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 timeva l 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;