struct sk_buff {/* 这两个结构必须放在此结构的前面，主要方便数据的强制转换*/struct sk_buff        *next; //双向链表结构，指向下一个sk_buffstruct sk_buff        *prev; //指向前一个sk_buff结构struct sock        *sk;     //这个指针指向一个套接字sock数据结构。当数据在本地产生或者本地进程接受时，需要这个指针；里面的数据会有tcp/udp和用户态程序使用。如果是转发此指针为NULL。后续详解。ktime_t            tstamp;    //包到达的时间戳struct net_device    *dev; //网络设备，哪个网卡、虚拟网卡，后续结构详解。unsigned long        _skb_dst; /** 这是控制缓冲区。 每层都可以自由使用 请把您的私有变量放在那里。 如果你想让他们跨层，你必须先做一个skb_clone（）。 这是由谁拥有skb排队的ATM拥有。*/char            cb[48];unsigned int        len, //数据包的全部数据长度，包括data指向的数据和end后面的分片的数据的总长data_len;  //本分片所包含的数据长度__u16            mac_len,    //mac包头长度hdr_len; //硬件头部长度union {__wsum        csum;struct {__u16    csum_start;__u16    csum_offset;};};  //校验和__u32            priority;  //QoS等级kmemcheck_bitfield_begin(flags1);__u8            local_df:1,cloned:1,ip_summed:2,nohdr:1,nfctinfo:3;__u8            pkt_type:3,        // 根据L2层帧的目的地址进行类型划分。fclone:2,                        //sk_buff克隆状态ipvs_property:1,        //IP虚拟服务器属性peeked:1,           //这个数据包已经被看到了，所以已经做了统计，不要再做了nf_trace:1;        //netfilter 包记录标识__be16            protocol:16; //从L2层设备驱动看使用在下一个较高层的协议。kmemcheck_bitfield_end(flags1);void            (*destructor)(struct sk_buff *skb); //析构函数
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)struct nf_conntrack    *nfct; skb与连接的关系struct sk_buff        *nfct_reasm; netfilter conntrack重组指针
#endif
#ifdef CONFIG_BRIDGE_NETFILTERstruct nf_bridge_info    *nf_bridge;//桥接帧数据
#endifint            iif; //到达的设备的索引，网卡索引编号
#ifdef CONFIG_NET_SCHED__u16            tc_index;    //流量控制索引
#ifdef CONFIG_NET_CLS_ACT__u16            tc_verd;    //流量控制决定
#endif
#endifkmemcheck_bitfield_begin(flags2);__u16            queue_mapping:16; //多队列网卡设备的映射关系
#ifdef CONFIG_IPV6_NDISC_NODETYPE__u8            ndisc_nodetype:2; //路由类型，来自链路层；
#endifkmemcheck_bitfield_end(flags2);/* 0/14 bit hole */#ifdef CONFIG_NET_DMAdma_cookie_t        dma_cookie; //被DMA相关函数完成的相关操作cookeie
#endif
#ifdef CONFIG_NETWORK_SECMARK__u32            secmark; //安全相关标记
#endif__u32            mark;  //通用标记__u16            vlan_tci; //vlan标签控制信息sk_buff_data_t        transport_header;  //传输层头sk_buff_data_t        network_header;    //网络层头sk_buff_data_t        mac_header;                 //以太网层头/* These elements must be at the end, see alloc_skb() for details.  */sk_buff_data_t        tail;             sk_buff_data_t        end;                           unsigned char        *head,                               *data;                                                    //head和end指向的是数据区的开端和尾、，data和tail指向的是实际数据的开头和结尾unsigned int        truesize;                            //此缓冲区总大小，包括sk_buff。sk_buff只不过是个指针的集合，他所指的才是真正的数据区，所以是两部分。atomic_t        users;  //引用计数，使用这个sk_buff的使用者的数目，可能有多个函数要使用同一个sk_buff所以防止提前释放掉，设置此计数
}; 

2.struct sock - scokets的网络层描述

struct sock {sock_common    __sk_common; //套接口在网络层的最小表示
#define sk_node            __sk_common.skc_node
#define sk_nulls_node        __sk_common.skc_nulls_node
#define sk_refcnt        __sk_common.skc_refcnt#define sk_copy_start        __sk_common.skc_hash
#define sk_hash            __sk_common.skc_hash
#define sk_family        __sk_common.skc_family
#define sk_state        __sk_common.skc_state
#define sk_reuse        __sk_common.skc_reuse
#define sk_bound_dev_if        __sk_common.skc_bound_dev_if
#define sk_bind_node        __sk_common.skc_bind_node
#define sk_prot            __sk_common.skc_prot
#define sk_net            __sk_common.skc_netkmemcheck_bitfield_begin(flags);unsigned int        sk_shutdown  : 2, //是一组标志位，SEND_SHUTDOWN and/or RCV_SHUTDOWN。sk_no_check  : 2,        //不对包进行检查标识sk_userlocks : 4,        // %SO_SNDBUF 和 %SO_RCVBUF 缓存设置锁sk_protocol  : 8,       sk_type      : 16;kmemcheck_bitfield_end(flags);int            sk_rcvbuf;                //接收缓存区大小socket_lock_t        sk_lock;  //同步锁/** The backlog queue is special, it is always used with* the per-socket spinlock held and requires low latency* access. Therefore we special case it's implementation.*/struct {struct sk_buff *head;struct sk_buff *tail;} sk_backlog;   //总是被自旋锁持有wait_queue_head_t    *sk_sleep; //在队列中等待的socketstruct dst_entry    *sk_dst_cache; //目的地址的缓存
#ifdef CONFIG_XFRMstruct xfrm_policy    *sk_policy[2];
#endifrwlock_t        sk_dst_lock;  //目的缓存读写锁atomic_t        sk_rmem_alloc; //表示接收队列已提交的字节数。atomic_t        sk_wmem_alloc; //表示发送队列已提交的字节数。atomic_t        sk_omem_alloc; //用“O”或“other”做选项int            sk_sndbuf;struct sk_buff_head    sk_receive_queue; //表示接收的数据包的队列。struct sk_buff_head    sk_write_queue;   //表示发送的数据包的队列。
#ifdef CONFIG_NET_DMAstruct sk_buff_head    sk_async_wait_queue; //DMA复制数据包
#endifint            sk_wmem_queued;            //维持的队列大小int            sk_forward_alloc;   //转发空间分配gfp_t            sk_allocation;        //分配空间的模式int            sk_route_caps;            //路由容量int            sk_gso_type;                //GSO type (e.g. %SKB_GSO_TCPV4)unsigned int        sk_gso_max_size;//最大的GSO段大小int            sk_rcvlowat;    //unsigned long         sk_flags; //%SO_LINGER (l_onoff), %SO_BROADCAST, %SO_KEEPALIVE, %SO_OOBINLINE 标识设定, %SO_TIMESTAMPING 标识设定unsigned long            sk_lingertime; //SO_LINGER设定struct sk_buff_head    sk_error_queue;  //非常少用struct proto        *sk_prot_creator; //原始socket创建器rwlock_t        sk_callback_lock;    //int            sk_err,sk_err_soft;atomic_t        sk_drops; //raw/udp drop计数unsigned short        sk_ack_backlog; //当前监听队列数unsigned short        sk_max_ack_backlog; //在listen()中设置的数目__u32            sk_priority;  //优先级struct ucred        sk_peercred;long            sk_rcvtimeo;long            sk_sndtimeo;struct sk_filter          *sk_filter; //socket 过滤结构void            *sk_protinfo;    //私有区域struct timer_list    sk_timer; //socket清理定时器ktime_t            sk_stamp;    //最后一包接收时间struct socket        *sk_socket;    //IO信号void            *sk_user_data;    //RPC层私有数据struct page        *sk_sndmsg_page; //sndmsg缓存struct sk_buff        *sk_send_head; //转发数据头__u32            sk_sndmsg_off; // sndmsg缓存偏移int            sk_write_pending;
#ifdef CONFIG_SECURITYvoid            *sk_security;
#endif__u32            sk_mark;/* XXX 4 bytes hole on 64 bit */void            (*sk_state_change)(struct sock *sk);void            (*sk_data_ready)(struct sock *sk, int bytes);void            (*sk_write_space)(struct sock *sk);void            (*sk_error_report)(struct sock *sk);int            (*sk_backlog_rcv)(struct sock *sk,struct sk_buff *skb); void                    (*sk_destruct)(struct sock *sk);
};struct sock_common {unsigned short      skc_family;         /*地址族*/volatile unsigned char  skc_state;      /*连接状态*/unsigned char       skc_reuse;          /*SO_REUSEADDR设置*/int         skc_bound_dev_if;struct hlist_node   skc_node;struct hlist_node   skc_bind_node;      /*哈希表相关*/atomic_t        skc_refcnt;             /*引用计数*/
};

struct net_device
{char            name[IFNAMSIZ]; //网络设备名称,如eth0struct hlist_node    name_hlist; //这个字段用于构建网络设备名的哈希散列表，而struct net中的name_hlist就指向每个哈希散列表的链表头；char             *ifalias; //网络设备的别名；/*网络设备内存映射时在主机中的内存区域*/unsigned long        mem_end;    /* 共享内存结束    */unsigned long        mem_start;    /* 共享内存开始    */unsigned long        base_addr;    /* 网络设备I/O基地址     */unsigned int        irq;        /* 设备终端号*/unsigned char        if_port;    /* 传输介质，如双绞线、同轴电缆等，在多端口设备中指定使用哪个端口*/unsigned char        dma;        /* DMA通道*/unsigned long        state; /* 网络设备物理上的工作状态 */struct list_head    dev_list; //网络设备链表struct list_head    napi_list;//支持NAPI传输的网络设备链表/* Net device features */unsigned long        features; //设备硬件功能特性
#define NETIF_F_SG        1    /* Scatter/gather IO. */
#define NETIF_F_IP_CSUM        2    /* Can checksum 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_IPV6_CSUM    16    /* Can checksum TCP/UDP over IPV6 */
#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_GSO        2048    /* Enable software GSO. */
#define NETIF_F_LLTX        4096    /* LockLess TX - deprecated. Please *//* do not use LLTX in new drivers */
#define NETIF_F_NETNS_LOCAL    8192    /* Does not change network namespaces */
#define NETIF_F_GRO        16384    /* Generic receive offload */
#define NETIF_F_LRO        32768    /* large receive offload *//* the GSO_MASK reserves bits 16 through 23 */
#define NETIF_F_FCOE_CRC    (1 << 24) /* FCoE CRC32 */
#define NETIF_F_SCTP_CSUM    (1 << 25) /* SCTP checksum offload */
#define NETIF_F_FCOE_MTU    (1 << 26) /* Supports max FCoE MTU, 2158 bytes*//* Segmentation offload features */
#define NETIF_F_GSO_SHIFT    16
#define NETIF_F_GSO_MASK    0x00ff0000
#define NETIF_F_TSO        (SKB_GSO_TCPV4 << NETIF_F_GSO_SHIFT)
#define NETIF_F_UFO        (SKB_GSO_UDP << NETIF_F_GSO_SHIFT)
#define NETIF_F_GSO_ROBUST    (SKB_GSO_DODGY << NETIF_F_GSO_SHIFT)
#define NETIF_F_TSO_ECN        (SKB_GSO_TCP_ECN << NETIF_F_GSO_SHIFT)
#define NETIF_F_TSO6        (SKB_GSO_TCPV6 << NETIF_F_GSO_SHIFT)
#define NETIF_F_FSO        (SKB_GSO_FCOE << NETIF_F_GSO_SHIFT)/* List of features with software fallbacks. */
#define NETIF_F_GSO_SOFTWARE    (NETIF_F_TSO | NETIF_F_TSO_ECN | NETIF_F_TSO6)#define NETIF_F_GEN_CSUM    (NETIF_F_NO_CSUM | NETIF_F_HW_CSUM)
#define NETIF_F_V4_CSUM        (NETIF_F_GEN_CSUM | NETIF_F_IP_CSUM)
#define NETIF_F_V6_CSUM        (NETIF_F_GEN_CSUM | NETIF_F_IPV6_CSUM)
#define NETIF_F_ALL_CSUM    (NETIF_F_V4_CSUM | NETIF_F_V6_CSUM)/** If one device supports one of these features, then enable them* for all in netdev_increment_features.*/
#define NETIF_F_ONE_FOR_ALL    (NETIF_F_GSO_SOFTWARE | NETIF_F_GSO_ROBUST | \NETIF_F_SG | NETIF_F_HIGHDMA |        \NETIF_F_FRAGLIST)/* Interface index. Unique device identifier    */int            ifindex;//标识网络设备的唯一索引号   int            iflink;//用于虚拟网络设备struct net_device_stats    stats; //统计信息#ifdef CONFIG_WIRELESS_EXT/* 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;
#endif/* Management operations */const struct net_device_ops *netdev_ops;//网络设备驱动程序需要实现的一组操作函数const struct ethtool_ops *ethtool_ops;//支持ethtool功能的一组操作函数   /* Hardware header description */const struct header_ops *header_ops;//数据链路层协议头相关的一组操作函数unsigned int        flags;    /* 它们的可能取值定义在linux-2.6.38.8/include/linux/if.h文件中。*/unsigned short        gflags;unsigned short          priv_flags; /* Like 'flags' but invisible to userspace. */unsigned short        padded;    /* 分配net_device结构体及其私有数据时为对齐所需的填充位数目*/unsigned char        operstate; /*//RFC 2863操作状态  */unsigned char        link_mode; /* 映射到RFC2863兼容状态的策略  */unsigned        mtu;    /* MTU        */unsigned short        type;    /* 网络设备硬件类型，如10Mbps以太网ARPHRD_ETHER       */unsigned short        hard_header_len;    /* 硬件数据帧头的长度，以太网为14字节       *//* extra head- and tailroom the hardware may need, but not in all cases* can this be guaranteed, especially tailroom. Some cases also use* LL_MAX_HEADER instead to allocate the skb.*/unsigned short        needed_headroom; //分配套接字缓冲区时预留空间的长度unsigned short        needed_tailroom;struct net_device    *master; /* 分组状态 *//* 硬件(如MAC)地址长度以及设备的硬件地址   */unsigned char        perm_addr[MAX_ADDR_LEN]; /* permanent hw address */unsigned char        addr_len;    /* hardware address length    */unsigned short          dev_id;        /* for shared network cards */struct netdev_hw_addr_list    uc;    /* 网络设备硬件地址组成的链表   */int            uc_promisc; //混杂模式时的单播地址个数   spinlock_t        addr_list_lock;//防止单播地址链表和组播地址链表被并发访问的自旋锁 struct dev_addr_list    *mc_list;    /* Multicast mac addresses    */int            mc_count;    /* Number of installed mcasts    */unsigned int        promiscuity; //混杂模式的计数器unsigned int        allmulti;//监听所有组播地址   /* 网络层协议特定数据 */#ifdef CONFIG_NET_DSAvoid            *dsa_ptr;    /* dsa specific data */
#endifvoid             *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 wireless_dev    *ieee80211_ptr;    /* IEEE 802.11 specific data,assign before registering *//** Cache line mostly used on receive path (including eth_type_trans())*/unsigned long        last_rx;    /* 最后接收数据包的时间   *//* Interface address info used in eth_type_trans() */unsigned char        *dev_addr;    /* hw address, (before bcastbecause most packets areunicast) */struct netdev_hw_addr_list    dev_addrs; /* //网络设备硬件地址组成的链表    */unsigned char        broadcast[MAX_ADDR_LEN];    /* //广播地址    */struct netdev_queue    rx_queue; //接收队列，RPS(Receive Packet Steering)特性   struct netdev_queue    *_tx ____cacheline_aligned_in_smp;/* Number of TX queues allocated at alloc_netdev_mq() time  */unsigned int        num_tx_queues; //发送队列/* Number of TX queues currently active in device  */unsigned int        real_num_tx_queues;/* root qdisc from userspace point of view */struct Qdisc        *qdisc;unsigned long        tx_queue_len;    /* Max frames per queue allowed */spinlock_t        tx_global_lock;
/** One part is mostly used on xmit path (device)*//* These may be needed for future network-power-down code. *//** trans_start here is expensive for high speed devices on SMP,* please use netdev_queue->trans_start instead.*/unsigned long        trans_start;    /* //最近传送数据包的时间       */int            watchdog_timeo; //发生传输超时时，设置的标志 struct timer_list    watchdog_timer;//网络层设置的传送数据包超时的时钟     /* Number of references to this device */atomic_t        refcnt ____cacheline_aligned_in_smp;/* delayed register/unregister */struct list_head    todo_list;//延迟注册/注销的网络设备链表   /* device index hash chain */struct hlist_node    index_hlist;//以索引号为关键字的网络设备哈希链表   struct net_device    *link_watch_next;/* register/unregister state machine */enum { NETREG_UNINITIALIZED=0,NETREG_REGISTERED,    /* completed register_netdevice */NETREG_UNREGISTERING,    /* called unregister_netdevice */NETREG_UNREGISTERED,    /* completed unregister todo */NETREG_RELEASED,        /* called free_netdev */NETREG_DUMMY,        /* dummy device for NAPI poll */} reg_state; //设备注册/注销状态机/* Called from unregister, can be used to call free_netdev */void (*destructor)(struct net_device *dev);#ifdef CONFIG_NETPOLLstruct netpoll_info    *npinfo;//NETPOLL相关信息
#endif#ifdef CONFIG_NET_NS/* Network namespace this network device is inside */struct net        *nd_net; //网络命名空间
#endif/* mid-layer private */void            *ml_priv; //中间层的私有数据/* bridge stuff */struct net_bridge_port    *br_port; //桥接模式/* macvlan */struct macvlan_port    *macvlan_port;/* GARP */struct garp_port    *garp_port;/* class/net/name entry */struct device        dev; //在sysfs文件系统中输出网络设备信息/* space for optional statistics and wireless sysfs groups */const struct attribute_group *sysfs_groups[3];/* rtnetlink link ops */const struct rtnl_link_ops *rtnl_link_ops; //rtnetlink操作函数   /* VLAN feature mask */unsigned long vlan_features; //虚拟局域网相关 /* for setting kernel sock attribute on TCP connection setup */
#define GSO_MAX_SIZE        65536unsigned int        gso_max_size; //GSO最大值   #ifdef CONFIG_DCB/* Data Center Bridging netlink ops */struct dcbnl_rtnl_ops *dcbnl_ops; //DCB操作函数
#endif#if defined(CONFIG_FCOE) || defined(CONFIG_FCOE_MODULE)/* max exchange id for FCoE LRO by ddp */unsigned int        fcoe_ddp_xid;
#endif
};