen;
比较抽象，看看书上那个图就明白内存布局了。
从前往后是name,unit,mask,分别由namelen,unitlen,masklen标识内存的长度
socksize = masklen + ifp->if_addrlen;
#define ROUNDUP(a) (1 + (((a) - 1) | (sizeof(long) - 1)))
socksize = ROUNDUP(socksize);
if (socksize < sizeof(*sdl))
socksize = sizeof(*sdl);
ifasize = sizeof(*ifa) + 2 * socksize;
这代码我是看的很晕，没细看，看71页的图就理解了
if (ifa = (struct ifaddr *)malloc(ifasize, M_IFADDR, M_WAITOK)) {
bzero((caddr_t)ifa, ifasize);
第一个sockaddr_dl 表示name和uinit信息，如eth0
物理地址是在后面的ether_attach中附给第一个sdl的
sdl = (struct sockaddr_dl *)(ifa + 1);
sdl->sdl_len = socksize;
sdl->sdl_family = AF_LINK;
bcopy(ifp->if_name, sdl->sdl_data, namelen);
bcopy(unitname, namelen + (caddr_t)sdl->sdl_data, unitlen);
sdl->sdl_nlen = (namelen += unitlen);
sdl->sdl_index = ifp->if_index;
sdl->sdl_type = ifp->if_type;
ifnet_addrs[if_index - 1] = ifa;
ifa->ifa_ifp = ifp;
ifa->ifa_next = ifp->if_addrlist;
ifa->ifa_rtrequest = link_rtrequest;
ifp->if_addrlist = ifa;
ifa->ifa_addr = (struct sockaddr *)sdl;
第2个sdl,表示netmask信息
sdl = (struct sockaddr_dl *)(socksize + (caddr_t)sdl);
ifa->ifa_netmask = (struct sockaddr *)sdl;
sdl->sdl_len = masklen;
while (namelen != 0)
sdl->sdl_data[--namelen] = 0xff;
}
/* XXX -- Temporary fix before changing 10 ethernet drivers */
if (ifp->if_output == ether_output)
ether_ifattach(ifp);
}
至此，over
