套接字不仅可以用于各种传输协议的IP连接，也可以用于内核支持的所有其他地址和协议类型,IPX、Appletalk、本地UNIX套接字/ TCP/UDP Linux网络核心架构分为三层：用户空间的应用层，内核空间的网络协议栈层，物理硬件层。其中最重要的核心是内核空间的协议格层。在整个栈按照严格分层设计思想可分为五层：系统调用接口层——＞协议无关的接口层——＞网络协议实现层——＞驱动接口层——＞驱动程序层。
(1.) 重要结构体定义： include/linux/socket.h
struct sockaddr {
sa_family_t sa_family; /* address family, AF_xxx */
char sa_data[14]; /* 14 bytes of protocol address */
};
clude/uapi/linux/in.h
struct sockaddr_in{
short sin_family;
unsigned short sin_port;
struct in_addr sin_addr;
......
}
struct sockaddr_in server;-->(struct sockaddr*)&server
通常在用户态程序需要赋值sockaddr_in，调用系统调用时转换为sockaddr.(2.) IP地址重要接口函数
//点分十进制（IPv4）或冒号分隔十六进制（IPv6）表示的 IP 地址转换为二进制形式
in_addr_t inet_addr(const char *cp);//废弃
int inet_pton(int af, const char *src, void *dst);
//二进制形式-->点分十进制（IPv4）或冒号分隔十六进制（IPv6）
const char *inet_ntop(int af, const void *src, char *dst, socklen_t size);(3.) USER Space--> socket(c library)-->system call(API)-->kerel socket API-->call serveral layer API socket(c library) in <sys/socket.h> system call-->arch/arm64/include/asm/unistd32.h
网卡作为一个硬件接收到网络包。处理刚才高效接受数据，减少对CPU的中断次NAPI，eg :在网卡驱动程序初始化的时候，就会调用ixgb＿init＿module（注册一个驱动ixgb＿driver）
struct sk_buff {
/* These two members must be first. */
struct sk_buff *next;
struct sk_buff *prev;
ktime_t tstamp; //rev/send time
struct sock *sk; //send/rev user sock point, NULL if forward
struct net_device *dev; //device object(may virsual dev)
struct net_device *real_dev; /* For support of point to point protocols
(e.g. 802.3ad) over bonding, we must save the
physical device that got the packet before
replacing skb->dev with the virtual device. */
int outdev;
int indev; /* Original interface */
/*
* 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[160] __aligned(8);
unsigned int len,
data_len;
__u16 mac_len,
hdr_len;
__be16 protocol;
void (*destructor)(struct sk_buff *skb);
int skb_iif;
__u32 rxhash;
__u16 queue_mapping;
sk_buff_data_t transport_header;
sk_buff_data_t network_header;
sk_buff_data_t mac_header;
/* 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;
unsigned int truesize;
atomic_t users;
struct ip_tuple *iptp;
int pxmit;
struct ip6_tuple *iptp6;
struct ips_sa_data * ips_sa; /* &ips_sa.ct_general */
struct virtual_firewall *vf;
unsigned int skb_vrf;
struct mac_host *host;
__u32 dos_id;
__u32 ips_view_id;
struct ha_profile ha;
// for ip flow trace
__u32 trace_id;
__u32 trace_flag;
__u16 socktype;
__u16 sockport;
unsigned short vlanid;
unsigned char vlan_cos;
unsigned char tos; /* DSCP value for L3 header */
/* transmit hash value for link aggregation slave selection*/
__u8 bond_xmit_hash;
unsigned int addr_generation;
int skb_pmtu;
struct multi_class_shaper *ingress_shaper;
__u8 class_id;
unsigned int qdisc_pkt_len;
struct skb_prp_trailer prp_trailer; //Parallel Redundancy Protocol
};
TO do list
include/linux/netdevice.h net_device结构体存储着网络设备的所有信息，每个设备都有这种结构。所有设备的net_device结构放在一个全局变量dev_base所有全局列表中。和sk_buff一样，整体结构相当庞大的。结构体中有一个next指针，用来连接系统中所有网络设备。内核把这些连接起来的设备组成一个链表，并由全局变量dev_base指向链表的第一个元素。 网络设备net_device结构体包含主要设备参数 设备的IRQ号、设备的MTU、设备的MAC地址、设备的名称(eth1,ethO)、设备的标志(up,down)、与设备相关 联的组播地址清单、设备支持的功能、网络设备回调函数的对象(net_device_ops).设备最后一次发送数据包的时 间戳、设备最后一次接收数据包的时间戳。
net_device结构体具体源码 分析如下：
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
* of the interface.
*/
char name[IFNAMSIZ];
char fs_name[IFNAMSIZ];
/* device name hash chain */
struct hlist_node name_hlist;
char *ifalias; /* interface alias */
/*
* 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 */
unsigned int irq; /* device IRQ number */
unsigned long state;
struct list_head dev_list; //global dev list
struct list_head napi_list; // from 2.6.x support
struct list_head unreg_list;// unreg global list
/* currently active device features */
u32 features;
u32 features_ex;
/* user-changeable features */
u32 hw_features;
/* user-requested features */
u32 wanted_features;
/* mask of features inheritable by VLAN devices */
u32 vlan_features;
/* Interface index. Unique device identifier */
int ifindex;
int iflink; // peer virtual tunnel device
int phyindex;
struct net_device_stats stats;
atomic_long_t rx_dropped; /* dropped packets by core network
* Do not use this in drivers.
*/
/* Management operations */
const struct net_device_ops *netdev_ops;
const struct ethtool_ops *ethtool_ops;
/* Hardware header description */
const struct header_ops *header_ops;
unsigned int flags; /* interface flags (a la BSD) */
unsigned int priv_flags; /* Like 'flags' but invisible to userspace. */
unsigned short gflags;
unsigned short padded; /* How much padding added by alloc_netdev() */
unsigned char operstate; /* RFC2863 operstate */
unsigned char link_mode; /* mapping policy to operstate */
unsigned char if_port; /* Selectable AUI, TP,..*/
unsigned char dma; /* DMA channel */
unsigned int mtu; /* interface MAC MTU value */
unsigned short type; /* interface hardware type */
unsigned short hard_header_len; /* hardware hdr length */
/* Interface address info. */
unsigned char perm_addr[MAX_ADDR_LEN]; /* permanent hw address */
unsigned char addr_assign_type; /* hw address assignment type */
unsigned char addr_len; /* hardware address length */
unsigned short dev_id; /* for shared network cards */
spinlock_t addr_list_lock;
struct netdev_hw_addr_list uc; /* Unicast mac addresses */
struct netdev_hw_addr_list mc; /* Multicast mac addresses */
bool uc_promisc; //Unicast dev model
unsigned int promiscuity; //model
unsigned int allmulti; // multicast model
struct in_device __rcu *ip_ptr; /* IPv4 specific data */
struct dn_dev __rcu *dn_ptr; /* DECnet specific data */
struct inet6_dev __rcu *ip6_ptr; /* IPv6 specific data */
struct vlan_range_list __rcu *vlan_filter_ptr; /* vlan filter specific data for virtual wire pair*/
void *ec_ptr; /* Econet specific data */
unsigned long last_rx; /* Time of last Rx
* This should not be set in
* drivers, unless really needed,
* because network stack (bonding)
* use it if/when necessary, to
* avoid dirtying this cache line.
*/
struct net_device *master; /* Pointer to master device of a group,
* which this device is member of.
*/
/* Interface address info used in eth_type_trans() */
unsigned char *dev_addr; /* hw address, (before bcast
because most packets are
unicast) */
struct netdev_hw_addr_list dev_addrs; /* list of device
hw addresses */
unsigned char dst_addr[MAX_ADDR_LEN];
unsigned char broadcast[MAX_ADDR_LEN]; /* hw bcast add */
rx_handler_func_t __rcu *rx_handler;
void __rcu *rx_handler_data;
struct netdev_queue __rcu *ingress_queue;
/*
* Cache lines mostly used on transmit path
*/
struct netdev_queue *_tx ____cacheline_aligned_in_smp;
/* Number of TX queues allocated at alloc_netdev_mq() time */
unsigned int num_tx_queues;
/* 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;
#ifdef CONFIG_XPS
struct xps_dev_maps __rcu *xps_maps;
#endif
/* 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; /* Time (in jiffies) of last Tx */
int watchdog_timeo; /* used by dev_watchdog() */
struct timer_list watchdog_timer;
int linkdown_timeo;
struct timer_list linkdown_timer;
/* Number of references to this device */
int __percpu *pcpu_refcnt;
/* delayed register/unregister */
struct list_head todo_list;
/* device index hash chain */
struct hlist_node index_hlist;
struct list_head link_watch_list;
/* 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:8;
bool dismantle; /* device is going do be freed */
enum {
RTNL_LINK_INITIALIZED,
RTNL_LINK_INITIALIZING,
} rtnl_link_state:16;
/* Called from unregister, can be used to call free_netdev */
void (*destructor)(struct net_device *dev);
#ifdef CONFIG_NET_NS
/* Network namespace this network device is inside */
struct net *nd_net;
#endif
/* mid-layer private */
union {
void *ml_priv;
struct pcpu_lstats __percpu *lstats; /* loopback stats */
struct pcpu_tstats __percpu *tstats; /* tunnel stats */
struct pcpu_dstats __percpu *dstats; /* dummy stats */
};
/* GARP */
struct garp_port __rcu *garp_port;
/* class/net/name entry */
struct device dev;
/* space for optional device, statistics, and wireless sysfs groups */
const struct attribute_group *sysfs_groups[4];
/* rtnetlink link ops */
const struct rtnl_link_ops *rtnl_link_ops;
/* for setting kernel sock attribute on TCP connection setup */
#define GSO_MAX_SIZE 65536
unsigned int gso_max_size;
#ifdef CONFIG_DCB
/* Data Center Bridging netlink ops */
const struct dcbnl_rtnl_ops *dcbnl_ops;
#endif
u8 num_tc;
struct netdev_tc_txq tc_to_txq[TC_MAX_QUEUE];
u8 prio_tc_map[TC_BITMASK + 1];
#if defined(CONFIG_FCOE) || defined(CONFIG_FCOE_MODULE)
/* max exchange id for FCoE LRO by ddp */
unsigned int fcoe_ddp_xid;
#endif
/* phy device may attach itself for hardware timestamping */
struct phy_device *phydev;
/* group the device belongs to */
int group;
/*---------------------fortinet---------------------------*/
unsigned int fw_flags; /* if 1 substitution is enabled */
unsigned long last_log; /* Time of last over shapping log */
/* bridge stuff */
struct{
rwlock_t ctx_lock;
struct net_bridge_port __rcu *ctx_br_port;
struct vlan_group * ctx_vlan_grp;
}if_ops_ctx;
#define if_ops_lock if_ops_ctx.ctx_lock
#define br_port if_ops_ctx.ctx_br_port
#define vlan_grp if_ops_ctx.ctx_vlan_grp
#ifdef CONFIG_SW_NET
void *vsdev_priv;
#endif
struct if_ops *ops;
struct list_head vf_link;
struct virtual_firewall __rcu *dev_vf;
int arp_entry;
int ha_flags;
unsigned int mgmt_ip;
struct list_head notif_list;
#ifdef CONFIG_NET_NPU
unsigned int npu_disable;
unsigned int oid;
u_int16_t oid_vid;
struct npu_netdev_ops *npu_ops;
#endif
u_int16_t rx_tcp_mss;
u_int16_t tx_tcp_mss;
struct dev_traffic_shaper in_shaper;
struct multi_queue_shaper out_shaper;
struct multi_class_shaper __rcu *in_cls_shaper;
struct multi_class_shaper __rcu *out_cls_shaper;
struct rtnl_link_stats64 base_stats;
struct net_dev_bps bps;
struct net_dev_bps ingress_bps;
struct net_dev_sampler sampler;
u_int32_t vrf;
u_int16_t vwl_zone_id;
u_int16_t vwl_intf_quality;
int weight;
};老式的网络设备工作在中断模式下面，每接受到一个包就中断一次，效率比较低，为此解决这个问题，开发一种新的软件技术-->NAPI (NewAPI) ₒ采用NAPI技术时，如果负载很高，网络设备驱动程序将在轮询模式，而不是中断驱动模式下运行。--2.6版本引入的。 Title 1.）数据包的收发：网络设备驱动程序主要任务：接收目的地为当前主机的数据包，并将其传递给网络层，之后再将其传递给 才专输层。传输当前主机生成的外出数据包或转换当前主机收到数据包。对于每个数据包，无论它是接收到还是发送出去， :都需要在路由子系统中执行一次查找操作。 2.）当数据包位于网络设备驱动程序接收路径的L2时，skb->data指向的是L2(以太网)报头；调用方法eth_type_trans()后， 激据包即将进入第3层，因此skb->data应指向网络层(L3)报头，而这个报头紧跟在以太网报头后面。