struct softnet_data
{
int throttle;
int cng_level;
int avg_blog;
struct sk_buff_head input_pkt_queue;
struct list_head poll_list;
struct net_device *output_queue;
struct sk_buff *completion_queue;

struct net_device backlog_dev; /* Sorry. 8) */
};



struct packet_type {
unsigned short type; /* This is really htons(ether_type). */
struct net_device *dev; /* NULL is wildcarded here */
int (*func) (struct sk_buff *, struct net_device *,
struct packet_type *);
void *af_packet_priv;
struct list_head list;
};


struct netif_rx_stats
{
unsigned total;
unsigned dropped;
unsigned time_squeeze;
unsigned throttled;
unsigned fastroute_hit;
unsigned fastroute_success;
unsigned fastroute_defer;
unsigned fastroute_deferred_out;
unsigned fastroute_latency_reduction;
unsigned cpu_collision;
};


struct net_device_stats
{
unsigned long rx_packets; /* total packets received */
unsigned long tx_packets; /* total packets transmitted */
unsigned long rx_bytes; /* total bytes received */
unsigned long tx_bytes; /* total bytes transmitted */
unsigned long rx_errors; /* bad packets received */
unsigned long tx_errors; /* packet transmit problems */
unsigned long rx_dropped; /* no space in linux buffers */
unsigned long tx_dropped; /* no space available in linux */
unsigned long multicast; /* multicast packets received */
unsigned long collisions;

/* detailed rx_errors: */
unsigned long rx_length_errors;
unsigned long rx_over_errors; /* receiver ring buff overflow */
unsigned long rx_crc_errors; /* recved pkt with crc error */
unsigned long rx_frame_errors; /* recv‘d frame alignment error */
unsigned long rx_fifo_errors; /* recv‘r fifo overrun */
unsigned long rx_missed_errors; /* receiver missed packet */

/* detailed tx_errors */
unsigned long tx_aborted_errors;
unsigned long tx_carrier_errors;
unsigned long tx_fifo_errors;
unsigned long tx_heartbeat_errors;
unsigned long tx_window_errors;

/* for cslip etc */
unsigned long rx_compressed;
unsigned long tx_compressed;
};


/* Media selection options. */
enum {
IF_PORT_UNKNOWN = 0,
IF_PORT_10BASE2,
IF_PORT_10BASET,
IF_PORT_AUI,
IF_PORT_100BASET,
IF_PORT_100BASETX,
IF_PORT_100BASEFX
};


struct net_device
{

/*
* This is the first field of the "visible" part of this structure
* (i.e. as seen by users in the "Space.c" file). It is the name
* the interface.
*/
char name[IFNAMSIZ]; //eth0 eth1 ... ethn

/*
* I/O specific fields
* FIXME: Merge these and struct ifmap into one
*/
unsigned long mem_end; /* shared mem end */
unsigned long mem_start; /* shared mem start */
unsigned long base_addr; /* device I/O address */ //網絡接口的I/O基地址，由驅動在設備探測時賦值 ifconfig可以顯示或
修改當前值，該字段可以在系統啟動時在內核命令行中顯式賦值，或者
在模塊加載時賦值。這個成員一般不被引用
unsigned int irq; /* device IRQ number */ //網絡設備使用的中斷號。irq值常常在網絡設備啟動時加載設置，
並且在後來由ifconfig打印出來。

/*
* Some hardware also needs these fields, but they are not
* part of the usual set specified in Space.c.
*/

unsigned char if_port; /* Selectable AUI, TP,..*/ //多端口設備中使用的端口。該成員在同軸線（IF_PORT_10BASE2)和
//雙絞線(IF_PORT_100BASET)以太網連接時使用
unsigned char dma; /* DMA channel */ //在某些外設總線時有意義，如ISA總線。它不在設備驅動自身以外使用

unsigned long state; //網絡設備和網絡適配器的狀態信息

struct net_device *next; //下一個struct net_device Linux中所有網絡設備都以dev_base指針開頭的單線行鏈表管理

/* The device initialization function. Called only once. */
int (*init)(struct net_device *dev); 用來搜索並初始化網絡設備。該方法負責尋找並初始化當前類型的網絡適配器。首選必須創建net_device結構並將網絡設備和網絡驅動程序的數據（驅動相關的）填充進去。其次，register_netdevice()註冊網絡設備


/* ------- Fields preinitialized in Space.c finish here ------- */

struct net_device *next_sched;

/* Interface index. Unique device identifier */
int ifindex;
int iflink;


struct net_device_stats* (*get_stats)(struct net_device *dev); 應用程序需要獲取網絡接口的統計信息時會調用這個方法。例如，在運行ifconfig或netstat -i時，會調用該方法
struct iw_statistics* (*get_wireless_stats)(struct net_device *dev);

/* List of functions to handle Wireless Extensions (instead of ioctl).
* See <net/iw_handler.h> for details. Jean II */
const struct iw_handler_def * wireless_handlers;
/* Instance data managed by the core of Wireless Extensions. */
struct iw_public_data * wireless_data;

struct ethtool_ops *ethtool_ops;

/*
* This marks the end of the "visible" part of the structure. All
* fields hereafter are internal to the system, and may change at
* will (read: may be cleaned up at will).
*/

/* These may be needed for future network-power-down code. */
unsigned long trans_start; /* Time (in jiffies) of last Tx */
unsigned long last_rx; /* Time of last Rx */

unsigned short flags; /* interface flags (a la BSD) */
unsigned short gflags;
unsigned short priv_flags; /* Like ‘flags‘ but invisible to userspace. */
unsigned short unused_alignment_fixer; /* Because we need priv_flags,
* and we want to be 32-bit aligned.
*/

unsigned mtu; /* interface MTU value */ //最大傳輸單元。它指定鏈路層每幀有效載荷最大長度。網絡層各協議必須
考慮該值，以確保不會向網絡適配器發送多余的字節，以太網1500，通
過ifconfig命令可改變
unsigned short type; /* interface hardware type */ //指定了網絡適配器的硬件類型。這個成員由ARP用來決定網絡適配器
支持的硬件地址。對以太網接口一般由ether_setup()函數設置其值為
ARPHRD_ETHER

unsigned short hard_header_len; /* hardware hdr length */ //指定鏈路層數據幀包頭長度。對於以太網接口為14
void *priv; /* pointer to private data */

struct net_device *master; /* Pointer to master device of a group,
* which this device is member of.
*/

/* Interface address info. */
unsigned char broadcast[MAX_ADDR_LEN]; /* hw bcast add */ //廣播地址
/*以太網地址長度是6個字節（我們指的是接口板的硬件ID），廣播地址由6個0xff字節組成。這些字段一般由ether_setup()函數設置。驅動程序必須以特定於設備的方式從接口板讀出，並復制到dev_addr結構。網絡設備的硬件地址用來產生正確的以太網頭*/
unsigned char dev_addr[MAX_ADDR_LEN]; /* hw address */ //存放設備硬件地址
unsigned char addr_len; /* hardware address length */ //硬件（MAC）地址長度

struct dev_mc_list *mc_list; /* Multicast mac addresses */ /*指向具有多播的第二層地址的線性表。當網絡適配器收集到具有包含在dev_mc_list中目標地址後，網絡適配器必須將包傳遞給更高層。驅動程序中方法set_multicast_list用來將該列表中的地址傳遞給網絡適配器。該網絡適配器的硬件過濾器（如果有）負責只將與該計算機有關的包傳遞給內核 */

int mc_count; /* Number of installed mcasts */ //dev_mc_list包含的地址數量
int promiscuity;
int allmulti;

/*下面兩個變量用來發現適配器在發送包時遇到的問題。
int watchdog_timeo;
struct timer_list watchdog_timer; /*在網絡設備啟動時打開，每經過watch_timeo時間後立即被調用。處理程序dev_watchdog()檢查從上一次（存儲在stans_start中）包傳輸後是否經過watch_timeo單位長度的時間。如果是，那麽上一個包的傳輸中出現問題，必須檢查網絡適配器。要檢查網絡適配器，需要調用驅動函數tx_timeout()。如果從上次傳輸開始還沒有經過足夠長的時間，那麽除了watchdog計時器啟動之外沒有發生其他網絡事件*/

/* Protocol specific pointers */
/*指向網絡適配器的第三層協議的信息。如果網絡設備被設置為Internet協議，那麽ip_ptr指向in_device類型的結構，它管理有關的IP實例的信息和配置參數。例如in_device結構管理包含網絡設備IP地址列表，包含多播組活動IP列表和ARP協議參數等*/

void *atalk_ptr; /* AppleTalk link */
void *ip_ptr; /* IPv4 specific data */
void *dn_ptr; /* DECnet specific data */
void *ip6_ptr; /* IPv6 specific data */
void *ec_ptr; /* Econet specific data */
void *ax25_ptr; /* AX.25 specific data */

struct list_head poll_list; /* Link to poll list */
int quota;
int weight;

struct Qdisc *qdisc;
struct Qdisc *qdisc_sleeping;
struct Qdisc *qdisc_ingress;
struct list_head qdisc_list;
unsigned long tx_queue_len; /* Max frames per queue allowed */ //該字段表示指定了網絡設備發送隊列中可以排列的最大幀數
這個值有ether_setup()設置為100.不要將tx_queue_len
與網絡適配器的緩沖區想混淆。通常網絡適配器有額外的環形
緩沖區，大小為16或32個包大小

/* ingress path synchronizer */
spinlock_t ingress_lock;
/* hard_start_xmit synchronizer */
spinlock_t xmit_lock;
/* cpu id of processor entered to hard_start_xmit or -1,
if nobody entered there.
*/
int xmit_lock_owner;
/* device queue lock */
spinlock_t queue_lock;
/* Number of references to this device */
atomic_t refcnt;
/* delayed register/unregister */
struct list_head todo_list;
/* device name hash chain */
struct hlist_node name_hlist;
/* device index hash chain */
struct hlist_node index_hlist;

/* register/unregister state machine */
enum { NETREG_UNINITIALIZED=0,
NETREG_REGISTERING, /* called register_netdevice */
NETREG_REGISTERED, /* completed register todo */
NETREG_UNREGISTERING, /* called unregister_netdevice */
NETREG_UNREGISTERED, /* completed unregister todo */
NETREG_RELEASED, /* called free_netdev */
} reg_state;

/* Net device features */
int features;
#define NETIF_F_SG 1 /* Scatter/gather IO. */
#define NETIF_F_IP_CSUM 2 /* Can checksum only TCP/UDP over IPv4. */
#define NETIF_F_NO_CSUM 4 /* Does not require checksum. F.e. loopack. */
#define NETIF_F_HW_CSUM 8 /* Can checksum all the packets. */
#define NETIF_F_HIGHDMA 32 /* Can DMA to high memory. */
#define NETIF_F_FRAGLIST 64 /* Scatter/gather IO. */
#define NETIF_F_HW_VLAN_TX 128 /* Transmit VLAN hw acceleration */
#define NETIF_F_HW_VLAN_RX 256 /* Receive VLAN hw acceleration */
#define NETIF_F_HW_VLAN_FILTER 512 /* Receive filtering on VLAN */
#define NETIF_F_VLAN_CHALLENGED 1024 /* Device cannot handle VLAN packets */
#define NETIF_F_TSO 2048 /* Can offload TCP/IP segmentation */
#define NETIF_F_LLTX 4096 /* LockLess TX */

/* Called after device is detached from network. */
void (*uninit)(struct net_device *dev); 用來註銷網絡設備，該方法用來執行驅動程序相關的函數，這些函數在刪除網絡設備時也是必須的。目前沒有驅動程序使用該方法

/* Called after last user reference disappears. */
void (*destructor)(struct net_device *dev);

/* Pointers to interface service routines. */
int (*open)(struct net_device *dev); 打開一個已經命名的網絡設備。可以使用ifconfig命令激活網絡設備，在激活過程中，open方法應當註冊它需要的系統資源（I/O口，IRQ，DMA，等等），以及進行其他的網絡設備要求
int (*stop)(struct net_device *dev); 停止網絡適配器的活動並釋放相關資源，此後網絡設備不能活動
int (*hard_start_xmit) (struct sk_buff *skb,
struct net_device *dev); 在網絡設備上發送數據包的方法。完整的報文（協議頭和所有其他數據）包含在一個socket緩沖區（sk_buff）結構中。數據包如果成功發送到網絡適配器該函數返回0，否則返回1
#define HAVE_NETDEV_POLL
int (*poll) (struct net_device *dev, int *quota);
int (*hard_header) (struct sk_buff *skb,
struct net_device *dev,
unsigned short type,
void *daddr,
void *saddr,
unsigned len); 用先前提取到的源和目的硬件地址來建立硬件頭的函數（在hard_start_xmit 前調用）。它的工作是將傳給它的參數信息組織成一個合適的特定於設備的硬件頭
int (*rebuild_header)(struct sk_buff *skb); 用來在ARP解析完成後、報文發送前，重建硬件頭的函數
#define HAVE_MULTICAST
void (*set_multicast_list)(struct net_device *dev); 將多播MAC地址列表傳遞給網絡適配器，適配器就可以根據這些地址接收包
#define HAVE_SET_MAC_ADDR
int (*set_mac_address)(struct net_device *dev,
void *addr); 改變網絡設備的硬件地址（MAC地址）
#define HAVE_PRIVATE_IOCTL
int (*do_ioctl)(struct net_device *dev,
struct ifreq *ifr, int cmd);
#define HAVE_SET_CONFIG
int (*set_config)(struct net_device *dev,
struct ifmap *map);
#define HAVE_HEADER_CACHE
int (*hard_header_cache)(struct neighbour *neigh,
struct hh_cache *hh);
void (*header_cache_update)(struct hh_cache *hh,
struct net_device *dev,
unsigned char * haddr); 在響應一個變化中，更新hh_cache結構中的目的地址方法
#define HAVE_CHANGE_MTU
int (*change_mtu)(struct net_device *dev, int new_mtu); 改變網絡設備最大傳輸單元（MTU）函數

#define HAVE_TX_TIMEOUT
void (*tx_timeout) (struct net_device *dev); 網絡驅動程序代碼沒有在一個合理的時間內將一個報文發送完成時會調用該方法，報文沒有被及時發送的原因可能是丟失一個中斷或某個接口被鎖。此時該函數處理這個問題並恢復報文發送

void (*vlan_rx_register)(struct net_device *dev,
struct vlan_group *grp);
void (*vlan_rx_add_vid)(struct net_device *dev,
unsigned short vid);
void (*vlan_rx_kill_vid)(struct net_device *dev,
unsigned short vid);

int (*hard_header_parse)(struct sk_buff *skb,
unsigned char *haddr); 該方法完成的工作包括從skb中的報文中抽取源地址，復制到haddr的緩沖區中。函數的返回值是地址的長度信息
int (*neigh_setup)(struct net_device *dev, struct neigh_parms *);
int (*accept_fastpath)(struct net_device *, struct dst_entry*);
#ifdef CONFIG_NETPOLL
int netpoll_rx;
#endif
#ifdef CONFIG_NET_POLL_CONTROLLER
void (*poll_controller)(struct net_device *dev);
#endif

/* bridge stuff */
struct net_bridge_port *br_port;

#ifdef CONFIG_NET_DIVERT
/* this will get initialized at each interface type init routine */
struct divert_blk *divert;
#endif /* CONFIG_NET_DIVERT */

/* class/net/name entry */
struct class_device class_dev;
/* how much padding had been added by alloc_netdev() */
int padded;
};



struct netdev_boot_setup {
char name[IFNAMSIZ];
struct ifmap map;
};


struct hh_cache
{
struct hh_cache *hh_next; /* Next entry */
atomic_t hh_refcnt; /* number of users */
unsigned short hh_type; /* protocol identifier, f.e ETH_P_IP
* NOTE: For VLANs, this will be the
* encapuslated type. --BLG
*/
int hh_len; /* length of header */
int (*hh_output)(struct sk_buff *skb);
rwlock_t hh_lock;

/* cached hardware header; allow for machine alignment needs. */
#define HH_DATA_MOD 16
#define HH_DATA_OFF(__len) \
(HH_DATA_MOD - ((__len) & (HH_DATA_MOD - 1)))
#define HH_DATA_ALIGN(__len) \
(((__len)+(HH_DATA_MOD-1))&~(HH_DATA_MOD - 1))
unsigned long hh_data[HH_DATA_ALIGN(LL_MAX_HEADER) / sizeof(long)];
};


struct dev_mc_list
{
struct dev_mc_list *next;
__u8 dmi_addr[MAX_ADDR_LEN];
unsigned char dmi_addrlen;
int dmi_users;
int dmi_gusers;
};


struct sk_buff_head {
/* These two members must be first. */
struct sk_buff *next;
struct sk_buff *prev;

__u32 qlen;
spinlock_t lock;
};

struct sk_buff;

/* To allow 64K frame to be packed as single skb without frag_list */
#define MAX_SKB_FRAGS (65536/PAGE_SIZE + 2)

typedef struct skb_frag_struct skb_frag_t;

struct skb_frag_struct {
struct page *page;
__u16 page_offset;
__u16 size;
};


struct sk_buff {
/* These two members must be first. */
struct sk_buff *next;
struct sk_buff *prev; //雙向鏈表指針

struct sk_buff_head *list; 指向套接字緩存在隊列中的當前位置
struct sock *sk; 指向創建報文的socket
struct timeval stamp; 報文到達Linux系統的時間
struct net_device *dev; 表明套接字緩存當前操作所在的網絡設備。網絡路由器被確定下來後，dev就指向報文離開計算機時經過的網絡適配器。知道報文的輸出適配器已知之前，dev都指向輸入適配器
struct net_device *input_dev;
struct net_device *real_dev;

union {
struct tcphdr *th;
struct udphdr *uh;
struct icmphdr *icmph;
struct igmphdr *igmph;
struct iphdr *ipiph;
struct ipv6hdr *ipv6h;
unsigned char *raw;
} h; 傳輸層報文幀頭的指針

union {
struct iphdr *iph;
struct ipv6hdr *ipv6h;
struct arphdr *arph;
unsigned char *raw;
} nh; 網絡層報文幀頭的指針

union {
unsigned char *raw;
} mac; MAC層報文幀頭的指針

struct dst_entry *dst; 指向路由高速緩存中的一條記錄，它包含著有關報文進一步前進的路由信息
struct sec_path *sp;

/*
* This is the control buffer. It is free to use for every
* layer. Please put your private variables there. If you
* want to keep them across layers you have to do a skb_clone()
* first. This is owned by whoever has the skb queued ATM.
*/
char cb[40];

unsigned int len, 指明套接字緩存所代表的報文長度，這裏只考慮內核可訪問的數據。在以太網報文中兩個MAC地址和類型/長度域被考慮其中。其他的域（報頭、鏈接和檢驗）以後再在網絡適配器中進行添加
data_len,
mac_len,
csum;
unsigned char local_df,
cloned,
pkt_type, 報文的類型
ip_summed;
__u32 priority;
unsigned short protocol,
security;

void (*destructor)(struct sk_buff *skb);
#ifdef CONFIG_NETFILTER
unsigned long nfmark;
__u32 nfcache;
__u32 nfctinfo;
struct nf_conntrack *nfct;
#ifdef CONFIG_NETFILTER_DEBUG
unsigned int nf_debug;
#endif
#ifdef CONFIG_BRIDGE_NETFILTER
struct nf_bridge_info *nf_bridge;
#endif
#endif /* CONFIG_NETFILTER */
#if defined(CONFIG_HIPPI)
union {
__u32 ifield;
} private;
#endif
#ifdef CONFIG_NET_SCHED
__u32 tc_index; /* traffic control index */
#ifdef CONFIG_NET_CLS_ACT
__u32 tc_verd; /* traffic control verdict */
__u32 tc_classid; /* traffic control classid */
#endif

#endif


/* These elements must be at the end, see alloc_skb() for details. */
unsigned int truesize;
atomic_t users;
unsigned char *head,
*data,
*tail,
*end;
};


struct skb_shared_info {
atomic_t dataref;
unsigned int nr_frags;
unsigned short tso_size;
unsigned short tso_segs;
struct sk_buff *frag_list;
skb_frag_t frags[MAX_SKB_FRAGS];
};


struct skb_iter {
/* Iteration functions set these */
unsigned char *data;
unsigned int len;

/* Private to iteration */
unsigned int nextfrag;
struct sk_buff *fraglist;
};



#ifdef CONFIG_NETFILTER
struct nf_conntrack {
atomic_t use;
void (*destroy)(struct nf_conntrack *);
};

#ifdef CONFIG_BRIDGE_NETFILTER
struct nf_bridge_info {
atomic_t use;
struct net_device *physindev;
struct net_device *physoutdev;
#if defined(CONFIG_VLAN_8021Q) || defined(CONFIG_VLAN_8021Q_MODULE)
struct net_device *netoutdev;
#endif
unsigned int mask;
unsigned long data[32 / sizeof(unsigned long)];
};

網絡設備驅動程序數據結構