TCP/IP Protocol detailed 2nd volume 3rd Chapter Interface Layer

This chapter is from ifnet, each network device has a own ifnet structure, this structure has ifaddr linked list, that is, each interface

All addresses, can be one, or can be multiple forms of linked lists. And then there's a ifqueue that's pointing to the Mbuf list; and then there's a lot

Handles function pointers to initialize interfaces, send packets, and so on.

struct ifnet {    /*  This is the record interface type, where the interface type is Ethernet/or       * slip or loopback interface  */ char *if_name;  /* name, e.g.  ' en '   or  ' lo '  */    /*  this is to form the ifnet structure list, because each interface has its own ifnet structure,      *  For example, there are two Ethernet cards, there are two of this structure, with this pointer to connect */ struct ifnet *if_next;  /* all  struct ifnets are chained */    /*  then each interface can have multiple addresses possible, such as Ethernet,      *  we can set multiple IP addresses to it, forming a chain  */ struct ifaddr *if_addrlist;  /* linked list of addresses per if */    /*  I don't know what it is yet, but the number of listeners in the mix makes me think of Libpcap library      *  set up promiscuous mode */         int if_pcount;  /* number of promiscuous listeners * /        /*  Package filter use, and then look at  */ caddr_t if_bpf;   /*  packet filter structure */    /*  This is almost the same as the one below, but it doesn't matter what the interface type is, it's all numbered       *  so the number is the only */ u_short if_index;  /* numeric  abbreviation for this if  */    /* has this type of interface in front of it, in case this interface has multiple,      *  then it is again identified as 0/1/...*/ short if_unit;  /* sub-unit for  lower level driver */    /* this recording time but the specifics are unclear */ short if_timer;   /* time  ' til if_watchdog called */    /*  The State and properties of this interface, such as the work is not working, can do  */ 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 *//*  This is the initialization of the handler function  */  int  (*if_init)   /*  init routine */  __p ((int)); int  (*if_output)   /* output  routine  (enqueue) &NBSp;*/  __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 *, u_long, caddr_t)) ; int  (*if_reset)    __p ((int));   /* new autoconfig will  permit removal */ int  (*if_watchdog)   /* timer routine */   __p ((int)); /*  This is the structure that points to the Mbuf list  */ struct ifqueue {  struct  mbuf *ifq_head;  struct mbuf *ifq_tail;  int ifq_len;  int ifq_maxlen;   int ifq_drops; } if_snd;   /* output queue */};

TCP/IP Protocol detailed 2nd volume 3rd Chapter Interface Layer